开云体育

I just completed the QCX No. 1747. I am unable to peak the trimmer cap. and the pots have no effect either. I have double checked all of the components, and rebuilt the T1 transformer. I have build several toroids before, so I am familiar with removing the insulation and checked that several times even removing the transformer and reinstalling it. The sound from the headphones sounds like a motorboat. The indicator indicated a “4” and does not move at all. I would appreciate any pointers of things to check. I am a very experienced kit builder, so I feel confident about my soldering, etc.
Thanks and 73
Rich W4WU

Rich

I would definitely check continiuity through each winding of the receiver transformer. My 40m version looks not as neat as the higher band version in the manual, but the calibration was amazing. Its easy to solder to the outside of the insulation only, so check continuity without touching wire. When all is well, the calibration nulling is amazing. Much of the receiver is audio circuitry. Mine was intermittent so I turned on the builtin signal source,? poked around a and quickly found a loose resistor.

The test audio should be clean. Unlike some qrp rigs, the qcx has generous audio. Maybe your volume control is too high. Peaking the trimmer is not that sharp on my 40m version. But nulling the pots is very sharp, leading to amazing image rejection. Don't fear when meter jumps back up, as the number will change indicating rescaling.?

Motorboating sound does seem to imply audio is overdriven. I would check bias voltage at the regulator.

Curt

Rich,

I had a working 40m QCX (#2536). I was able to build it completely with out issue. Took the unit in a little Plastic case on vacation and came back home without taking it out of its case. Came back home, hooked it up for some WSPR after installing a balun. Fired it up and had a soft motorboating sound slightly louder than the LCD update noise.

This is why I know the motorboating some speak of is getting confused for the S-Meter when they have a real issue.

Well I started to tune up and did an idiot thing that I can't prove if related. I turned the inductor switch on my T-match tuner one click while keyed down. I left the QCX to do its work as a beacon and thought nothing more of it.

Fast forward to this afternoon, I pulled out the QCX after working on my Bitx40. Was having transmit troubles there as well after moving to a new case. When I fired up the QCX today, the motorboating is deafening! I checked my joints visually and noticed IC9 pin 8 hadn't been trimmed and was folded over on to C21 positive pin, but I hadn't really found more tonight. I trimmed that bit and checked the schematic. Seemed to be little issue as those two are connected by a trace if my eyes haven't deceived me. Tomorrow I am going to touch up my joints and add solder where I can see some have too little.

I also checked the data sheet and it looks like even with a 14.8V battery packed hooked up it shouldn't bee an issue for the LM4562 op-amps to have short-circuited temporarily.

I am getting 3.5W-4W out on my SWR meter but it sounds like the motorboating is all that is being transmitted via my Shortwave radio on SSB. I only hear the sound on the Shortwave when the QCX is transmitting.

I haven't yet been able to see the transmit on my RTL-SDR so I'm short once of my diagnostic tools.

I hope to hear of your success!

73 de Jacob AG7CT