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LF: Re: RA1792

To: [email protected]
Subject: LF: Re: RA1792
From: "Andy" <[email protected]com>
Date: Tue, 31 May 2005 14:00:09 +0100
Delivery-date: Tue, 31 May 2005 14:02:13 +0100
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I used an RA1792 for all my narrow band LF work, and it was performed admirably.  The PLL synthesizers appear to have good phase noise performance, and they can be used down to 8kHz  - at which point you can just begin to hear the BFO noise.
 
The filter leak around that some have mentioned is noticeable, I measured it at between 45 to 55dB depending on the filter selected.
 
One feature that this Rx does off that I have never seen on any amateur receiver, but have on all professional comms receivers, is wide CW mode reception.    By setting the RA1792 to its 15kHz filter setting, CW mode, then adjusting the BFO to its limit of -8kHz, you can receive a wide swath of spectrum 15kHz wide - which just happens to be the right bandwidth to feed into a soundcard at 44kHz sampling rate.  
 
My model only has 10Hz tuning steps, which was a major limitation initially, but the EVM and Soundcard software all offers the choice of fine tuning now so that is less of a problem.  Other models of the Rx do have 1Hz steps.
 
Being able to lock all the internal sources to a master input of 1, 5 or 10MHz is invaluable
 
Thses days, I don't go on LF much, but I did make a custom LF receiver to try to improve on the RA1792 when using very narrow band modes.  This Rx used a DDS for the LO and directly derived all BFO frequencies from a master input.  (In fact the IF used a 300Hz BW mechanical filter from a defunct RA1792)  The close in phase noise perfomance of this Rx was marginally better than the 1792, and I had proper calibrated gain control (no AGC needed) and higher resolution frequency setting, but was a complicated way to go for a very minor performance improvement.
 
Andy  G4JNT
-----Original Message-----
From: Walter Blanchard <[email protected]>
To: [email protected] <[email protected]>
Date: 2005/05/31 12:33
Subject: LF: RA1792

 
The performance of a modern rx with a good infinitely-variable DSP filter at very narrow bandwidths is better than older rxs because they don't ring at the edges as xtal-based filters do.  I had an Icom 756 PRO3 that was very good in this respect and now an Icom 7800 that is really excellent - at 10 Hz bandwidth it still works - no xtal filter will do that. A good test if you haven't got a good SG is to tune to Loran then look at the i.f. on a scope and see where the pulse tails go to. 
 
Walter G3JKV.
 
---- Original Message -----
Sent: Tuesday, May 31, 2005 10:04 AM
Subject: Re: LF: RE: RA1792

========================================
Message date : May 30 2005, 03:11 PM
From : "Alberto di Bene"
To : [email protected]
Copy to :
Subject : LF: RE: RA1792
Marco Bruno wrote:

> I would add: quite easy to maintain, no custom ICs, only a few
> outdated parts
> but still available on the market. The synthesizer is remarkably
> performant, and
> the 3rd order IMD is in the 102-103 dB range.
> [...]

Marco, Jim, Tracey, Laurie, Alan and Dave (am I forgetting somebody?)

thanks for your opinions about that Rx. The latest messages seems to
correct somehow the not so bright impression that initially had formed
in my mind, so I will have to reconsider my decision. Next week I will
have (probably) the chance to examine more carefully that radio. Apart
from checking the LCDs and the keypad for deterioration, what else would
you suggest me to check? Which are the IF filters that I must expect it
to have installed ? Any other weak points to watch ?

And now the one-million-dollar question... given that my intended usage
for that radio would be mainly the reception of digital (or
pseudo-digital) signals across the various bands, from LF to 30 MHz, if
you had to choose between the RA1792 and the Icom R75 (for 2/3 of the
price), which one would be your choice ? I am not interested in
reception of broadcast stations or CW/SSB signals (for this I have a JRC
NRD-525), but, as said, narrow band (from a few Hz to 3 kHz) digital
signals only.

Thanks again guys,

73 Alberto I2PHD

There is no doubt that I would chose the RA1792, I  Have done all my digital work with it and would miss it greatly, and at that price ! go for it.

Laurie.




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