Topband: Ant Analyzer Assistance request -- funky readings

[Tom Rauch]

> Jim: MFJ makes a filter for the 259 and etc.
>
> I believe that it must be a series resonate circuit across 
> the input,
> tunable to the interfering stations freq. Z=0.


The MFJ filter PARALLEL resonates across the input.  Z is 
thousands of ohms.

In parallel with that parallel resonant circuit is a series 
tuned circuit in the BC band. This has a residual inductive 
reactance on 160 and higher. To cancel it you just tweak the 
capacitance that sets SWR to minimum into a dummy load.

Now you are left with a series to ground trap that shorts 
the BC station RF to ground and looks like 1-4K ohms pure 
resistance on the measurement frequency.

See how simple the design is?  ....and it doesn't modify the 
impedance of the system very much.

The limitations are the Q of the tuning capacitor and 
(mostly) Q of the inductors. With better inductors it would 
an almost perfect filter. The cost and size prohibits using 
really good inductors.

73 Tom