Date   

Re: modulator mod

Arv Evans <arvevans@...>
 

Allison

Would it be possible for you do a quick schematic of the changes and store it
in the FILES section of this forum? That way it will be available for others
who might not understand all that was changed from just the textual
description.

Thanks,

Arv K7HKL
_._

On Thursday 28 July 2005 09:20 pm, ajparent1 wrote:
One of the things I didn't like in the 20m proto BITX I'd built
was the presence of audio getting into the IF amp on transmit and IF
noise in to the audio on recieve.  I'd gone the route of adding an
47uh RF choke from the intersection of the balance pot wiper to ground
which helped greatly.  However, it always bothered me. 

So I opened it up and tried a design change that I find pleasing and
also elimiates a number of components.  As an engineer I'm the sort
that looks at a design and says "what if..?".  The solution was
staring me in the face and also eliminates the PI attenuator as well.
The change is to turn the balanced modulator around and feed the IF
in on the transformer and RF (bfo) in at the balance potentiometer
via the .1uf capacitor.  This eliminated the need for the 3 resistors
and the rf choke.  I noted cleaner modulation, less RX noise and more
gain available in both RX and TX.

Might as well add this mod to the collection.  I plan to use this
mod in the 6M version.

Allison
KB1GMX







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modulator mod

ajparent1 <kb1gmx@...>
 

One of the things I didn't like in the 20m proto BITX I'd built
was the presence of audio getting into the IF amp on transmit and IF
noise in to the audio on recieve. I'd gone the route of adding an
47uh RF choke from the intersection of the balance pot wiper to ground
which helped greatly. However, it always bothered me.

So I opened it up and tried a design change that I find pleasing and
also elimiates a number of components. As an engineer I'm the sort
that looks at a design and says "what if..?". The solution was
staring me in the face and also eliminates the PI attenuator as well.
The change is to turn the balanced modulator around and feed the IF
in on the transformer and RF (bfo) in at the balance potentiometer
via the .1uf capacitor. This eliminated the need for the 3 resistors
and the rf choke. I noted cleaner modulation, less RX noise and more
gain available in both RX and TX.

Might as well add this mod to the collection. I plan to use this
mod in the 6M version.

Allison
KB1GMX


Re: Pre driver output

ajparent1 <kb1gmx@...>
 

Hi,

2mw is very low from the driver. Mine I see nearly 1mw at the output
of the bandpass filter (L1, L1,L3). The driver stage brings that up
to near 300mW on mine. I don't use the IRF510 as the output is more
than sufficient to drive a TenTec 1208 transverter at 100mW,
1mW however was not adaquate. Driver transistor used on mine was
2N2219A with bifilar transformer wound on a 2 hole core of -43
material to match 50 ohms. Without the 5db output attenuator it
measures as 3.8V rms across 50 ohms which is actually 288.8mW using
a HP rf voltmeter. Thats close enough to 300mW.

If you are using a trifilar transformer on the driver and measure
the power to the IRF then the driving impedence is around 10-12 ohms
and a 50ohm power meter will be inaccurate. Even then I'd expect
to see about 1.7-1.9V of rf at that point.

In any case 300mV is invalid. The gate of IRF needs to be driven
with several volts of RF to develop expected power without instability.

On mine the Q14 (predriver) device is 2N2222A and driver is 2N2219A
both have FT ratings of 350mhz which is adaquate to get good gain at
14mhz.

Measurements at the output of the filter (at 50ohms) is .9-1mw.
After Q14 I get 40mW. Adding the driver brings that to 300mW.
I used ferrite loaded transformers at T1, t2 and T3 as well as
collector of 2n2219A. Also added a choke coil (DC return) at RF
mixer (100uh molded type) and at modulator. Transistors used
are Q1,Q13,Q7 are 2n2222A, Q2,3,12,11,9,8,10 are all 2n3904.
This version uses a different VFO (Hartly with fet buffer).
All circuits are bypssed with more than shown is schemtic
and some sections are shielded (modulator and bfo). Construction
is dead bug (ugly on ground plane OF unetched PCB).

A newer version is being built that will use a PLL to provide LO
and the output will be for 6m using 9.6mhz filter, 40mhz LO and
I may try commercial DBM (anzac MD108) for both modulator and
mixer. Since this one is to be small power will be limited to
around 3-5W and use a RF transistor 2sc1971 for the final.

More information than asked for but, measurements are how I know
a circuit does indeed perform as expected.

