Date   
Re: Question for Arv

Allison Parent <kb1gmx@...>
 

--- In BITX20@..., arv evans <arvid.evans@...> wrote:

I have done that exact thing before with BJTs but was hoping that it
would not be necessary for MOSFETs.
_._
Well if you keep the heatsink large and the power low you can get
aways with it. But for a stable design you need a bias source that
tracks temperature. The good news is unlike BJTs that have to have
fairly high bias current from a stiff source the FETs do not have
the current requirement and as a result it can be easier to do.

I've tried a negative coefficient thermistor I had and basically
use it to form a active part of a voltage divider that feed the
bias pot so that the set bias would decrease as the thermister
got warm (mounted on the FET case with a dab of epoxy). It worked well.

The alternate is to use a diode as a temperature sensor. The
problem with a diode is it is .7V and FET bias is in the 2-5V
range. I suspect a stack (multiple series diodes) would work
but mounting 5-8 diodes near the FET may prove problematic.
The good news is the diode can be small like 1n4148 as the
current needed is trivial.

Allison


wimmie262000 wrote:

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@> wrote:
I thought that FET current was supposed to decrease with increasing
temperature. Isn't that why they are supposedly better than BJTs for
thermal characteristics?
It is, in the sense of channel resistance increasing. So the infamous
hotspots do not occur with FETs.
However if you examine the Id versus Vgs curve, you will notice that
given the same gate voltage, the drain current increases with
temperature.

Maybe a temp sensor coupled to the bias
circuit would help this situation?
Yes, sometimes the bias voltage is obtained from a circuit with a
series diode to ground. Mounting the diode close to (or onto) the
heatsink of the FETs will lower the gate bias voltage with increasing
temperature. Look around for some schematics and you will see what
people have done.

Joop


[Non-text portions of this message have been removed]

Re: Question for Arv

Allison Parent <kb1gmx@...>
 

--- In BITX20@..., arv evans <arvid.evans@...> wrote:

Allison

That is good info to remember. I'll keep it in mind for future
experiments.

I thought that FET current was supposed to decrease with increasing
temperature. Isn't that why they are supposedly better than BJTs for
thermal characteristics? Maybe a temp sensor coupled to the bias
circuit would help this situation? The power dissipation and resulting
better thermal characteristics is why I wanted to try IRF540s in place
of the IRF510s.
Thats the dirty thing they didn't tell you. ;) Unfortunatly the
the gate threshold shifts with die temp and higher temp means
lower threshold. So as the device heats up with fixed bias the
drain current goes up and if things get warm enough it runs away.
The solution is same as BJTs, make the bias temperature sensitive
so it reduces with increasing devide temp.

Dan did use feedback with a 0.1mfd and a small resistance in one of the
interim layouts for the new kit. I don't think he tried the tube
trick of cross-neutralization.
I was thinking about something along the lines of work done by Lloyd
VK5BR:

http://users.tpg.com.au/users/ldbutler/MosfetLinear.htm

He used fairly heavy gate loading (200 ohms) but not any
neutralization. Of course his IRF430s had problems getting above 7
MHz,
but I am hoping that the IRF540's might do a bit better.
They will, and there lies the problem. I'd expect at 20M you want
the gate loading down around 50 ohms or less.

It will be quite interesting to see if this can be made to work with
a > BITX transceiver. At 40 or so watts it would definitely take
the rig out of the QRP category. What makes this possible with
the new kit is Dan's work on cleaning up the output so that any
linear amplifier would be starting with a signal that meets FCC
requirements.
That is important. A clean signal is both a requirement by FCC and
the like plus its good operating practice. Low power does not
justify a poor signal and if anything quite the reverse. My
experinces on 6m and other bands is that when your running limited
power the signal must be as good as possible.

At 40W the design must adhere to more strict construction and
would not be buildable for some.

Myself I'm not promoting any particular power level. I'm just
pointing out articles I've read and experiments I've done. One
of the things I've seen with the power fets is at low voltage
(12V) power output is poor and distortion is much higher. To
that I say at the 4-6W level and 12V operation there are plenty
of inexpensive transistors like the 2sc2166 (usually run about
$1.40 or so) that will perform far better. When you move up to
higher power in the 20W bracket this is no longer true and the
power fets are a desireable candidate especially at 20-24V.
But the higher voltage then excludes simple 12V operation.

First rule of engineering, Good, fast, cheap, now pick any two.

Allison



Arv
_._



Allison Parent wrote:

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@> wrote:

Allison

After the kit boards are built and working properly, I have some
IRF-540's that are begging to be tried in this rig with 24 volts on
their drains. Not yet sure what to expect but it could be very
interesting.

Arv
_._
Can you say, smoke! I found PP amplifiers with the larger
IRF5xx devices needed care as the gate to drain capcitance can
make them into very good power oscillators. Some have applied
feedback and I've seen one design that used tube(valve) style
cross coupled neutrialization to quiet things down. That said
I've tried the HFpacker design (2 IRF510s PP) at HF and at 24V
it does a respectable 40-50W which is pushing near the thermal
capabilities of the part. There was a design published in QST
back in March 1999 that details how to acomplish this.

The original Bitx design with 24V on the final does around
10-12W at 20m using IRF510, and the IMD is better. The stability
needs some work. I tried adding a 500ohm and 0.1uf cap in series
from gate to drain (like applied in wideband amps) and it gave a
better behaved response. I didn't like the thermal stability
as the standing current tends to creep up as the device heats
if you increase the bias enough to get decent IMD.

