开云体育

Hello all,

Looked through the archives and see many complex (for me) topics covered, so this one should be simple -- for someone else on this list, that is.

Built an earlier, through-the-hole BitX 20 kit (QRPKits.Com) for someone. ?Looks great! ?Doesn't work great, however.

Problems:?

1.) Received SSB signal audio fairly weak, but nice strong birdie on ~14.300. ?Audio stage appears pretty functional with 'finger test' on components.

2.) PTT switch produces nice strong 9 watt carrier. ?But this isn't supposed to be an AM rig. ?What's up with that, please?

Any and all help would be greatly appreciated. There are three of us trying to figure this out, all older hams, and not one of us has a clue.

Thank you,
72/73,
Don McBride, K3RLL ? ?<>< ? ? ? ???
K1 #2613 | KX1 #2396 | K2 #1569 | KX3 #4565 | ?K3 #8404?
PB #187 ?| ? NAQCC #1905 FC7 ? | ?FISTS #13504cc 2064?
FP #1843 ? ? | ? ? QRPARCI #3881 ? ? | ? ?SKCC #3133 c337

Hello Don,

Does your kit look like this

It's known as the Hendricks BitX20a kit.??

This is the one I have and modified it to work on 40m.? It's a great kit but it is very very touchy about the bandpass filter caps and toroid turns and the mixer toroid windings.

Also make sure they are well scraped of varnish. Just touching around can yield results.

I think the guys who designed the kit are on this group.

I have lots of pictures, files etc should they be of any use to you.? Including a larger circuit diagram roughly divided up into the working sections.

Rob G4NQX

I found this helps when fault tracing.

This would be a good place to start.

Leonard

Hi Don,

In addition to the other very valuable insights and suggestions you've received, for the specific problem of the carrier behaving as an "AM transmitter", I'd suggest you check the balanced modulator and/or the filter as the carrier without modulation could not get pass through these stages. On the other hand, check if there is no audio oscillation which could be getting into the modulator and them the transmitter would be legitimately send the tone as it were CW (in fact for working in CW some BitXs have a small audio oscillator which is fed in the modulator chain to that effect).

HTH

--

Cesar Rabak, PY2CSH?

Hello Don,

By checking that the audio amplifier is working you have already started back tracking the circuit.

Have you got a RF probe or oscilloscope etc. for RF voltage measurements ? If not make a simple

RF probe with a germanium / schottkey ?diode. First thing is to check that the final IRF 510 is not

oscillating by removing the mike, pressing PTT and in the same condition i.e. mike removed check that there is

no carrier ( RF voltage ) present after the 2 diode Balance Modulator / De-modulator. My experience is there is

heavy carrier leakage. ( I am facing the same problem of removing the carrier leakage here ). You can check the

carrier leakage before the crystal filter and even after the Ring diode mixer as there will be RF voltage present

in athe all of the above stages without any audio signal from mike. Go stage by stage measuring forward or backward.

Hope this will help you.

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