Allison

--- In BITX20@..., "vdberghak" <vdberghak@z...> wrote:
Hi Milarepa,
based on my measurements, it is only a few mw, so the oposite of
what Allison measured.
I searched for you in the older postings (I have often the feeling
that older messages are not red) and you can find my answer in
message 375 (containing a mistake) and 387.
Good luck,
Chris.

--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Based on my proto 300mW is correct. If there were 300mV the power
would be about 2mW which is way to little.

Allison
KB1GMX


--- In BITX20@..., "MILAREPA" <MILAREPA@T...> wrote:
Dear forum,
I have read somewhere from the posting messages that the output
of pre
driver should be about 300 mWatts,
but I read from the article it should be about 300 mVolts.
Which is right ?
-------
I begin to test the tx section,
rx section test is good in 3.5; 7; 10; 14 MHz.
-------
Thanks.


Re: Pre driver output

Chris van den Berg
 

Hi Milarepa,
based on my measurements, it is only a few mw, so the oposite of
what Allison measured.
I searched for you in the older postings (I have often the feeling
that older messages are not red) and you can find my answer in
message 375 (containing a mistake) and 387.
Good luck,
Chris.

--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Based on my proto 300mW is correct. If there were 300mV the power
would be about 2mW which is way to little.

Allison
KB1GMX


--- In BITX20@..., "MILAREPA" <MILAREPA@T...> wrote:
Dear forum,
I have read somewhere from the posting messages that the output
of pre
driver should be about 300 mWatts,
but I read from the article it should be about 300 mVolts.
Which is right ?
-------
I begin to test the tx section,
rx section test is good in 3.5; 7; 10; 14 MHz.
-------
Thanks.


Re: Pre driver output

ajparent1 <kb1gmx@...>
 

Based on my proto 300mW is correct. If there were 300mV the power
would be about 2mW which is way to little.

Allison
KB1GMX

--- In BITX20@..., "MILAREPA" <MILAREPA@T...> wrote:
Dear forum,
I have read somewhere from the posting messages that the output of pre
driver should be about 300 mWatts,
but I read from the article it should be about 300 mVolts.
Which is right ?
-------
I begin to test the tx section,
rx section test is good in 3.5; 7; 10; 14 MHz.
-------
Thanks.


BITX PA

g0fuw@...
 

Folks
I am working from the (c)2004 circuit on Ashar's web page and have very low
output from PA. I am using cheap general purpose transistors (ME4003) and
changed pre-driver for 2N2222. Better but still only about 1W out.
I have used a very similar PA in the TCF transceiver by VK3XU and it works
fine. That is on 40m though.
I have read through previous postings and applied mods by Chris, PA3CRX.
I now have full 6W output. Well done Chris!
I see Ashar has adopted the trifilar transformer and the extra 200pF capacitor
in his simple dual band transceiver design. Is there a definitive revision,
or is it a case of 'suck it and see'?
73, Steve, G0FUW


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Pre driver output

MILAREPA <MILAREPA@...>
 

Dear forum,
I have read somewhere from the posting messages that the output of pre
driver should be about 300 mWatts,
but I read from the article it should be about 300 mVolts.
Which is right ?
-------
I begin to test the tx section,
rx section test is good in 3.5; 7; 10; 14 MHz.
-------
Thanks.


Re: need help for vfo

ajparent1 <kb1gmx@...>
 

Hi Chris,

Rather than guess at Gautams question it is easy to ask. Saves
giving multiple conflicting answers.

I may add my favorite "cheap" Varactor [tuning] diode is 1n4007
rectifier. It also makes a fair substitute for a PIN diode
in switches and attenuators. Not as good as the real thing but
far less cost.


Allison
KB1GMX

--- In BITX20@..., "vdberghak" <vdberghak@z...> wrote:
Hi,
I think the tuning range is found to be to small.
Likely because the tuning capacitor does not have enough capacitance.
(the LC combination defines the frquency and if the L is fixed, only
the C can be responsible?).
If there are more capacitors inside the housing, just connect them
also. Otherwise an other type of capacitor is needed.
An other possibility is to have the range in two bands, by switching
an additional capacitor in parallel.
Regards,
Chris.

--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Hello,

First the transistor used. The 2n222a or 2n3904 are excellent for
this type VFO.

I have tried to understand what problem you are having. I suspect
the range of tuning 0-230khz is either too small or too great for
you. The ability to adjust the frequency using the trimmer says
the coil and other components are close.

