EMRFD Message Archive 2269

Message Date From Subject
2269 2008-10-17 05:19:39 ea3ghs the flea, a 40m minimalist transceiver
Hello,

I would like to introduce to you a very simple transceiver
using only two transistors or one transistor and a LM386.

This circuit has been developed by Joan EA3FXF and me,
EA3GHS using a previous work from AE6C.

There are a lot of unclear things, but the circuit is
perfectly usable on air, and to do brainstorming in the
workbench.

Details can be found here
http://ea3fxf.googlepages.com/flea
and here
http://ea3fxf.googlepages.com/SPRAT-FLEA.doc

Things TODO:
A 20meters version (spice simulation working)
a IRF510 version
a BD135 (low beta) version
a ECC83 triode version
check if the xtal are in secure operation (power<10..100mW)

73 from Catalonia,
Eduardo, EA3GHS@qrp.cat
2284 2008-10-19 07:29:58 jocjo_john Re: the flea, a 40m minimalist transceiver
2303 2008-10-21 10:54:10 ea3ghs Re: the flea, a 40m minimalist transceiver
Hello,

> How about giving us the SPICE model for your "3866"?

Yes,

.model 3866 NPN (IS = 9.798605E-15 BF = 145.568899 VAF = 64.3030691)

> Also note that SPICE does not know what to do with the "7=B5" value

Sorry, something went wrong in googlepages upload processing.
The inductor value is 7uH

Please, get the new SPICE files here
http://ea3fxf.googlepages.com/pulgaspice.zip

or view some interesting waveforms here
http://ea3fxf.googlepages.com/pulga40m-spice.pdf

73/DX Eduardo
2306 2008-10-22 08:11:05 Ashhar Farhan Re: the flea, a 40m minimalist transceiver
joan,

i am a great fan of one-eveningers like the flea. i think they are a
great challenge to design as they stress on our ability to extract
maximum bang-for-buck (which is our main job as an engineer). so, my
comments are not to be see as someone who looks down upon them but i'd
prefer to open up these issues for all of us here who are serious
about simple rigs.

1. they are illuminating.
it is better to have made one, and learned from it rather than never
have build it at all. so, they serve a useful purpose of presenting a
bare-bones, minimalist circuit.

2. the maybe unreliable.
unreliability comes from any angles, for a receiver it might be
unstable (if the vfo wasn't well buffered), it maybe insensitive
(insufficient gain), it might overload (poor signal handling), etc. On
the other hand, pushing maximum output from fewer stages of a
transmitter is a recipe for instability.

3. they maybe difficult to understand.
at times, minimum component count can force the designer to resort to
innovative circuits that are difficult to understand (try explaining a
super regenerative circuit to a teenager). on the other hand, a
slightly more elaborate arrangement with clearly separated functional
blocks is easier to understand, though it might take few more minutes
and cents to build.

4. may not be reusable.
as a school boy, after repeated failures at building something, the
first thing that worked for me at all was a hartley oscillator (as an
outboard BFO for my SW radio). three decades later, it continues being
my favourite. we tend to stick to functional blocks that 'work for
us'. these blocks should ideally have standard (50 ohms)
interconnects, scalable (in terms of frequency of operation), stable,
etc.

5. inexpensive
a dollar's worth components and an evening is well spent learning
something new on the bench. this is quite worthwhile investment, as
long as the circuit is stable, otherwise, it could lead to
frustrations.

what does this group feel about these simple circuits? is there value
in these super simple circuits as opposed to slightly more elaborate
circuits. For instance, given a few more components, the Flea could be
improved thus:

1. oscillator's biasing is critically dependent upon the hFE. this can
easily lead to burn outs. The tickler circuit can also be confusing if
the secondary winding's polarity is not done correctly. It will not
really add to complexity to have two transistors in the transmitter
instead of one in the transmitter. this would make the circuit more
explanatory and stable with a choice of devices with varying
characteristics.

2. the receiver will probably be swamped with AM broadcast. the
components include one diode already, adding a second diode and a
broadband coil can enhance the performance immensely.

