[Boatanchors] RE [Boatanchors} RCA Marine Receivers

[Richard Knoppow]

      Both of the receivers I asked about are are RCA 
commercial/marine receivers c.1960, they are almost identical 
except the AR version is designed to run on DC. The have the same 
specs. These were supposed to be advanced design receivers for 
operation in difficult circumstances so the spec surprized me. 
They are both double conversion with fairly high first IF. The 
handbooks for both are on the BAMA site.
    Finding comparitive specs is somewhat difficult but National 
and some others published image rejection specs for  a number of 
their receivers. The RCA AR-88 and its relations, are famous no 
limit designs. The AR-88 has a 455Khz IF and is rated at 200:1 
image ratio at 30Mhz. Partly this is due to its use of very low 
loss coil forms. It just surprised me that a twenty year new 
design had much poorer image response. I thought perhaps someone 
on this list might have one of the later receivers and be able to 
confirm the spec is correct. Even some double conversion 
receivers do not have exceptional image rejection, for instance 
the Collins 51J-3/R-388 has something like 40db rejection at 30Mhz.
    The Hammarlund SP-600, with a considerably higher first IF 
and two RF stages has, by memory, something like 60db rejection 
at any frequency it covers. The MacKay 3010C is speced at 80db at 
all frequencies it covers (up to 30Mhz).
     Anyway, I will never have either of the RCA areceivers but 
am interested in design so though I would ask here.

On 5/28/2022 11:14 AM, JAMES HANLON wrote:
> Richard,
> 
> I have no direct knowledge of the receivers you are concerned about, but I can offer one possible reason for the difference in Image Rejection.
> 
> It's possible that the receiver with only 30 dB rejection has a lower frequency IF than 455 kHz.  The Navy had National build the RSS for them that was an HRO-Junior but with a 175 kHz IF rather than a 455 KHz IF.  I have an RSS waiting in the attic for restoration.  Just got some additional coils sets for it that will allow me to cover all of the traditional ham bands from 160 through 10 includinbg, I hope, 15 meters.
> 
> Jim, W8KGI
> 
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL