Date   

Re: 6M power chain working

ajparent1 <kb1gmx@...>
 

Hello,

--- In BITX20@..., Rahul Srivastava <vu3wjm@y...> wrote:
Hi!

As far as BITX design is concerned it is well done. The IF gain
issue arises only due to varying characteristics of same devices
available worldwide.

Even within the USA there are poor spec parts problems and
availability issues.

Where noise figure is concerned under ideal components there is a
limitation to what we can get in a negative feedback config. BITX
nature and paralleling of the amps further effects the feedback and
consequently affects the noise figure on the whole.

Very true, for the IF stages the is not a big problem unless poor
devices are used. The Q1/Q13 stage has more than adaquate noise
figure for 20m or lower HF bands. For 15/17/12/10M bands I'd
want a better device than the 2n3904/2n2222 in the recieve path
a 2sc2570 or 2n5179 would do well there. At VHF we want better
as the band noise is much lower.

Another device that needs some attention is mixer driver Q7. At
above 25mhz the 2n3904 is getting near it's limits though a
2n4124 worked well at 41mhz.

Where BJT preamps are concerned a grounded base cofig provides
better performance though at a lesser gain. A Norton noiseless preamp
provides very low NF probably the best in BJT. Even the Icom IC7800
uses it.

Grounded base BJT is stable but low gain and generally requires
a propper input match for good noise performance. I've looked
at a Norton amp as they are quieter for the same BJT
though they tend to run lower gain. I can get a U310 common gate
fet to a below 1db noise figure and 12db gain with less effort.
However I'd need two stages to overcome the DBM and image filter
losses. Based on earlier work with DBMs at 6m if I want a good NF
and MDS a dual gate MOSFET with around 20db gain is successful.
The idea is enough RF gain to overcome the image filter and DBM
losses (typically -10 to -12DB) with a little extra. The only
problem is that is a more difficult amplifier due to high gain.
The positive is the IP for a dual gate mosfet is very good for the
power required.

Maybe we ought to look at the unique switching arrangement used in
RU design Desna already under files for improved NF.

I am considering splitting the path at the mixer with a optimized RX
path to mirror the TX. It's a trivial thing to use a diode switch
at that point. Building a second filter for the RX is trivial.

Other considerations is balancing power consumption as this is for
portable ops and making fit the intended package. That and keeping
it simple to reproduce at least in part. The PLL I use may be a
parts procurement problem for some.


Allison


Re: 6M power chain working

Rahul Srivastava
 

Hi!
 
As far as BITX design is concerned it is well done. The IF gain issue arises only due to varying characteristics of same devices available worldwide.
 
Where noise figure is concerned under ideal components there is a limitation to what we can get in a negative feedback config. BITX nature and paralleling of the amps further effects the feedback and consequently affects the noise figure on the whole.
 
Where BJT preamps are concerned a grounded base cofig provides better performance though at a lesser gain. A Norton noiseless preamp provides very low NF probably the best in BJT. Even the Icom IC7800 uses it.
 
Maybe we ought to look at the unique  switching arrangement used in RU design Desna  already under files for improved NF.
 
Just my suggestions.
 
73
 
Rahul VU3WJM
 
PS: BTW , BITX and ARRL PP mosfet amp. is becoming big hit here in N India.
 

ajparent1 wrote:
This morning I tested the 6m power chain.  Results are very good
with more power than expected.  When integrated on the bench
a two tone SSB signal nets 4.5W.  I made the first local contact
after connecting to the antenna. Reports were good as expected as
I first tested with a local reciever before putting it on the air.
A check on the spectrum analyser says harmonics and spurs at least
-50dbc. That will require a bit of minor work to the output low pass
filter get it in the range I consider clean.  Also I think a bit of
ALC for TX would help. The ciruit for that would be rectify the RF and
use that voltage to throttle the gain of the microphone amplifier.
This will help prevent overdrive.

Reciever proved to be a bit weak during testing. The problem was
not an IF gain issue.  The 6m band requires a lower noise front
end than HF.  The changes were using a 2n5179 for Q1 initially.
I also tried a MAR-6 MIMIC (20dbgain 3db noise figure), it did
not improve matters and verified the bandpass filter loss
was significant.  Later I added a U310 JFET preamp before the
bandpass filter.  The loss through the filter (at 6m) is great
enough that the noise figure of the reciever is compromized without
12db of gain before it.  Measured MDS was -130dbm with the preamp
without it it was a very weak -118Dbm. For 6M operation _my_ goal is
-137Dbm or better.  Either way this will recieve some work as there
is to much wide band gain before the crystal filter.  This is
important on 6M because of the sometimes very strong signals that
appear during band openings.  I also have commercial television
broacast less than 10 miles away on US CH-2 (56mhz) so intermodulation
performance is important. A  better layout would be preselector
filter, RF amp, image filter, then mixer.  The preselector filter
would be low loss and the image reject filter would be the higher
order bandpass.  The revised topology would permit applying AGC
to the RF amp if a dual gate MOSFET such as 2sk122 or BFR988 is
used. I am also considering cascode MPF102 JFET.

