[Lowfer] MFJ-249 Antenna Analyser Mod.

[Cliff Sojourner]

On 2015-11-24 20:32, KD7JYK DM09 wrote:
> I opened up my MFJ-249 antenna analyser today to get an idea of what it does
> and how.  I also found a pdf file of the manual and a relatively poor
> quality- but good enough, schematic.
>
> It's pretty straight forward.  The oscillator is a free-running L/C network
> covering six bands, inductors ranging from a single turn of tinned wire to
> four slug tuned inductors of varying value.
>
> Frequency readout is via a counter covering a few Hz (according to the
> manual) to about 200 MHz.  Band selection is by a six-position switch, the
> inductors are easy to see.  The tuneable inductors are easy to get to
> without taking the unit apart, just take the back cover off.
>
> I didn't have a tuning tool so I didn't diddle the oscillator to see what it
> was capable of without modification.  I bought four diddle sticks today.
>
> I didn't look too closely for placement of a switch for the inductor mod,
> but I'm thinking on top of the unit with the other controls fed with RG-174.
> I find the 249 fussy so I think it'd be wise to shield the leads.
>
> While I'm at it...  Each time I use my analyser, I screw an Archer 5W dummy
> load to the top and sweep the band in question looking for a flat response
> before connecting to the device under test.  I'm thinking of adding a
> "Calibrate" switch with a precision non-inductive 50 Ohm resistor as well!

yeah my 249 is sort of fussy too, in a way that my 269 is not.  I just 
figured it's the crummy SO-239 with a phenolic insulator.  I looked at 
replacing it with a good one (teflon insulator) or even an N connector, 
but it's a big job so put it off.

you're right, there's lots of room in there.  I thought I'd put the 
switch for the inductor on the top panel, because there are already lots 
of switches there.

Cliff K6CLS  CM87