Return-Path: Received: from rly-mg03.mx.aol.com (rly-mg03.mail.aol.com [172.20.83.109]) by air-mg10.mail.aol.com (v121.4) with ESMTP id MAILINMG104-a034787ca5ead; Fri, 11 Jan 2008 14:58:39 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mg03.mx.aol.com (v121.4) with ESMTP id MAILRELAYINMG035-a034787ca5ead; Fri, 11 Jan 2008 14:58:24 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1JDQ0e-0007YI-FN for rs_out_1@blacksheep.org; Fri, 11 Jan 2008 19:57:44 +0000 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1JDQ0d-0007Y9-J2 for rsgb_lf_group@blacksheep.org; Fri, 11 Jan 2008 19:57:43 +0000 Received: from ug-out-1314.google.com ([66.249.92.175]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1JDQ0b-0002G7-9F for rsgb_lf_group@blacksheep.org; Fri, 11 Jan 2008 19:57:43 +0000 Received: by ug-out-1314.google.com with SMTP id a2so647658ugf.13 for ; Fri, 11 Jan 2008 11:57:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; bh=96quItBtAfAj8PvdlIAyUkeRjazeOz1wOv3j+Jy3PEg=; b=Xjs78R/z5NBIj7Uc285HD55XpeXh4eUMB3LfGZDVd6taRWbJNL6mQ+xy1JgYwkxEmeDJLL6CmmQNlniQlolHOD3RlEesxiK2m0KKsrNKbkkibjC9sxFTJKaVy/cHx/h2PKQQK4S/phW/bEV9cRTg7OsSLFKtQpiV8++/TiwtGvo= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; b=dsG575S8cr4+HWYXFnRtFia9sBS34Gtzj881ugRpjd16YlM76ycIyqr9nzg+yYS6fvmpL7q3EC5zwdXU7dw5nXowpW3gbnb0ztizt2uYkWDFuj8j7PBdllY2jWjPgaxwXXRNLwz0/vinCWe2JwCSDgw49gJH6VDXxHtI4X7IVQs= Received: by 10.66.249.8 with SMTP id w8mr555824ugh.75.1200081460497; Fri, 11 Jan 2008 11:57:40 -0800 (PST) Received: by 10.66.224.12 with HTTP; Fri, 11 Jan 2008 11:57:40 -0800 (PST) Message-ID: Date: Fri, 11 Jan 2008 19:57:40 +0000 From: "Andy Talbot" To: rsgb_lf_group@blacksheep.org In-Reply-To: <008e01c85487$c0230da0$0900a8c0@Lark> MIME-Version: 1.0 References: <88d2415e0801111045t1e31ee78vbaf955f4f2a9f3a8@mail.gmail.com> <008e01c85487$c0230da0$0900a8c0@Lark> DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: LF Receiver Content-Type: multipart/alternative; boundary="----=_Part_375_19185605.1200081460493" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-AOL-IP: 193.82.116.20 X-AOL-SCOLL-AUTHENTICATION: listenair ; SPF_helo : n X-AOL-SCOLL-AUTHENTICATION: listenair ; SPF_822_from : ? X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d067.1 ; domain : googlemail.com DKIM = 1 X-Mailer: Unknown (No Version) ------=_Part_375_19185605.1200081460493 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline Yes, that's a good point. What has failed on the RA1792, Laurie. I've got a service manual for that Rx filed away somewhere. Andy G4JNT On 11/01/2008, Alan Melia wrote: > > Hi Andy most if not all of the amateur receivers sold recently have not > AGC-off function. As I told Laurie the only one I know is the AOR 7030 > which > has performance as good, if not better in some aspects that the 1792 (well > it was British designed and manufactured). The Lowe HF 150, 225 and most > of > the Japanese designed receivers seem to rely on have a mode-selected agc > time constant. It means you dont need manual gain controls, cleaner panel, > never mind the performance look at the acreage of chrome etc. Even quite > expensive wideband receiver like the Icom R8500 have to be "bodged" to put > the AGC off. This is despite them having IF output for spectrum monitors. > > I am too far away but isnt there anyone that could look at Laurie's RX > they > are not really anything out of the ordinary and should be repairable. Full > service gen is available. We cant afford to lose LF stalwarts that easily > !! > > Alan G3NYK > > ----- Original Message ----- > From: "Andy Talbot" > To: > Sent: Friday, January 11, 2008 7:11 PM > Subject: Re: LF: LF Receiver > > > > Which are the receivers you have encountered that *do* suffer this > problem > > of non-switchable AGC? It doesn't sound like a very healthy trend at > all > ! > > > > I'd use an SDR-IQ for LF these days. In fact I use one for most > > listening/monitorinf now. Its better, more adaptable and just generally > > nicer to use than the RA1792. And infinitley better to tune with point > and > > click on the waterfall display. The only thing it suffers from is not > > having a clock locked to a master reference. Needs 66.667MHz and I've > just > > never got round to making a locked clock yet. But its probably stable > > enough for QRSS as it is. > > > > AGC can be disabled, and is only used for demod anyway, to keep volume > > constant. The waterfall display operates independently of the demod > and > is > > always at fixed gain. > > > > Andy G4JNT > > > > > > On 11/01/2008, lawrence mayhead wrote: > > > > > > I have for a long time used a Racal 1792 reciever for QRSS modes on > LF. > > > This receiver failed recently,and I have been looking for a > replacement > > > receiver. > > > This search reveals a problem most modern receivers use DSP techniques > > > for filtering and the AGC is derived from the filtered signal. None of > the > > > receivers > > > I have looked at have an AGC OFF facility.This means that if one of > these > > > receivers > > > is used with ARGO or similar FFT programs a strong signal within the > pass > > > band > > > will desensitise the Rx. It seems quite possible that a weak signal > could > > > quite > > > disapear. It also appears that some AGC is applied before the digital > > > filter so that > > > signals within the roofing filters bandwith will also produce > > > de-sensitisation, and this > > > could be as much as 15kHz away from the tune freq. > > > Any ideas on receivers not using DSP filtering ? > > > Or do I look for another R1792 > > > > > > 73 Laurie G3AQC > > > > > > > > > > > -- > > Andy G4JNT > > www.scrbg.org/g4jnt > > > > > -- Andy G4JNT www.scrbg.org/g4jnt ------=_Part_375_19185605.1200081460493 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline
Yes, that's a good point.  What has failed on the RA1792,  Laurie. 
I've got a service manual for that Rx filed away somewhere.
 
