Topband: New MFJ 259C available

[Tom W8JI]

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 at arrl.net>
To: "topband" <topband at 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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