Date   
Re: VFO Stability (slightly OT)

ki6ds@...
 

Thanks Greg. I agree that the choke is easier. I was just curious to see
if the toroid would work as well, and it seems to. I bet lots more guys
have a toroid in their junkbox and can use it to reproduce your circuit to
test rather than order the choke. That was my purpose to show the
tinkerers out there that they have the parts to reproduce your efforts for
testing purposes. Neat work and thanks for sharing. That's how we
improve. 72 Doug

Hi Doug

Perhaps I counted wrong , but mine needed 39 turns to get to 471uH.
Not that it's a critical value, the bought inductor was 483uH.

It needed 0.2mm wire to fit all those turns and its a pain to work
with that size.
A bought choke is worth the extra cost.(if any)

http://oh2ffy.50webs.com/cb/choke01.jpg
http://oh2ffy.50webs.com/cb/Oscope01.jpg

It seemed to work the same , although my testing only went for an hour
and a half.
The scope looked clean with no sign of any problems.

Regards

gregW:-) OH2FFY

======================================================================



--- In BITX20@..., ki6ds@... wrote:

Greg, have you tried using a toroid for the 470uH inductor? I used a
toroid calculator to come up with the following:

37 turns on a FT37-43 toroid will give you pretty close to 470uH. Is
there any way that you can sub the toroid in your circuit for the fixed
inductor and report what the effect is? Thanks, Doug, KI6DS

Re: BITX20A PA Oscillation?

w8vrt
 

Mark,

One other comment I wanted to make. Definitely terminate the radio
into a 50 ohm noninductive load when setting the biases. Even though
you are not putting out any power at that point, both fet and bipolar
transistors are quite unstable if their terminatng impedances are not
correct.
Goodluck, Len


-- In BITX20@..., "Mark" <Mark@...> wrote:

Hi Guys

I've built my 20A kit and got ready to set everything up today. The
receiver is working fine and I've been following Leonard's videos
for
balanced modulator and PA today, also using his excellent idea of
generating audio with the soundcard.

Now, when I came to set the driver and PA bias pots I have hit a
problem.

With all four pots fully counter clockwise - that includes the drive
level pot - and the mic input shorted to ground I'm pulling 186mA in
TX which looks about right.

I can set the driver bias for an increase of 20mA easily. But when I
come to set the IRF510 bias pots, no matter in which order, I can
set
the first to give me an increase of 50mA but when I increase the
second I go from zero increase to about 800mA increase - and I am
being very gentle. Looking at the output with a scope it appears
that
the PA is oscillating. This is still the case with no driver bias
setting.

I'm stuck - any clues what to look for?

Thanks.

Mark.

G0MGX

Re: VFO Stability (slightly OT)

n7ve <dan.Tayloe@...>
 

This looks like an oscillator for 4.4 MHz. At this frequency, 470 uH
looks like 13K of inductive reactance. The 933 pf caps this is across
looks like 38 ohms of reactance at 4.4 MHz. A less expensive 100 uH
molded choke (2K ohms) or 47uH (1K ohms) molded choke would likely do
just fine in this application.

- Dan, N7VE

--- In BITX20@..., ki6ds@... wrote:

Thanks Greg. I agree that the choke is easier. I was just curious
to see
if the toroid would work as well, and it seems to. I bet lots more guys
have a toroid in their junkbox and can use it to reproduce your
circuit to
test rather than order the choke. That was my purpose to show the
tinkerers out there that they have the parts to reproduce your
efforts for
testing purposes. Neat work and thanks for sharing. That's how we
improve. 72 Doug

Hi Doug

Perhaps I counted wrong , but mine needed 39 turns to get to 471uH.
Not that it's a critical value, the bought inductor was 483uH.

It needed 0.2mm wire to fit all those turns and its a pain to work
with that size.
A bought choke is worth the extra cost.(if any)

http://oh2ffy.50webs.com/cb/choke01.jpg
http://oh2ffy.50webs.com/cb/Oscope01.jpg

It seemed to work the same , although my testing only went for an hour
and a half.
The scope looked clean with no sign of any problems.

Regards

gregW:-) OH2FFY

======================================================================



--- In BITX20@..., ki6ds@ wrote:

Greg, have you tried using a toroid for the 470uH inductor? I used a
toroid calculator to come up with the following:

37 turns on a FT37-43 toroid will give you pretty close to 470uH. Is
there any way that you can sub the toroid in your circuit for the
fixed
inductor and report what the effect is? Thanks, Doug, KI6DS

Re: BITX20A PA Oscillation?