Allison



Allison Parent wrote:

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>
<mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@> wrote:

Leonard

Dan Tayloe might be better to answer your question than me. He
designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as 13
turns, wound bifilar (wires twisted together before winding) to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between
windings.

I've used fewer turns as the type 43 material has a very high
ui (850)
and the number of turns needed are bounded at the low end by
too high
and RF current and inadaquate coupling and at teh high end
(too many
turns) due to excessive capacitance.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy
at the operating frequency. I usually design (?) them empirically
(i.e. wind them and test power transfer with proper terminating
impedances on each end). In operation these are really more like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular
frequency.

Exactly. there is a fair amount of latitude in their design.


* The transformer T1 is shown on the schematic as 8 turns, wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it may
be hard to get a good inductance meter reading because of
the very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant
element.
Tie the wires in parallel together and then measure it as if
it were
one fatter wire. With more than 4 turns it will be high (4
turns on
FT37-43 is ~5.6uh).

I might note here that the RF PA design in the 1-17-2007 kit
schematic
has been abandoned because we could not make it stable enough
for all
kit builders to be assured success with it. Dan could only
reliably
get
3 watts output, and that was not with a good RF waveform.
This one
section is the primary reason that we had to re-design the PCB
and thus
delay kit availability for an additional 3 to 4 weeks. The
present kit
schematic is the one with a date of 2-21-2007.
Not surprized. The power fet used it a fairly high gain device and
the loading impedence is marginal for 20M so layout and lead
lenghts
could make it unstable. Testing I've done at 20m wanted the fet to
driving a lower output impedence (I got 6W) with a lower driving
impedence that was heavily swamped with resistive loading.
However,
further testing indicated the IMD was poor at 12V. Redesign
for 24V
power to the final made higher power both easy and impoved the IMD
and power output. The IRF510 was designed for high speed switching
not RF service so it's being asked to do a lot.

Since that 1-17-2007 schematic Dan has re-designed the RF PA
section
to use push-pull drivers and a push-pull RF PA section. This
promises to be more stable and should offer a better chance of
kit builders being successful in building this kit. The output
power is now 7 watts and Dan's spectrum analysis indicates a
better
signal quality.
I had the same experience using two IRF510s in PP form at 12V.
I found it tended to take off if the RF load was either reactive
or resitive but >100ohms (2:1 swr).

I've desided to abandon the FET and use low cost power
transistors.
At the 10W power level a pair of 27Mhz CB finals such as MRF 472,
2sc1969, 2sc2166 and a long list of others are easier to work
with and inexpensive (2sc2166 usually run under 2$US) and durable.

Allison


[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

about IRF840

Benigno R. Santi III
 

good day fellow hams.

ive tinkering in the bitx. my bitx version started from simple
original bitx, and always evolving/modification thus my bitx did not
have the oportunity to be put in a chassis or case (due to eternal
tinkering hehe), anyways its working dead bug style. its on 40meters.
originally, i homebrewed a linear amp made from CB transistors the
2SC2078 and its quite good.

now, my concern is.. there are IRF840 mosfets, in fact i found a
schematic on the internet, and its not QRP anymore. can I run these
IRF840 using 220VAC, because thats the standard voltage the power
company supplies us. i have a heatsink, so thermal solutions are not
an issue. thanks guys.

btw, if i will use IRF840 as an amp, what input power is required. and
what is the minimum and maximum values this mosfet capable of.

thanks.

DW1SCO - nonoy

Re: BITX shoes?

Arv Evans
 

Jim

Definitely a few good ideas there. The bias switching arrangement
immediately caught my attention.

Thanks,

Arv
_._

Jim wrote:


I saw this in another group...

Italy has slightly different radio laws than the US, so dealers there
can sell QRP HF amps.
This unit was deconstructed (in other words, hacked to bits) in the
name of science:

http://www.rmitaly.com/scheda.asp?IDGr=1&cat=0&tipo=93
<http://www.rmitaly.com/scheda.asp?IDGr=1&cat=0&tipo=93>

http://www.rmitaly.com/download/manuals/KL203-manual_rel_600.pdf
<http://www.rmitaly.com/download/manuals/KL203-manual_rel_600.pdf>

It's a 4W in, 70W out FET-based amp.

The un-builder found this number on one of the FETS: P16NF06L and was
able to determine
that it is a STP16NF06L. Datasheet at:

http://www.farnell.com/datasheets/45682.pdf
<http://www.farnell.com/datasheets/45682.pdf>

I hope this gives folks some ideas. Incidentally, those transformers
are probably 4:1
broadband units, and you can use molded-inferrite beads salvaged from
computer video or
power cables for the cores.

Jim N6OTQ

BITX shoes?

Jim <n6otq@...>
 

I saw this in another group...

Italy has slightly different radio laws than the US, so dealers there can sell QRP HF amps.
This unit was deconstructed (in other words, hacked to bits) in the name of science:

http://www.rmitaly.com/scheda.asp?IDGr=1&cat=0&tipo=93

http://www.rmitaly.com/download/manuals/KL203-manual_rel_600.pdf

It's a 4W in, 70W out FET-based amp.

The un-builder found this number on one of the FETS: P16NF06L and was able to determine
that it is a STP16NF06L. Datasheet at:

http://www.farnell.com/datasheets/45682.pdf

I hope this gives folks some ideas. Incidentally, those transformers are probably 4:1
broadband units, and you can use molded-inferrite beads salvaged from computer video or
power cables for the cores.

