Antenna or cable or either?

[gadgetwiz]

I have a problem with a new Tram 1477-B dual band antenna. The SWR at 70cm is 1.02, but it’s 6.7 o the 2m band.

Running 25’ of LMR400 on the mast, and then 15’ of RG58 into the house. I’m trying to figure out if it’s the antenna or the cabling before I pull everything down.

It seems like it must be the antenna, but I’m new to Ham, and possibly 100% wrong.

 

[krokus]

What is near the antenna? Something could be at the correct distance to cause a reflection at a bad phase.

 

[Lauri-CoyoteFrostbite]

It could be a number of things, G-Wiz.

Before you start pulling things totally apart I would try testing your antenna setup in sections.
First off, I'd see what the SWR is from the LM400 up to the antenna - that is, remove that piece of RG58.
It could be that 15 foot length may --May-- be throwing you a weird match match (velocity factor v.s wavelength etc.)
If there is no change, try another cable or two.

Actually, lacking a serious antenna issue I'd put my money on that piece of RG58... but you should double check the quality of your coax connectors and that the coax shielding and internal conductors are soldered properly in place.... good solid connections.

Good luck-- let us know how this works out





Lauri

.

 

[prcguy]

If you go on the roof with your VSWR meter and a short jumper you can test right at the antenna. Just have someone key the radio in the house. That will isolate the antenna and all the feedline in one test.

 

[KE5MC]

I recommend running low power until you get it sorted out. Transceivers are good at protecting the output stage, but best not to exercise that protection at higher power levels more than needed.

 

[gadgetwiz]

Thanks for responding. There isn’t anything near the antenna. It clears the roofline by several feet.

It is mounted 25’ on a pole. I have a couple wires below the virtual ground plane to stabilize it, and a GMSA antenna about 7ft below the Tram (unplugged when I ran my tests).

The LMR400 transitions to RG58 at the lightning surge arrestor (diamond). It’s on the roof where the cable enters my house so it’s not an easy place to get to with a radio and PS. I will try to find a way to connect directly to it. It won’t be easy though. Might try a handheld with it and see how that works.

I ordered a nanovna. Hoping that will give me sone more insight once I re-learn how they work.

I ordered a Diamond and will try it out this week if nothing else works. I also ordered 75’ of LMR400 and SP connectors from DX Eng.

I do appreciate the responses, and I will let you know what I find.

 

[gadgetwiz]

So my nanovna came in, and I figured out the problem.

I swapped my GMRS and Ham antenna wires.

This is what my “GMRS” antenna looked like.

Haha. Now, I will replace the RG58, but this is manageable until it arrives.

Thanks everybody.