Need help with M2 6M3

[KB2FCV]

Hi everyone. I am working on the finishing touches of my new 6M3 6 meter antenna and I am getting a peculiar problem. I think it is getting some kind of feedback to the radio. The reason I say this is that even though I am putting out 10 or 15 watts, my meter on the radio will say I am putting out 75 watts with an SWR of 10:1.

The radio is an Icom 746 Pro.
The feedline is about 75 feet of new Andrew Heliax LDF50A, with about 10 feet of LMR-400 Ultraflex at the rotator.

I took a dummy load and put it at the very end of the coax at the antenna, and everything looks normal. My meter then indicates 10 or 15 watts with a flat SWR. I wonder what could be going on here? I am pretty sure I followed the instructions carefully and went over everything. Any ideas what could be going on or suggestions of things to try? Do you think it would help to call M2 or do they not offer that sort of support? I would check with another wattmeter but I don't have a slug in that range for my Bird.

Many thanks,

James KB2FCV

[K7FE]

James,
Go over the antenna instructions again. You appear to have an error in assembly, bad LMR-400 or a connector problem. The reflected RF (common mode current) from the antenna end of things is traveling back down the outside of the coax shield to your shack and causing a VSWR measurement error.

73,
Terry

[WB2WIK]

My first guess is a bad/loose/open/shorted connection somewhere.

The M2 has three connectors on the T-match block: Feedline, and (2) for the balun. If any of those has any problem at all, obviously it won't match, and won't work.

Re-check everything.

[KB2FCV]

My first guess is a bad/loose/open/shorted connection somewhere.

The M2 has three connectors on the T-match block: Feedline, and (2) for the balun. If any of those has any problem at all, obviously it won't match, and won't work.

Re-check everything.

I wound up calling M2 and they sent me a troubleshooting doc to check the T-match block. It turns out there is an open connection between one of the balun connectors and the rod (we went over it on the phone). New one will be on it's way in the next day or so. You hit the nail on the head!

[KB2FCV]

James,
Go over the antenna instructions again. You appear to have an error in assembly, bad LMR-400 or a connector problem. The reflected RF (common mode current) from the antenna end of things is traveling back down the outside of the coax shield to your shack and causing a VSWR measurement error.

73,
Terry

Thanks Terry, well sounds like it was a defective T-match block! Luckily it wasn't an installation error There was an open connection between the balun connector and one the t-match rods. Called up M2, new one on it's way. Thanks for the help and suggestions!

[KB2FCV]

It looks like I'm back to square one with this antenna and I need to investigate further. I received the new T-match block the other day and I checked it out. It had all the correct continuity as expected. I installed the t-match and put everything back up. When it came time to test, the original problem was still there! I then ran another continuity check it just to make sure I didn't damage anything when re-installing the driven element. The continuity check was fine.

I'm at a loss at what to check next. The coax is brand new LDF4-50 1/2" coax. The jumper is brand new LMR-400UF. All connectors were put on professionally.

I checked the coax by putting a dummy load on at the end at the antenna and It showed a nice flat SWR and the power meter showed the correct output on the radio. I reconnect the antenna - RF is getting back.

Is there something I'm missing with the heliax? I've seen heliax grounding kits, are those required? I'm not quite sure what else I can try. The antenna installation is pretty simple and straightforward. The driven element block is screwed into the T-Match block through the boom. The feedline connector faces forward. The spacers are set 8" apart for the lower end of the band (where I set it for). Is there anything special with the balun/choke (i forget which it is)? I asked how many turns it needed and M2 said it didn't matter, so I put 3 or 4 turns in. I'm runnin' out of ideas as to what to check for..

Thanks,

James

[WB2WIK]

Is there something I'm missing with the heliax? I've seen heliax grounding kits, are those required? I'm not quite sure what else I can try. The antenna installation is pretty simple and straightforward. The driven element block is screwed into the T-Match block through the boom. The feedline connector faces forward. The spacers are set 8" apart for the lower end of the band (where I set it for).

Normally you adjust these shorting blocks (they're not really "spacers," they are shorting blocks) distance from the boom while monitoring SWR. The blocks must be clamped tightly so they make excellent contact with the driven element and the T-match rods below it. When you adjust the block spacing, adjust both sides equally.

Is there anything special with the balun/choke (i forget which it is)? I asked how many turns it needed and M2 said it didn't matter, so I put 3 or 4 turns in.

It wouldn't matter if you put "no" turns in and just run the balun down the boom and back again, since this isn't a "choke" balun, it's a 1/2-wave coaxial balun: Different function. You must take some care with that coax obviously, as it's RG6 with a copperclad steel center conductor. If you accidentally misalign the F connector while plugging it into the T-match block and then try to turn the nut on the connector, you can damage the center conductor or even snap it off completely. Since that seems to be a "common component" that you used and then re-used (same one) with the new T-match block, possibly the balun itself is damaged. Check it carefully.

[KB2FCV]

Normally you adjust these shorting blocks (they're not really "spacers," they are shorting blocks) distance from the boom while monitoring SWR. The blocks must be clamped tightly so they make excellent contact with the driven element and the T-match rods below it. When you adjust the block spacing, adjust both sides equally.

My bad on the terminology... They are clamped tightly, they are good and secure and equally spaced according to the directions

It wouldn't matter if you put "no" turns in and just run the balun down the boom and back again, since this isn't a "choke" balun, it's a 1/2-wave coaxial balun: Different function. You must take some care with that coax obviously, as it's RG6 with a copperclad steel center conductor. If you accidentally misalign the F connector while plugging it into the T-match block and then try to turn the nut on the connector, you can damage the center conductor or even snap it off completely. Since that seems to be a "common component" that you used and then re-used (same one) with the new T-match block, possibly the balun itself is damaged. Check it carefully.

I double checked the RG6 connectors and the center conductors are straight as an arrow, no damage, they look as they should.

I'm at a loss what to try next. Even with the power completely turned to 0 I still get the 75w out reading and 5 or 10:1 SWR. If I put the dummy load at the end of the coax at the antenna the power out reads as it should and the swr is flat. I'm starting to run out of ideas..

[WB2WIK]

My bad on the terminology... They are clamped tightly, they are good and secure and equally spaced according to the directions





I double checked the RG6 connectors and the center conductors are straight as an arrow, no damage, they look as they should.

I'm at a loss what to try next. Even with the power completely turned to 0 I still get the 75w out reading and 5 or 10:1 SWR. If I put the dummy load at the end of the coax at the antenna the power out reads as it should and the swr is flat. I'm starting to run out of ideas..

Did you remove the balun entirely, make measurements on it, and inspect it and its connectors, as well as the receptacles on the T-match block, to assure nothing is damaged?

[KB2FCV]

Did you remove the balun entirely, make measurements on it, and inspect it and its connectors, as well as the receptacles on the T-match block, to assure nothing is damaged?

I removed the balun entirely. I performed the continuity checks provided by M2 on the T-match block. My original T-match block was faulty and had to be replaced (it had an open solder connection and they fill the block with some sort of goo). The new one M2 sent me checked out ok. What sort of measurements should I make on the balun other than making sure it isn't shorted out between the center conductor and the braid (which I checked)?