3. the audio maybe a little low. providing an (optional) preamp with
one or two transistors could make it almost as good a receiver as a
commercial grade rig.

i would imagine an overall net increase of another 10 components to
make rig that is slightly more complex but a better performer with
repeatable results.

where we draw a line between performance and complexity is a purely a
subjective matter. i would prefer to trade slightly higher complexity
for far more acceptable performance.

- farhan
2333 2008-10-28 10:12:29 ea3fxf Re: the flea, a 40m minimalist transceiver
2343 2008-10-31 13:51:58 ea3ghs Re: the flea, a 40m minimalist transceiver
Hello Aisea,

2363 2008-11-04 05:56:38 ea3ghs Re: the flea, a 40m minimalist transceiver
HELLO NICK, TERRY, GROUP,...

> [4SQRP] Fw: [emrfd] the flea, a 40m minimalist transceiver
> Nick-WA5BDU nick-wa5bdu at suddenlink.net
> Sun Oct 19 10:07:49 PDT 2008
>
> I was highly impressed with it too, Terry. I've got to work it in as
> soon as I get a chance. I like the 2-transistor version since it is
> more minimalist than the Pixie 2. It seems to be using regeneration
> to get receiver gain, instead of a high gain audio IC.
>
> 72--Nick, WA5BDU
>
> WA0ITP wrote:
> > -------- 4 State QRP List :: The Friendly One --------
> > This was posted on the EMRFD reflector. Very interesting little
> > rig. Anyone interested in building one? Maybe a group build?

Thanks for your interest in this little transceiver.
The receiver IS NOT working as regenerative receiver.

A regenerative receiver is a tuned RF (TRF) receiver and here
I can listen the local oscillator in a secondary receiver !!.

This is very important, and it makes me think that the
detector is working between regenerative (left hand semiplane)
and superregenerative (right hand semiplane in control theory jerga).

Here the first transistor works as mixer and oscillator
as a classical direct conversion receiver.
I am not sure if the transistor amplifies regenerating
the antenna signal, too.

I do not test how works the receiver in
regenerative mode (without oscillation).
I do not know if I could get more gain if the transistor do not
oscillates.

/*
The oscillation do not stop if I reduce/cut the bias current!
I need to change a little the bias network, maybe with a R
between base and ground.
*/

Any case, the crystal in the feedback path it's a
element that I do not found in any other regenerative receiver
and this makes the receiver stable in frequency.
Nice to work in very narrow modes like PSK31 without
huff&puff complexity.

See this nice receiver:
http://py2ohh.w2c.com.br/trx/curruira/curruira.htm but the author says
it's working as a direct
converter too.

Comments will be welcome.
I like very much to talk about classic radio philosophy and
architectures.

73 from Catalonia,
Eduardo EA3GHS
2664 2009-01-31 09:41:37 ea3ghs Re: the flea, a 40m minimalist transceiver
Hello Stephen VE7NSD,

First, please accept my apologies for not answer you soon.
You are asking me a very complex questions, and write a
right answer is a bit difficult.

Currently I am studying the flea circuit and his circuit brother,
the "mosca" flies. it's the same circuit but
without feedback diode

i read you are trying to make an 80 meters version
and you have found problems recalculating the correct
values of the capacitive and inductive transformers.

experiences from ea4bvz and joan ea3fxf says that is
more easy work with an low Q transformer.

i am studying the correct bias of the transistor because
it's easy to change fastly from one technical concept
to another because there are high coupled subcircuits.

hi hi hi, sorry...

i will try to run the spice circuit in 80 meters band.
I will be checking qrpedia for news experiments from you.

thanks for your accurate work

73 from catalonia
eduardo
2669 2009-02-03 16:09:50 Stephen Wandling Re: the flea, a 40m minimalist transceiver
Hello Eduardo,

Thank you for your detailed response. Yes, changing from one band to
another does seem to involve multiple factors, and is more difficult
than I anticipated. I have done a lot of modeling in Spice for the 80M
version. I chose a value for L1 that had the same XL as the 40M
version, which is something I remembered reading somewhere. Then I
built a spreadsheet that allowed me to choose C1/C2 for the capacitive
transformer, that would have the same reactance ratio as you had in the
40M version, and allowed for C3 to be about 20pF when the circuit was
resonant with the crystal used (3579 Khz). Since this is controlling
the feedback, this ratio may vary with frequency? I have not made any
actual changes to the biasing of Q1, but I have played with it in
Spice. My biasing tests were inconclusive, based on my very limited
knowledge.

