SWR trouble shooting

[SkylinesSuck]

My old antenna setup was a copper J-pole on top of a 10' PVC pipe and a lightning arrestor with all UHF connectors. I recently changed that out for an Ed Fong DBJ -UHF with all N connectors on top of a 24' aluminum military surplus pole (the kind with 4' sections that link stack together). I am using an N connector lightening arrestor where it enters the wall to go inside the treehouse. The pole is electrically grounded at the base to a rod in the ground.

 

With my previous setup I had 1.1 swr. Now it's 4.3. Taking the pole down is going to suck. Can somebody walk me through some trouble shooting steps? I don't even know where to start. The only idea I had is to replace the top pole section with a fiberglass one to get the metal pole farther from the antenna itself. Thoughts?

[tweiss3]

When you ordered, did you tell him it is for GMRS? His jpole is wonderful, but it is only for 10MHz bandwidth. Outside of that tuned 10MHz, bandwidth spikes pretty quickly.

[SkylinesSuck]

Yep, I told him and it was labeled gmrs.

[mbrun]

My old antenna setup was a copper J-pole on top of a 10' PVC pipe and a lightning arrestor with all UHF connectors. I recently changed that out for an Ed Fong DBJ -UHF with all N connectors on top of a 24' aluminum military surplus pole (the kind with 4' sections that link stack together). I am using an N connector lightening arrestor where it enters the wall to go inside the treehouse. The pole is electrically grounded at the base to a rod in the ground.

 

With my previous setup I had 1.1 swr. Now it's 4.3. Taking the pole down is going to suck. Can somebody walk me through some trouble shooting steps? I don't even know where to start. The only idea I had is to replace the top pole section with a fiberglass one to get the metal pole farther from the antenna itself. Thoughts?

 

From the sounds of it everything is 100% new. Different antenna, different mast material, different mast height, feed-line changes. Perhaps even a different location? A lot of variables now to investigate.

 

Is the Ed-Fong antenna perched fully on top of the mast or beside it? If it is beside the mast the metal mast itself would affect it where as the PVC would not have.

 

What was the SWR of the antenna alone before putting it up? What was it with just a short jumper between the meter and antenna. What was it mounted to when you measured it and at what elevation above the ground? What was it when on the ground and attached to just 1 section of metal mast.

 

Is the antenna now at is higher elevation located near something that the previous antenna was not?

 

Has there been some damage/deformation of the cable? Are all the connections tight? Have the connections been exposed to rain before they where sealed and made moisture tight?

 

There are so many factors that could contribute to the current value. It would be good to know what you started with and which factors caused the change.

 

I recently installed an antenna. I started by measuring the antenna while located 6’ of the ground on a homemade tripod and PVC pole. I then made measurements after every change I made so I could see the effect of each action so I could take remedial action if saw something I did not like.

 

BTW, I am using a NanoVNA H4 to make my measurements.

 

Hope some of this helps.

 

 

Michael

WRHS965

KE8PLM

[SkylinesSuck]

Basically everything is new, yes.

 

The antenna is on top of, not beside the metal pole. Sounds like there is no shortcut and I'm going to have to pull it all down and go piece by piece. SWR meter is a cheap little Surecomm 33 from amazon. Might try and bypass the lightening arrestor first too.

 

LMR400 cable with no kinks btw.

[SkylinesSuck]

And I never measured anything before I put it all the way up there. I see now that was a mistake.

[gortex2]

Most likely the antenna. You did use the correct PVC for the antenna ? Or did you guy it complete ? The antenna is not the best on the market but many like them because they are cheap. I'd start there.

[SkylinesSuck]

I used the correct thin pvc he recommended. Guy it complete? I'm not tracking there, sorry.

[tweiss3]

Most likely the antenna. You did use the correct PVC for the antenna ? Or did you guy it complete ? The antenna is not the best on the market but many like them because they are cheap. I'd start there.

