?

John,

there seems to be an strong 18 KHz moduation on the transmitted signal. i have a home-built spectrum analyzer that I have used to see the output spectrum. There was a strong spur in the output just below 5 MHz. It is well below 43 dbc that the FCC mandates. The other was the second harmonic at 14 MHz, again below the -43 dbc level.

I ran the scan again, just now, to be doubly sure. I set my resolution bandwidth to 1 KHz and ran the scan at 100 KHz span with a 2 tone, 50 mv audio injected into. I did notice a number of distortion products, but nothing 18 KHz away. The crystal filter took them al out.

The 18 KHz modulation could only be coming from the circuit after the crystal filter. try running this from clean battery to see if this persists. i would suspect, given the 18khz murmer, it is from an smps.

- f

On Fri, Dec 9, 2016 at 9:30 AM, John Sutter jds@... [BITX20] <BITX20@...> wrote:

?

I noticed that my BIT40v3 was well shy of the top of the band.
On the spectrum analyzer, I noticed two other peaks about 18KHz
on each side. They seem to be a bit higher than I'd expect,
but I'm a relative newbie on what's allowable.

I have a snapshot of the spectrum at:


First, is there a problem with my board or is that within limits?
I remember when I was setting up an SDR other signals were down by
47 or 48 dBm.

Second, does this mean I should adjust the trimmer to move the max
operating frequency to 7.3 MHz minus about 20 KHz?

I few minutes later I noticed that the other signals had pushed out about
6.5 KHz more:


The only change I've made to the RF side of things is replacing the
resistors
to reduce drift.

- John
W1JDS