Jim N6OTQ

Re: Question for Arv

Arv Evans
 

I have done that exact thing before with BJTs but was hoping that it
would not be necessary for MOSFETs.
_._


wimmie262000 wrote:


--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@...> wrote:
I thought that FET current was supposed to decrease with increasing
temperature. Isn't that why they are supposedly better than BJTs for
thermal characteristics?
It is, in the sense of channel resistance increasing. So the infamous
hotspots do not occur with FETs.
However if you examine the Id versus Vgs curve, you will notice that
given the same gate voltage, the drain current increases with
temperature.

Maybe a temp sensor coupled to the bias
circuit would help this situation?
Yes, sometimes the bias voltage is obtained from a circuit with a
series diode to ground. Mounting the diode close to (or onto) the
heatsink of the FETs will lower the gate bias voltage with increasing
temperature. Look around for some schematics and you will see what
people have done.

Joop

Re: Question for Arv

wimmie262000 <wvh@...>
 

--- In BITX20@..., arv evans <arvid.evans@...> wrote:
I thought that FET current was supposed to decrease with increasing
temperature. Isn't that why they are supposedly better than BJTs for
thermal characteristics?
It is, in the sense of channel resistance increasing. So the infamous
hotspots do not occur with FETs.
However if you examine the Id versus Vgs curve, you will notice that
given the same gate voltage, the drain current increases with
temperature.

Maybe a temp sensor coupled to the bias
circuit would help this situation?
Yes, sometimes the bias voltage is obtained from a circuit with a
series diode to ground. Mounting the diode close to (or onto) the
heatsink of the FETs will lower the gate bias voltage with increasing
temperature. Look around for some schematics and you will see what
people have done.

Joop

Re: Question for Arv

Arv Evans
 

Allison

That is good info to remember. I'll keep it in mind for future experiments.

I thought that FET current was supposed to decrease with increasing
temperature. Isn't that why they are supposedly better than BJTs for
thermal characteristics? Maybe a temp sensor coupled to the bias
circuit would help this situation? The power dissipation and resulting
better thermal characteristics is why I wanted to try IRF540s in place
of the IRF510s.

Dan did use feedback with a 0.1mfd and a small resistance in one of the
interim layouts for the new kit. I don't think he tried the tube trick
of cross-neutralization.

I was thinking about something along the lines of work done by Lloyd VK5BR:

http://users.tpg.com.au/users/ldbutler/MosfetLinear.htm

He used fairly heavy gate loading (200 ohms) but not any
neutralization. Of course his IRF430s had problems getting above 7 MHz,
but I am hoping that the IRF540's might do a bit better.

It will be quite interesting to see if this can be made to work with a
BITX transceiver. At 40 or so watts it would definitely take the rig
out of the QRP category. What makes this possible with the new kit is
Dan's work on cleaning up the output so that any linear amplifier would
be starting with a signal that meets FCC requirements.

Arv
_._



Allison Parent wrote:


--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@...> wrote:

Allison

After the kit boards are built and working properly, I have some
IRF-540's that are begging to be tried in this rig with 24 volts on
their drains. Not yet sure what to expect but it could be very
interesting.

Arv
_._
Can you say, smoke! I found PP amplifiers with the larger
IRF5xx devices needed care as the gate to drain capcitance can
make them into very good power oscillators. Some have applied
feedback and I've seen one design that used tube(valve) style
cross coupled neutrialization to quiet things down. That said
I've tried the HFpacker design (2 IRF510s PP) at HF and at 24V
it does a respectable 40-50W which is pushing near the thermal
capabilities of the part. There was a design published in QST
back in March 1999 that details how to acomplish this.

The original Bitx design with 24V on the final does around
10-12W at 20m using IRF510, and the IMD is better. The stability
needs some work. I tried adding a 500ohm and 0.1uf cap in series
from gate to drain (like applied in wideband amps) and it gave a
better behaved response. I didn't like the thermal stability
as the standing current tends to creep up as the device heats
if you increase the bias enough to get decent IMD.

Allison



Allison Parent wrote:

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>
<mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@> wrote:

Leonard

Dan Tayloe might be better to answer your question than me. He
designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as 13
turns, wound bifilar (wires twisted together before winding) to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between windings.
I've used fewer turns as the type 43 material has a very high ui (850)
and the number of turns needed are bounded at the low end by too high
and RF current and inadaquate coupling and at teh high end (too many
turns) due to excessive capacitance.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy
at the operating frequency. I usually design (?) them empirically
(i.e. wind them and test power transfer with proper terminating
impedances on each end). In operation these are really more like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular
frequency.

Exactly. there is a fair amount of latitude in their design.


* The transformer T1 is shown on the schematic as 8 turns, wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it may
be hard to get a good inductance meter reading because of the very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant
element.
Tie the wires in parallel together and then measure it as if it were
one fatter wire. With more than 4 turns it will be high (4 turns on
FT37-43 is ~5.6uh).

