[ARC5] Q-5er

[Kenneth G. Gordon]

On 6 Mar 2011 at 15:17, Bill Cromwell wrote:

> Hi Ken,
> 
> I vaguely remember something about a signal report of Q5 or some such
> thing that meant a good copy. That might not be quite right or
> completely wrong. But the Q5ers I have and others I know about don't
> have a Q multiplier involved so that might not be right, too. Maybe
> earlier "Q5ers" did use a Q multiplier - before there were R-23 radios.
> 
> Any help here?

Hello, Bill:

My answer to most of your questions above is, basically, a 
qualified, "Yes" except the very last one.

The term "Q-5" when applied to a signal report means simply, 
"Perfect Copy, not effected by noise, fading, interference, etc."

And, yes, NONE of the "Q-5ers" referenced in our various posts 
has anything whatever to do with "Q-multipliers" as such, 
although they both serve to fulfill about the same function: i.e., 
increase selectivity.

The idea behind using an R-23/ARC-5 or a BC-453 as a "Q-5er" 
was to couple its antenna input to the output of the mixer stage, 
or after the 1st IF stage of the usual station receiver, then tune 
the R-23 or BC-453 to the IF frequency (usually 455 Khz), then 
take the output from ONLY the R-23 or BC-453, and use ITS 
BFO, detector, and audio output stages instead of those in the 
regular receiver. In fact, some guys used to pull all the tubes out 
of the station receiver after the mixer or 1st IF stage as those 
were no longer needed.

This idea was first written up in QST very shortly after WWII in a 
note, then was expanded upon later by other authors.

Since the R-23 or BC-453 has a VERY narrow IF passband 
(something like 2.5 Khz at 60 db down), and that IF is at 85 Khz, 
what you end up with is a double-conversion receiver with very 
much improved selectivity.

1st IF at 455 Khz (let's say) and the second IF at 85 Khz.

You would leave the BC-453 or R-23 tuned to 455 Khz, and did all 
your tuning from the regular station receiver.

If you wanted really GREAT selectivity, you would often add a "Q-
multipiler" to the original station receiver in addition to the BC-453 
or R-23.

You would then use the "Q-multiplier" to notch out interereing 
signals.

Worked beautifully....IFF the regular receiver was stable enough 
to handle the very high selectivity....some were but many weren't.

In most cases it worked like a charm, giving poor hams with 
cheap receivers the equivalent of a much, much more expensive 
receiver.

In the case of the BC-348, which has a 915 Khz IF and really 
wide passband, addition of a BC band ARC-5 would very, very 
significantly improve the selectivity, and you would end up with a 
double-conversion receiver with IFs at 915 (good image rejection) 
and 239 Khz (good selectivity). The BC-348, after having warmed 
up, was quite capable of the necessary stability to handle the 
much increased selectivity.

One could add a "Q-multiplier" at the 915 Khz IF and have a really 
superb receiver with no significant modification having been done 
to either receiver.

Does this help?

Ken W7EKB