Allison
KB1GMX


--- In BITX20@..., kumar gautam <fromgautam@y...>
wrote:
hi,
in my bitx20 vfo frequency is 4.000 to 4.230MHz or trimming the
trimmer i found 4.200 to 4.430 (i.e 0 to 0.230 MHz tuning range).
aftyer several changing in coil and various types of capacitor(2j
or
2x type) i coul'd not achive the desired frequency. i used 2n2222a
transistors for VFO and BFO and for rest 2n3904.
kindly anyone help me in this regard
with 73's
de kumar gautam


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Re: IRF510 on higher voltage?

Rahul Srivastava
 

Hi!
 
Arv is quite right. Here we also took a similar route. First was the need for a cheap common PSU so we selected a portable BW TV transformer sec abt 20V AC unloaded around 1.25amp. Unreg DC goes to IRF.
 
Later I realised that 2N3866 is 24V device so I gave it unreg DC too on collector thru a simple choke on the binocular cores abt 9-10turns. Emitter resistor 10ohms, base to gnd 2k2 and base to 12V TX for bias 10-12K. The collector director drives the gate via a 0.1 cap of IRF530. Current drawn is abt 1amp now and power more than 12W.
 
Incidently the Mousefet series of TX also drive the power fets in similar manner.
 
Rest of the ckt is powered thru reg 13.6VDC by a LM317 as evident from my linear board layout. This scheme of 3866 on unreg DC also reduces some load on 317.
 
BTW I have stacked 2-3 nos of tap washer for LPF, the number of turns for required inductance is less and more manageable.
 
73
 
Rahul VU3WJM
 
 


Arv Evans wrote:
Chris

My BITX40 uses 24 volts on the IRF510 for a power output of 11 watts.  It
required the addition of separate sheilding, 2 ferrite beads on the gate
lead, and a paracitic suppressor (2 ohm 2 watt carbon resistor wound with 4
turns of #16 AWG) between drain and output filter to tame it.

If you have a variable power supply, try bringing the voltage up slowly once
you have it working properly with 12 volts.  I did not do this the first time
and it cooked an IRF510!       8-(

My IRF510 is mounted on the heat sink for a computer CPU.  The original CPU
fan is mounted on the other side of the heat sink and turns on with the PTT
controlled voltage for the IRF510.  I bolted the IRF510 directly to the heat
sink, which is mounted to the chassis via 1/2 inch (1.3 cm) nylon standoffs. 
The fan housing is plastic so this isolates it from RF on the heat sink.

Next step might be to replace the IRF510 with push-pull IRF510s or IRF630s and
a 48 volt supply!

Arv K7HKL
_._


On Wednesday 20 July 2005 03:17 am, vdberghak wrote:
>  Hi all,
>  did anyone tried to put higher voltage on the IRF stage?
>  If so, I am interrested about the results like:
>  - stability,
>  - increase of output power.
>  If the output power is not much higher and other problems will show up,
>  I will not try it...
>  Thanks,
>  Chris.
>
>
>
>
>  YAHOO! GROUPS LINKS
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>
>  Visit your group "BITX20" on the web.
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>  BITX20-unsubscribe@...
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Re: need help for bitx VFO & BFO

Arv Evans <arvevans@...>
 

Gautam

I am assuming that you are using the same size VFO inductor and capacitors as
specified by Farhan. If you are using the original design with the 36V zener
diode as a VFO fine tuning capacitor, you might try a different diode. They
do not all show the same capacitance value or range. If this does not work,
it is possible to use other diodes in place of the zener. My BITX20 uses a
Red LED as the tuning diode.

It is possible that you have connected the tuning diode using the wrong
polarity. Try reversing it to see what the results might be.

Since the tuning diode contributes only 10 pf, it can be disconnected
temporarily and the VFO tested without it.

If you do not have a way to measure capacitance, the value of your variable
capacitor can be measured using the simple capacitance test circuit shown in
<http://www.geocities.com/k7hkl_arv/Capacitor_Measuring_Tool.png>. This
might help to verify that your tuning capacitor is really 365 pf. With the
capacitor completely open it should measure less than 20 pf.

Arv K7HKL
_._

On Saturday 23 July 2005 09:08 am, ajparent1 wrote:
gautam


Re: need help for bitx VFO & BFO

ajparent1 <kb1gmx@...>
 

--- In BITX20@..., kumar gautam <fromgautam@y...> wrote:
Hello,
In my bitx20 BFO shows 9.995 MHz. and in VFO section when i add 2j
gang capacitor my VFO shows 4.000 to 4.180 MHz(when trimmer shifted to
4.000MHz) and after tuning Trimmer(shifted to 4.150MHz) it shows 4.180
to 4.410Mhz.
After trying various type of variable capacitors i coul'd not find
entire range i.e. 4.000 to 4.400MHz.
Kindly help me in this regard i.e.
1. what is the exact frequency of BFO.
Varies depending on the crystal filter characteristics. Ideally
it should be tuned to 300hz down the lower frequency edge (assuming
upper sideband) of the filter slope. To do that precisely you have
to know the filter shape. The alternate way is to listen to good
signals and start with the bfo low and tune it up for natural
sounding recieve signal. Then there may be some fine tuning of the
BFO once you have a QSO for best TX sound.