I might note here that the RF PA design in the 1-17-2007 kit
schematic
has been abandoned because we could not make it stable enough
for all
kit builders to be assured success with it. Dan could only reliably
get
3 watts output, and that was not with a good RF waveform. This one
section is the primary reason that we had to re-design the PCB
and thus
delay kit availability for an additional 3 to 4 weeks. The
present kit
schematic is the one with a date of 2-21-2007.
Not surprized. The power fet used it a fairly high gain device and
the loading impedence is marginal for 20M so layout and lead lenghts
could make it unstable. Testing I've done at 20m wanted the fet to
driving a lower output impedence (I got 6W) with a lower driving
impedence that was heavily swamped with resistive loading. However,
further testing indicated the IMD was poor at 12V. Redesign for 24V
power to the final made higher power both easy and impoved the IMD
and power output. The IRF510 was designed for high speed switching
not RF service so it's being asked to do a lot.

Since that 1-17-2007 schematic Dan has re-designed the RF PA section
to use push-pull drivers and a push-pull RF PA section. This
promises to be more stable and should offer a better chance of
kit builders being successful in building this kit. The output
power is now 7 watts and Dan's spectrum analysis indicates a better
signal quality.
I had the same experience using two IRF510s in PP form at 12V.
I found it tended to take off if the RF load was either reactive
or resitive but >100ohms (2:1 swr).

I've desided to abandon the FET and use low cost power transistors.
At the 10W power level a pair of 27Mhz CB finals such as MRF 472,
2sc1969, 2sc2166 and a long list of others are easier to work
with and inexpensive (2sc2166 usually run under 2$US) and durable.

Allison



AGC Kit

g0fuw <g0fuw@...>
 

Folks
Just a quick posting to say that I successfully added audio AGC to my
BITX 20 at the weekend. The little board came as a kit from Tim
Walford's Somerset range. He calls it his 'Meter Kit' as it drives a
nice S little edgeway meter (not very accurate, but it looks the part)
and it also includes a resistive SWR bridge so the meter provides tune
up facility too. It was intended for use with his Bristol transceiver
project, but it works very well with the BITX.
I had to reduce the gain on the AF amp (remove C between pins 1 & 8)
and add a 10k above the AF gain pot to stop it overloading but other
than that it fits straight in.
The AGC now works a treat so I no longer fall off my chair when 'the
big boys' wade in with 1kW and a yagi at 120'!
I have no connection with Tim's business, just a satisfied customer.
See www.walfordelectronics.co.uk
73, Steve, G0FUW

Re: Question for Arv

kc0wox <bitx@...>
 

I ordered 20 IRF510's so I have a little margin for error. I should
get them tomorrow. I'll pretend I'm building an oscillator so it
will be sure to act like an amplifier.

I appreciate the transformer comments as I have never wound any
toroids before and all of this has been a great learning experience.
Leonard


--- In BITX20@..., "Allison Parent" <kb1gmx@...> wrote:

--- In BITX20@..., arv evans <arvid.evans@> wrote:

Allison

After the kit boards are built and working properly, I have some
IRF-540's that are begging to be tried in this rig with 24 volts
on
their drains. Not yet sure what to expect but it could be very
interesting.

Arv
_._
Can you say, smoke! I found PP amplifiers with the larger
IRF5xx devices needed care as the gate to drain capcitance can
make them into very good power oscillators. Some have applied
feedback and I've seen one design that used tube(valve) style
cross coupled neutrialization to quiet things down. That said
I've tried the HFpacker design (2 IRF510s PP) at HF and at 24V
it does a respectable 40-50W which is pushing near the thermal
capabilities of the part. There was a design published in QST
back in March 1999 that details how to acomplish this.

The original Bitx design with 24V on the final does around
10-12W at 20m using IRF510, and the IMD is better. The stability
needs some work. I tried adding a 500ohm and 0.1uf cap in series
from gate to drain (like applied in wideband amps) and it gave a
better behaved response. I didn't like the thermal stability
as the standing current tends to creep up as the device heats
if you increase the bias enough to get decent IMD.


Allison







Allison Parent wrote:

--- In BITX20@... <mailto:BITX20%
40yahoogroups.com>, arv
evans <arvid.evans@> wrote:

Leonard

Dan Tayloe might be better to answer your question than me.
He
designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as
13
turns, wound bifilar (wires twisted together before winding)
to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between
windings.

I've used fewer turns as the type 43 material has a very high
ui (850)
and the number of turns needed are bounded at the low end by
too high
and RF current and inadaquate coupling and at teh high end
(too many
turns) due to excessive capacitance.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy
at the operating frequency. I usually design (?) them
empirically
(i.e. wind them and test power transfer with proper
terminating
impedances on each end). In operation these are really more
like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular
frequency.

Exactly. there is a fair amount of latitude in their design.


* The transformer T1 is shown on the schematic as 8 turns,
wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it
may
be hard to get a good inductance meter reading because of
the very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant
element.
Tie the wires in parallel together and then measure it as if
it were
one fatter wire. With more than 4 turns it will be high (4
turns on
FT37-43 is ~5.6uh).

I might note here that the RF PA design in the 1-17-2007 kit
schematic
has been abandoned because we could not make it stable enough
for all
kit builders to be assured success with it. Dan could only
reliably
get
3 watts output, and that was not with a good RF waveform.
This one
section is the primary reason that we had to re-design the
PCB
and thus
delay kit availability for an additional 3 to 4 weeks. The
present kit
schematic is the one with a date of 2-21-2007.
Not surprized. The power fet used it a fairly high gain device
and
the loading impedence is marginal for 20M so layout and lead
lenghts
could make it unstable. Testing I've done at 20m wanted the
fet to
driving a lower output impedence (I got 6W) with a lower
driving
impedence that was heavily swamped with resistive loading.
However,
further testing indicated the IMD was poor at 12V. Redesign
for 24V
power to the final made higher power both easy and impoved the
IMD
and power output. The IRF510 was designed for high speed
switching
not RF service so it's being asked to do a lot.

