EMRFD Message Archive 5159

Message Date From Subject
5159 2010-09-17 07:27:20 Chris Trask X-Mode Mixer (was mixers: strong signal immunity)
>
>> I'll be testing this thoroughly once I have the better diodes
>>installed. The transformers in it now are just my generic 4 turns
>>of trifilar wire in a 2402 binocular core. I use those for just
>>about everything when prototyping.
>
>Yes, I use those and keep a supply of them in 33/43/73 ferrite plus
>the larger and smaller cousins.
>
>I didn't think they were anything special but for upper VHF low UHF
>or low HF to MW maybe below the transformers require attention to be
>adequate.
>

Yes, and at that point I would be considering powdered iron balun cores and smaller wire. But, Fair-Rite 61 is reasonably good material up to UHF.

>
>If symmetric layout is observed and the transformers are as well
>made I'd expect very good isolation as every path by eye has it's
>mirror suggesting excellent balance is possible.
>

My prototype is pretty sloppy, even for my standards. It was intended to be nothing more than "proof of concept" and the performance at this level surprised me. I had to do the OIP3 test a few times before I believed what I was seeing.

>
>Looks like a good solution for where the SBL1 (level-7 mixer) is
>not adequate and the H-mode might be unsuitable/exotic for the VHF
>and up.
>

I might be encroaching on level-10 mixer territory with this, but it's much too early to tell. I've been going over what's readily available for the diodes and came up with the following:

BAV70S Pair of isolated CC duals, 4nS, 5pF
BAS40-05V Pair of isolated CC duals, 100pS, 5pF (best overall)

BAS40-05 CC dual, 100pS, 5pF (cheap)
BAT54C CC dual, 5nS, 5pF
BAV70 CC dual, 4nS, 5pF
HSMS-2804 CC dual, 100pS, 0.5pF (expensive, scarce)
HSMS-2814 CC dual, 100pS, 0.5pF (expensive, scarce)
HSMS-2824 CC dual, 100pS, 0.5pF (expensive, scarce)

BAS40-06 CA dual, 100pS, 5pF (cheap)
BAT54A CA dual, 5nS, 5pF
HSMS-2803 CA dual, 100pS, 0.5pF (expensive, scarce)
HSMS-2813 CA dual, 100pS, 0.5pF (expensive, scarce)
HSMS-2823 CA dual, 100pS, 0.5pF (expensive, scarce)

>
>When I look at the schematic the first thing that pops into mind
>is a pair of singly balanced mixers arranged to be balanced against
>each other.
>

Yes, that's it in a nutshell, except for the crossover. Two more transformers than in a traditional DRM like the SBL1-1.


Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/
5161 2010-09-17 07:53:56 Chris Trask Re: X-Mode Mixer (was mixers: strong signal immunity)
Ooops! Got the capacitances in that list of diodes a little mixed up. Here's the corrected version:

BAV70S Pair of isolated CC duals, 4nS, 5pF
BAS40-05V Pair of isolated CC duals, 100pS, 5pF (best overall)

BAS40-05 CC dual, 100pS, 5pF (cheap)
BAT54C CC dual, 5nS, 5pF
BAV70 CC dual, 4nS, 5pF
HSMS-2804 CC dual, 100pS, 2pF (expensive, scarce)
HSMS-2814 CC dual, 100pS, 1.2pF (expensive, scarce)
HSMS-2824 CC dual, 100pS, 1pF (expensive, scarce)

BAS40-06 CA dual, 100pS, 5pF (cheap)
BAT54A CA dual, 5nS, 5pF
HSMS-2803 CA dual, 100pS, 2pF (expensive, scarce)
HSMS-2813 CA dual, 100pS, 1.2pF (expensive, scarce)
HSMS-2823 CA dual, 100pS, 1pF (expensive, scarce)

I managed to find some affordable HSMS-2804 diodes on eBay, so I'll have the opportunity to test those as well.


Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/