The Ham Radio Thread

TurboMinivan

Still plays with cars
Location
Lehi, UT
This week I placed the same antenna on a magnetic base on top of the 4runner and was able to hit the repeater from my house in West Layton and communicate fairly well from Farmington.

Okay, it sounds like you've verified the antenna itself is not the problem. Good so far.

I am looking for some suggestions on how to determine if my problem is with my mounting location on the spare tire mount or do I have a problem with the NMO base/mount and cable?

I've seen many many people state (or complain) that tire mounts on the back of a Jeep are the single worst place to attach an antenna--CB or ham. Sure, it is extremely common to see CB antennas put there... but it's also extremely common to see Jeeps with CBs that don't perform worth a damn. Coincidence? Maybe.

Either way, I am not going to rush to judgement about your particular situation without further testing. If you want to do a test that won't cost any money, remove the mount from your tire carrier and relocate it elsewhere on your vehicle, then see if performance improves. If it does, the location is likely to blame. If not, then I'd start looking at the mount and/or cable itself.
 

lhracing

Well-Known Member
Location
Layton, UT
So I found a problem in the P-259 connector and I repaired it and the tire carrier mount works much better. I checked the SWR on the magmount and the tire carrier. The tire carrier is much worse. The average in testing at 144.5 and 147.5 on the tire carrier is about 3.0 and on the magmount it is about 1.8. Any ideas?
 

Kevin B.

Big hippy
Moderator
Location
Vehicular limbo
So I found a problem in the P-259 connector and I repaired it and the tire carrier mount works much better. I checked the SWR on the magmount and the tire carrier. The tire carrier is much worse. The average in testing at 144.5 and 147.5 on the tire carrier is about 3.0 and on the magmount it is about 1.8. Any ideas?

I'm out of ideas, other than to maybe make a new short-run coax to isolate issues with the antenna itself?

But school me on SWR testing. Is the meter you use different than the one you'd use for CB or are they the same beast?
 

moab_cj5

Well-Known Member
Supporting Member
I'm out of ideas, other than to maybe make a new short-run coax to isolate issues with the antenna itself?

But school me on SWR testing. Is the meter you use different than the one you'd use for CB or are they the same beast?

You use an antenna analyzer for HAM, and don't test the same way you would with CB. With HAM, the analyzer does all the testing independent of the transceiver. With CB the meter goes inline between the transceiver and the antenna.

@lhracing What wave length is your antenna? If it is a 1/2 wave, it doesn't require a ground plane (a large flat reflective surface under the base of the antenna) so the spare rack might be fine. If it is a 5/8 wave or 1/4 wave, it will require a ground plane for optimal performance. Also, some of the antenna's have a small metal tab in the base that makes contact to the center of the mount. You may want to ensure to bend that down to make sure it is coming in contact with the connector on the mount.

You are close enough to me we can check it out sometime and see if we can figure out what's going on.
 

lhracing

Well-Known Member
Location
Layton, UT
You use an antenna analyzer for HAM, and don't test the same way you would with CB. With HAM, the analyzer does all the testing independent of the transceiver. With CB the meter goes inline between the transceiver and the antenna.

@lhracing What wave length is your antenna? If it is a 1/2 wave, it doesn't require a ground plane (a large flat reflective surface under the base of the antenna) so the spare rack might be fine. If it is a 5/8 wave or 1/4 wave, it will require a ground plane for optimal performance. Also, some of the antenna's have a small metal tab in the base that makes contact to the center of the mount. You may want to ensure to bend that down to make sure it is coming in contact with the connector on the mount.

You are close enough to me we can check it out sometime and see if we can figure out what's going on.

The antenna is listed as a 1/2 wave. I think the mount is a little low, it places the antenna between the tire and the runner's back door so it is fairly shrouded. In this location it may be as good as it gets.

It would be great if you wanted to look at, any help is appreciated.
 
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lhracing

Well-Known Member
Location
Layton, UT
I'm out of ideas, other than to maybe make a new short-run coax to isolate issues with the antenna itself?

But school me on SWR testing. Is the meter you use different than the one you'd use for CB or are they the same beast?

I used a CB SWR meter because that is what I have. I did use the procedure shown in this link, https://www.kb6nu.com/no-vhf-swr-meter-no-problem/

My actual readings may not be exact but the difference in the readings between the two mounts I think is telling me something is still off with the tire carrier mount.
 
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