Since that 1-17-2007 schematic Dan has re-designed the RF PA
section
to use push-pull drivers and a push-pull RF PA section. This
promises to be more stable and should offer a better chance
of
kit builders being successful in building this kit. The
output
power is now 7 watts and Dan's spectrum analysis indicates a
better
signal quality.
I had the same experience using two IRF510s in PP form at 12V.
I found it tended to take off if the RF load was either
reactive
or resitive but >100ohms (2:1 swr).

I've desided to abandon the FET and use low cost power
transistors.
At the 10W power level a pair of 27Mhz CB finals such as MRF
472,
2sc1969, 2sc2166 and a long list of others are easier to work
with and inexpensive (2sc2166 usually run under 2$US) and
durable.

Allison



Re: Question for Arv

Allison Parent <kb1gmx@...>
 

--- In BITX20@..., arv evans <arvid.evans@...> wrote:

Allison

After the kit boards are built and working properly, I have some
IRF-540's that are begging to be tried in this rig with 24 volts on
their drains. Not yet sure what to expect but it could be very
interesting.

Arv
_._
Can you say, smoke! I found PP amplifiers with the larger
IRF5xx devices needed care as the gate to drain capcitance can
make them into very good power oscillators. Some have applied
feedback and I've seen one design that used tube(valve) style
cross coupled neutrialization to quiet things down. That said
I've tried the HFpacker design (2 IRF510s PP) at HF and at 24V
it does a respectable 40-50W which is pushing near the thermal
capabilities of the part. There was a design published in QST
back in March 1999 that details how to acomplish this.

The original Bitx design with 24V on the final does around
10-12W at 20m using IRF510, and the IMD is better. The stability
needs some work. I tried adding a 500ohm and 0.1uf cap in series
from gate to drain (like applied in wideband amps) and it gave a
better behaved response. I didn't like the thermal stability
as the standing current tends to creep up as the device heats
if you increase the bias enough to get decent IMD.


Allison







Allison Parent wrote:

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@> wrote:

Leonard

Dan Tayloe might be better to answer your question than me. He
designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as 13
turns, wound bifilar (wires twisted together before winding) to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between windings.
I've used fewer turns as the type 43 material has a very high ui (850)
and the number of turns needed are bounded at the low end by too high
and RF current and inadaquate coupling and at teh high end (too many
turns) due to excessive capacitance.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy
at the operating frequency. I usually design (?) them empirically
(i.e. wind them and test power transfer with proper terminating
impedances on each end). In operation these are really more like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular
frequency.

Exactly. there is a fair amount of latitude in their design.


* The transformer T1 is shown on the schematic as 8 turns, wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it may
be hard to get a good inductance meter reading because of the very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant
element.
Tie the wires in parallel together and then measure it as if it were
one fatter wire. With more than 4 turns it will be high (4 turns on
FT37-43 is ~5.6uh).

I might note here that the RF PA design in the 1-17-2007 kit
schematic
has been abandoned because we could not make it stable enough
for all
kit builders to be assured success with it. Dan could only reliably
get
3 watts output, and that was not with a good RF waveform. This one
section is the primary reason that we had to re-design the PCB
and thus
delay kit availability for an additional 3 to 4 weeks. The
present kit
schematic is the one with a date of 2-21-2007.
Not surprized. The power fet used it a fairly high gain device and
the loading impedence is marginal for 20M so layout and lead lenghts
could make it unstable. Testing I've done at 20m wanted the fet to
driving a lower output impedence (I got 6W) with a lower driving
impedence that was heavily swamped with resistive loading. However,
further testing indicated the IMD was poor at 12V. Redesign for 24V
power to the final made higher power both easy and impoved the IMD
and power output. The IRF510 was designed for high speed switching
not RF service so it's being asked to do a lot.

Since that 1-17-2007 schematic Dan has re-designed the RF PA section
to use push-pull drivers and a push-pull RF PA section. This
promises to be more stable and should offer a better chance of
kit builders being successful in building this kit. The output
power is now 7 watts and Dan's spectrum analysis indicates a better
signal quality.
I had the same experience using two IRF510s in PP form at 12V.
I found it tended to take off if the RF load was either reactive
or resitive but >100ohms (2:1 swr).

I've desided to abandon the FET and use low cost power transistors.
At the 10W power level a pair of 27Mhz CB finals such as MRF 472,
2sc1969, 2sc2166 and a long list of others are easier to work
with and inexpensive (2sc2166 usually run under 2$US) and durable.

Allison



Re: Question for Arv

Arv Evans
 

Allison

After the kit boards are built and working properly, I have some
IRF-540's that are begging to be tried in this rig with 24 volts on
their drains. Not yet sure what to expect but it could be very interesting.

Arv
_._



Allison Parent wrote:


--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, arv
evans <arvid.evans@...> wrote:

Leonard

Dan Tayloe might be better to answer your question than me. He
designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as 13
turns, wound bifilar (wires twisted together before winding) to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between windings.
I've used fewer turns as the type 43 material has a very high ui (850)
and the number of turns needed are bounded at the low end by too high
and RF current and inadaquate coupling and at teh high end (too many
turns) due to excessive capacitance.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy
at the operating frequency. I usually design (?) them empirically
(i.e. wind them and test power transfer with proper terminating
impedances on each end). In operation these are really more like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular
frequency.

