국외 에서는 이렇게 개조도 합니다.
외부에 미터를 달고, 별도의 코일을 추가해서 SWR 을 장파인 100KHz 까지 측정 가능하도록 한 것입니다.
259 에 해당되지만, 회로를 이해하면 다른 시리즈에도 당연히 가능 합니다.
아마 힘들겁니다.별로 추천하고 싶지 않습니다.
다만 100KHz 개조는 해볼만 할거 같습니다.(중파 및 장파의 안테나까지 튜닝이 가능하니..)
참고만 하세요.
WB6VKH 님의 95 년도 자료 입니다.
아래는 원문과 그림 파일 입니다.
INTRODUCTION
I'm uploading this file because the interest in this modification
(adapting the MFJ-259 to tune down to 100 kHz) has been huge, to
say the least. A third of the letters received have been from
outside the US.
The 3 pictorials associated with this version of the file can
be viewed with Windows Paintbrush or any PCX viewer. There are
also GIF versions on the BBS: mfjboard.gif, mfj-batt.gif, and mfj-259.gif.
VERY BRIEF HISTORY
A few years ago, about 5 years, one of our popular amateur magazines published an article
about an antenna analyzer using a signal generator and a frequency counter. Though I did not
build the project from this article, I have on many occasions used the article s idea by using a
signal generator (Lamkin) and a frequency counter to find the resonance of either an LC circuit
or antenna.
Later, MFJ came out with the 249 antenna analyzer which consisted of the same components:
a simple generator and a frequency counter. MFJ later last year came out with the newer model
259, which also reads impedance. I personally have the model 259, though frankly if you look at
the impedance scale, you'll find the analyzer responds best in the 25 - 75 ohm load anyway. Which
means if you get a good dip in the SWR reading, you re most likely in the 25 - 75 ohm range.
Being interested in VLF and MF for many years (30 years), I had the need to tool up the MFJ 259
to respond to that portion of the band.
THE MODIFICATION
Believing the MFJ 259 frequency counter was every bit as good as my own frequency counter
(0 - 500 MHz), the limitation to the low band conversion would only be by the LC network of the
259's signal generator. This turned out to be the case.
Upon removing the back cover (there are a few screws), you will see the foil side of the PC
board. Most soldered connections will be on this side of the board. This board will have to be
detached from the rest of the hardware so it can be slightly cocked to fit in the parts and drill the
necessary holes.
(Refer now to the illustrations.)
CONCLUSION
Since the the MFJ write up, I've again modified my MFJ-259
and removed the 2 ferrite adjustable coils and replaced them with
a tapped coil using a 1/2 inch ferrite rod. The taps are switched
by a multi switch mounted where the toggle switch would be mounted.
No more screwing in or out of the loop sticks, just band switching.
This provides continuous tuning from 100khz to 170Mhz.
Small banana jacks were placed where the loop sticks were mounted
and are wired to the multi switch so that external coils can be
attached without tearing into the unit. I use the external connection for coil
testing. I thought I'd throw that info in.
Well, Have fun, I'm off working on a new type of antenna.
73's
Dave - WB6VKH