Mark Jones <Mark@...>
 

Hi Guys

I removed the heatsinks for a better view of the board and checked T1,
8turns on the top end of the board and 6turns closer to the bottom. I
also have a 50ohm dummy load connected to the antenna jack, so that's OK
too. I have also checked all component values around that part of the
circuit and they also appear correct. I've set the TX drive pot to mid
way and tried initially to go for half the recommended current draw. So
I have 10mA current increase set with the driver pot and 25 mA each for
the IRF510s.

Now, using the soundcard sine generator and a pot to attenuate it down
to about 25mV peak to peak, and starting with the TX drive pot at zero
as I increase the TX drive pot whilst monitoring the input waveform I
see some extremely odd behavior, which has me totally confused. I've
taken some photos of the scope waveforms and added some commentary to
the images here:

http://www.bartg.org.uk/G0MGX/

If anyone would be kind enough to take a look and offer some sanity to
G0 who is rapidly losing the will to live then I would be extremely
grateful.

Regards,

Mark.

G0MGX

w8vrt wrote:


---
Mark,
I had same problem which is ok now. Verify that you have T1, the
bifilar winding in corrrectly and not reversed, and also turn the Tx
drive pot (r83) to midpoint when setting the biases. It worked for me.

Len

In BITX20@... <mailto:BITX20%40yahoogroups.com>, "Mark"
<Mark@...> wrote:

Hi Guys

I've built my 20A kit and got ready to set everything up today. The
receiver is working fine and I've been following Leonard's videos
for
balanced modulator and PA today, also using his excellent idea of
generating audio with the soundcard.

Now, when I came to set the driver and PA bias pots I have hit a
problem.

With all four pots fully counter clockwise - that includes the drive
level pot - and the mic input shorted to ground I'm pulling 186mA in
TX which looks about right.

I can set the driver bias for an increase of 20mA easily. But when I
come to set the IRF510 bias pots, no matter in which order, I can
set
the first to give me an increase of 50mA but when I increase the
second I go from zero increase to about 800mA increase - and I am
being very gentle. Looking at the output with a scope it appears
that
the PA is oscillating. This is still the case with no driver bias
setting.

I'm stuck - any clues what to look for?

Thanks.

Mark.

G0MGX

Re: BITX20A PA Oscillation?

Leonard <bitx@...>
 

I've
taken some photos of the scope waveforms and added some commentary to
the images here:

http://www.bartg.org.uk/G0MGX/
What is the scope sweep speed and vertical settings on the next to last
picture? Is that 14mhz and what is the measured amplitude? Does it
increase as you increase the drive level? If it's a few volts with your
settings, I'd remove the mike input and check the carrier level out to
make sure the carrier is balanced out. Fropm what I've seen before, if
the output waveform is at 14mhz and there is "fuzz" on the sinewave,
it's residual carrier.

I'm asking to determine in the output is trying to act normally.

What it looks like to me if it is 14 mhz is some residual carrier on
the waveform.
Leonard

BITX20 PA Inductor values

maredman <mick.redman@...>
 

Hi Guys

I have built the original BITX20 Main Panel and I'm very pleased with
the results on recieve. I'm now building the PA stage and wonder if
anyone could tell me the inductance values for T2 and RFC1.

Thanks

Mick

M0BBH

"Minimalist" Bitx20 alignment

Leonard <bitx@...>
 

In the past, most of my videos have used a fairly extensive, but if
old, amount of test equipment. You say, "I don't have all of that
stuff!". Well the next video is for you!

I just shot it today and I'm in the process of editing it. The
editing part is mainly so I look somewaht intelligent. I demonstrate
on it the process of aligning your bitx with just a DVM which reads
current, a dummy load, an antenna, and another receiver to align the
vfo. In fact, I use my Far Circuits bitx with a digital dial for the
extra receiver.

With this procedure, you should be able to make the adjustments
required to get you on the air. This assumes that your assembly was
good and all of the parts were good. The "all of the parts were all
good" is probably a good assumption. I'll try to upload it tomorrow
morning. I should finish editing it today and when I go the coffe
shop in the morning, I'll upload it using their highspeed internet
connection.

This was the first time I have actually had a microphane on my kit.
The scope display looked pretty good. I'm about ready to quit filming
and put this kit in a box where I can start using it.