Exactly. there is a fair amount of latitude in their design.


* The transformer T1 is shown on the schematic as 8 turns, wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it may
be hard to get a good inductance meter reading because of the very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant
element.
Tie the wires in parallel together and then measure it as if it were
one fatter wire. With more than 4 turns it will be high (4 turns on
FT37-43 is ~5.6uh).

I might note here that the RF PA design in the 1-17-2007 kit schematic
has been abandoned because we could not make it stable enough for all
kit builders to be assured success with it. Dan could only reliably
get
3 watts output, and that was not with a good RF waveform. This one
section is the primary reason that we had to re-design the PCB and thus
delay kit availability for an additional 3 to 4 weeks. The present kit
schematic is the one with a date of 2-21-2007.
Not surprized. The power fet used it a fairly high gain device and
the loading impedence is marginal for 20M so layout and lead lenghts
could make it unstable. Testing I've done at 20m wanted the fet to
driving a lower output impedence (I got 6W) with a lower driving
impedence that was heavily swamped with resistive loading. However,
further testing indicated the IMD was poor at 12V. Redesign for 24V
power to the final made higher power both easy and impoved the IMD
and power output. The IRF510 was designed for high speed switching
not RF service so it's being asked to do a lot.

Since that 1-17-2007 schematic Dan has re-designed the RF PA section
to use push-pull drivers and a push-pull RF PA section. This
promises to be more stable and should offer a better chance of
kit builders being successful in building this kit. The output
power is now 7 watts and Dan's spectrum analysis indicates a better
signal quality.
I had the same experience using two IRF510s in PP form at 12V.
I found it tended to take off if the RF load was either reactive
or resitive but >100ohms (2:1 swr).

I've desided to abandon the FET and use low cost power transistors.
At the 10W power level a pair of 27Mhz CB finals such as MRF 472,
2sc1969, 2sc2166 and a long list of others are easier to work
with and inexpensive (2sc2166 usually run under 2$US) and durable.

Allison

Re: Question for Arv

Arv Evans
 

Leonard

I put the Version 1.1 kit schematic (the one dated 2-20-2007) on my blog
site. You might want to take a look and see what was done to stabilize
and clean up the RF PA sections.

http://arvevans.livejournal.com

Scroll back to the entry on unpacking Version 1.1 parts and you will
find the schematic at the end of that posting.

Arv
_._


kc0wox wrote:


Thanks. I'll try what I have wound and then try your suggestions. I
should get the transistors tomorrow then I can do some testing.
Leonard
KC0WOX

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>,
"Allison Parent" <kb1gmx@...> wrote:

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>,
"kc0wox" <bitx@> wrote:

I'm assembling the linear and I wound T1 and T2 using FT37-43
cores and
the number of turns specified in your 1/17/2007 kit schematic. T1
ended
up measuring 20uh and T2 55uh.

The original Ashhar schematic calls for 3uh inductance for 14mhz
on T1
and doesn't specify inductance for T2.

Is this another place where the turns ratio is the major factor
rather
than inductance?
Yes, these are transformers not tuned circuits. There is a minimum
inductance you need to achieve but using FT37-43 material that takes
only a few turns. For 20m and using FT37-43 the driver transformer
would be 8 turns bifiler of #28 or even #30 wire (Bifiler is a pair
of
wires twisted) and the correct start end ends connected to form a
4:1
transformer (turns ratios is 2:1). The output transformer I'd stack
two or maybe 4 FT37-43 and use 6 Turns bifiler of #22 wire.

That would work for most any thing from 6 to 30 mhz. You could
substitue balun cores (those two hole cores) and reduce the wire
size
so it fits. At 6m I used 4turns on BN43-202 balun core and the
final
I used two FB43-6301 (large bead) side by side like a balun core.

For the mixer, predriver, and modulator tansformers I used BN-43-
2402
balun cores for small size and 6 turns bifiler (#32 wire) worked
well.
At 6m I used a 2sc2166 transistor instead of the IFR510 as the FET
does not do as well at that high frequency.

Hope that helps some.

Allison

Re: Question for Arv

Allison Parent <kb1gmx@...>
 

--- In BITX20@..., arv evans <arvid.evans@...> wrote:

Leonard

Dan Tayloe might be better to answer your question than me. He
designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as 13
turns, wound bifilar (wires twisted together before winding) to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between windings.
I've used fewer turns as the type 43 material has a very high ui (850)
and the number of turns needed are bounded at the low end by too high
and RF current and inadaquate coupling and at teh high end (too many
turns) due to excessive capacitance.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy
at the operating frequency. I usually design (?) them empirically
(i.e. wind them and test power transfer with proper terminating
impedances on each end). In operation these are really more like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular
frequency.

Exactly. there is a fair amount of latitude in their design.


* The transformer T1 is shown on the schematic as 8 turns, wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it may
be hard to get a good inductance meter reading because of the very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant
element.
Tie the wires in parallel together and then measure it as if it were
one fatter wire. With more than 4 turns it will be high (4 turns on
FT37-43 is ~5.6uh).

