why TRF?

[Mike Langner]

Hello John and fellow boatanchor lovers!


I used an RAL-7 in my early ham radio days.

Advantages:

Very, very smooth cw reception -- The RAL-7 goes in and out of oscillation
better than any regen radio I ever used.


And -- no images -- example:

I once tried to use a standard superhet tuner as an air monitor for a radio
station studio in Albuquerque.

The station was on 610.  The receiver's IF was 455.

Bad birdies from a nearby station on 1520 that had a tower about a mile
away.  In fact, if 610 signed off, all the hallways were filled with 1520.

Next idea:

Tried an automobile radio with an IF of 265.

Bad birdies from a nearby station on 1150 (image was on 1140) and again, if
610 signed off, all the hallways were filled with music from the 1150
station.  Ended up using a TRF!

Also: for military purposes -- oscillator radiation was a real problem at
clandestine receiver locations -- that's how the Germans & Japanese sought
to find many receivers.  The National 120 was a variant in its line of
wartime receivers that added an additional RF stage (no gain, just
isolation) in a small box on the back panel of the receivers.  It was
designated RAO by the navy and had no local oscillator radiation the enemy
could use. The "outboard" RF stage came to be called the "back porch" by
users -- and later by collectors.

Other reason:  in civilian receivers, RCA/Hazeltine still held all the
superhet patents -- some manufacturers kept making TRF's to avoid royalty
payment.  Also -- some Hi-Fi buffs preferred the TRF -- evidence the Millen
model 4 home Hi-Fi tuner -- which, in fact, is what finally solved my
monitoring problem at the then (long since gone) KGGM AM radio here in
Albuquerque!

And there are a couple of reasons the dinosaur circuitry continued on past
the superhet (for a while!)

73 !

Mike/ K5MGR
_______________________________________________________________________



-----Original Message-----
From: Boat Anchor Owners and Collectors List
[mailto:BOATANCHORS at LISTSERV.TEMPE.GOV]On Behalf Of John N. Ritter
Sent: Sunday, July 09, 2006 11:16 AM
To: BOATANCHORS at LISTSERV.TEMPE.GOV
Subject: why TRF?


Was just looking at this massive boatanchor:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=150005276611&ssPageName=M
ERC_VIC_ReBay_Pr4_PcY_BID_IT

and wondered what advantage a TRF receiver could have over
a superheterodyne, at a time when superhets were a well established
technology.

Thanks for any responses,

John

K7VGF

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