[TenTec] Omni VI+ IF board gain: what is normal?

[Phil Erickson]

Hi Pete,

  Scratch that - forgot a square.  The range of LO drive is actually +7 dBm
to +15 dBm.  The +7 dBm is in fact on 40 meters where I was testing -
definitely low.  Maybe that increases the conversion loss beyond the 7 dB
quoted at full drive - and for which the second GG amplifier is
compensating?  And what to do about it if so?  I have deliberately not gone
into the Xtal Osc / LO generation board because it's buried.

73
Phil W1PJE

On Sat, Jan 26, 2019 at 11:14 AM Phil Erickson <phil.erickson at gmail.com>
wrote:

> 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 at 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
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>
>
> --
> ----
> Phil Erickson
> phil.erickson at gmail.com
>


-- 
----
Phil Erickson
phil.erickson at gmail.com