Topics

question re performance of bidirectional amplifier (corrected)


eternalesquire <eternalsquire@...>
 

All,

Thanks for the info re crystals, it will come in handy when I am ready.

Next question: I have now finished building the first bidirectional
amplifier after the preselector. I injected a 3 mV signal at 3579 khZ
in each direction, and got out a 20mV phase-inverted copy of the same
signal when power in the correct direction was applied.

The fidelity is good, but the gain stages are not even a factor of 10.
Is this the expected performance? I am using all parts as specified,
for transistors I am using MPS2222 and for switching diodes I am using
1N4148.

I know these are probably not the best of transistors, but I want to
attempt to duplicate the results per the web article.

Thanks,

The Eternal Squire


ajparent1 <kb1gmx@...>
 

Inline and edited.

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
All,
Next question: I have now finished building the first bidirectional
amplifier after the preselector. I injected a 3 mV signal at
3579 KhZ in each direction, and got out a 20mV phase-inverted
copy of the same signal when power in the correct direction was
applied. The fidelity is good, but the gain stages are not
even a factor of 10. Is this the expected performance?
This is very low gain. The expected should be far higher in the
order of of around 16DB. I would expect to see around 100mv
for 3mv in.

I'm curious why 3.579nmhz? IS thise going to be 80M version?
If so I'd suggest using T50-2(red) ferrite rings for the bandpass
filter or the required turns will be very high.


I am using all parts as specified, for transistors I am using
MPS2222 and for switching diodes I am using 1N4148.

I know these are probably not the best of transistors, but I
want to attempt to duplicate the results per the web article.
Those should be more than adaquate at 4mhz. However, I'd suggest
rechecking your wiring. Make sure the capacitors are in the correct
places.



Allison
KB1GMX


eternalesquire <eternalsquire@...>
 

Allison,

No, I intend this to be used as 20M. I just use a colorburst crystal
oscillator for signal tracing, and I used a scope to compare the
incoming and outgoing signals to measure gain.

I wired up a second stage and checked it against the schematic as I
was doing it, every trace is accounted for.

I had used ground-plane component support construction. Could that
technique reduce the gain?

--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Inline and edited.

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
All,
Next question: I have now finished building the first bidirectional
amplifier after the preselector. I injected a 3 mV signal at
3579 KhZ in each direction, and got out a 20mV phase-inverted
copy of the same signal when power in the correct direction was
applied. The fidelity is good, but the gain stages are not
even a factor of 10. Is this the expected performance?
This is very low gain. The expected should be far higher in the
order of of around 16DB. I would expect to see around 100mv
for 3mv in.

I'm curious why 3.579nmhz? IS thise going to be 80M version?
If so I'd suggest using T50-2(red) ferrite rings for the bandpass
filter or the required turns will be very high.


I am using all parts as specified, for transistors I am using
MPS2222 and for switching diodes I am using 1N4148.

I know these are probably not the best of transistors, but I
want to attempt to duplicate the results per the web article.
Those should be more than adaquate at 4mhz. However, I'd suggest
rechecking your wiring. Make sure the capacitors are in the correct
places.



Allison
KB1GMX


ajparent1 <kb1gmx@...>
 

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
Allison,

No, I intend this to be used as 20M. I just use a colorburst crystal
oscillator for signal tracing, and I used a scope to compare the
incoming and outgoing signals to measure gain.
Ok, just curious.

Either those are very poor quality versions of MPS2222 (defective
lot?) or something is very wrong. Could it be measurement error?

I wired up a second stage and checked it against the schematic as I
was doing it, every trace is accounted for.

I had used ground-plane component support construction. Could that
technique reduce the gain?
That works well you unless you use really long leads.
I do groundplane AKA "dead bug", Ugly or Manhattan style mostly
as I can fabricate faster than creating a PCB first. Also ground
loops are unheard of with deadbug. I've used this method to
frequencies up to 1296mhz!

Allison
Kb1GMX


--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Inline and edited.

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
All,
Next question: I have now finished building the first bidirectional
amplifier after the preselector. I injected a 3 mV signal at
3579 KhZ in each direction, and got out a 20mV phase-inverted
copy of the same signal when power in the correct direction was
applied. The fidelity is good, but the gain stages are not
even a factor of 10. Is this the expected performance?
This is very low gain. The expected should be far higher in the
order of of around 16DB. I would expect to see around 100mv
for 3mv in.

I'm curious why 3.579nmhz? IS thise going to be 80M version?
If so I'd suggest using T50-2(red) ferrite rings for the bandpass
filter or the required turns will be very high.


I am using all parts as specified, for transistors I am using
MPS2222 and for switching diodes I am using 1N4148.

I know these are probably not the best of transistors, but I
want to attempt to duplicate the results per the web article.
Those should be more than adaquate at 4mhz. However, I'd suggest
rechecking your wiring. Make sure the capacitors are in the correct
places.



Allison
KB1GMX


ajparent1 <kb1gmx@...>
 

Edited. inline comments.

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
I wired up a second stage and checked it against the schematic as I
was doing it, every trace is accounted for.
Another thought..

One possible is that the 10 ohm emitter resistor (in series with
capacitor) is not 10 ohms! It is sometimes easy to get 100ohm
and 10 ohm by error. Rough calculation suggests that might be the error.

Another source of error is if any of the capacitors are not
the correct value (too small).

I'd also check the transistors used. Is the gain going TX and RX the
same? It could be possible one transistor is shorted collector to
base internally.

Just thinking out loud.

Allison
KB1GMX


eternalesquire <eternalsquire@...>
 

1) Checked. These are 10 ohm resistors. I've made 2 stages so far
and had double checked all values of resistors going in.

2) I had been using 0.1 microfarad (value code 104) for all of the
capacitors of these units.

3) On a hunch that this was a bad type of transistor, I substituted a
2N2222A transistor. Gain was acutally worse, X6 rather than X10, so I
put it back.

I strongly suspect that whatever mistake I am making, I am making it
consistently.

Now, the original schematic specifies 220 Ohm emitter bias resistors
in parallel with the emitter degeneration leg, for 2 of these units.
A 440 Ohm resistor is specified for the unit after the crystal filter.

Were the original values wrong?

Should I make DC voltage readings and show them to you?

Thanks,

The Eternal Squire



--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Edited. inline comments.

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
I wired up a second stage and checked it against the schematic as I
was doing it, every trace is accounted for.
Another thought..

One possible is that the 10 ohm emitter resistor (in series with
capacitor) is not 10 ohms! It is sometimes easy to get 100ohm
and 10 ohm by error. Rough calculation suggests that might be the
error.

Another source of error is if any of the capacitors are not
the correct value (too small).

I'd also check the transistors used. Is the gain going TX and RX the
same? It could be possible one transistor is shorted collector to
base internally.

Just thinking out loud.

Allison
KB1GMX


Ashhar Farhan <farhan@...>
 

I dont see the problem at all.
If you inject a 3mv signal, and you get a 20mv signal, the circuit is working just fine.

here is how, you need to check the power gain, not the voltage gain.

Now, a voltage gain of 6.6 translates to 6.6 x 6.6 = 44.4 power gain. (assuming that the input and output impedances are the same). That is smack down 16db as promised.

- farhan

On Mon, 22 Aug 2005, eternalesquire wrote:

1) Checked. These are 10 ohm resistors. I've made 2 stages so far
and had double checked all values of resistors going in.

2) I had been using 0.1 microfarad (value code 104) for all of the
capacitors of these units.

3) On a hunch that this was a bad type of transistor, I substituted a
2N2222A transistor. Gain was acutally worse, X6 rather than X10, so I
put it back.

I strongly suspect that whatever mistake I am making, I am making it
consistently.

Now, the original schematic specifies 220 Ohm emitter bias resistors
in parallel with the emitter degeneration leg, for 2 of these units.
A 440 Ohm resistor is specified for the unit after the crystal filter.

Were the original values wrong?

Should I make DC voltage readings and show them to you?

Thanks,

The Eternal Squire



--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
Edited. inline comments.

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
I wired up a second stage and checked it against the schematic as I
was doing it, every trace is accounted for.
Another thought..

One possible is that the 10 ohm emitter resistor (in series with
capacitor) is not 10 ohms! It is sometimes easy to get 100ohm
and 10 ohm by error. Rough calculation suggests that might be the
error.

Another source of error is if any of the capacitors are not
the correct value (too small).

I'd also check the transistors used. Is the gain going TX and RX the
same? It could be possible one transistor is shorted collector to
base internally.