Experiments with the mixer indicate the two transformer doubly
balanced works better at 6m and substituting a commercial DBM
(Minicircuits TUF-1) gave similar performance. Transformers
were wound using two hole ferrite balun cores using 6 turns of
#32 wire x3 (trifilar). Diodes used were 1n4148 type matched
for same forward voltage at 1mA.

This makes the second operational BITx. I need to fine tune the
design for best performance on 6M and package it so it's portable.
I tend to be fussy about reciever performance and transmitted signal
quality but so far this version is behaving like the 20m version
allowing for the differences needed for 6M operation.


Allison
KB1GMX



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6M power chain working

ajparent1 <kb1gmx@...>
 

This morning I tested the 6m power chain. Results are very good
with more power than expected. When integrated on the bench
a two tone SSB signal nets 4.5W. I made the first local contact
after connecting to the antenna. Reports were good as expected as
I first tested with a local reciever before putting it on the air.
A check on the spectrum analyser says harmonics and spurs at least
-50dbc. That will require a bit of minor work to the output low pass
filter get it in the range I consider clean. Also I think a bit of
ALC for TX would help. The ciruit for that would be rectify the RF and
use that voltage to throttle the gain of the microphone amplifier.
This will help prevent overdrive.

Reciever proved to be a bit weak during testing. The problem was
not an IF gain issue. The 6m band requires a lower noise front
end than HF. The changes were using a 2n5179 for Q1 initially.
I also tried a MAR-6 MIMIC (20dbgain 3db noise figure), it did
not improve matters and verified the bandpass filter loss
was significant. Later I added a U310 JFET preamp before the
bandpass filter. The loss through the filter (at 6m) is great
enough that the noise figure of the reciever is compromized without
12db of gain before it. Measured MDS was -130dbm with the preamp
without it it was a very weak -118Dbm. For 6M operation _my_ goal is
-137Dbm or better. Either way this will recieve some work as there
is to much wide band gain before the crystal filter. This is
important on 6M because of the sometimes very strong signals that
appear during band openings. I also have commercial television
broacast less than 10 miles away on US CH-2 (56mhz) so intermodulation
performance is important. A better layout would be preselector
filter, RF amp, image filter, then mixer. The preselector filter
would be low loss and the image reject filter would be the higher
order bandpass. The revised topology would permit applying AGC
to the RF amp if a dual gate MOSFET such as 2sk122 or BFR988 is
used. I am also considering cascode MPF102 JFET.

Experiments with the mixer indicate the two transformer doubly
balanced works better at 6m and substituting a commercial DBM
(Minicircuits TUF-1) gave similar performance. Transformers
were wound using two hole ferrite balun cores using 6 turns of
#32 wire x3 (trifilar). Diodes used were 1n4148 type matched
for same forward voltage at 1mA.

This makes the second operational BITx. I need to fine tune the
design for best performance on 6M and package it so it's portable.
I tend to be fussy about reciever performance and transmitted signal
quality but so far this version is behaving like the 20m version
allowing for the differences needed for 6M operation.


Allison
KB1GMX


Re: question re performance of bidirectional amplifier (corrected)

eternalesquire <eternalsquire@...>
 

Thanks, Ashar!

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

The Eternal Squire


Re: Bidirectional amplifier, DC measurements.

ajparent1 <kb1gmx@...>
 

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

Here are my AC and DC measurements for the Q3 amplifier circuit. I
had used a scope to measure rather than my voltmeter, so measurements
are eyeballed.
Not useful.

With R set to 12V from an external power supply.
Anode of diode is 9 V
Cathode of diode/collector of Q3 = 8 V
Base = 3 V
Emitter = 3 V (probably a tad less due to BE voltage drop)
If you'd used a accurate voltmeter or DVM you would see more
like 2.7V emitter and 3.4V on the base and that small difference
can be telling.


