[Elecraft] Sub-Rx Filters

[Richard Ferch]

Your understanding of diversity mode is incorrect. What you described is 
NON-diversity mode, i.e. normal or default use of the subRX. In this 
normal subRX mode, the two receivers are on different frequencies - the 
main RX (left ear) is on the VFO A frequency (upper display) and the 
subRX (right ear) is on the VFO B frequency (lower display). The 
transmitter is on VFO A if SPLIT is off, and on VFO B if SPLIT is on. 
You can use this for split operation in either orientation (RX on A, TX 
on B or RX on B, TX on A), or you can use it to monitor two frequencies 
at once, and choose which of the two to work on depending on whether you 
turn SPLIT mode on or off. You can also control which RX is/are heard in 
each ear with a configuration option, but the default is A(main) left, 
B(sub) right.

Diversity mode is quite different. In Diversity mode, BOTH receivers are 
on VFO A (upper display). You would use a different antenna for each 
receiver (otherwise there is no point) - because the two receivers are 
using the same VFO and are phase-locked, the relative strengths and 
arrival times of signals in the two ears gives you a kind of panoramic 
soundscape, where the signal you want is localized at a particular 
position in space (seems to come from a particular direction), while 
noise is spread over the whole space, and QRM often comes from a 
different direction relative to the signal you want. It's kind of like 
stereo (diversity) vs. mono (non-diversity, both receivers on the same 
antenna).

In Diversity mode, the lower VFO B display works just like it does with 
a single receiver - it tells you where the transmitter will be when 
SPLIT is on, but it has no connection with either receiver. Do not make 
the mistake of thinking it tells you where the subRX is - that is only 
true in non-diversity mode.

Normal non-diversity dual receive is usable in all modes, including 
phone modes, although the level of activity and the likelihood of split 
operation might be low enough in AM and FM that it might not be 
economically worthwhile to add subRX filters for these modes.

Diversity mode is very useful in CW. It is not useful in digital modes 
(unless someone can write software to emulate what the human brain does 
with the inputs from two ears). I don't know how useful it would turn 
out to be in wider bandwidth modes like SSB, AM and FM - never tried.

I don't know how the filters are installed in a factory build, but the 
arrangement you suggested looks reasonable to me. I don't think there is 
a hardware requirement to line the filters up in corresponding slots in 
both receivers, but from a human interface point of view that makes 
sense. Certainly that's what I did, and like you I left room for the 
filters I thought I would be most likely to want to add later.

73,
Rich VE3KI


(unknown call sign) wrote:

> My understanding of diversity reception is that I can receive two different
> frequencies and though used more for CW when working pile-ups, it's not
> something I'd likely use for FM, hence the single FM roofing filter. So I
> was wondering about installing AM on the sub just so that I could have that
> as well.