Andy  G4JNT


 
On 11/01/2008, Alan Melia <alan.melia@btinternet.com> wrote:
Hi Andy most if not all of the amateur receivers sold recently have not
AGC-off function. As I told Laurie the only one I know is the AOR 7030 which
has performance as good, if not better in some aspects that the 1792 (well
it was British designed and manufactured). The Lowe HF 150, 225 and most of
the Japanese designed receivers seem to rely on have a mode-selected agc
time constant. It means you dont need manual gain controls, cleaner panel,
never mind the performance look at the acreage of chrome etc. Even quite
expensive wideband receiver like the Icom R8500 have to be "bodged" to put
the AGC off. This is despite them having IF output for spectrum monitors.

I am too far away but isnt there anyone that could look at Laurie's RX they
are not really anything out of the ordinary and should be repairable. Full
service gen is available. We cant afford to lose LF stalwarts that easily !!

Alan G3NYK

----- Original Message -----
From: "Andy Talbot" <andy.g4jnt@googlemail.com >
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, January 11, 2008 7:11 PM
Subject: Re: LF: LF Receiver


> Which are the receivers you have encountered that *do* suffer this problem
> of non-switchable AGC?  It doesn't sound like a very healthy trend at all
!
>
> I'd use an SDR-IQ for LF these days. In fact I use one for most
> listening/monitorinf now. Its better, more adaptable and just generally
> nicer to use than the RA1792.  And infinitley better to tune with point
and
> click on the waterfall display.  The only thing it suffers from is not
> having a clock locked to a master reference.   Needs 66.667MHz and I've
just
> never got round to making a locked clock yet.  But its probably stable
> enough for QRSS as it is.
>
> AGC can be disabled, and is only used for demod anyway, to keep volume
> constant.   The waterfall display operates independently of the demod and
is
> always at fixed gain.
>
> Andy  G4JNT
>
>
> On 11/01/2008, lawrence mayhead < laurie.mayhead@googlemail.com> wrote:
> >
> > I have for a long time used a Racal 1792 reciever for QRSS modes on LF.
> > This receiver failed recently,and I have been looking for a replacement
> > receiver.
> > This search reveals a problem most modern receivers use DSP techniques
> > for filtering and the AGC is derived from the filtered signal. None of
the
> > receivers
> > I have looked at have an AGC OFF  facility.This means that if one of
these
> > receivers
> > is used with ARGO or similar FFT programs a strong signal within the
pass
> > band
> > will desensitise the Rx. It seems quite possible that a weak signal
could
> > quite
> > disapear. It also appears that some AGC is applied before the digital
> > filter so that
> > signals within the roofing filters bandwith will also produce
> > de-sensitisation, and this
> > could be as much as 15kHz away from the tune freq.
> > Any ideas on receivers not using DSP filtering ?
> > Or do I look for another R1792
> >
> > 73 Laurie G3AQC
> >
>
>
>
> --
> Andy  G4JNT
> www.scrbg.org/g4jnt
>





--
Andy  G4JNT
www.scrbg.org/g4jnt ------=_Part_375_19185605.1200081460493--