Haven't seen any discussion on this but lots on cascading filters. If
you have a radio with an IF output (or can modify it to get the IF
out) and a second radio that can receive the first one's IF, you can
cascade them for some amazing results. I did this with a pair of
DX-394's. You get sharper selectivity on AM due to the cascading of
filters, continuously variable selectivity by tuning RX1 off frequency
and RX2 off RX1's IF, extra gain to pull up the weak ones into the
incredible AGC range. With 5kHz steps, tuning across the SWBC bands is
like changing channels on a TV set. In the case of the DX-394, the
overall SSB/CW bandwidth is automatically one-half that of one radio
without any tricky tuning and can be narrowed further if you don't
mind losing the accuracy of the frequency displayed. For more on how I
did it with two of the DX-394, visit
http://groups.yahoo.com/group/RADIOS...4/message/1748 and follow
the thread.

Tom

Do you use two widely separated antennas in order to get diversity reception
thus eliminating fade?

Bill, K5BY

No, sorry if I was not clear. The 455kHz 2nd IF output of the first receiver
feeds the input of the 2nd receiver. With the two DX-394's, that results in
a quadruple conversion receiving system. This radio has pretty wide filters
for AM and SSB. For the latter, almost 7 kHz. By cascading the radios, the
combined bandwidth is inherently reduced to 3.5 kHz due to its conversion
scheme. Bandwidth for both AM and SSB can be made arbitrarily narrow with
tricky tuning.

Of course with two radios, they could alternatively be used for diversity
reception. With appropriate RF switching, they could be used as two
independent radios (with diversity as a special mode) or as cascaded radios.
Cascading itself reduces the effects of fading by providing a greater range
of AGC control.

Tom

"WShoots1" wrote in message
...
Do you use two widely separated antennas in order to get diversity
reception
thus eliminating fade?

Bill, K5BY

Tom: No, sorry if I was not clear. The 455kHz 2nd IF output of the first
receiver feeds the input of the 2nd receiver. With the two DX-394's, that
results in a quadruple conversion receiving system.

Ah so... Interesting.

I once put two Tektronix oscilloscopes in series to get more gain on a weak
signal, so I understand what you're doing. Neat!

Hmm... Maybe I could use my B&H (or one of my other little radios) as a preamp
for my DX-392 -- if I can just find the 10.7 IF output in that thing. Then the
392 would just -- hopefully -- clean up the signal.

Of course, GIGO. Maybe I should reverse them. G

Bill, K5BY

"WShoots1" wrote in message
...
[snip]
Hmm... Maybe I could use my B&H (or one of my other little radios) as a
preamp
for my DX-392 -- if I can just find the 10.7 IF output in that thing. Then
the
392 would just -- hopefully -- clean up the signal.

Of course, GIGO. Maybe I should reverse them. G

The better receiver should go first. Front end overload performance will be
determined by it and AGC pumping by nearby signals will be mainly determined
by the first one, also. It's best to use radios with non-identical
intermediate frequencies so that the 2nd receiver does not tune to its own
IF. There could be self-interference - a problem I have with two DX-394's in
cascade and may end up having to remove the built-in LW/MW ferrite rod
antenna from the second radio, having already done so from the first for
other reasons.

Good luck - let us know how your combo works out.

Tom

Tom: The better receiver should go first.

It would seem so.

It's best to use radios with non-identical intermediate frequencies so that
the 2nd receiver does not tune to its own IF.

True. I have the service manual for my DX-392. Its IFs on SW a
1st -- 55, 845 kHz
2nd -- 450 kHz

My Grundig eTR7, a basic radio but the best of my four baby radios, has a 10.7
MHz IF for SW (and?), and its tuning skips the area between 10.4 and 11.0.
There is a birdie at 10.26. I don't know yet what its 2nd IF is -- probably in
the 450-460 range, although that birdie should give me a clue. (440?)

Because the eTR7 tunes down to only 530 kHz and nowhere near 55+ MHz on the
high end, I'm thinking of maybe putting it in front of the DX-392 as a tunable
preselector. It does have good sensitivity and selectivity. Without a
schematic, though, physically finding its IF output to its AM detector will be
a challenge.

But that will all have to wait. Other stuff around me is still breaking, which
I have to fix first.

Barry: I did that with a valve shortwave receiver. It had the usual 455 Khz
IF with fairly broad selectivity. I fed the IF to an aircraft receiver that
tunes from 190 to 550 Khz,
and which has an 80 Khz IF.

Neat! That's the elegance of tube/valve receivers. Modifications are relatively
easy.

73 all,
Bill, K5BY

In article ,
says...
Haven't seen any discussion on this but lots on cascading filters. If
you have a radio with an IF output (or can modify it to get the IF
out) and a second radio that can receive the first one's IF, you can
cascade them for some amazing results. I did this with a pair of
DX-394's. You get sharper selectivity on AM due to the cascading of
filters, continuously variable selectivity by tuning RX1 off frequency
and RX2 off RX1's IF, extra gain to pull up the weak ones into the
incredible AGC range. With 5kHz steps, tuning across the SWBC bands is
like changing channels on a TV set.

"snip" Us old farts call this a "Q-5 er" Did this once
with a navy surplus 3 bander which had a 75khz IF intended for about 700
hrz bandwidth for cw in LW, tuned the front end to 455 and tapped into
the last IF stage of my SX-28. The accumulated 60 hz hum made it an ear
breaker, but if I really wanted to pull weak cw on 80 meters out of a
net there was all the gain I could use.