was Re: [Collins] Best Receivers; now 51S1 critics.

[Gerald]

On Thu, 2005-08-11 at 09:26 -0700, Park, Ted wrote:
>  Team
> 
> I have a number of receivers including among others a Collins 75S-3B, a
> Collins 51S-1 and a Collins R 388. I like every one of them! For amateur
> communications using SSB and CW I prefer the 75S-3B. For ease of use in
> SWLing and general band cruising I prefer the 51S-1 and for AM
> ragchewing on 75 meters and actually listening to foreign broadcast
> station music I prefer the R 388 although I do *not* like the standard
> audio on the R 388...for either AM ragchewing or listening to foreign
> broadcast stations....so I have installed an optional switchable wide
> bandwidth filter for AM reception and I use a retuned Central
> Electronics "SIDEBAND SLICER" hooked up between  the standard 500 KHz IF
> output of the R 388 and an old (but fully restored) Heathkit A9A 20 watt
> push pull 6L6 high fidelity amplifier connected to a good Jenson 10 inch
> high fidelity speaker and enclosure...the R 388 now sounds *great* for
> AM ragchewing and foreign broadcast listening..at least to my ears.
> Yes...I understand and appreciate that the R 388 audio was intentionally
> designed by Collins to enhance military voice communications capability
> and not high fidelity.....I simply wanted to hear AM fidelity from my R
> 388 the way it was appreciated 50 to 60 years ago on the old high end
> boat anchor National (e.g NC-183)and Hallicrafters receivers (e.g. SX-42
> and R-42 Bass Reflex Speaker). :-)
> 
> Best regards, Ted, K6XN 
> 
> Ps The 20 watt high fidelity amplifier and the Jensen speaker ensemble
> in retrospect may seem to be overkill for the R 388...but I had them on
> hand already and the combination really sounds *great* and visibly
> impresses non-ham visitors to the radio room :-)

Single ended audio stages designed for communications bandwidth never do
justice to good broadcast signals. But often those "good" broadcast
signals have frequency bias built in (especially LF and HF enhancements)
to compensate for 3 or 4" speakers in the typical kitchen radio. So then
the midrange is a bit weak when run through a good audio system.

A good wide range speaker helps most any radio. I prefer the Motrac era
Motorola speakers for communications, but something of a bass reflex
design for better listening to programs.

There may be a market for a DSP based detector to work with 455 and 500
KHz IFs with capabilities of independent sideband, a number of receiver
filter widths, and there's no reason it couldn't do wide AM possibly
even compensating for the ordinary IF sideband roll off. I'm studying
the necessary techniques this week but I've not committed any design to
paper or any bounds on the specifications yet. Though the fancier it
gets the closer it gets to being a complete receiver needing only a
minuscule front end such as the ham radio SDR radios already on the
market like the on that uses DSP in the shack computer.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer