Examining the Johnson Matchbox ATU

[ke7trp]

I thought you could run a test for us. But if you dont own them, I guess you cant.

C

[K5UJ]

<<<RX Matching
On the 30K station, I do run the 75A1 through the Matchbox for receive, does seem to help the signal level, suspect its more of a matter of impedance matching with the front end of the Collins receiver. I've read that you can change the tap point on the inductor for the rx input, have not changed mine, seems to work fine.>>>

I think the stock matchbox had two taps on the link, one for tx and one in another point a few turns away for rx which was of course switched in by the stock TR relay.   Many (including mine) were modded at some point with the relay and rx tap removed.    I guess that rx tap was for older rx like the A1 that had 300 or 600 ohm antenna terminals on the back.  There was a KW MB on eBay a few weeks ago that still had the TR relay so a few survive I guess.

Rob 

[ke7trp]

Yes. Exactly.  Mine, Is straight through.  If you use the TR, on RX, It will match to the older 300 ohm recievers. This is why some are missing performance on RX using 50 ohm recievers.

C

[KD6VXI]

I have the original 275 matchbox owned at one time by W6PIG.

It's been modified so that the TR switch is still in service, but the receiver tap was moved for 50 ohms.

It has the instructions on how to move it BACK to 300 ohms written in pencil.

I can pop it open and count turns if anyone wants one designed to have 50 ohms on the receiver tap.


--Shane

[ke7trp]

That might be good info to have posted.  You can use an MFJ to figure it out. Recently, I have been experimenting with matching the Rxer to the antenna. It makes a big difference for weak signal. But I fully realize why most people dont bother. I normaly talk AM when the band is in. If I guy is showing 40 over to me, It wont make any difference in the copy.

Good to see you posting shane.

C

[KM1H]

Which well-known DXers were these and what was the basis of their statements?

Carl, can you explain why the KW version receives better than the 275W version. IMHO, that concept is what is absurd.

Walt

No, as I dont have one, dont intend to get one, and have never used either. Just saying it is absurd without doing an evaluation is the real absurdity particularly since several well known DXers have stated differently.

Carl
KM1H

Written in various old paper DX and contest journals back when 5BDXCC was announced. Back then 80M DX was a rarity and requirements little known. Then a 160M DXCC came along.

[flintstone mop]

This is vy interesting.  Maybe EFJ used the four section cap to make folks think they couldn't homebrew their own tuner? hi hi.

  At least I have not seen any vswr creep during long transmissions like I saw with my old bal. tuner, the Bliss Matchmaster. 




Rob

WOW I thought I was the only one who fell into that trap!!

The Bliss tuner did pass muster for the lowest loss, but when components started to fail as that POS coil did, the manufacturer-owner said there were no replacement parts. And talk about a real POS to get into the DAM thing....geesh.
It's in pieces and I built the K1JJ SuperTuner.
Nice info on this thread BTW.
Fred

[ke7trp]

We had one of those Bliss tuners. The big one.  I think my elbow still hurts sometimes from turning that damn Crank on the side.  It was sold off.

C

[WA1GFZ]

my KW match box produced exactly the same feeder current as the much larger HB fugly