I might note here that the RF PA design in the 1-17-2007 kit schematic
has been abandoned because we could not make it stable enough for all
kit builders to be assured success with it. Dan could only reliably
get
3 watts output, and that was not with a good RF waveform. This one
section is the primary reason that we had to re-design the PCB and thus
delay kit availability for an additional 3 to 4 weeks. The present kit
schematic is the one with a date of 2-21-2007.
Not surprized. The power fet used it a fairly high gain device and
the loading impedence is marginal for 20M so layout and lead lenghts
could make it unstable. Testing I've done at 20m wanted the fet to
driving a lower output impedence (I got 6W) with a lower driving
impedence that was heavily swamped with resistive loading. However,
further testing indicated the IMD was poor at 12V. Redesign for 24V
power to the final made higher power both easy and impoved the IMD
and power output. The IRF510 was designed for high speed switching
not RF service so it's being asked to do a lot.

Since that 1-17-2007 schematic Dan has re-designed the RF PA section
to use push-pull drivers and a push-pull RF PA section. This
promises to be more stable and should offer a better chance of
kit builders being successful in building this kit. The output
power is now 7 watts and Dan's spectrum analysis indicates a better
signal quality.
I had the same experience using two IRF510s in PP form at 12V.
I found it tended to take off if the RF load was either reactive
or resitive but >100ohms (2:1 swr).

I've desided to abandon the FET and use low cost power transistors.
At the 10W power level a pair of 27Mhz CB finals such as MRF 472,
2sc1969, 2sc2166 and a long list of others are easier to work
with and inexpensive (2sc2166 usually run under 2$US) and durable.


Allison

Re: Question for Arv

kc0wox <bitx@...>
 

Thanks. I'll try what I have wound and then try your suggestions. I
should get the transistors tomorrow then I can do some testing.
Leonard
KC0WOX

--- In BITX20@..., "Allison Parent" <kb1gmx@...> wrote:

--- In BITX20@..., "kc0wox" <bitx@> wrote:

I'm assembling the linear and I wound T1 and T2 using FT37-43
cores and
the number of turns specified in your 1/17/2007 kit schematic. T1
ended
up measuring 20uh and T2 55uh.

The original Ashhar schematic calls for 3uh inductance for 14mhz
on T1
and doesn't specify inductance for T2.

Is this another place where the turns ratio is the major factor
rather
than inductance?
Yes, these are transformers not tuned circuits. There is a minimum
inductance you need to achieve but using FT37-43 material that takes
only a few turns. For 20m and using FT37-43 the driver transformer
would be 8 turns bifiler of #28 or even #30 wire (Bifiler is a pair
of
wires twisted) and the correct start end ends connected to form a
4:1
transformer (turns ratios is 2:1). The output transformer I'd stack
two or maybe 4 FT37-43 and use 6 Turns bifiler of #22 wire.

That would work for most any thing from 6 to 30 mhz. You could
substitue balun cores (those two hole cores) and reduce the wire
size
so it fits. At 6m I used 4turns on BN43-202 balun core and the
final
I used two FB43-6301 (large bead) side by side like a balun core.

For the mixer, predriver, and modulator tansformers I used BN-43-
2402
balun cores for small size and 6 turns bifiler (#32 wire) worked
well.
At 6m I used a 2sc2166 transistor instead of the IFR510 as the FET
does not do as well at that high frequency.

Hope that helps some.

Allison

Re: Question for Arv

Allison Parent <kb1gmx@...>
 

--- In BITX20@..., "kc0wox" <bitx@...> wrote:

I'm assembling the linear and I wound T1 and T2 using FT37-43 cores and
the number of turns specified in your 1/17/2007 kit schematic. T1 ended
up measuring 20uh and T2 55uh.

The original Ashhar schematic calls for 3uh inductance for 14mhz on T1
and doesn't specify inductance for T2.

Is this another place where the turns ratio is the major factor rather
than inductance?
Yes, these are transformers not tuned circuits. There is a minimum
inductance you need to achieve but using FT37-43 material that takes
only a few turns. For 20m and using FT37-43 the driver transformer
would be 8 turns bifiler of #28 or even #30 wire (Bifiler is a pair of
wires twisted) and the correct start end ends connected to form a 4:1
transformer (turns ratios is 2:1). The output transformer I'd stack
two or maybe 4 FT37-43 and use 6 Turns bifiler of #22 wire.

That would work for most any thing from 6 to 30 mhz. You could
substitue balun cores (those two hole cores) and reduce the wire size
so it fits. At 6m I used 4turns on BN43-202 balun core and the final
I used two FB43-6301 (large bead) side by side like a balun core.

For the mixer, predriver, and modulator tansformers I used BN-43-2402
balun cores for small size and 6 turns bifiler (#32 wire) worked well.
At 6m I used a 2sc2166 transistor instead of the IFR510 as the FET
does not do as well at that high frequency.

Hope that helps some.

Allison

Re: Question for Arv

kc0wox <bitx@...>
 

Thanks for the answer. I will go ahead and try a few things. I'd like
to get this board working as I'm sure others may be using the same
circuit.

Your blog has been a lot of help. It has helped me over a few spots
that I didn't know the answer.

I'm looking forward to the rollout of the kit. I want to build one.
Leonard
KC0WOX

--- In BITX20@..., arv evans <arvid.evans@...> wrote:

Leonard

Dan Tayloe might be better to answer your question than me. He
designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as 13
turns, wound bifilar (wires twisted together before winding)
to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between
windings.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy
at
the operating frequency. I usually design (?) them
empirically
(i.e. wind them and test power transfer with proper
terminating
impedances on each end). In operation these are really more
like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular
frequency.

