[time-nuts] Double-balanced RF mixer L-R symmetry

[ed breya]

I'm wondering if anyone has dissected enough common canned RF mixers, to 
know how symmetric they are, internal construction-wise, or knows of 
available info, especially on specific models.

I have taken some apart over the years, and I believe they generally are 
made highly symmetric wrt the LO and RF ports. I typically use them 
either way around, for units that have the same band specs on both. But, 
the specs typically are with the given port assignments, so there may be 
some questions, depending on application.

The particular models in this situation are the WJ M9D, and MCL SRA-1H, 
which are high level +20 and +17 dBm, respectively. I have only one M9D, 
and two SRA-1H - they're all I have in this class, with a favorable 
pinout that I need. I want the IF port to be DC-isolated from ground 
(but RF-shorted with C between commons).

Both units appear to be OK for the pinning I need, but with slightly 
different arrangement. Having the option of L-R end and phase swapping 
(along with IF pinning for best shielding), gives more hookup flexibility.

Since I only have three good candidate mixers, I need to be very careful 
to not burn any out, as I'll be driving from an amp capable of over +30 
dBm* (with lots of padding and maybe a limiter). Also, the signal input 
will be fairly big, up to +6 dBm average, and possibly +20 dBm peak. 
This is for that noise source down-converter project I mentioned before. 
I'm trying to go as big as possible on signal levels, both to maximize 
the output power after conversion and filter loss, and preserve fairly 
high crest factor.

The above conditions are about the maximum - in reality, by the time all 
the signals are properly padded, the levels will be more realistic. I'm 
trying to minimize the padding of course, even looking at using a 
diplexer at the IF to absorb the upper image power, to avoid padding the 
reflection off the LPF.

*That's at normal 24 V supply. I'm going to try running at 15 V, 
unspecified. The maximum Po should be greatly reduced at the lower supply.

Ed