[Premium-Rx] Racal RA1772

Sat Aug 7 15:22:50 EDT 2010

--- El sáb, 7/8/10, Enrique Fernandez García <enriqueeeeee2001 at yahoo.es> escribió:

De: Enrique Fernandez García <enriqueeeeee2001 at yahoo.es>
Asunto: Re: [Premium-Rx] Racal RA1772
Para: premium-rx at mailmsn.qth.net
Fecha: sábado, 7 de agosto, 2010 21:21

Hello Michael,

 Following your useful advice, I have decided to save some money and not to get the Plessey.

 Maybe, in a near future I will buy the EK070. Not long time I asked about its perfomance on the Perseus SDR forum, and the answer was that the EK070 has much better AM audio recovery. It is said that  the EK070 employs very high grade ITT crystal filters which stand
comparison with the best of today's DSP filter systems, but spend almost 2000 Euro in a 25 years old receiver it is very risky, recently I saw on ebay some Watkins Johnson 8718A for much less, I was tempted but I did not much about these receivers.

              http://groups.yahoo.com/group/perseus_SDR/message/9145

Regarding to the Racal, my only complaints are, as Michael says, the AGC could have been better and the weakest point, the PSU failures.

Recently, I have replaced the 150uf blue capacitors on the IF/AF board but not significant improvement.
Also I have made the IF GAIN modification, seen on the maintenance manual, in order to have it in junction with the AGC.
I replaced the carrier IF filter for a McCoy 6.8Khz but I think that a narrower would be better.
The only issue that I have had until now has been that the OUT OF LOCK does not work.

Next week I will sart with the PSU modification, I will replace the bridge rectifier diode D2 in a fresher place.
You can see the steps here:

                http://www.observations.biz/Observations_from_Scotland/Observations_2009_12_29.htm

Also I will replace the four large electrolytic capacitors , I have purchased high end Epcos Sikorel.
Another interesting project, I have already all components, it is a elliptic low pass filter, designed by Dallas Landford, this device can be very useful for the Racal.
http://www.kongsfjord.no/dl/Audio/ELPAFs.pdf

So, I am going to have a busy summertime.  I realized that the phone output is 600 Ohms, I have a pair of Japan Radio Company ST-3 headphones but the audio it is too bassy and muffled for my taste and I can not understand the speech or ID,s of the weak signals.
I will try with a Telex or a Clevite brush headphones instead.

To sum up, I am very happy with the 1772 it is worth having it and waste the extra money that it needs.

Thank you very much for your help and advices.

Kind Regards.

--- El sáb, 7/8/10, Thomas Adams <quixote2 at ix.netcom.com> escribió:

De: Thomas Adams <quixote2 at ix.netcom.com>
Asunto: Re: [Premium-Rx] Racal RA1772
Para: richardreich at aol.com, "Michael O'Beirne" <michaelob666 at ntlworld.com>, premium-rx-bounces at mailman.qth.net, "PREMIUM-RX" <premium-rx at mailman.qth.net>
Fecha: sábado, 7 de agosto, 2010 19:05

One more endorsement in favor of the RA-1772.

I was lucky and got into them before the market 
went crazy; I currently have THREE of the
beasties here, plus an MA-168 Diversity Adaptor box.

For my money, it's the best design Racal ever came up with.

Mr. T.   W9LBB

At 01:20 07-08-10, richardreich at aol.com wrote:
>For what it is worth, I agree with Michael 100%.
>
>Richard
>Sent from my BlackBerry® wireless device
>
>-----Original Message-----
>From: "Michael O'Beirne" <michaelob666 at ntlworld.com>
>Sender: premium-rx-bounces at mailman.qth.net
>Date: Thu, 5 Aug 2010 21:41:17
>To: PREMIUM-RX<premium-rx at mailman.qth.net>
>Subject: [Premium-Rx] Racal RA1772
>
>
>----- Original Message -----
>From: "Michael O'Beirne" <michaelob666 at ntlworld.com>
>To: "Enrique Fernandez García" <enriqueeeeee2001 at yahoo.es>
>Sent: Thursday, August 05, 2010 9:34 PM
>Subject: Re: [Premium-Rx] R&S EK 070 Availability?
>
>
> >
> > Dear Enrique
> >
> > I will give you some advice.  This is based on having owned 4 RA17s with
> > various adaptors, a RA217, RA1217, RA1772, RA1792, RA3701, PR155G, PR2250,
> > PR2280 and STC STR8212 (with complex DSP), not to mention various
> > Eddystones old and new.
> >
> > The nicest quality AM reception is still the RA1772 in my opinion.  It may
> > have a simple detector and not synchronous nor have all the modern frills
> > such as DSP, but it uses a AM precision detector with less distortion than
> > a conventional diode and sounds good, and my ears are backed up by
> > distortion measurements with professional test gear.
> >
> > In short, hang on to your RA1772.
> >
> > The 1772 also gives very low SSB distortion, of around 0.75% THD on a
> > single CW tone.  It's shortcomings are the AGC, which is semi-hang.  The
> > AGC on the RA1792 is better but I don't like that set as much.
> >
> > The other shortcoming is the PSU.  The +20V regulator is notorious for
> > failing due usually to a dry solder joint caused by the high temperature
> > inside the case.  This regulator provides the voltage reference to the
> > other voltage regulators and its failure causes the whole set to fail.
> > However it's easy to repair, though the mass of wiring gets in the way,
> > but be patient and you will succeed.
> >
> > The tuning on the 1772 is well weighted and super smooth, eons better than
> > on any Harris or Collins gear.  Almost as good is the RA3701 series, but I
> > still prefer the 1772.
> >
> > The 2280 is a good set with excellent audio but there are problems.
> >
> > 1.    Many of the Plessey ICs are no longer available.
> > 2.    The tuning seems to have a very very long time constant in the
> > synthesiser.  It sounds distinctly "rubbery" as the signal tunes in.
> > 3.    If you have the optional half octave filter module, be prepared to
> > have to change many of the small Clare DIL relays thta switch the ranges.
> > The reason is that the relays carry no DC wetting current and sometimes go
> > open circuit.  This is quite major surgery as there is not much room on
> > the PCB.
> > 4.    You will need the rare extender board to work on the module in
> > circuit.
> >
> >
> > 73s
> > Michael
> > G8MOB
> >
> >
> > ----- Original Message -----
> > From: "Enrique Fernandez García" <enriqueeeeee2001 at yahoo.es>
> > To: <premium-rx at mailman.qth.net>
> > Sent: Thursday, August 05, 2010 6:51 PM
> > Subject: Re: [Premium-Rx] R&S EK 070 Availability?
> >
> >
> > Hello,
> >
> > Owning just a RACAL 1772 I have always wanted to buy one too in order to
> > improve the reception with faint AM signals, but I think that the prices
> > have skyrocketed.
> > Another interesting option it is a Plessey 2280 but I do not if it could
> > surpass the Racal.
> >
> > Here you have a nice sample:
> >
> > http://www.helmut-singer.de/stock/1225203598.html
> >
> >
> >
>
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