[Milsurplus] LO radiation

[J. Forster]

Is there no preselector (cavity?) before the mixer? What do they do about images. If
not, the reason may be that they are for airborne use. DFing an aircraft is less
useful than a ship, because they don't stay in one place nearly as long. Also, since
they are designed to detect the much higher EIRP of a radar set, they could well do
so from far beyond an range a LO might be detectable.

BTW, my comment quoted below is really about HF and below.

FWIW,
-John



WA5CAB at cs.com wrote:

> The Radar Search Receivers AN/APR-1, AN/SPR-1 and RDO (38-3200 MC, Navy c.
> 1943) and AN/APR-4 (38-4000 MC, AAF c. 1944) each have four plug-in tuning
> units.  The two lower frequency ones in each case have RF amplifiers and vacuum
> tube mixers.  The two higher frequency ones have inputs directly to crystal diode
> mixers (no RF amp.).
>
> In a message dated 3/28/2005 1:05:40 AM Central Standard Time, jfor at quik.com
> writes:
> > IMO, 3 dB is on the low side. AFAIK, receivers where the antenna goes
> > directly
> > into a mixer are a post WW II development. The first such design I am aware
> > of
> > is a roughly 1965 Racal design where the RF is mixed with a LO somewhere in
> > the
> > 30 to 70 MHz range, and later down converted again. This design has problems
> > even with today's high intercept mixers and Racal and Harris receivers often
> > require pre selectors.
>
> Robert Downs - Houston
> <http://www.wa5cab.com> (Web Store)
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