Stupid MFJ Ham Tricks

[ka1tdq]

I use a hidden dipole on the 2nd floor of my house roof for my rice box. At the feed point is an LDG remote tuner that uses 12 volts DC on the coax. The DC is supplied by a small LDG coupler in the shack that attaches between the radio and the antenna. The radio never sees the 12 volts on the coax because it is isolated by capacitors.

Well, my HOA just granted me permission to install a full sized 75 meter dipole. I still want to use my hidden antenna with the tuner for my rice box, but also remotely switch from the shack my 75 meter dipole into and out of the feedline. It would be difficult because both the remote tuner and the remote antenna switch require 12 volts DC to operate, and the remote antenna switch doesn't pass DC.

What to do?

I modified the MFJ remote antenna switch to pass DC by removing the coupling caps and shorting the connections with jumper wires underneath the circuit board, as shown in the picture.

Now when I want to use the rice box, I apply power to the LDG antenna coupler and it supplies DC to both the coax switch and tuner. When I want to use the 75 meter dipole, I turn off the LDG box and the feedline is just a straight through shot to the dipole.

Jon

[WD8BIL]

Hey Jon...…… if you can now hang a 75 meter dipole why not consider making it a fan dipole for 80/40? Mine works really well on 15 too!

[ka1tdq]

I'm restricted to the plans that I submitted. Basically an inverted V with the single wire. I don't want to push the issue either because it took months of waiting to get this far.

The LDG feed point tuner works pretty slick for multi band operation. Pick any frequency and it tunes to resonance in a few seconds. If it's a frequency you've used before, it'll remember and tunes and 1 second. That's why I want to keep that one for the plastic radio.

Now that I have permission, I do want to use something fairly decent for the 75m AM window.

Jon

[W6TOM]

  My DPRK urban lot is 50' X 100', in the back corner is a 50 foot redwood tree. I had a tree climber put a support with pulleys up at 45 feet. I hung a window line fed dipole  130 feet in length and used a Palstar BT1500A balanced line antenna tuner, expensive but better than either of the Johnson match boxes. The antenna is in a sharp V to fit in my yard, it has lobes but works better than the coax fed 80/40 meter fan dipole that preceded it. I get 80 to 17 meter coverage.

[KD6VXI]

I'm restricted to the plans that I submitted. Basically an inverted V with the single wire. I don't want to push the issue either because it took months of waiting to get this far.

The LDG feed point tuner works pretty slick for multi band operation. Pick any frequency and it tunes to resonance in a few seconds. If it's a frequency you've used before, it'll remember and tunes and 1 second. That's why I want to keep that one for the plastic radio.

Now that I have permission, I do want to use something fairly decent for the 75m AM window.

Jon

Maybe go very close spaced balanced line?  That would get you multiband and can be argued as per plan?.??


--Shane
KD6VXI

[ka1tdq]

Twin lead is a good idea... didn't think of that one actually. But I've already got a plan into place to eventually get back on 75m with high power. I made this center insulator this morning. It'll be mounted at the rear peak of the house.

Now, it'd be fun to watch what happens to the MFJ antenna switch at 2kw. I'll need to scale up that with a home-brew version when the time comes.

I'll also need to ensure not to supply 12 volts to the coax during high power transmissions. I'm sure that LDG tuner also at the peak of the house would explode.

https://www.youtube.com/watch?v=rMWlBZ63dcI

Jon

[W6TOM]

  I first built one of these antennas to use at my sister's houses in Massachusetts while visiting, I wanted an antenna that could be deployed and taken down easily and gave me broad band coverage. This worked very well, the tuner was the expensive part, I bought one for $400 used from a guy in Vermont and was pleased. I had tried both Johnson match boxes and the Harvey  Wells Z Match, neither had close to the tuning range or was as easy to use as the Palstar BT1500A, new these go for $800.

  Now that I'm retired I spend a month a year in MA, I would be there now except I had to cancel my trip on account of the Wuhan Virus.

   I bought the ladder line, stealth wire and a WA1FFL Center Support for the antenna from Amateur Radio Supply in NH. I was so happy with how this antenna worked I decided to use the same here.

[KC4VWU]

Big Strap AM + MFJ = POOF!