* The transformer T1 is shown on the schematic as 8 turns, wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it
may
be hard to get a good inductance meter reading because of the
very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant
element.

I might note here that the RF PA design in the 1-17-2007 kit
schematic
has been abandoned because we could not make it stable enough for
all
kit builders to be assured success with it. Dan could only
reliably get
3 watts output, and that was not with a good RF waveform. This one
section is the primary reason that we had to re-design the PCB and
thus
delay kit availability for an additional 3 to 4 weeks. The present
kit
schematic is the one with a date of 2-21-2007.

Since that 1-17-2007 schematic Dan has re-designed the RF PA
section to
use push-pull drivers and a push-pull RF PA section. This promises
to
be more stable and should offer a better chance of kit builders
being
successful in building this kit. The output power is now 7 watts
and
Dan's spectrum analysis indicates a better signal quality.

At present Jim Kortge and myself are assembling prototypes from the
newest PCB to insure that there are no serious problems with the
new
layout. I have not yet got as far as the RF PA, but will post
results
on my blog site as soon as info is available:

http://arvevans.livejournal.com

This blog covers my early construction of the Version-1 PCB, and
the
more recent build of the new Version 1.1 PCB. I am adding pages as
assembly of each section is completed.

Arv
_._


kc0wox wrote:

I'm assembling the linear and I wound T1 and T2 using FT37-43
cores and
the number of turns specified in your 1/17/2007 kit schematic. T1
ended
up measuring 20uh and T2 55uh.

The original Ashhar schematic calls for 3uh inductance for 14mhz
on T1
and doesn't specify inductance for T2.

Is this another place where the turns ratio is the major factor
rather
than inductance?

Leonard
KC0WOX



Re: Question for Arv

Arv Evans
 

Leonard

Dan Tayloe might be better to answer your question than me. He designed
those transformers specifically for this kit.

However, I will hazard a guess or two:

* The Transformer T2 is shown on the 1-17-2007 schematic as 13
turns, wound bifilar (wires twisted together before winding) to
make up a transmission-line transformer. Due to the twisted
wires, it may be hard to get a good inductance meter reading
because of the very high distributed capacitance between windings.

The real key to this, and other transmission-line type
transformers, is that it must efficiently transfer RF energy at
the operating frequency. I usually design (?) them empirically
(i.e. wind them and test power transfer with proper terminating
impedances on each end). In operation these are really more like
a balun than an inductive element. This transformer is for
impedance matching and is not resonant on any particular frequency.

* The transformer T1 is shown on the schematic as 8 turns, wound
bifilar (wires twisted together before winding) to make up a
transmission-line transformer. Due to the twisted wires, it may
be hard to get a good inductance meter reading because of the very
high distributed capacitance between windings. Again, this
transformer is for impedance matching and is not a resonant element.

I might note here that the RF PA design in the 1-17-2007 kit schematic
has been abandoned because we could not make it stable enough for all
kit builders to be assured success with it. Dan could only reliably get
3 watts output, and that was not with a good RF waveform. This one
section is the primary reason that we had to re-design the PCB and thus
delay kit availability for an additional 3 to 4 weeks. The present kit
schematic is the one with a date of 2-21-2007.

Since that 1-17-2007 schematic Dan has re-designed the RF PA section to
use push-pull drivers and a push-pull RF PA section. This promises to
be more stable and should offer a better chance of kit builders being
successful in building this kit. The output power is now 7 watts and
Dan's spectrum analysis indicates a better signal quality.

At present Jim Kortge and myself are assembling prototypes from the
newest PCB to insure that there are no serious problems with the new
layout. I have not yet got as far as the RF PA, but will post results
on my blog site as soon as info is available:

http://arvevans.livejournal.com

This blog covers my early construction of the Version-1 PCB, and the
more recent build of the new Version 1.1 PCB. I am adding pages as
assembly of each section is completed.

Arv
_._


kc0wox wrote:


I'm assembling the linear and I wound T1 and T2 using FT37-43 cores and
the number of turns specified in your 1/17/2007 kit schematic. T1 ended
up measuring 20uh and T2 55uh.

The original Ashhar schematic calls for 3uh inductance for 14mhz on T1
and doesn't specify inductance for T2.

Is this another place where the turns ratio is the major factor rather
than inductance?

Leonard
KC0WOX

Question for Arv

kc0wox <bitx@...>
 

I'm assembling the linear and I wound T1 and T2 using FT37-43 cores and
the number of turns specified in your 1/17/2007 kit schematic. T1 ended
up measuring 20uh and T2 55uh.

The original Ashhar schematic calls for 3uh inductance for 14mhz on T1
and doesn't specify inductance for T2.

Is this another place where the turns ratio is the major factor rather
than inductance?

Leonard
KC0WOX

It looks like the main board is complete

kc0wox <bitx@...>
 

I fired up the vfo on the board today and it seems like the board
functions as it should. With the board complete, it seems that the
adjustments are far less critical. They were much easier to do.

I drew component location prints for the linear board, (I'll post them
on my website, http://golddredgervideo.com/bitx20/ soon), and ordered
the parts. The IRF510's were about 50 cents each through Newark
Electronics. I have a couple of problems with the vfo but I will wait
until this weekend to fix them so I can take video of them before I fix
them. Both the transmit and the receive appear to work properly.

After I get the linear functioning, I will document voltages throughout
each stage so you can get an idea if your build is performing about
normal.

Leonard
KC0WOX