 

 

I used the correct thin pvc he recommended. Guy it complete? I'm not tracking there, sorry.

 

I think he is asking if you used guy wires to secure the mast, and ensure the guy wires are all below the antenna.

 

I would also suggest making sure any clamps and the mast pole are within the bottom 10" (clamp area). See if you can adjust it to be only 8" or so from the bottom.

 

Also, check the N connectors, that pins are not bent and they are all tight.

[SkylinesSuck]

Gotcha. No guy wires at all which I will eventually rectify. The antenna basically only has the pvc pipe cap with the n connector in it inside the mast pole. The radiating part of the antenna is basically as far away from the mast as you can possibly get without adding additional pieces.

 

Sent from my Pixel 5 using Tapatalk

[OldRadioGuy]

You could start by trying a dummy load at the antenna connection.

That would rule out the coax and connectors if the SWR looks good.

 

Vince

[axorlov]

Most likely you have your coax coupling with aluminum mast. J-poles create significant common-mode current on the outside of the coax. If mast is not metal, you may be able to get away with that. To verify, pull the coax away from the mast and check SWR again. If you see it changed, then this is it: coax coupling with the mast. To rectify add RF choke made of ferrites for UHF frequencies, or change antenna.

 

Off tangent: this forum has strange fascination with Ed Fong's antenna. It's cheap, sure. But it's a kit, that is missing important and expensive part: RF choke. There are better options for the GMRS antenna. The Browning BR-6140 was available for below $40 for long time, but sadly not anymore. It now commands the whopping $50 at AntennaFarm. If you are also into Ham, the dual-band Diamond X50 has acceptable SWR on GMRS, at around 1.7.

[SkylinesSuck]

I forgot to mention I used the same snap on ferrite bead choke baluns (sp?) that were recommended for the original copper J-pole on the current Ed Fong. But on that note, I have the cable run inside the mast pole. Maybe not a good idea?

[axorlov]

I forgot to mention I used the same snap on ferrite bead choke baluns (sp?) that were recommended for the original copper J-pole on the current Ed Fong. But on that note, I have the cable run inside the mast pole. Maybe not a good idea?

So, cannot pull antenna off from the mast to check the coupling? Too bad. Is there is a chance that the loop on the cable to pull it through the mast is too tight? The ferrite choke should be something like in the following link, installed as close as possible to antenna.

https://palomar-engineers.com/ferrite-application-experts-2/Dual-Band-VHF-UHF-Antenna-Feed-line-Choke-J-Pole-Verticals-Hand-Held-Beams-Choose-1-4-1-2-3-4-cable-size-100-500-MHz-p165437793

[SkylinesSuck]

Also, on the antenna, the Ed Fong is has 5.5 dbi gain. I moved from the copper J-pole because it was a unity gain as is the Browning. Not really trying to spend $600 on an antenna for the treehouse, but I am okay with more than $50 if you have any suggestions with some gain.

[SkylinesSuck]

So, cannot pull antenna off from the mast to check the coupling? Too bad. Is there is a chance that the loop on the cable to pull it through the mast is too tight? The ferrite choke should be something like in the following link, installed as close as possible to antenna.

https://palomar-engineers.com/ferrite-application-experts-2/Dual-Band-VHF-UHF-Antenna-Feed-line-Choke-J-Pole-Verticals-Hand-Held-Beams-Choose-1-4-1-2-3-4-cable-size-100-500-MHz-p165437793

 

That is very similar to what I have on there now. 3 of them, right at the base of the antenna. I will eventually try pulling the cable away from the pole, but I will have to take the whole thing down, so I will try a few other things first, like bypassing the lightning arrestor.

 

I'm not following the loop on thr cable thing.

[axorlov]

At the base of the antenna, meaning close to the connector on the antenna? If at the base of the mast, then the choke will not prevent coupling with the mast.

