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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
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.
Whatever you Wanadoo
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