Hi Pete,
Hmm - already checked the LO level coming in to the BPF board on
connector 26 during an earlier investigation. Depending on band, I got a
sine wave with +/- 0.5 to 1.35V using a 1 Mohm input to a scope. Assuming
the mixer is matched to 50 ohms, that seems to work out to +10 to 14 dBm.
The Synergy CMP-231 mixer (only PDF I could find but supposed to be drop-in
replacement for the CMP-A12 used on the board) is a Level 17 mixer:
https://www.datasheets360.com/pdf/-7158805956350539594
So maybe the LO drive is a bit off? Is starving the mixer by a few dBm
like this a problem?
Will check the grounded gate amps - you've given a few quick things to
do. Will report back in a couple days.
73
Phil W1PJE
On Sat, Jan 26, 2019 at 10:41 AM Peter Bertini <radioconnection@gmail.com>
wrote:
> Phil
>
> Make sure the LO injection to the DBM is where it should be.
>
> One thing you can check is the gain of the two grounded gate amplifiers
> stages, each uses four J310 FET devices in parallel.
>
> A long shot, but the problem could be a bad FET in either stage. Measure
> the voltage across each 100 drain resistor--voltages should be close....
> depending on well the devices were matched, if TenTec even bothered to do
> so. Also make sure the 100uH chokes used for the DC return path for the FET
> drains are soldered.
>
> I have a spare board with similar problems that I am going to be working on
> when I have time. Sounds like the same problem you are having.
>
> Pete
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Phil Erickson
phil.erickson@gmail.com
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