[Premium-Rx] 590H Filters?

Wed Jan 7 17:36:11 EST 2009

Good evening members.

First of all a very Happy New Year to everyone and I hope this year proves 
to be less gloomy than the last (though somehow I doubt it).

Secondly John Reed's mail tonight shows that despite what some would have us 
believe, microprocessor control is not the be all and end all.  It's really 
rather an idle way of using a radio, with the bandwidth and AGC tied to the 
mode (though in many radios the factory settings can be overridden).  For me 
I far prefer to be able to select any mode with any AGC with any bandwidth 
using a "proper" rotary switch.  We should remember that many of our PR 
devices were in fact designed for semi-skilled operators and all were 
designed for remote control, hence the wholesale abandonment of rotary 
switching.

It may be heresy on this site to say this but I prefer the Racal RA1772 with 
its traditional switching to the "microd" RA1792.  I have little use for the 
latter's 100 memories, though others will no doubt disagree.  I like to be 
able to "drive" a radio.

It's like with some digital cameras.  I have a fancy expensive Canon EOS 30D 
with untold numbers of modes and variables, and it takes good pics, but to 
be honest, I preferred my older "analogue" Nikon FA which would do exactly 
what I want it to do and was not tied up in the knots of a microprocessor or 
two.  When you understand the interplay between depth of focus, aperture and 
speed and can allow for the effect of sun, snow and sea, there is little 
need for a fully automatic system unless you are a lazy snapper.  However, 
theft of the FA intervened and I would not now go back and pay a fortune in 
film, and the immediate transfer of the image to the PC is such an 
advantage.

I have too have noticed excessive MP noise on the AF output of the RA1792. 
The problem is pick up on the ribbon cable via the memory and display boards 
to the AF gain potentiometer and back again to the AF amp, but that can be 
mostly eliminated by adding a decoupling capacitor of 1nF between the audio 
signal input to the AF amplifier IC and ground.  On the 1792 apply the 1nF 
capacitor between pins 9 and 10 of IC U26.   [Thanks go to to Pat McAlistair 
G3YFK for this mod].  I anticipate that the same mod could be done 
successfully with the 6790 and 6793, though the IC details may be different.

In truth the AF feed along the unscreened ribbon cable exposed to the MP 
gunge was a cheap way of building the radio.  There is no such MP pick up in 
the successor, the RA3701 series, thanks to the vastly better screening 
applied.

73s
Michael O'Beirne
G8MOB

----- Original Message ----- 
From: "John Reed" <ka5qep at sbcglobal.net>
To: <premium-rx at mailman.qth.net>
Sent: Wednesday, January 07, 2009 6:41 PM
Subject: Re: [Premium-Rx] 590H Filters?

> John Reed here.
>
> I'm a member of this group and have been watching this topic for the past
> few days.  I built this board quite a few years ago, and it's still
> performing well.  My idea was to take the control of the filters away from
> the microprocessor since it wouldn't do what I wanted.  It's not difficult
> to do this.  I just added a rotary switch on the front panel in place of 
> the
> squelch control and let that control the relays that I use on the board to
> switch the filters.  There were a few other components needed on the 
> board,
> and I still have the notes if there are questions.  On the Harris, the
> addition of the post IF board made little difference except for very 
> narrow
> bandwidths, less than 100 Hz.  On my Racal (RA6793A) it made a big
> difference, even on 1 KHz filters.  By the way, I've compared both these
> receivers and I like the RF-590 better.  The only place where the Racal
> beats the Harris is when I want to receive a weak signal close to a strong
> one.  Otherwise, the Harris is a lot quieter.  There seems to be a lot of
> microprocessor noise in the Racal.
>
> John Reed, KA5QEP
>
>
> ----- Original Message ----- 
> From: <ToddRoberts2001 at aol.com>
> To: <cntaty at wcc.net>; <premium-rx at mailman.qth.net>
> Sent: Tuesday, January 06, 2009 10:05 PM
> Subject: Re: [Premium-Rx] 590H Filters?
>
>
>>
>> In a message dated 1/6/2009 7:55:51 P.M.  Eastern Standard Time,
>> _cntaty at wcc.net_ (mailto:cntaty at wcc.net)   writes:
>> To all:
>>
>> I have tried to get information about the 590H from Harris...nada!! 
>> They
>> won't even talk about it and will not give you any hints.  I have  two of
>> the
>> items and they are good receivers except for this "painus in the  a_us."
>> The
>> unit was designed for frequency hopping service and its  reputation
>> indicates
>> it is well designed for this and most other services: it  is also much
>> heavier than the 6790 RACAL series.  Frankly, I prefer  RACALs over the
>> Harris but some people like Chevys and some like Fords.   I worked at
>> Collins
>> (Dallas) way back in the Sixties and during that time  made friends with
>> many
>> people in the industry...some still at Harris and  neither I nor any of 
>> my
>> friends from that period have been successful with  Harris (collectively)
>> in
>> getting the necessary information that would a allow  a modification of
>> the
>> receiver such that it will perform as Todd's  acquaintance's.
>>
>> Frankly that is not a bad way to proceed and If Todd could come by  the
>> information in a more graphic form, I, for one, would give it a  try...it
>> doesn't seem too hard at first blush!
>>
>> Bill
>> W5STP
>> _______________________________________________________________
>>
>> Hi Bill,
>> John Reed KA5QEP is  the one who built his own IF boards for his RF-590.
>> Actually he built two boards  - a Pre-IF board with set of filters and a
>> Post-IF
>> board with another set of  filters. He found that he was able to improve
>> the
>> S/N ratio of very weak signals  in the narrower bandwidths by cascading
>> two
>> narrow filters in series. He found  the improvement wasn't too much in 
>> the
>> wider
>> bandwidths so he concentrated on  cascading  narrow cw filters.
>> A few years ago he sent me a collection of notes on his homemade IF 
>> boards
>> with  schematics. I made pdf copies of them and would be glad to email 
>> you
>> copies of  them if you are interested. I was planning to make up my own
>> custom
>> RF-590H IF  board someday and it is one of those projects I haven't 
>> gotten
>> around
>> to yet.  John's notes should be enough to show someone how to do it.
>> Someone
>> could make  just one IF board if they didn't want to fool with having to
>> use
>> two in series  if they didn't really need to cascade  filters.
>> I haven't corresponded  with John Reed in about a year. I am sure he 
>> would
>> be
>> glad to help with any  advice or info he still has.  Here is his last
>> email
>> address of a year  ago:
>>
>> _jreed at alum.mit.edu_ (mailto:jreed at alum.mit.edu)
>>
>> 73 - Todd WD4NGG
>>
>> **************New year...new news.  Be the first to know what is making
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>
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