From BFO through an attenuator, I am applying 10.7 Mhz signal of
5mV pp seen by scope injected at junction of input capacitors

25 mV pp same frequency seen at junction of output capacitors.
25/5=5, way low. for 5MV in I'd expect 100mV or more.

I get no amplification whatever when power is removed or reversed,
which is what we want.
What happens if you reverse the signal (TX direction) same?


Except for the AC gain, this appears to be a properly DC biased small
signal transistor amplifier.

On the other sets of amplifier circuits, I see 50 mV pp at junction of
output capacitors.

Could it be that I am using the wrong techniques to view the signal
with my scope, rather than there being a bug in the circuit? I'm
halfway tempted to try putting this circuit in LTSpice as a sanity
check.

I do question scope calibration from range to range and at that frequency.

Me too. I'm building my second and it's mostly a straight up deal.
Sure I have made mods and used ferrite loaded rather than washers
for the transformers but those are not going to affect the amps.
I may add that I've built a large number of these style (RC feedback)
amps and they work or are broken. the latter is often due to bad part
or the occasional use of 100ohm where I meant to pull 10ohm from the
parts bin.

Just for reference I haywaired that stage on the desk to try it
standalone. Used 2n3904s as they were handy, MSP2222 and 2N2222
have roughly the same DC beta so the biasing will be similar.
With Q3/Q11 biasing (470ohm emitter reistor) at 10mhz I got a
voltage gain of just under 7.2 ( IE: 5mV in and 36 out). Voltages
from ground were emitter 2.4V, Base 3.1V, Collector 10.0V and other
side of diode 10.7V. I was using nominal 13.8V supply for this. When
I changed the biasing to Q1/Q13 (220 ohm) I got a bit more gain 8.4
as measured. Gain fall off at lower current is not unusual and the
overall design of BITx is to not use a lot of RF gain as it favors
stability and resistance to overload. The later is important as
theres no AGC in the base design so it must handle big signals
without distortion. So all in all those MPS2222s are usable but
maybe not the best choice.


I used a 50 ohm loaded scope probe and precision 50ohm step
attenuator for the tests. So the gains are likely lower than
in circuit as a result of the 50ohm loading. By calculation
and eyeball the numner I got numbers look right for that
loading at 10mhz.


Allison
Kb1GMX


Re: question re performance of bidirectional amplifier (corrected)

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

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Re: question re performance of bidirectional amplifier (corrected)

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


Re: question re performance of bidirectional amplifier (corrected)

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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 To unsubscribe from this group, send an email to:
 BITX20-unsubscribe@...
 
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Re: question re performance of bidirectional amplifier (corrected)

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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Re: Bidirectional amplifier, DC measurements.

Rahul Srivastava
 

Hi! 
 
Just keep in mind 2N2222 metal and PN2222 plastic have different lead configration.
 
Its C B E  L to R for metal where as it is E B C     L to R for plastic when viewed from front. Leads going down.
 
73
 
Rahul VU3WJM
 


eternalesquire wrote:
Allison,

Here are my AC and DC measurements for the Q3 amplifier circuit.  I
had used a scope to measure rather than my voltmeter, so measurements
are eyeballed.

With R set to 12V from an external power supply.
Anode of diode is 9 V
Cathode of diode/collector of Q3 = 8 V
Base = 3 V
Emitter = 3 V (probably a tad less due to BE voltage drop)

From BFO through an attenuator, I am applying 10.7 Mhz signal of
5mV pp seen by scope injected at junction of input capacitors

25 mV pp same frequency seen at junction of output capacitors.

I get no amplification whatever when power is removed or reversed,
which is what we want.

Except for the AC gain, this appears to be a properly DC biased small
signal transistor amplifier.

On the other sets of amplifier circuits, I see 50 mV pp at junction of
output capacitors.

Could it be that I am using the wrong techniques to view the signal
with my scope, rather than there being a bug in the circuit?  I'm
halfway tempted to try putting this circuit in LTSpice as a sanity check.

Scratching my head in confusion,

The Eternal Squire




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Bidirectional amplifier, DC measurements.

eternalesquire <eternalsquire@...>
 

Allison,

Here are my AC and DC measurements for the Q3 amplifier circuit. I
had used a scope to measure rather than my voltmeter, so measurements
are eyeballed.

With R set to 12V from an external power supply.
Anode of diode is 9 V
Cathode of diode/collector of Q3 = 8 V
Base = 3 V
Emitter = 3 V (probably a tad less due to BE voltage drop)

From BFO through an attenuator, I am applying 10.7 Mhz signal of
5mV pp seen by scope injected at junction of input capacitors

25 mV pp same frequency seen at junction of output capacitors.