Just thinking out loud.

Allison
KB1GMX





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Arv Evans <arvevans@...>
 

Hi

On my first BITX (a BITX20) I used PN2222s and also found the gain to be quite
low. After substituting a handfull of 2N3904s my gain became much better.

Another early BITX builder found that his VFO was unstable, until he replaced
a 2N2222 with a 2N3904.

There have been recent suggestions that VHF transistors be used in the IF & RF
sections of the BITX. There seems to be some merit in that idea.

It seems that some providers of 2N2222 & PN2222 maybe assume that any
transistor that is NPN and not something else, is a 2N2222. My 2N2222s that
were purchased from DigiKey were all good in the BITX but those that were
purchased from another source (100 each 2N2222s for $1.50 USD) show very poor
HF gain, but they are just fine for audio applications.

Arv K7HKL
_._

On Sunday 21 August 2005 21:28, eternalesquire wrote:
1) Checked.  These are 10 ohm resistors.   I've made 2 stages so far
and had double checked all values of resistors going in. 

2) I had been using 0.1 microfarad (value code 104) for all of the
capacitors of these units. 

3) On a hunch that this was a bad type of transistor, I substituted a
2N2222A transistor.  Gain was acutally worse, X6 rather than X10, so I
put it back.

I strongly suspect that whatever mistake I am making, I am making it
consistently.  

Now, the original schematic specifies 220 Ohm emitter bias resistors
in  parallel with the emitter degeneration leg, for 2 of these units.
A 440 Ohm resistor is specified for the unit after the crystal filter.

Were the original values wrong?

Should I make DC voltage readings and show them to you?

Thanks,

The Eternal Squire

--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
> Edited. inline comments.
>
> --- In BITX20@..., "eternalesquire" <eternalsquire@c...>
>
> wrote:
> > I wired up a second stage and checked it against the schematic as I
> > was doing it, every trace is accounted for.
>
> Another thought..
>
> One possible is that the 10 ohm emitter resistor (in series with
> capacitor) is not 10 ohms!  It is sometimes easy to get 100ohm
> and 10 ohm by error.  Rough calculation suggests that might be the

error.

> Another source of error is if any of the capacitors are not
> the correct value (too small).
>
> I'd also check the transistors used.  Is the gain going TX and RX the
> same?  It could be possible one transistor is shorted collector to
> base internally.
>
> Just thinking out loud.
>
> Allison
> KB1GMX

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 Visit your group "BITX20" on the web.
 
 To unsubscribe from this group, send an email to:
 BITX20-unsubscribe@...
 
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ajparent1 <kb1gmx@...>
 

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
1) Checked. These are 10 ohm resistors. I've made 2 stages so far
and had double checked all values of resistors going in.
Ok, there must be something...

2) I had been using 0.1 microfarad (value code 104) for all of the
capacitors of these units.
Ok,

3) On a hunch that this was a bad type of transistor, I substituted
a 2N2222A transistor. Gain was acutally worse, X6 rather than X10,
so I put it back.
Should have either made no difference or better. Worse is totally
unespected!

I strongly suspect that whatever mistake I am making, I am making it
consistently.

Now, the original schematic specifies 220 Ohm emitter bias resistors
in parallel with the emitter degeneration leg, for 2 of these
units. A 440 Ohm resistor is specified for the unit after the
crystal filter.

When you say 440 did you really mean 470? Thats what was on the
original schematics.

Were the original values wrong?
No they are well chosen.

Should I make DC voltage readings and show them to you?
Ok, just the preselector stage. Use the same component call outs
(IE: Q1 and Q13) as I will use the publish drawings.

Allison
KB1GMX


ajparent1 <kb1gmx@...>
 

Hi,

I've found the MSP2222, PN2222, 2n2222A to be interchangeable
assuming good parts. However, depending on the source and how
they got in to the product stream they can be out of spec devices.
A good 2N2222a has an Ft of not less than 350mhz and good gain
at 5ma Ic. The 2n3904 however is a little quieter and slightly
better gain even though the Ft is the same. A 2n5179
or other VHF device will not achieve much more gain as the
amplifiers are of RC feedback type and component values set
the gain not the transistor used unless the transistor is
poor quality or simply not reasonable for the frequency
in use.

