Tweaking the MFJ-2982

[poppafred]

Hi folks,

PLEASE READ THE ENTIRE POST BEFORE REPLYING!

I bought an MFJ-2982 Feather-lite vertical for camping and travel but can't seem to get it to work properly. We tried it for Field day last week and it was a bust again. I am wanting to tweak this antenna and get it to at least function marginally as I think is has potential but MFJ did not do a good job in making or documenting it.

I have checked the balun and the coax shield has good continuity with the counterpoise lug, so that is correct. The radiator wire is 34' 11 1/2" long and the counterpoise has 4 wires about 14' long, I mount it on a folding tripod so the counterpoise lug is about 12"-16" off the ground.

I am a klutz with EZ-NEC and antenna modeling software so that is out of the question for me.

This antenna has potential f I could just find the optimum lengths on the radiator and counterpoise wires.

READ THIS:
IF YOU HATE MFJ, GOT IT, THERE IS NO NEED TO REPLY, MOVING ON.
I HAVE A HUSTLER 6BTV AT HOME AND IT WORKS GREAT.
I DON'T NEED "BUY A DIFFERENT ANTENNA" SUGGESTIONS, I HAVE THIS ONE AND I WANT IT TO WORK..

Now, any helpful suggestions?

 

[AK9R]

Any idea what the turns ratio is in the "balun". 4:1? 9:1?

 

[prcguy]

This antenna is a tunable base loaded groundplane, have you run the tapped coil through all its potential adjustment points for each band? The antenna may not need a tuner on some bands and others its mandatory.

 

[poppafred]

Any idea what the turns ratio is in the "balun". 4:1? 9:1?

Not a clue.

The toroid is 1.4" outside diameter, 0.8" inside diameter, looks to be iron.
12 turns with a thin enameled wire inside a silicone tubing.

Other info:

The coil is 1,8" outside diameter, 1.7" inside
3.87" long
39 turns
wire 0.05" diameter with 0.05" spacing

That came out to 220.539" total wire in the coil with 5.65" length per turn.
That would be 18' 4.5" of wire in the coil.

As I posted, the radiator wire I received is 34' 11.5" long.
The 4 wire counter poise is 14" per wire approx. with all 4 soldered to a common lug for attachment.

Like I told Bil in a pm, I intend to set it up in the yard and run a graphic antena analyzer on each coil tap/turn just to get a plot.

But the heat index right now is 114 degrees, so I'll wait to do that.

Wouldn't it be neat to take this cheap antenna and make it work?

I think so!

 

[poppafred]

This antenna is a tunable base loaded groundplane, have you run the tapped coil through all its potential adjustment points for each band? The antenna may not need a tuner on some bands and others its mandatory.

Have not done that yet but I plan to when the outside temp drops a little.

 

[prcguy]

If you don't specifically tune this antenna for your operating frequency it will not work. The balun should be a 1:1 current choke type.

Have not done that yet but I plan to when the outside temp drops a little.

 

[poppafred]

If you don't specifically tune this antenna for your operating frequency it will not work. The balun should be a 1:1 current choke type.

I'm trying to work with what I got when I bought the antenna, if possible. The schematic in the instructions might as well be drawn by a 5 year old.

After running the analyzer on every other turn, I found good tuning points for 80m and 40m. Everything else is 5:1 or worse. One chap on a different board mentioned how to check for correct balun connection but, knowing how MFJ contractors make their products, I'm still not sure it is properly wound or connected.

I tried saving the files from the analyzer but they only plot using their software and it consists of 3 numbers. The only one I can identify is the frequency. The software will plot impedance, resistance, reactance, return loss and phase angle, based on those two other numbers.

I guess I need to learn more about baluns and ununs so I can figure out what the heck these guys did. Tech support won't even answer my emails.

 

[prcguy]

This antenna is supposed to have a low SWR on 80, 40, 60 and 17m. A tuner is needed for all other bands meaning the match will be bad. Have you tried 60 and 17m? Do you have the counterpoise hooked up?

I know its more $$, but in my experience something like a 30-35ft vertical with some ground wires and an auto tuner at the base can work ok on most bands. The tuner will provide a perfect match everywhere but 10m and 6m will suffer because the radiation pattern will have a null at the horizon.

I'm trying to work with what I got when I bought the antenna, if possible. The schematic in the instructions might as well be drawn by a 5 year old.

After running the analyzer on every other turn, I found good tuning points for 80m and 40m. Everything else is 5:1 or worse. One chap on a different board mentioned how to check for correct balun connection but, knowing how MFJ contractors make their products, I'm still not sure it is properly wound or connected.

I tried saving the files from the analyzer but they only plot using their software and it consists of 3 numbers. The only one I can identify is the frequency. The software will plot impedance, resistance, reactance, return loss and phase angle, based on those two other numbers.

I guess I need to learn more about baluns and ununs so I can figure out what the heck these guys did. Tech support won't even answer my emails.

 

[poppafred]

This antenna is supposed to have a low SWR on 80, 40, 60 and 17m. A tuner is needed for all other bands meaning the match will be bad. Have you tried 60 and 17m? Do you have the counterpoise hooked up?

I know its more $$, but in my experience something like a 30-35ft vertical with some ground wires and an auto tuner at the base can work ok on most bands. The tuner will provide a perfect match everywhere but 10m and 6m will suffer because the radiation pattern will have a null at the horizon.

Yes.counterpoise connected and wires stretched to their full length during testing. Sadly, they were just laid out on the ground and not fully extended during Field Day which was probably our problem ( I forgot the plastic tent stakes)- Next year we will use a multiband dipole that is a proven performer.

At least with the testing, I now have the tuning points for 80m and 40m if I take it camping.