In Spice, with a given L1, I have modeled a whole range of values for L2
& L3, on both transmit and receive. On the 40M version, on receive, the
LO signal measured at the antenna, was about 100 mV. Unfortunately,
Spice gives me values that are much larger than that, a couple of orders
of magnitude. Once again, I get relative values, but can't compare to
what I have measured on the actual rigs.

I recently built an AADE L/C meter and found it interesting to measure
the transformer(s) that I have produced. L1 was usually what I
expected, but L2 & L3, which I have wound on top of L1, were 2 or 3
times their calculated value. I still have no explanation for that.

I will await any further information that you are able to provide. I am
subscribed to the Google radiofrecuencia group, which I have to read
with a little computer translator (No comprendo, escribo o hablo mucho
Español). I have tried to post to the group, but my posts don't seem to
come through? There is lots of good minimalist work going on with your
group.

72 & 73 from Canada to Catalonia
Stephen
VE7NSD

ea3ghs wrote:
> Hello Stephen VE7NSD,
>
> First, please accept my apologies for not answer you soon.
> You are asking me a very complex questions, and write a
> right answer is a bit difficult.
>
> Currently I am studying the flea circuit and his circuit brother,
> the "mosca" flies. it's the same circuit but
> without feedback diode
>
> i read you are trying to make an 80 meters version
> and you have found problems recalculating the correct
> values of the capacitive and inductive transformers.
>
> experiences from ea4bvz and joan ea3fxf says that is
> more easy work with an low Q transformer.
>
> i am studying the correct bias of the transistor because
> it's easy to change fastly from one technical concept
> to another because there are high coupled subcircuits.
>
> hi hi hi, sorry...
>
> i will try to run the spice circuit in 80 meters band.
> I will be checking qrpedia for news experiments from you.
>
> thanks for your accurate work
>
> 73 from catalonia
> eduardo
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>

--
"You never change things by fighting the existing reality.
To change something, build a new model that makes the
existing model obsolete." -- Buckminster Fuller

"First they ignore you, then they ridicule you, then they
fight you, then you win" -- Gandhi
3962 2010-01-11 03:11:34 Dominic Re: the flea, a 40m minimalist transceiver
Eduardo,

Built this last night based on information from GQRP SPRAT #137.
http://m1kta-qrp.blogspot.com/2010/01/flea-40m-cw-minimalist-tcvr.html

Nice fun little rig. RX signals from a Vertical 6BTV perfectly readable. The winding direction of T1 is critical though I wired the antenna connecton in reverse initially once corrected adjusting C3 brought in the signals.

Managed to use it on 7.025 (FT243), 7.030 (HC49) and 7.040 (HC6) and I have used one half of a turned 8pin DIL socket for the crystal between two manhatten pads so changing frequency is not a problem.

Using a small 10uV signal source and step attenuator I could receive signals down to about 0.4uV.

Changing C1/C2 and using a different C3 would mean bands 80m-20m should be possible anyone else had success on other bands that they might share with this design?

Also...
A 2N2222A also works for Q1 but with a much lower output c150mW.
Increasing V1 to 50K seemed to shift the RX offset (syntony=tuning?) a lttle bit more.

72

Dom
M1KTA
3963 2010-01-11 12:32:12 Eduardo Alonso Re: the flea, a 40m minimalist transceiver
HELLO DOM,

THANKS FOR YOUR SMALL REPORT ABOUT YOUR EXPERIENCE WITH THE "FLEA".

> Nice fun little rig. RX signals from a Vertical 6BTV perfectly readable. The winding direction of T1 is critical though I wired the antenna connecton in reverse initially once corrected adjusting C3 brought in the signals.

YES, THE WINDINGS DIRECTION AFFECTS TO THE PHASE OF THE FEEDBACK
IN THE AMPLIFIER.

> Using a small 10uV signal source and step attenuator I could receive signals down to about 0.4uV.