2. What modification should i do for correcting the VFO.
Try fewer turns on VFO coil. The tuning diode the 22pf capacitor
connected to the tuning diode may need a slight increase in value.

also could i connect T1,T2 and T3 legs in any direction or it is
coneected in any direction.

?? I am not certain what you are asking.

Allison
KB1GMX


Re: need help for vfo

Chris van den Berg
 

Hi,
I think the tuning range is found to be to small.
Likely because the tuning capacitor does not have enough capacitance.
(the LC combination defines the frquency and if the L is fixed, only
the C can be responsible?).
If there are more capacitors inside the housing, just connect them
also. Otherwise an other type of capacitor is needed.
An other possibility is to have the range in two bands, by switching
an additional capacitor in parallel.
Regards,
Chris.

--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Hello,

First the transistor used. The 2n222a or 2n3904 are excellent for
this type VFO.

I have tried to understand what problem you are having. I suspect
the range of tuning 0-230khz is either too small or too great for
you. The ability to adjust the frequency using the trimmer says
the coil and other components are close.

Allison
KB1GMX


--- In BITX20@..., kumar gautam <fromgautam@y...>
wrote:
hi,
in my bitx20 vfo frequency is 4.000 to 4.230MHz or trimming the
trimmer i found 4.200 to 4.430 (i.e 0 to 0.230 MHz tuning range).
aftyer several changing in coil and various types of capacitor(2j
or
2x type) i coul'd not achive the desired frequency. i used 2n2222a
transistors for VFO and BFO and for rest 2n3904.
kindly anyone help me in this regard
with 73's
de kumar gautam


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Re: need help for vfo

ajparent1 <kb1gmx@...>
 

Hello,

First the transistor used. The 2n222a or 2n3904 are excellent for
this type VFO.

I have tried to understand what problem you are having. I suspect
the range of tuning 0-230khz is either too small or too great for
you. The ability to adjust the frequency using the trimmer says
the coil and other components are close.

Allison
KB1GMX


--- In BITX20@..., kumar gautam <fromgautam@y...> wrote:
hi,
in my bitx20 vfo frequency is 4.000 to 4.230MHz or trimming the
trimmer i found 4.200 to 4.430 (i.e 0 to 0.230 MHz tuning range).
aftyer several changing in coil and various types of capacitor(2j or
2x type) i coul'd not achive the desired frequency. i used 2n2222a
transistors for VFO and BFO and for rest 2n3904.
kindly anyone help me in this regard
with 73's
de kumar gautam


---------------------------------
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need help for vfo

kumar gautam <fromgautam@...>
 

hi,
in my bitx20 vfo frequency is 4.000 to 4.230MHz or trimming the trimmer i found 4.200 to 4.430 (i.e 0 to 0.230 MHz tuning range). aftyer several changing in coil and various types of capacitor(2j or 2x type) i coul'd not achive the desired frequency. i used 2n2222a transistors for VFO and BFO and for rest 2n3904.
kindly anyone help me in this regard 
with 73's
de kumar gautam


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Re: need help for IRF540

Rahul Srivastava
 

Hi!
 
Go ahead with 540. Let me know someone coming this side 510 is available at Lucknow.
 
73
 
Rahul VU3WJM
 


kumar gautam wrote:
HI,
HERE IN MARKET IRF510 IS NOT AVAILABLE, ONLY IRF540 IS AVAILABLE. ANY ONE HELP ME THAT IRF540 IS EQUIVALENT OF IRF510 OR I CAN SUBSTITUTE THIS FET.
WITH 73'S
DE KUMAR GAUTAM


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FW: Re: IRF510 on higher voltage?

ajparent1 <kb1gmx@...>
 

Hello Hans,

I do hope you got my initial response. The blocking may be enroute,
it's not anything I can control. Do try to reply to the arrl.net
address rather than direct.

High power (greater than 20w or so) solid state amps are not trivial
design exercises. As a result experiments can easuly destroy
transistors. This is why the IRF510 became so popular, they are
inexpensive (compared to true RF power fets) and work acceptably.

