[Premium-Rx] Radios and High RF powers

[refmon]

Hi,

A short amplification by example on the points in the email, below, all of
which I have found to be true.  I am using the Cubic R3030 series receivers
and find each receiver has the octave filter-type bullet proofing along with
diode and gas-discharge limiters...input volts not to exceed are in the
neighborhood of 100 volts.  Now, in addition to this, Cubic has the F-1611/U
Multicoupler, which has 8 ports, each of which has access to one of two
antenna inputs:  LF/MF OR HF.  Within those choices, the multicoupler has a
series of switchable and tunable band-stop and notch filters.  These may be
tuned by hand or via the GPIB bus, which is common to the receivers.

While this setup is intended for use in shipboard setups where receivers and
transmitters coexist in very close proximity, it works wonders for single or
multi source strong signal situations in my listening setup.  Obviously, one
minor drawback is that even though the notches are quite sharp, receive
performance is degraded not only by the original problem signal, but by the
bandwidth of the notch...we're often fiddling with signals that are hundreds
of Hz apart, which can be easily sucked into the notch.

Generally speaking, I am able to run everything in the no-filter mode and
rely on the receiver front ends...every once in a while, though, a situation
will come up where the notches work magic.  Except in situations requiring
severely limited size, I have always found a long wire or dipole to be
plenty of antenna and out-perform an active antenna...some fine results in
my younger days with a 10-30 log periodic, but that was one of those
once-in-a-lifetime opportunities...not many folks offer up LPDA's these
days.

regards

John Collins
____________________________________________
----- Original Message ----- 
From: "Richard Reich" <richard.reich at saatt.co.uk>
To: <premium-rx at ml.skirrow.org>
Sent: Friday, May 30, 2003 04:08 AM
Subject: [Premium-Rx] Radios and High RF powers


Hello list.

The problem of making receivers work in strong RF fields is not a new one.
I would suggest that one of the prime criteria for the design of a 'military
(or
commercial) application' receiver - our premium receivers - is that it
should
work satisfactorily in very high RF fields (we are talking of Volts not
milliVolts).
In the commercial world - where there is a receiver, there is usually a
transmitter in action very close-by. In reality, this design requirement may
actually make professional receivers a little insensitive (perhaps almost
deaf)
compared to some ham equipment - but some of us know and accept that - you
can't
compare the two radios at all. Putting a wideband active antenna at the
input
un-does all the work the designer put in place with regard to the 'bullet
proof'
front end. Professional users of these radios deal with the problem of
'blocking' and 'splatter' by fitting notch filters at the frequencies
causing a
problem - usually a cavity type, so that a high Q is achieved. On-frequency
stability is maintained by careful selection of metals, and design, so that
temperature effects (the main cause of canned filter drift) are cancelled
out.
Unfortunately, it must be remembered, receiver specifications are written to
impress the less informed reader (usually an accountant) - to sell the
radio.
The upshot being, don't believe everything you read. I like to think that I
have
always approached radio engineering problems with an open mind, wearing a
'common sense hat'.
If your radio is being overwhelmed by something you don't want to hear -
notch
it out before it eats your mixer or RF amp.
Notching is easy when dealing with broadcast transmissions because they
don't
change frequency by very much (usually just a few 10s Hz).
I have worked at many professional broadcasting stations in the UK where
there
are hundreds of transmitters (kWatts) and receivers in close proximity - and
there are few problems to speak of, because of thoughtful design. I can't
think
of one single installation where an active antenna is used (apart from
receiving
a LW time signal).

Regards to all....  Richard

***************************************************************
Richard Reich
Principal Engineer Hardware
SAAT Technology Ltd
Web: http://www.saatt.co.uk

DDI: +44(0)1420 545388
Fax: +44(0)1420 87259

Privileged, confidential and/or copyright information may be contained
in this e-mail. This e-mail is for the use only of the intended addressee.
If you are not the intended addressee, or the person responsible for
delivering it to the intended addressee, you may not copy, forward,
disclose or otherwise use it or any part of it in any way whatsoever.
To do so is prohibited and may be unlawful.

If you receive this e-mail by mistake please advise the sender
immediately by using the reply facility in your e-mail software.

This message is subject to and does not create or vary any contractual
relationship between SAAT Technology Limited and you.

Registered Office: Test House, Mill Lane, Alton, Hampshire, GU34 2QG
Registered in London. No. 4106589


_______________________________________________

Premium-Rx Mailing List
To Post: premium-rx at ml.skirrow.org
For Info: http://ml.islandnet.com/mailman/listinfo/premium-rx