[Milsurplus] RBM - MF question

[Hubert Miller]

I wanted to know the -60 db selectivity of some receivers, since, AFAIK, that's a good judgment point for overall selectivity.
I looked at the RBM graph, per Robert's attached graphic, and the RAX manual,
http://www.radiomanual.info/schemi/Surplus_NATO/RAX-1_user_1945.pdf
page 86. Here are my conclusions:
RAX  IF=160 kHz   -60 db  -6.8 kHz  +6.8 kHz
RBM IF=112 kHz  -60 db  -7.5 kHz   +8  kHz   ( switch= Narrow )
I think it's interesting the RAX with higher IF is a wee bit more selective.
The asymmetry of the RBM curve is maybe to be expected at the lower IF.
For some comparison, I think I recall the HRO-60 is +-5 kHz at -60 db. The earlier, very expensive RCA AR-60 comes in at something
like -12 kHz. I think most communications receivers come in around the 10 kHz figure, measuring with just their LC filtering.
I recall the old Lafayette valved receivers of the 1960s even came in at around this number, due to their large size, quality IF cans.
Right now I'm wondering what the German vehicle receiver MWEc rates; it has a variable bandwidth crystal filter. Also the German
LWEa.  Those will have to wait for me to investigate, and maybe a real long time.
I do have the RAS manual, so I'll look that up.
The BC-969 would be another interesting one, but I don't have the manual for it.
-Hue

From: WA5CAB at cs.com [mailto:WA5CAB at cs.com]
Sent: Monday, October 30, 2017 9:16 PM
To: Kargo_cult at msn.com; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] RBM - MF question

Yes.  See attached PDF.

In a message dated 10/30/2017 19:39:31 PM Central Daylight Time, Kargo_cult at msn.com<mailto:Kargo_cult at msn.com> writes:


Does one of the RBM manuals spec the selectivity of the MF receiver?

I am trying to decide whether to keep the MF receiver for AM-band DXing.

-Hue

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