[Lowfer] Antenna Analyser Mod?

[Cliff Sojourner]

(another delayed reply, corporeal QRSS)

hi John, thanks for the encouragement from your web pages.  Today I 
modified my '249 with a switch and 940uH inline.  the '249 board gives 
even easier access to the switch than the '259.

Why 940uH?  because 470uH wasn't enough and 470s are all I had here.

anyways the frequency range is now ~240kHz to ~680kHz.  The '249's 
stability is terrible but that doesn't matter.

I took some pictures of the modification.  I think I shouldn't post them 
on this email list.  I don't have a place to host them but I will email 
them to you or anyone else that wants.

(editorial note - I got this '249 for $cheap and modifying it was an 
easy, fun project.  but I can't recommend doing this vs. springing for a 
new fancy analyzer with DDS and LCD graph showing sweep and computer 
interface and ...)

Cliff K6CLS

On 2015-11-23 16:49, John Langridge wrote:
> Ive added a 2nd switched mod to get down to 137.. I think I bottomed out
> around 110 kHz.  I dont trust R or X at all down there as it shows 1:1
> around 40 ohms into a known 50 ohm load and known good diodes in the
> detector but SWR on the analog meter seems consistent with what I see with
> other tests here on 137.  The 472 mod is generally pretty good as long as
> you don't get too hung up on the numbers, although they seem to be more
> accurate than lower down... the further away from 50 ohms resistive you get
> the less accurate the numbers seem to be...Its a descent instrument that
> most hams already have and will get you in the ball park if you trying to
> get a system going.  But don't mistake it for an accurate, high-performance
> system.
>
> On the 472 mod, I did one for someone recently using the Mouser inductor
> specified at the top of the article, mounting the inductor directly to the
> board where the trace is cut with short leads to the switch.  this actually
> worked better than the mess that I outline in pics in the article.  I've
> since gone back and added the "improved" mod to my instrument and it doesnt
> seem worse for it.
>
> As to how low will the existing slug will go, I dont know.  I didnt want to
> lose 160m so I didnt try but the new 259 "C" (I think that's the model)
> apparently comes with enough slug to get down to 460, or so say the MFJ
> people...
>
> 73 and good luck!
>
> John KB5NJD / WG2XIQ...
>
>