I do not know the PL5xx Valves but I will assume they are not unlike
the US Television sweep tubes. Typically those tubes are rated for
30-40W plate dissipation or around 80w for intermittent SSB service.
These tubes are related in design to the famous 6146 final valve used
in a large number of transmitters. Running them hot (plates glowing)
is not good for their life or quality of signal. It would be better
to run several in parallel and abuse them less. Also running higher
plate voltages 500-800v will give a better signal and easier plate
matching.

A suitable mains transformer is always troublesome to obtain but it's
possible to wind one. There are sites that discuss this and it's
not unreasonable. Finding used equipment that can donate a
transformer is another path..

Good luck,
Allison
KB1GMX (@arrl.net)

--- In BITX20@..., Hans Summers <Hans.Summers@t...> wrote:

Apologies list, for the bandwidth - I am having some trouble emailing
Allison on private email. Seems I am blocked somewhere :-(

73 Hans G0UPL
http://www.HansSummers.com

-----Original Message-----
From: Hans Summers
Sent: 22 July 2005 15:40
To: 'Allison'
Subject: RE: [BITX20] Re: IRF510 on higher voltage?



Hello Allison

I love Huff & Puff. These days DDS is so easy, but H&P is still
simpler and
suitable for many people with no microcontroller etc skills. Though
I built
a microcontroller-less DDS:
http://www.hanssummers.com/radio/dds/index.htm

Thanks for the advice. I actually have been planning to build a
valve linear
for quite a while. I have accumulated more than sufficient number of
PL519 /
PL509 TV sweep valves - there are several designs on the internet
providing
for 400+ W using four PL509/519's paralleled. Very cheap and
reliable. What
I am lacking is the HT transformer. I quite liked Arv's idea of a solid
state linear because the PSU is there, all ready and waiting and
cabinetted!

Thanks for the links, I had a good look around. You're right, it doesn't
look very cheap. The very real possibility of frying the transistors
makes
the idea even more expensive. From what I hear, those PL5xx sweep
valves are
virtually indestructible, even if you make them practically red hot.

All of my ham stuff to date has been at 10W or below. See my TX and
RX at:

http://www.hanssummers.com/radio/cwtx/index.htm
http://www.hanssummers.com/radio/polyphase/index.htm

I had my first ever QSO in March 2002 (a mere 8 years after getting my
license!). I've had over 500 QSO's now, all using that 1-valve crystal
controlled CW transmitter. Mostly on 80m, but also on 40 and 30 once I'd
converted the transmitter for those bands.

I'm not a committed QRP'er, I like to operate QRP but I'm not averse
to QRO
either, just so long as it's homebrew. I've never touched a
commercial rig
and gonna keep it that way!

I did make a 2m AM handheld see
http://www.hanssummers.com/radio/fredbox/index.htm - it's not
finished yet,
some trouble with the crystal oscillator multipliers. Needs a bit
more work.

Tnx again for the advice and links.

73 de QTH nr London, UK
Hans G0UPL

-----Original Message-----
From: Allison [mailto:ajp166@b...]
Sent: 22 July 2005 13:30
To: Hans Summers
Subject: Re: [BITX20] Re: IRF510 on higher voltage?


Hans Summers wrote:
Hi Allison

I am moderator of the BITX20 and have been following your postings
with interest. I have a partially built BITX20 awaiting a little
debugging and perhaps some of the mods. Unfortunately very little
time
to work on it at the moment. The pictures are in the G0UPL folder on
the group page.
Hello Hans,

I have built and experimented with you milimal H&P circuits. Good
ideas!

I was thinking of using this PSU with switching, as a variable
medium-high voltage supply for whatever I needed it for - but Arv
K7HKL (who you'll know from the BITX group) suggested, why not
turn it
into a solid state linear? 50V should suit MOSFET's quite well for
400W and the current capability more than adequate. I have attached a
couple of (poor quality) photos of this monster PSU. You'll see that
the it's divided into two compartments, the top contains just the
choke and three capacitors. It should be possible for me to move
those
caps elsewhere which would leave quite a lot of space, I think enough
for the linear. I could bolt on four aluminium panels, one of
which to
function as front panel for metering, low pass filter switching, etc.
Opinion, doing that would represent the hard way with limited success.

To get to 400W is a significant endevor and trying with unknown RF
performance power fets is likely failure prone. All of the 100W or
more
designs for RF power use known RF transistors (bipolar or fet) that are
expensive (.5-2$/watt US). Most of the high voltage switching FETs
are fast
enough to operate at RF but Miller capcitance and input capacitance
will make themm very hard to drive at HF especially 10M.

