A LISN is a very useful device for those doing compliance EMC testing and
for anyone (especially hams and SWLs) who want to know the noise
contribution from their various equipment at home and around the shack.
While you do not need a calibrated receiver to make reference comparisons
between pieces of equipment that have RF emissions, you do need a
calibrated receiver if you are going to start talking in terms of actual
levels observed. You may have stated your receiver in one of your other
posts, and if so, sorry that I missed it. However, making reference to
specific emission levels without having run a calibration on the subject
receiver with a known good sig gen is rather useless. I say that because,
with limited exceptions, the S meters on receivers appear to mostly not
adhere to any sort of calibration standard.
I own 2 Collins S-Line receivers and a Hammarlund HQ-110C, all dating from
the "good old days". They are the ONLY receivers I have which conform to
one standard, that being 50 microvolts input signal = S9. Also, the 10dB
per division marks above S9 are reasonably accurate on all 3 receivers up
to at least 40 over 9. The S meter performance of my modern receivers
(those being the receive portion of transceivers), whether for HF or
VHF/UHF, are all over the map. I have one very sorry excuse for a radio
that has all of 30 dB dynamic range between S1 and 40 over 9!!! (The radio
works just fine as a transceiver, but I just can't put any useful meaning
into S meter readings on it.)
I've said it before and I say it here again: if you are going to work in
absolute numbers, the receiver's S meter calibration must be known.
> [Original Message]
> From: KD7JYK DM09 <firstname.lastname@example.org>
> To: Larry Benko <email@example.com>; <firstname.lastname@example.org>
> Date: 2/29/2012 4:54:03
> Subject: Re: [RFI] A fun and educational RFI toy.
> : Be careful with LISNs and preamps. Turning on and off the DUT (device
> : under test) will create significant transients to the receiver. I have
> : never hurt a receiver or spectrum analyzer but have killed a couple of
> : preamps.
> I have not experienced this with my unit (hopefully won't). The output
> very low, I can
> only make an educated guess at the moment without equipment set up to
> it, but based on the sensitivity of my receiver and the "S" meter reading
> equating to
> about -120 dB and looking at a conversion chart for 50 Ohms I would say
> around 225nV.
> I have an idea for simple device similar to a LISN box that most anyone
> build, trying to figure out how to sample the AC lines safely, thinking a
> torroid and only a turn or two of wire on the receiver side to keep
> low and provide adequate signal strength, I'll play around.
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