Hi Paul,
Reading the link, it looks like there are very few analyzers that use
receivers, either superheterodyne or direct conversion. The AA-54 is in the
class of broadband detectors, which are all sensitive to external RF.
http://www.rigexpert.com/index?s=articles&f=aas
Scrolling down the page to near the bottom, we find the superheterodyne or
direct conversion frequency selective types. This is the mistake I think MFJ
made, not doing a selective detector. The single overwhelming problem is
external voltage.
73 Tom
.
----- Original Message -----
From: "Paul Christensen" <w9ac@arrl.net>
To: "topband" <topband@contesting.com>
Sent: Wednesday, March 05, 2014 2:03 PM
Subject: Re: Topband: New MFJ 259C available
Where is a selectivity spec or a description??
73 Tom
Tom,
Apart from the N2PK analyzer, I don't know any published selectivity spec.
The detector minimum res. bandwidth of the N2PK unit is 7 Hz and produces
+4dBm into 50 ohms.
FWIW, RigExpert put together a comparison of analyzers based on
measurement topology. For sure, it's a biased piece -- especially when
the MFJ product is discussed. So, keep that in mind.
http://www.rigexpert.com/index?s=articles&f=aas
The plot below shows how well the N2PK analyzer can selectivly ignore a
large multi-volt base voltage from three nearby AMBC stations located 2
miles to the south. Two of the AM stations are Non-D in the daytime. One
is 15KW, the other is 5KW. Note that the T is resonated to 1420 kHz,
right where the stations transmit (look for 1320, 1460, and 1530 kHz).
The attached plot shows total RF immunity on the X trace. On the R trace,
small "blips" do show - each representing the local AMBC stations.
However, even these can be easily ime-averaged away in the software.
http://72.52.250.47/images/N4NN.jpg
Paul, W9AC
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