I may add that the IMD performace for IRF510 and friends is terrible and
that translates to RF polution. They were not developed for linear
service, they were intended as power switches. The other thing is the
TO220 tab cases have poor thermal dissapation. That makes getting
thermal stability hard.

IF you were into AM phone, it's possible to use switching fets in a
class E design (Not FOR SSB). There are several here doing that with
power to 1.5KW. There are websites that discuss this.

Now, if you really still up for the idea.. Heres a possible path to
follow.

Expect to use parallel devices (seperate bias for each device) in push
pull configuration. You will need to accomodate the very high
(800-2000pF) input capacitance and low impedences involved. Expect
elaborate groundplanes and input/output transformers with quality
ferrite. A design of four IRF510s in pushpull (pairs of parallel
devices in pushpull) might get you to 80-100W at 24V or about 1Sunit
down
from 400W. Generally parallel devices are touchy and each has to
be biased independent of others.

So, I wondered what you thought of this crazy idea, and can you
suggest any web references on solid state linears at this power? I
did
some googling but didn't manage to find anything particularly
applicable. I have heard that Motorola might have some good App notes
about this.
Yes they do but, not for common HEXfets or other low cost power fets.
DEVICES like MRF140 and the like are used and they are not inexpensive.
Typical Vdd for these parts is in the 50V region (at up to 20A!).

Start with this site: http://www.communication-concepts.com/eb104.htm

Comm Concepts sells kits for power amps based on Mototrola app notes.
Browse the site for examples, schematics and some of the apnotes.
Also you
can find some of the appnotes on the net. However, none
specify low cost fets and likely would not support low cost power fets.

Also, what is your opinion about valve vs solid state? It seems
strange that such a large number of linears are still valve based?
Even the newest models.
Simple, valve designs using obtainable valves are fairly straight
foward and
well documented. A 3-500 or 4-400 in grounded grid with 2000V on
the plate will easily hit 400W for 80-10m. A pair of 811/572B are in
the same league as well as a long list of other Valves that maybe had
used or surplus.

Why Valves(tubes)? They are known, durable within experience of most
hams and often can be had inexpensively. When you consider a 3-500Z can
often be had new for around 150$us and MRF150(x4) will cost 200$us
and the
FETs may destruct on power up it's not too hard to visualize.

This outfit sells RF power transistors and other items like
tubes(valves).

http://www.rfparts.com/product.html

While I've done commercial work at high power I choose to do most of
the ham activity at under 20W. My unusual twist on that is my station
while low powered is supported off of solar pannels and batteries. I
may add
that I prefer VHF and up for my experiements.


Regards,
Allison
KB1GMX


Re: need help for IRF540

ajparent1 <kb1gmx@...>
 

Hello,

That IRF540 will be very difficult to drive with increasing frequency.
The input will be very reactive and will require a more complex
network to get the needed RF power (and voltage) impressed across
that gate capacitance. That takes greater power and the driver may
not be up to the task. A first order calculation says driving
impedence will be 1/10th (.1) times that of the IRF510. None of the
input or output networks used will perfom as well with the irf540
due to it's differences. At 80m this will not be as bad as 20 or 10m.

I'd try it but do not be surprized if the results require redesign
to achive adaquate gain. If you are successful you may be rewarded
with greater power than the IRF510. A scratch evaluation suggests
if accomodated the IRF540 could be capable of 60-80w output with
about 4-5W drive at the lower HF frequencies aassuming it's not
bandwidth limited.

There are several parameters to look at besides those quoted.
Gate turn on voltage (lower the better). Output capacitance
as well as Drain to Gate capacitance are also functional
parameters of importance. The drain to gate capacitance is
can be thought of as a negative feedback capacitor from Drain
to gate and limits gain with increasing frquency. The result
is that you need to feed both the gate and extract power from the
drain at low impedences or the implied feedback will reduce gain to
below zero (less out that in). At 20m these will look like around 7
and 2 ohms for the IRF540 where the IRF510 they are around 65
and 10-12 ohms. Accomodating these new conditions were not
anticipated in the original design.

I hope this gives a starting point to a successful design.