NICE! I WILL UPDATE THE RIG SPECS, HI HI
SWEEP THE SIGNAL SOURCE AND YOU WILL CAN SEE (LISTEN)
THE SELECTIVITY OF THE RECEIVER.

> Changing C1/C2 and using a different C3 would mean bands 80m-20m should be possible anyone else had success on other bands that they might share with this design?

YES YES YES
TOO MUCH CIRCUITS, TOO LITTLE TIME
CURRENTLY WE ARE WORKING IN A SUPERHETEREODYNE TRX
WITH A 4MHZ FI BASED IN THIS RECEIVER, BUT WITH A FET BF245
WORKS VERY WELL

AS YOU SAY, MUST BE VERY EASY CHANGE THE BAND OF OPERATION
7MHZ,10MHZ,14MHZ FOR EXAMPLE,MAYBE WITHOUT CHANGING ANYTHING.

> A 2N2222A also works for Q1 but with a much lower output c150mW.

THIS IS ANOTHER IMPORTANT THING, THE 2N3866 IS NOT EASILY
FOUND IN ELECTRONICS SHOPS.
EA4BVZ TRIED TO PUT THREE 2N2222 IN //

OUR SOLUTION WAS A IRF510 MOSFET
http://ea3ghs.googlepages.com/mosquito

IF YOU HAVE ENOUGH TIME, CAN BE VERY VERY
INTERESTING TO USE A TUBE HERE, PCL86, PL504
OR SOMETHING LIKE THIS
WE CAN HELP YOU IF YOU HAVE INTEREST.

73/DX EDUARDO
SORRY FOR ENGLISH MISTAKES
3964 2010-01-11 12:49:02 Stephen Wandling Re: the flea, a 40m minimalist transceiver
Dom,

This is great to hear! As you may recall, I too built the "Pulga" or
Flea xcvr. My trials and tribulations are to be found here:
http://www.qrpedia.com/book/200812/flea-catalonias-answer-pixie

I did get it working, "sort of", on both 40M and 80M. Reading through
my notes there, its obvious that most of the problems were created by me
and not the circuit. But, since learning was my prime goal, it all
worked out great in the end.

I was initially plagued by 'fake' 2N3866 transistors: low Beta. I
finally got some 2N3553 and the improvement on receive was amazing.
But, I kept toasting them during the tuning procedure.

Eduardo had said in an earlier post :
> Yes, FLEA is not very reproducible, you need all the components
> and EMRFD book to understand what happens when it does not run.
> This TRX is like the Arecibo Observatory receivers,
> they are designed and manually tuned for performance,
> not for reproducibility.
So congratulations to you are definitely in order!

72
Stephen
VE7NSD

Dominic wrote:
> Eduardo,
>
> Built this last night based on information from GQRP SPRAT #137.
> http://m1kta-qrp.blogspot.com/2010/01/flea-40m-cw-minimalist-tcvr.html
>
> Nice fun little rig. RX signals from a Vertical 6BTV perfectly readable. The winding direction of T1 is critical though I wired the antenna connecton in reverse initially once corrected adjusting C3 brought in the signals.
>
> Managed to use it on 7.025 (FT243), 7.030 (HC49) and 7.040 (HC6) and I have used one half of a turned 8pin DIL socket for the crystal between two manhatten pads so changing frequency is not a problem.
>
> Using a small 10uV signal source and step attenuator I could receive signals down to about 0.4uV.
>
> Changing C1/C2 and using a different C3 would mean bands 80m-20m should be possible anyone else had success on other bands that they might share with this design?
>
> Also...
> A 2N2222A also works for Q1 but with a much lower output c150mW.
> Increasing V1 to 50K seemed to shift the RX offset (syntony=tuning?) a lttle bit more.
>
> 72
>
> Dom
> M1KTA
>
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>
3967 2010-01-12 01:17:57 Dominic Baines Re: the flea, a 40m minimalist transceiver
>
3968 2010-01-12 01:24:16 Dominic Baines Re: the flea, a 40m minimalist transceiver
Stephen,

Wow this created a bit of email traffic overnight...