[serrasalmus]

i went from a jpole i made to the https://dpdproductions.com/collections/gmrs-base-mobile-antennas/products/gmrs-vertical-outdoor-base-antenna 

according to my nano vna my swrs are in the 1.02-1.08 on a 10ft top rail chain link pole and a chimney mount. been working really good for me.

[SkylinesSuck]

At the base of the antenna, meaning close to the connector on the antenna? If at the base of the mast, then the choke will not prevent coupling with the mast.

Top of the mast, just before the connector to the antenna. They are inside the the mast along with the connector. Maybe that inch after the chokes but before the connector is doing it?

[SkylinesSuck]

Well, the one easy thing I wanted to try didn't work. I just bypassed the lightning arrester and associated cable and ran the cable from the antenna directly into the meter then radio. Measured at 2.9 and while I'm curious why it dropped that much, it doesn't solve the issue. I guess the antenna and mast are coming down in the next couple of days for trouble shooting.

[SkylinesSuck]

Just an update; I pulled the Ed Fong and N terminated lmr400 cable down and put back up my old copper pipe J-pole and UHF lmr400 cable inside the same new metal pipe mast I had on the Ed Fong setup.  SWR's are back down to 1.2'ish.  

That would seem to narrow it down to the antenna or the cable.  I took my HT and connected it to the Ed Fong antenna with a short jumper cable and some adapters.  2.6 swr standing inside my living room.  Then I connected a spare tiny 1/4 wave mag antenna that came with my mxt275 using the N terminated lmr400 and got 1.06.  Looks like the antenna, right?  I still haven't been able to replicate the 4.3 swr I had when it was mounted on the treehouse though.

[mbrun]

Just an update; I pulled the Ed Fong and N terminated lmr400 cable down and put back up my old copper pipe J-pole and UHF lmr400 cable inside the same new metal pipe mast I had on the Ed Fong setup.  SWR's are back down to 1.2'ish.  
That would seem to narrow it down to the antenna or the cable.  I took my HT and connected it to the Ed Fong antenna with a short jumper cable and some adapters.  2.6 swr standing inside my living room.  Then I connected a spare tiny 1/4 wave mag antenna that came with my mxt275 using the N terminated lmr400 and got 1.06.  Looks like the antenna, right?  I still haven't been able to replicate the 4.3 swr I had when it was mounted on the treehouse though.

Ed warrants his antennas, so perhaps it is worth a call to him. Before you do, check it one more time outdoors away from the building.


Michael
WRHS965
KE8PLM

[SkylinesSuck]

Just to close the loop on this, I talked with Ed and he gave me a couple of trouble shooting tips, but none of them helped.  Best I can get is an swr of 2.2 with any cable, standing in the middle of my lawn with the antenna above my head, and that's on 2 different meters including a Micro VNA.  He said to get back to him and I think he would/will take the antenna back and make sure it's right, but I haven't gotten back to him yet.  I instead purchased a Comet CA-712EFC and it's awesome. SWR is no higher than 1.3 and I can easily open up 3-4 new repeaters.  This is using all the same cabling so pretty sure the old antenna was the culprit.  I'm looking forward to trying some simplex testing to see what's what.  Only downside I have noticed so far is my air band reception seems to have disappeared.  Maybe because it's so directional now?  Not a huge deal for me except now the kids can't listen to me at work.

[mbrun]

...Only downside I have noticed so far is my air band reception seems to have disappeared.  Maybe because it's so directional now?  Not a huge deal for me except now the kids can't listen to me at work.

You likely have two things that can explain that. First is the radiation/pickup pattern you just surmised. Second, the Ed-Fong GMRS antenna is technically a dual band antenna, and by design will work well in the MURS portion of the VHF band as well. Perhaps because air band frequencies reside in the 50MHz below that the antenna is more sensitive to them.

BTW, I just checked my Ed-Fong GMRS roll-up with my VNA and it shows an SWR of 1.2 in the MURS range.


Michael
WRHS965
KE8PLM