Re: BITX40, are these SA traces as they should be? #bitx40help

Thomas Sharka

If you have a cell phone,tablet or even a laptop/desktop then you have an audio generator.

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On Sunday, March 18, 2018 1:41 PM, "news1@..." <news1@...> wrote:

Hi all,

Built my Bitx40, mostly to learn more about troubleshooting radios. I know a bit about measuring and how things "work" but just from reading theory. Practice is clearly different, and a good way to actually get some understanding.
As a result, my setup and measurements may be flawed from the beginning, though I try to do things the "right" way.

As I didn't receive much when trying to listen to the Bitx40 on my TS-870, I started looking at the schematic and trying to figure out what was going on.

Measurement setup:
Bitx40 through 20dB attenuator into a SA. VFO/DDS frequency set at 7110 kHz, no modulation into the microphone (shorted the pins) except for the screenshot with the 10kHz span.

In the 2MHz span, note the strongest peak is at -12dBm around 7333 kHz.
There's another peak around -18dBm at 7110 kHz (which I suppose is the DDS)
Another peak at 7555 kHz, about -41dBm.

In a 10MHz span, I see peaks at 14.218 kHz (-78dBm, obviously harmonic of DDS freq, right?) and 14.445 kHz (-68 dBm, no idea where this comes from).

I don't have a audio freq generator, will build one to inject a know signal into the mic input.

So, a couple of questions:
  1. As the tranceiver uses SSB, shouldn't the carrier be much more suppressed? Ideally, no carrier?
  2. Is the strong peak at 7333 supposed to be there? That's +6dBc, correct?
  3. What's with the 14445kHz peak? There's no peak at/around 7222 kHz...
  4. If I inject a 1kHz signal into the microphone input, what kind of voltage RMS should I use?
  5. A 1kHz on the input should show up as a 7109 kHz signal, is that correct? I tried some "steady" whistling and got a peak at -8 dBc at 7108.4 kHz and another at 7112.1 around -45 dBc (see the 10kHz span screenshot)
  6. In the 10 kHz whistling screenshot, I suppose the signal (result of the whistling) is at 7108.4 kHz, but -8 dBc. Shouldn't this be much more?

I might be missing something obvious, but have been looking a it for a couple of evenings now.

Thank you,


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