The next video project just arrived in the mail yesterday. A
http://www.norcalqrp.org/ FCC1 and FCC2 DDS VFO and frequency
readout. Guess where it is going to go.

Leonard
KC0WOX
http://kc0wox.com

Re: "Minimalist" Bitx20 alignment

christopher660559
 

hi i look forward to seeing the video i dont have any test gear ive just compleated
my bitx20a the rx side is working fine ive set the pa and driver idling current thats ok
i have no rf showing if i key up without a mic with a 12v supply i can get 10w rf out
talking into the mike my vfo ive built into a small box 1and 1/2in sq box made from copper clad i copyed the bitx20 vfo im just useing q 8,7 q 6 i left on the main bord
it seams to work well with little drift ive had fun makeing this kit im just waiting for
the frq display kit to come lost in the post i think then i can have some fun useing it
chris g0wfh

Vericaps

Sudipta Ghose VU2UT
 

Can anybody provide me with idea or description of a gadget or setup
that can be used to know characteristics of unmarked Vericaps?

Re: VFO Stability (slightly OT)

robdale54 <robyounce@...>
 

I just wanted to mention, in follow-up, that ( since I started the
recent VFO STABILITY thread and the ensuing threads revealed a part
problem ) I have replaced the critical NPO caps that were missing in my
kit and VFO stability is very acceptable now. I have not measured the
performance ( obviously we all know that drift in a vfo is really
difficult to determine due to all the variables ) but I find now that,
in use, the drift ( after warm-up ) is likely to be measured in cycles
per hour where originally it would have been measured in cycles/minute.
Changing C15 to a Silver Mica cap made the most significant difference,
as we would expect.

I thank Doug for reading these threads and having the integrity to look
into his end for possible problems. Alot of folks would not have done
that; thanks, Doug.

Rob N8BEG

Re: Vericaps

Arv Evans
 

Ghose

You might try building an oscillator and use the unknown varicaps as
part of the LC network. By varying the reverse bias while measuring
oscillator frequency you should be able to calculate the value of those
varicaps for various levels of bias.

An alternative way to do this might be to calibrate an air variable with
capacitance indications on it's knob or dial and use this along with the
varicap in your oscillator circuit. With this calibrated capacitor in
parallel with your unknown varicap you can determine how much offset you
have to have in the air variable for each setting of varicap bias to
keep the oscillator at a set frequency. This could be done with just a
receiver to indicate oscillator frequency.

You could also use any of the popular capacitance meter circuits to
measure varicap capacitance versus reverse bias. Use a high value
series capacitor to keep varicap bias voltage off the capacitance meter
input. These circuits might be of interest:

http://nov55.com/cap/cap1.htm

http://members.shaw.ca/roma/dcm.html

http://www.circuitcellar.com/library/print/0605/Popov179/index.htm

http://www.qsl.net/iz7ath/web/02_brew/21_LCMeter01/

http://www.electronics-lab.com/projects/test/006/index.html

And there are many more similar circuits. Each ham will probably have
his own favorite circuit and method.

Hope this helps,

Arv - K7HKL
_._



Sudipta Ghose wrote:


Can anybody provide me with idea or description of a gadget or setup
that can be used to know characteristics of unmarked Vericaps?

.

--
======================================
Web: http://K7HKL.homelinux.net
http://bitx20a.livejournal.com
http://home.earthlink.net/~arvevans/
http://www.geocities.com/k7hkl_arv/
======================================

Re: Vericaps

Sam Caldwell <samc@...>
 

On Mon, 21 Jan 2008 01:20:46 -0000, you wrote:

Can anybody provide me with idea or description of a gadget or setup
that can be used to know characteristics of unmarked Vericaps?
You could try

www.hanssummers.com

in the first instance.

Regards, Sam C.

Re: BITX20 PA Inductor values

Steve G0FUW <g0fuw@...>
 

Hi Mick
I wound mine on T-50-43 cores, same number of turns that Farhan used on the binocular cores.
Found that the binocular cores shorted the enamel wire all too easily. No problem with toroids, which came from G-QRP Club.
Several of our class students completed likewise with good results.
Hope this helps
73, Steve, G0FUW

----- Original Message -----
From: maredman
To: BITX20@...
Sent: Sunday, January 20, 2008 9:20 PM
Subject: [BITX20] BITX20 PA Inductor values


Hi Guys

I have built the original BITX20 Main Panel and I'm very pleased with
the results on recieve. I'm now building the PA stage and wonder if
anyone could tell me the inductance values for T2 and RFC1.