I get no amplification whatever when power is removed or reversed,
which is what we want.

Except for the AC gain, this appears to be a properly DC biased small
signal transistor amplifier.

On the other sets of amplifier circuits, I see 50 mV pp at junction of
output capacitors.

Could it be that I am using the wrong techniques to view the signal
with my scope, rather than there being a bug in the circuit? I'm
halfway tempted to try putting this circuit in LTSpice as a sanity check.

Scratching my head in confusion,

The Eternal Squire


FA: Matched SSB/CW sets of 10.7 Mhz IF crystals.

eternalesquire <eternalsquire@...>
 

Hi,

I just won on Ebay a large lot of 10.7 Mhz Crystals. If anyone wants
to use this intermediate frequency I can provide a matched set of 4
plus a 5th for BFO. This IF would be useful primarly in ITU region
2, where WWB makes it impossible to use 10 Mhz as the IF.

I am willing to sell matched sets on the following terms:

1) I will only sell to people in North or South America, exclusive of
Cuba and other countries that US citizens are forbidden to sell to.

2) You will be getting 4 matched crystals, plus a fifth unmatched
crystal for BFO.

3) Before you send money I will send you an invoice containing exact
measurements for each crystal, including the BFO crystal. This
invoice also contains the exact cost of postage to your destination
depending on available carrier. You are responsible for your own
customs duties, import fees, and excise taxes.

4) Each crystal in the package of 5 will be packed in its own bag
marked with its frequency measurement.

5) SSB matching will be within 100 hz of average frequency for
matched set of 4 where each crystal is measured in series with a 33 pF
silver mica capacitor having 20% tolerance.

6) CW matching will be withing 30 hz of average frequency for matched
set of 4 where each crystal is measured in series with a 33 pF silver
mica capacitor having 20% tolerance.

7) Each crystal matched to SSB specifications would cost $2.00 USD,
so a set of 4 will cost you $8.00 USD.

8) Each crystal matched to CW specifications would cost $5.00 USD, so
a set of 4 will cost you $20.00 USD.

9) Your unmatched BFO crystal comes at no extra cost.

10) Payment shall be made by PayPal, US postal money order, or
International Reply Coupons. Personal checks not accepted. No
exceptions.

I don't believe this is an unreasonable cost for my time and labor to
handmatch crystals, to spare somebody else the same effort of having
to buy a lot and sift through them with a test oscillator and
frequency counter.

If the majority of you disagree, please tell me and I will reconsider.

Thanks,

The Eternal Squire


Re: question re performance of bidirectional amplifier (corrected)

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


Re: question re performance of bidirectional amplifier (corrected)

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


Re: question re performance of bidirectional amplifier (corrected)

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


Nicely Drafted Schematics, Revision C

eternalesquire <eternalsquire@...>
 

All,

Here is the new archive for BITX20 Engineering diagrams.

I have reposted a new archive, EGR&#92;BITX_REV_C, containing all the
corrections for Revision B diagrams, plus GIF translations done by Rod.

The Eternal Squire


New file uploaded to BITX20

BITX20@...
 

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the BITX20
group.

File : /EGR/BITX_rev_C.zip
Uploaded by : eternalesquire <eternalsquire@...>
Description : BITX20 Engineering Diagrams, Rev C, 21 August 2005. Rev B diagrams + GIFS

You can access this file at the URL:
http://groups.yahoo.com/group/BITX20/files/EGR/BITX_rev_C.zip

To learn more about file sharing for your group, please visit:
http://help.yahoo.com/help/us/groups/files

Regards,

eternalesquire <eternalsquire@...>


Re: question re performance of bidirectional amplifier (corrected)

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


Re: TOKO transformer colour code

ajparent1 <kb1gmx@...>
 

Hi,

Orange, pink and purple/violet are common to 10.7 IF coils.

Allison
KB1GMX

--- In BITX20@..., "bambazonke01" <jimandruth@s...> wrote:
Does anyone know the colour code for TOKO 10.7 Mhz printed citcuit
transformers?
Which are the IF , oscillator and dicriminator colours?
Jim VE3DDY


Equation for resonance frequency

eb7hpm
 

For calculate resonant frecuency in used TOKO or FI cans can be used a
practical old know formulae:

F(MHz)= sqrt(25330/(L(uH) * C(pF))) or L(uH)=25330/(F*F(MHz) * C(pF))
or C(pF)=25330/(F*F(MHz) * L(uH)).

73s
Manuel
EA7ARX