[Boatanchors] Receiver questions

[Carl]

----- Original Message ----- 
From: "Ian Wilson" <ianmwilson73 at gmail.com>
To: <boatanchors at mailman.qth.net>
Sent: Thursday, December 16, 2010 12:16 PM
Subject: [Boatanchors] Receiver questions


>I was using a Drake 2-B this morning. This receiver has some very nice
> things about it
> (the preselector, and the variable IF bandwidths). On the other hand, the
> product detector
> isn't very strong, and I imagine that front end large signal handling is
> moderate.

I had a 2B in 63-64 and it was an overload nightmare in a contest and with 
good antennas. It helped me lose the ARRL CW DX Contest Section award by 
making 40M in particular an absolute time wasting struggle. I wound up using 
a HQ-129X/BC-453/QF-1 just on 40 the next evening and 2nd weekend.

On SSB the audio is horrible.


>
> In the 3-30MHz range, what receiver(s) has(ve) the "best" (CW and SSB,
> primarily):
>  - performance in the presence of large adjacent interferers?

R-390A, modified 75A4, NC-303. SX-115, modified R-4C, 75S3B and C

>  - product detector?

Same as above with a HC-1 or TMC sideband adaptor on the 390A plus AGC mods

>  - legibility?

The SX-115 is better out of the box and the 390A is only useful with 
headphones without an external audio amp.

>  - audio?

HRO-60 but it needs a mechanical/xtal filter adaptor, product detector and 
AGC mods.


>  - AGC?
>  - product detector?

Just the NC-303 and SX-115 out of the box.

Collins never could provide a ham requirement AGC until the very end with 
the 75S3B/C. I included it in my modified Drake C lines in the 80's which 
were great battle condition radios after lots of mods.


>
> Using tube-only technology, it seems to me that the best architecture for 
> an
> HF receiver would
> be something like the Squires-Saunders(sp?) SS1:
>  - no RF amplifier
>  - beam deflection mixer (single conversion)
>  - crystal filter immediately following the mixer
>  - frame grid IF amplifier tubes (e.g. 6EH7)
>  - beam deflection product detector(?)


And a horrible front end full of birdies if it didnt have very close to a 50 
Ohm load. No front end isolation as obtained with an RF stage. Tribanders, 
multiband verticals, trap dipoles, etc, decimated them. Great concept, poor 
execution. There is nothing wrong with an RF amp, just the gain distribution 
and poor mixers often used for convenience.

>
> Questions:
>  - IF- or audio-derived AGC?

IF with enough loops to give full control.


>  - audio? (Single-ended triode for AM? <g>)

PP 6V6's


>  - single conversion means problems with oscillator stability, or
> difficulties
>    with birdies if using heterodyne schemes. Double conversion is much
> easier
>    but significantly weakens the front end performance. What to do?

6GM6 RF stage with just enough gain, 6ES8 Pullen mixers in both conversions 
(they can be AGC controlled if desired) and product detector


>  - how useful are audio CW filters?

Great until you try anything else or enjoy AGC pumping, distortion and 
ringing. I tried that junk with outboard filters, passive and active plus 
bought a TenTec Paragon and Omni V; both were junk. There are workarounds 
with DSP.




>
> I would like to look at real circuits, so observations about receivers for
> which
> schematics are readily accessible would be helpful.
>
> 73, ian K3IMW
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