Thanks

Mick

M0BBH

Re: BITX20A PA Oscillation?

Martien <sproet01@...>
 

Hello Mark,

In addition you could also check the transmit/receive FET switches that
bridge the PA during reception.
If something has gone wrong in assembling this part of the PCB there
could be not enough isolation during TX operation resulting in feedback
from the PA output to the input and thus possible PA oscillation.

Succes,

Martien PE1BWI

Re: BITX20A PA Oscillation?

Mark Jones <Mark@...>
 

Hi Leonard

Sweep frequency is 50ns/division and the vertical is 1V/division with a
x10 probe so it's 10V/division.

I'm running trough all tests again and will report back.

Mark.

Leonard wrote:


I've
taken some photos of the scope waveforms and added some commentary to
the images here:

http://www.bartg.org.uk/G0MGX/ <http://www.bartg.org.uk/G0MGX/>
What is the scope sweep speed and vertical settings on the next to last
picture?

Is that 14mhz and what is the measured amplitude? Does it
increase as you increase the drive level? If it's a few volts with your
settings, I'd remove the mike input and check the carrier level out to
make sure the carrier is balanced out. Fropm what I've seen before, if
the output waveform is at 14mhz and there is "fuzz" on the sinewave,
it's residual carrier.

I'm asking to determine in the output is trying to act normally.

What it looks like to me if it is 14 mhz is some residual carrier on
the waveform.
Leonard

Re: BITX20A PA Oscillation?

 

Martien,

I think you are right.

Advancing the R83 increases the Tx amp gain inside the TX/RX
loop.

Mark,

Scope the live junction of R87 and also check the junction of R85.
If RF is present then:

Q22 and Q24 could be open/blown or wrongly connected.
Q21, Q23 or Q26 could be shorted/blown or wrongly connected.

My assumptions just by looking at the diagram of Bitx20A, I have not
built one (as yet). Hope that helps.

73 Raj vu2zap

Hello Mark,

In addition you could also check the transmit/receive FET switches that
bridge the PA during reception.
If something has gone wrong in assembling this part of the PCB there
could be not enough isolation during TX operation resulting in feedback
from the PA output to the input and thus possible PA oscillation.

Succes,

Martien PE1BWI

Re: "Minimalist" Bitx20 alignment

ragavan
 

Hey there!

Nice site. Has ayone tried 1n4148 instead of those germanium diodes in
a RF probe? I heard they work well when the signal level is high(?)

73
Ragav
VU3VWR

Re: "Minimalist" Bitx20 alignment

Leonard <bitx@...>
 

Nice site. Has ayone tried 1n4148 instead of those germanium diodes
in
a RF probe? I heard they work well when the signal level is high(?)
I initially used a 1N4148 but changed to a 1N34a. The 1N4148 gives a .7
volt diode drop instead of .3 volts. It worked but the germanium give a
higher reading and and can measure smaller signals. In my alignment
video, which I'll upload in the morning, I measured the BFO output with
my "Sharpie" rf probe and it measured .72 volts. The scope showed 2.5
volts pk-pk. The VFO measured .54 volts and the scope shows 1.5 volts
pk-pk. Both of these waveforms are not sinusoidal so the readings don't
come out as calculated.
Leonard
KC0WOX

Bitx20a kit basic alignment video

Leonard <bitx@...>
 

This is a 24 minute video on basic alignment. This only requires a vom
with current scale, a dummy load, an antenna, and a second receiver for
frequency calibration. This makes the assumption that everything works
but just needs adjustment. It is not a troubleshooting video.

http://golddredgervideo.com/kc0wox/basicalignment.wmv

24 minutes and 124 meg in size.

Re: BITX20A PA Oscillations

George Silver <GSilver2@...>
 

Greetings Gentlemen.

With regard to PA oscillations when close coupled to "50 ohm simulated antenna".

the type of resistive load used to make up the 50 ohm simulated antenna is quite important. You are all aware I'm sure, but sometimes a slip is made. The load should be pure resistive. Most resistors these days contain some inductive elements. try measuring one with a L meter with leads about the same length as your using on your breadboards. Since you are working at a near fixed frequency, that L can be tuned out with a bit of C.

The sensitivity to the use of a capacitor, or a resistor for coupling the MIC input to the PA is a classic example of signal/feedback coupling phase sensitivity. Rerouting, or shielding the MIC wiring clear into the first active element will often soften these effects and allow the circuits to perform as intended. Or the phase coupling must be counteracted..


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