To be honest I must be lucky as mine works, admittedly not first time... I had reversed the windings between earth and antenna initially, and forgotten the 1K resistor between C8 and C10.
However I don't have a copy of EMRFD to have checked circuit theory that I may not have understood anyway (I borrowed a copy once from MI5MTC).
I have never run SPICE, modelled a filter or a tuned circuit either. If I have to do a calculation for a tuned circuit it is usually done long hand on a scrap of paper. I'm not hot on theory as was never taught that much and tend to work things out by doing.

Asked a few things off list so rather than answer individually I hope this answers everyones questions:
The T1 to be honest I just wound all three windings in the same direction, right handed and held toroid in left hand
and passed wire up though the centre from underneath for each turn, no rocket science or theory involved.
The primary wound first then each of the secondaries wound on top one either side of the primary ends. Imagine pairs of wires come out on three sides of a square, primary in the middle (make sense?). I have since heard that the winding of this is the critical bit. See http://www.qrpedia.com/book/200812/flea-catalonias-answer-pixie for a picture, that is what mine looked like, don't think I would have wound it differently though. I'll take a close up image of T1 as asked by a few and it'll be on blog http://m1kta-qrp.blogspot.com/ when I can get back in the shack
The 2N3866 was from a batch from GQRP I cannot remember who donated them but they are not marked as such. I use them a drivers for a PA stage usually.
The trimmer capacitor there was probably only 10% movement between hearing signals, lots and then nothing again so the tuning is sharp.
I might investigate adding a smaller value cap in parallel to see if the tuning can be improved.
C2 and C3 I use a silver mica and a polystyrene, both were salvaged junk box components.
All the 10nF were box ceramics and had them for years.
All the R were 1/4W
The 1N4148 was actually a 1N914 I use whatever I have interchangably.
The LPF caps were either silver mica or disk ceramics (not NPO).
Q1 gets very hot without a heatsink. Ditto if use 2N2222A
SLA battery was providing 12.8V
If I used shack supply that is fine for normal use a little extra audio 'buzz' heard adding a 12uH choke and a 0.1uF to ground into the +ve lead reduced this.
LM386 used was a 386-1 and the headphones were elcheapo 99p ones from Tescos (similar to WallMart for those in US)
10uV signal source was from NorCal by WA6AYQ, W3CD. I had it callibrated for 50uV, 10uV and 1uV (I added an extra output), nothing difficult about building your own, it is just a 2N3904 oscillator, using HC49 crystals, I added an attenuation pad to obtain 10uV.
The manhatten pads were made using a Harbour hand punch http://m1kta-qrp.blogspot.com/2008/09/2n2-40-build.html
I have no idea why these were asked but:
The glue was poundshop regular super glue.
The yellow cable is solid core.

The shack temp (inside) when I built it was well below freezing as the concentrated FeCL etch solution I use for projects was like a slush puppy
and I added a pad or two extra and the super glue I used didn't always bond to the board (I had to heat up the board using a heat gun on the undersde a couple times to get them to 'stick'). Given your's and few others comments I bet if I tried to reproduce now I couldn't, I'll be jinxed now. Anyway boxing it up with a keyer (prob KD1JV simple keyer, no memories etc) and hope to have some trial qso with G3XBM who is sort of local, but 1.3W
3974 2010-01-12 13:16:42 Stephen Wandling Re: the flea, a 40m minimalist transceiver
Dom,

In looking back on my Flea experience, I suspect my biggest problem was
never knowing how many variables were involved when I ran into a
problem. Believing that my 2N3866 was actually a Motorola transistor, I
spent lots of time on T1 and the various ways you can wind it and wire
it in. But, since my 2N3866 was a 'fake', none of this helped.

Later I was informed that I was probably voltage stressing the C1/C2 50V
NP0 caps I was using in the tank circuit, where they could be seeing
200-300 Vp-p, with similar potential problems of too much current
through the HC-49 crystal.

Yes, the tuning on C3 is pretty sharp, and that's where I ran into more
problems. With C3 you are doing three things at the same time: 1)
enabling regeneration for the receiver, 2) getting the cleanest transmit
CW signal possible, 3) maximizing the transmit output. Using a good
transistor (e.g., 2N3553), it was clear when the receiver was working
well. But, when listening in the station receiver and measuring the
output into the antenna tuner, I would key the transmit and adjust C3
for clean keying and maximum output. At the 'edges' of the 'receive'
setting, if I moved it just a bit further the output would shoot up, but
not be heard on the station receiver. Subsequent experiments showed
that at these points the rig wasn't oscillating at anywhere near the
xtal frequency, but much lower. Eventually, I had damaged all of the
2N3553 I had and their Beta had dropped to a very low level and
therefore no more receive.

