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V6 BFO alignment problems after installing AGC


Jack Hunt
 

Hi everyone,

I installed the AGC board from kit projects, following which I had some gain issues. I think that was my fault now, but I thought that maybe the BFO needed aligning. So I did that, but still had problems. So I tried again and noticed the following behaviour (see attached video). When I touch the radio or wiggle the coax, the noise characteristics change dramatically.

Does this point to anything in particular that I might have broken?

I have also installed the BCI filter after the AGC board (after just due to space). The AGC switch is mounted on the front of the unit and the volume input to the AGC board has the 10ohm resistor in series.

73s
Jack 2E0GDV


IW4AJR Loris <lorisbollina@...>
 

Hi Jack 2E0GDV,
 
the problem you filmed in the video would seem to derive from a strange ground loop that somehow affects the receiver, perhaps due to the two ciscuiti added in cascade or perhaps to the arrangement of the AGC switch.
I can't help you more because in my case I don't have this problem, instead, the sensitivity reduction seems to be a typical "disease" of this circuit, in my µBITS.V6 are lost  about 2 S points (10/15 dBµV), I think it is due to the internal resistance of the 2N7000 in series with the antenna, which is always present and which, even if polarized, has a significant loss.
Obviously all is only my opinion, I may be wrong in the measures or have a bit obsolete instrumentation, but my ear does not deceive me, the sensitivity drops a lot!
73 de IW4AJR Loris


Jack Hunt
 

Hi Lori's,
Thank you for your input. After posting this I did wonder about a potential ground loop. 

I have noticed that the radio is a lot less sensitive. A +10 station on my Yaesu was lost in the noise on my ubitx, but I put this down to poor BFO alignment.

73s
Jack 2E0GDV


On Mon, Nov 23, 2020 at 07:53 PM, IW4AJR Loris wrote:
Hi Jack 2E0GDV,
 
the problem you filmed in the video would seem to derive from a strange ground loop that somehow affects the receiver, perhaps due to the two ciscuiti added in cascade or perhaps to the arrangement of the AGC switch.
I can't help you more because in my case I don't have this problem, instead, the sensitivity reduction seems to be a typical "disease" of this circuit, in my µBITS.V6 are lost  about 2 S points (10/15 dBµV), I think it is due to the internal resistance of the 2N7000 in series with the antenna, which is always present and which, even if polarized, has a significant loss.
Obviously all is only my opinion, I may be wrong in the measures or have a bit obsolete instrumentation, but my ear does not deceive me, the sensitivity drops a lot!
73 de IW4AJR Loris


Jack Hunt
 

Update - I tracked down the problem. I had soldered the ground of the BCI filter to what I thought was ground, it was not...

Now I have noise consistently within the band on the BFO alignment tool. Now I just need to do the frequency calibration. I'll do that tomorrow when propagation is better for WVV.

73s


KE2GKB
 

If you continue to have issues Jack feel free to reach out to me or David (N8DAH), Here or at info @ kit-projects and we can help fix and make things right if need be! Almost a thousand happy customers. Let us know how your BFO calibration goes!

-- Tim Keller - KE2GKB https://shop.kit-projects.com


Jack Hunt
 

Thank you Tim,
I seem to have the coarse BFO alignment ok now. I'm just trying to get the frequency calibration correct now.

73s