Allison

--- In BITX20@..., Heinz Schnait <oe5eep@q...> wrote:
Hi Kumar,

The datasheets give the following parameters:

IRF510: RDS = 0.54 Ohms; ID(continous) = 5.6 A; maxPower = 43W; Input
capacitance = 180 pF
IRF540: RDS = 0.077 Ohms; ID(continous) = 28A; max Power = 150W; Input
capacitance = 1700 pF

The IRF540 is a more robust version than the IRF510. It looks to me
as if
the 540 has more junctions wired internally in parallel. This is also
reflected in the input capacitance, which is much higher for the
540. I am
afraid this might cause problems for the gate driving circuit,
especially
at higher frequencies.

Is anybody out there with a working IRF510 amp who would like to do
some
experiments with a IRF540 replacement? Please share your results!

73 Heinz, OE5EEP

Am Freitag, 22. Juli 2005 07:33 schrieb kumar gautam:
HI,
HERE IN MARKET IRF510 IS NOT AVAILABLE, ONLY IRF540 IS AVAILABLE. ANY
ONE HELP ME THAT IRF540 IS EQUIVALENT OF IRF510 OR I CAN
SUBSTITUTE THIS
FET. WITH 73'S
DE KUMAR GAUTAM


Re: need help for IRF540

Heinz Schnait <oe5eep@...>
 

Hi Kumar,

The datasheets give the following parameters:

IRF510: RDS = 0.54 Ohms; ID(continous) = 5.6 A; maxPower = 43W; Input
capacitance = 180 pF
IRF540: RDS = 0.077 Ohms; ID(continous) = 28A; max Power = 150W; Input
capacitance = 1700 pF

The IRF540 is a more robust version than the IRF510. It looks to me as if
the 540 has more junctions wired internally in parallel. This is also
reflected in the input capacitance, which is much higher for the 540. I am
afraid this might cause problems for the gate driving circuit, especially
at higher frequencies.

Is anybody out there with a working IRF510 amp who would like to do some
experiments with a IRF540 replacement? Please share your results!

73 Heinz, OE5EEP

Am Freitag, 22. Juli 2005 07:33 schrieb kumar gautam:

HI,
HERE IN MARKET IRF510 IS NOT AVAILABLE, ONLY IRF540 IS AVAILABLE. ANY
ONE HELP ME THAT IRF540 IS EQUIVALENT OF IRF510 OR I CAN SUBSTITUTE THIS
FET. WITH 73'S
DE KUMAR GAUTAM


FW: Re: IRF510 on higher voltage?

Hans Summers <Hans.Summers@...>
 

Apologies list, for the bandwidth - I am having some trouble emailing
Allison on private email. Seems I am blocked somewhere :-(

73 Hans G0UPL
http://www.HansSummers.com

-----Original Message-----
From: Hans Summers
Sent: 22 July 2005 15:40
To: 'Allison'
Subject: RE: [BITX20] Re: IRF510 on higher voltage?



Hello Allison

I love Huff & Puff. These days DDS is so easy, but H&P is still simpler and
suitable for many people with no microcontroller etc skills. Though I built
a microcontroller-less DDS: http://www.hanssummers.com/radio/dds/index.htm

Thanks for the advice. I actually have been planning to build a valve linear
for quite a while. I have accumulated more than sufficient number of PL519 /
PL509 TV sweep valves - there are several designs on the internet providing
for 400+ W using four PL509/519's paralleled. Very cheap and reliable. What
I am lacking is the HT transformer. I quite liked Arv's idea of a solid
state linear because the PSU is there, all ready and waiting and cabinetted!

Thanks for the links, I had a good look around. You're right, it doesn't
look very cheap. The very real possibility of frying the transistors makes
the idea even more expensive. From what I hear, those PL5xx sweep valves are
virtually indestructible, even if you make them practically red hot.

All of my ham stuff to date has been at 10W or below. See my TX and RX at:

http://www.hanssummers.com/radio/cwtx/index.htm
http://www.hanssummers.com/radio/polyphase/index.htm

I had my first ever QSO in March 2002 (a mere 8 years after getting my
license!). I've had over 500 QSO's now, all using that 1-valve crystal
controlled CW transmitter. Mostly on 80m, but also on 40 and 30 once I'd
converted the transmitter for those bands.

I'm not a committed QRP'er, I like to operate QRP but I'm not averse to QRO
either, just so long as it's homebrew. I've never touched a commercial rig
and gonna keep it that way!

I did make a 2m AM handheld see
http://www.hanssummers.com/radio/fredbox/index.htm - it's not finished yet,
some trouble with the crystal oscillator multipliers. Needs a bit more work.

Tnx again for the advice and links.

73 de QTH nr London, UK
Hans G0UPL

-----Original Message-----
From: Allison [mailto:ajp166@...]
Sent: 22 July 2005 13:30
To: Hans Summers
Subject: Re: [BITX20] Re: IRF510 on higher voltage?