I have some bad commercial experience with parts that just were
not up to spec. I had this once back around '78 with MPS1764s,
bought a bag of them from Motorola and tested them with 100%
yeild to spec. Purchasing bought another 1000 from a cheaper
source and the failure rate was 25% to spec. Showed Motorola
and they wanted to know where they came from. Seems they were
purchased as known offspec for a non critical app the excess
were being resold as full spec. I've been similary burned with
2n3866s and 2n5109s (low Ft and beta), 2n5179s (noisy and low Ft)
to name a few.

So when talking parts like transitors simple DC tests do not tell
all. Measured in an RF test circuit it's easy to spot.


Allison
KB1GMX

--- In BITX20@..., Arv Evans <arvevans@e...> wrote:
Hi

On my first BITX (a BITX20) I used PN2222s and also found the gain
to be quite
low. After substituting a handfull of 2N3904s my gain became much
better.

Another early BITX builder found that his VFO was unstable, until he
replaced
a 2N2222 with a 2N3904.

There have been recent suggestions that VHF transistors be used in
the IF & RF
sections of the BITX. There seems to be some merit in that idea.

It seems that some providers of 2N2222 & PN2222 maybe assume that any
transistor that is NPN and not something else, is a 2N2222. My
2N2222s that
were purchased from DigiKey were all good in the BITX but those that
were
purchased from another source (100 each 2N2222s for $1.50 USD) show
very poor
HF gain, but they are just fine for audio applications.

Arv K7HKL
_._


On Sunday 21 August 2005 21:28, eternalesquire wrote:
1) Checked. These are 10 ohm resistors. I've made 2 stages so far
and had double checked all values of resistors going in.

2) I had been using 0.1 microfarad (value code 104) for all of the
capacitors of these units.

3) On a hunch that this was a bad type of transistor, I substituted a
2N2222A transistor. Gain was acutally worse, X6 rather than X10,
so I
put it back.

I strongly suspect that whatever mistake I am making, I am making it
consistently.

Now, the original schematic specifies 220 Ohm emitter bias resistors
in parallel with the emitter degeneration leg, for 2 of these units.
A 440 Ohm resistor is specified for the unit after the crystal
filter.

Were the original values wrong?

Should I make DC voltage readings and show them to you?

Thanks,

The Eternal Squire

--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
> Edited. inline comments.
>
> --- In BITX20@..., "eternalesquire"
<eternalsquire@c...>
>
> wrote:
> > I wired up a second stage and checked it against the
schematic as I
> > was doing it, every trace is accounted for.
>
> Another thought..
>
> One possible is that the 10 ohm emitter resistor (in series with
> capacitor) is not 10 ohms! It is sometimes easy to get 100ohm
> and 10 ohm by error. Rough calculation suggests that might be the

error.

> Another source of error is if any of the capacitors are not
> the correct value (too small).
>
> I'd also check the transistors used. Is the gain going TX and
RX the
> same? It could be possible one transistor is shorted collector to
> base internally.
>
> Just thinking out loud.
>
> Allison
> KB1GMX

YAHOO! GROUPS LINKS


Visit your group "BITX20" on the web.

To unsubscribe from this group, send an email to:
BITX20-unsubscribe@...

Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.


eternalesquire <eternalsquire@...>
 

Thanks, Ashar!

I think that Allison might need to catch up to you, too.

The Eternal Squire


ajparent1 <kb1gmx@...>
 

HI,

Catch up how? I have two 20m SSB home brew radios one being BITx
and the BITx for 6M makes the fifth homebrew for that band alone.
I can add a few tube design I've done as well for HF. I enjoy
building and trying new ideas.

Generally I find Ashar's design a very good one and remarkably
reproducable. It represents a well executed minimalist design
that doesn't require exotic components or as some of us call
"unobtainium", those rare parts that only few can find. When
built with good quality parts and a few minor mods the performance
at 20m is excellent. That and it assembled in a few nights as
ugly form with minimal startup problems is impressive.

It's that reason I built the first BIX as 20M just to see it work.
The second for 6M is an experiment and also because I want a small
transceiver of modest power for portable ops. Besides building for
VHF is interesting for it's own sake.

Then I get into the wish list mods..


Allison
KB1GMX

--- In BITX20@..., "eternalesquire" <eternalsquire@c...>
wrote:
Thanks, Ashar!

I think that Allison might need to catch up to you, too.

The Eternal Squire