EMRFD Message Archive 13887

Message Date From Subject
13887 2017-05-18 20:17:55 nothdurftm Help with non-performing Updated Universal QRP Transmitter
I'm embarrassed that I'm unable to find the problem with the Updated Universal QRP Transmitter I recently built.  I'm only getting milliwatts out.  I've uploaded a pdf file under the K5ESS folder that gives voltage measurements and scope traces along with the as-built schematic.  Any thoughts on what to try / look into would be greatly appreciated.
MIke
K5ESS


13888 2017-05-19 04:44:46 John Marshall Re: Help with non-performing Updated Universal QRP Transmitter
Mike,

Your scope shows about 3 Vpp at the emitter of Q2, which should show an RF resistance of just over 8 ohms to ground. I would be looking for too high a value for R21, too low a value for C24, or a bad solder joint in that path.

John, KU4AF
Pittsboro, NC

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13889 2017-05-19 05:15:49 Nick Kennedy Re: Help with non-performing Updated Universal QRP Transmitter
​NPN Q1's base is 0.4 V lower than Q1 emitter.  Should be 0.6 V higher.  Do you have the leads of Q1​ swapped?

73-

Nick, WA5BDU


13890 2017-05-19 06:00:39 Nick Kennedy Re: Help with non-performing Updated Universal QRP Transmitter
It's fun to work on puzzles.

One of the most error-likely places in a circuit like this is the 4:1 transformers with polarity issues, as well as having all wires stripped properly. Or not.

I don't understand the scope scales.  Is the first value the voltage per division and the second is ... ?

I see you are using a 1x probe. At 14 MHz, I think a 10x would be better, although I'm not sure what the result of a 1x would be.

T1 is resonated with C14.   Do voltages peak up when you adjust C14 and drop off on both sides?  

Do downstream RF voltages change as expected when you adjust R17?

73-

Nick, WA5BDU
13891 2017-05-19 09:43:04 Steve Ratzlaff Re: Help with non-performing Updated Universal QRP Transmitter

There is also an updated oscillator circuit on Wes' site, adding a cap from base to emitter. I don't see that cap in your schematic.

http://w7zoi.net/mark2.html

Steve AA7U


13892 2017-05-19 10:51:16 Raj Re: Help with non-performing Updated Universal QRP Transmitter
Mike,

Temporarily short out the xtal and then measure the DC voltages. I guess they will be fine.
You have a blown Q3 or D1.

Raj, vu2zap


At 19/05/2017, you wrote:
 

​NPN Q1's base is 0.4 V lower than Q1 emitter.  Should be 0.6 V higher.  Do you have the leads of Q1​ swapped?

73-

Nick, WA5BDU


13893 2017-05-19 20:06:38 K5ESS Re: Help with non-performing Updated Universal QRP Transmitter
Raj, Steve, Nick, John,

Thanks for the replies. Still no joy,

Did short out the crystal and the base DC level now reads around +0.6v relative to the emitter instead of the other way around.

Removed Q1 and checked it. Looks OK HFE 218.

Replaced crystal – same result. These crystals are HC49/US microprocessor type. Don’t know if another type crystal would give greater oscillator output.

I didn’t include C1 because I didn’t see any of the problems that Wes ZOI said it cured. I have since added it but no improvement.

Have double checked the transformers and they check out as they should with an ohmmeter (didn’t tie both ends of the same winding together and insulation stripped OK) and did tie end of one winding to opposite end of other winding.

Scope pictures show volts per division on bottom left and trigger level to the right.

No difference seen using 1:1 or 10:1 probe.

T1/C14 peaks as it should. As mentioned, two turns were removed to lower inductance. I measured T1 inductance and verified it would resonate at 14.060 MHz with the capacitor I used for C14

Downstream voltages vary as R17 is adjusted. I’m not sure what is expected in terms of amplitude.



I’ve etched a couple of boards based on the original Universal QRP Transmitter in Solid State Design for the Amateur.

I think I’ll wire one of these up and maybe it will give me some insight into the problem.



Again thanks for the replies.



Mike

K5ESS







13894 2017-05-19 20:21:48 K5ESS Re: Help with non-performing Updated Universal QRP Transmitter

An added note.  Current draw for entire unit with R17 set for minimum is around 40 mA.  At maximum its around 110 mA .

Mike

K5ESS

 

13895 2017-05-19 20:39:00 AncelB Re: Help with non-performing Updated Universal QRP Transmitter
Can u guys link me to an updated schematic for that TX? I have the old
edition of emrfd with a lot of errata and non available parts
thx
13896 2017-05-20 10:07:02 Raj Re: Help with non-performing Updated Universal QRP Transmitter
Check RFC1 - your Q3 Collector wave form seems low.

If RFC1 is an encapsulated one then it could have internally fried and the inductance will not be what it should be.
Check inductance.

Raj

At 20/05/2017, you wrote:
>
>
>Raj, Steve, Nick, John,
>
>Thanks for the replies. Still no joy,
13897 2017-05-20 11:05:54 K5ESS Re: Help with non-performing Updated Universal QRP Transmitter
13898 2017-05-20 12:43:51 K5ESS Re: Help with non-performing Updated Universal QRP Transmitter

Raj,

I did suspect RFC1 in that it was marked only with 3.9.  I thought it might be nH instead of µH so I added another in series (10 turns on an FT37-43 core) but no change.

Mike

K5ESS

 

13899 2017-05-20 13:58:52 Steve Ratzlaff Re: Help with non-performing Updated Universal QRP Transmitter

What is max level at point Y? (Lift T3/C20 connection, put two 100 ohm 1/4W resistors in parallel to C20 and ground, measure voltage across that load). The article says 300 mw/50 ohms max available there = about 11 volts peak to peak.

Steve AA7U


13900 2017-05-20 14:11:13 K5ESS Re: Help with non-performing Updated Universal QRP Transmitter

Good suggestion Steve.  I’ll try that.  My suspici