Hans Summers wrote:
Hi Allison

I am moderator of the BITX20 and have been following your postings
with interest. I have a partially built BITX20 awaiting a little
debugging and perhaps some of the mods. Unfortunately very little time
to work on it at the moment. The pictures are in the G0UPL folder on
the group page.
Hello Hans,

I have built and experimented with you milimal H&P circuits. Good ideas!

I was thinking of using this PSU with switching, as a variable
medium-high voltage supply for whatever I needed it for - but Arv
K7HKL (who you'll know from the BITX group) suggested, why not turn it
into a solid state linear? 50V should suit MOSFET's quite well for
400W and the current capability more than adequate. I have attached a
couple of (poor quality) photos of this monster PSU. You'll see that
the it's divided into two compartments, the top contains just the
choke and three capacitors. It should be possible for me to move those
caps elsewhere which would leave quite a lot of space, I think enough
for the linear. I could bolt on four aluminium panels, one of which to
function as front panel for metering, low pass filter switching, etc.
Opinion, doing that would represent the hard way with limited success.

To get to 400W is a significant endevor and trying with unknown RF
performance power fets is likely failure prone. All of the 100W or more
designs for RF power use known RF transistors (bipolar or fet) that are
expensive (.5-2$/watt US). Most of the high voltage switching FETs are fast
enough to operate at RF but Miller capcitance and input capacitance
will make themm very hard to drive at HF especially 10M.

I may add that the IMD performace for IRF510 and friends is terrible and
that translates to RF polution. They were not developed for linear
service, they were intended as power switches. The other thing is the
TO220 tab cases have poor thermal dissapation. That makes getting
thermal stability hard.

IF you were into AM phone, it's possible to use switching fets in a
class E design (Not FOR SSB). There are several here doing that with
power to 1.5KW. There are websites that discuss this.

Now, if you really still up for the idea.. Heres a possible path to follow.

Expect to use parallel devices (seperate bias for each device) in push
pull configuration. You will need to accomodate the very high
(800-2000pF) input capacitance and low impedences involved. Expect
elaborate groundplanes and input/output transformers with quality
ferrite. A design of four IRF510s in pushpull (pairs of parallel
devices in pushpull) might get you to 80-100W at 24V or about 1Sunit down
from 400W. Generally parallel devices are touchy and each has to
be biased independent of others.

So, I wondered what you thought of this crazy idea, and can you
suggest any web references on solid state linears at this power? I did
some googling but didn't manage to find anything particularly
applicable. I have heard that Motorola might have some good App notes
about this.
Yes they do but, not for common HEXfets or other low cost power fets.
DEVICES like MRF140 and the like are used and they are not inexpensive.
Typical Vdd for these parts is in the 50V region (at up to 20A!).

Start with this site: http://www.communication-concepts.com/eb104.htm

Comm Concepts sells kits for power amps based on Mototrola app notes.
Browse the site for examples, schematics and some of the apnotes. Also you
can find some of the appnotes on the net. However, none
specify low cost fets and likely would not support low cost power fets.

Also, what is your opinion about valve vs solid state? It seems
strange that such a large number of linears are still valve based?
Even the newest models.
Simple, valve designs using obtainable valves are fairly straight foward and
well documented. A 3-500 or 4-400 in grounded grid with 2000V on
the plate will easily hit 400W for 80-10m. A pair of 811/572B are in
the same league as well as a long list of other Valves that maybe had
used or surplus.

Why Valves(tubes)? They are known, durable within experience of most
hams and often can be had inexpensively. When you consider a 3-500Z can
often be had new for around 150$us and MRF150(x4) will cost 200$us and the
FETs may destruct on power up it's not too hard to visualize.

This outfit sells RF power transistors and other items like tubes(valves).

http://www.rfparts.com/product.html

While I've done commercial work at high power I choose to do most of
the ham activity at under 20W. My unusual twist on that is my station
while low powered is supported off of solar pannels and batteries. I may add
that I prefer VHF and up for my experiements.


Regards,
Allison
KB1GMX


need help for IRF540

kumar gautam <fromgautam@...>
 

HI,
HERE IN MARKET IRF510 IS NOT AVAILABLE, ONLY IRF540 IS AVAILABLE. ANY ONE HELP ME THAT IRF540 IS EQUIVALENT OF IRF510 OR I CAN SUBSTITUTE THIS FET.
WITH 73'S
DE KUMAR GAUTAM


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