A friend of mine here in BC got interested in the Flea and had Far
Circuits make a few boards, as shown in the Sprat article, and he sent
me a couple. I still intend to re-build the Flea on one of these boards.

72
Stephen
VE7NSD

Dominic Baines wrote:
> Stephen,
>
> Wow this created a bit of email traffic overnight...
>
> To be honest I must be lucky as mine works, admittedly not first time... I had reversed the windings between earth and antenna initially, and forgotten the 1K resistor between C8 and C10.
> However I don't have a copy of EMRFD to have checked circuit theory that I may not have understood anyway (I borrowed a copy once from MI5MTC).
> I have never run SPICE, modelled a filter or a tuned circuit either. If I have to do a calculation for a tuned circuit it is usually done long hand on a scrap of paper. I'm not hot on theory as was never taught that much and tend to work things out by doing.
>
> Asked a few things off list so rather than answer individually I hope this answers everyones questions:
> The T1 to be honest I just wound all three windings in the same direction, right handed and held toroid in left hand
> and passed wire up though the centre from underneath for each turn, no rocket science or theory involved.
> The primary wound first then each of the secondaries wound on top one either side of the primary ends. Imagine pairs of wires come out on three sides of a square, primary in the middle (make sense?). I have since heard that the winding of this is the critical bit. See http://www.qrpedia.com/book/200812/flea-catalonias-answer-pixie for a picture, that is what mine looked like, don't think I would have wound it differently though. I'll take a close up image of T1 as asked by a few and it'll be on blog http://m1kta-qrp.blogspot.com/ when I can get back in the shack
> The 2N3866 was from a batch from GQRP I cannot remember who donated them but they are not marked as such. I use them a drivers for a PA stage usually.
> The trimmer capacitor there was probably only 10% movement between hearing signals, lots and then nothing again so the tuning is sharp.
> I might investigate adding a smaller value cap in parallel to see if the tuning can be improved.
> C2 and C3 I use a silver mica and a polystyrene, both were salvaged junk box components.
> All the 10nF were box ceramics and had them for years.
> All the R were 1/4W
> The 1N4148 was actually a 1N914 I use whatever I have interchangably.
> The LPF caps were either silver mica or disk ceramics (not NPO).
> Q1 gets very hot without a heatsink. Ditto if use 2N2222A
> SLA battery was providing 12.8V
> If I used shack supply that is fine for normal use a little extra audio 'buzz' heard adding a 12uH choke and a 0.1uF to ground into the +ve lead reduced this.
> LM386 used was a 386-1 and the headphones were elcheapo 99p ones from Tescos (similar to WallMart for those in US)
> 10uV signal source was from NorCal by WA6AYQ, W3CD. I had it callibrated for 50uV, 10uV and 1uV (I added an extra output), nothing difficult about building your own, it is just a 2N3904 oscillator, using HC49 crystals, I added an attenuation pad to obtain 10uV.
> The manhatten pads were made using a Harbour hand punch http://m1kta-qrp.blogspot.com/2008/09/2n2-40-build.html
> I have no idea why these were asked but:
> The glue was poundshop regular super glue.
> The yellow cable is solid core.
>
> The shack temp (inside) when I built it was well below freezing as the concentrated FeCL etch solution I use for projects was like a slush puppy
> and I added a pad or two extra and the super glue I used didn't always bond to the board (I had to heat up the board using a heat gun on the undersde a couple times to get them to 'stick'). Given your's and few others comments I bet if I tried to reproduce now I couldn't, I'll be jinxed now. Anyway boxing it up with a keyer (prob KD1JV simple keyer, no memories etc) and hope to have some trial qso with G3XBM who is sort of local, but 1.3W
3975 2010-01-13 00:34:01 Dominic Baines Re: the flea, a 40m minimalist transceiver
>