SWR Question

[Santiam]

I have a roll up Slim Jim antenna..I got it for easy packing and set up in the mountains for my portable repeater..On all simplex channels the SWR is perfect or near perfect with little fluctuation thru the channels..The SWR goes through the roof on repeater channels..Like 3.6 through the roof.. I have eliminated,radios and coax by going through my base station antenna, a J-POLE... SWR goes up a tad on repeater channels , 1.0 to 1.3,  so the problem must be in the Slim Jim.. Near as I can tell there is no tuning.. Hoping someone has a idea or it's time trash it and do something different..If it doesn't work for a repeater I have no use for it..

 

  Thanks

[Lscott]

The RigExpert antenna analyzers are nice. The main attraction I have for them is the scan function. As a Ham you don't operate on just one fixed frequency. It's important to know what your antenna tuning looks like of the range you are going to use.

I built one of the cheap 300 ohm TV twin line J-Pole antennas just for fun to see how well they work. These are the type recommended to have newbies build because they are simple to make and usually work well enough for an HT indoors or out on a field trip. The SWR is also reasonable.

You ABSOLUTELY need the RF choke at the base of the antenna. I just used about 10 to 15 turns, single layer, of RG-58 rolled up on a 1 inch wood dowel pin.

Good luck trying to find 300 ohm TV twin lead now days. Oh well.

http://hamuniverse.com/2meter300ohmslimjim.html

Antenna Scan Results (2M Roll Up Twin Lead).pdf

[Lscott]

I did a test on the N9TAX antenna a while ago. It’s similar to a simple Slim-Jim. The SWR isn’t outrageous on the GMRS frequencies.

There are two versions. One tuned for MURS/GMRS. The other for 2M/70cm.

N9TAX-MURS-GMRS-VHF Scan.pdf N9TAX-MURS-GMRS-UHF Scan.pdf N9TAX-2M-70CM-VHF Scan.pdf N9TAX-2M-70CM-UHF Scan.pdf

[SpeedSpeak2Me]

2 hours ago, Lscott said:

I did a test on the N9TAX antenna a while ago. It’s similar to a simple Slim-Jim. The SWR isn’t outrageous on the GMRS frequencies.

There are two versions. One tuned for MURS/GMRS. The other for 2M/70cm.

N9TAX-MURS-GMRS-VHF Scan.pdf 284.88 kB · 2 downloads N9TAX-MURS-GMRS-UHF Scan.pdf 284.32 kB · 1 download N9TAX-2M-70CM-VHF Scan.pdf 285.04 kB · 1 download N9TAX-2M-70CM-UHF Scan.pdf 285.33 kB · 0 downloads

Interesting... I'm glad someone else analyzed the N9TAX Labs antennas.  I also have both the 2m/70cm and MRUS/GMRS versions, both with 16' of RG58U.  For the MURS/GMRS (on GMRS) using a RigExpert Stick Pro, with the antennas hanging about 12' AGL (away from vegetation), I got slightly better results:

 

2m/70cm (UHF)

 

I also found that the Surecom SW-102's (mine is the "S" model)l are wildly inaccurate.  I know they are popular, but the readings they give can be very misleading.  As an example, it told me my Browning BR-6155 (fed with 50' of LMR400UF) has an SWR of 1.01:1 at 467.6000 MHz.  My RigExpert Stick Pro, and my friend's AA-1400 both show 1.37:1 at that frequency. 

[Lscott]

8 hours ago, SpeedSpeak2Me said:

Interesting... I'm glad someone else analyzed the N9TAX Labs antennas.  I also have both the 2m/70cm and MRUS/GMRS versions, both with 16' of RG58U.  For the MURS/GMRS (on GMRS) using a RigExpert Stick Pro, with the antennas hanging about 12' AGL (away from vegetation), I got slightly better results:

 

2m/70cm (UHF)

 

I also found that the Surecom SW-102's (mine is the "S" model)l are wildly inaccurate.  I know they are popular, but the readings they give can be very misleading.  As an example, it told me my Browning BR-6155 (fed with 50' of LMR400UF) has an SWR of 1.01:1 at 467.6000 MHz.  My RigExpert Stick Pro, and my friend's AA-1400 both show 1.37:1 at that frequency. 

I used the Rigexpert AA-1000 to make my measurements. 
 

The antennas are a bit sensitive to the environment where you make the measurements so I’m not a bit surprised by slightly different results. Also the antennas are all hand built and tuned. That can result in differences too.

I haven’t heard good comments about the Surecom meter. Most are about the same as yours, inaccurate results. But people like them and they keep selling. 

[Sshannon]

9 minutes ago, Lscott said:

Good luck trying to find 300 ohm TV twin lead now days. Oh well.

HRO carries 300 ohm ladder line:

https://www.hamradio.com/detail.cfm?pid=H0-016485

[WRYZ926]

Your antenna must be extremely narrow banded or something is wrong for you to get those kind of SWR readings. Normally you will find SWR around 1.0 - 1.2 on 462 and up to 1.8 on 467. Or you will get 1.0 - 1.2 on 467 and up to 1.8 on 462 with most antennas.

[Santiam]

Yes, seemed weird to me also, but I did get an answer.. Nothing to worry about as the repeater transmits on 462, only listens on 467.. So obvious that it makes me feel stupid...LOL..   I was doing my antenna testing using HT's.. When I went thru the repeater it was a perfect 1.0..

 

  Still, that is a awful big jump from 462 to 467..  Hmmm?

[WRYZ926]

Yeah it will surprise you when testing a HT antenna's SWR with something like the Surecom-102. The SWR can be all over the place since there is not a good enough ground plane. I've seen big differences when checking the same antenna with my Surecom-102 and my Comet CA-500 analyzer.

[Santiam]

Yes, I have the 102, but the HT's were connected to the Slim Jim, so that should have negated the ground plane problem? 

[WRYZ926]

6 minutes ago, Santiam said:

Yes, I have the 102, but the HT's were connected to the Slim Jim, so that should have negated the ground plane problem? 

You are correct on that one. Glad that the Slim Jim's working for you.

[Lscott]

3 minutes ago, Sshannon said:

HRO carries 300 ohm ladder line:

https://www.hamradio.com/detail.cfm?pid=H0-016485

Use to be able to go to Radio Shack, Best Buy etc and they had rolls hanging on the display pegs in the TV accessories area. I think If one wanted to build a Slim-Jim I would try the 450 ohm ladder line. That's what the N9TAX ones use.

[Sshannon]

50 minutes ago, Lscott said:

Use to be able to go to Radio Shack, Best Buy etc and they had rolls hanging on the display pegs in the TV accessories area. I think If one wanted to build a Slim-Jim I would try the 450 ohm ladder line. That's what the N9TAX ones use.

Used to be able to go to Radio Shack. 

[Lscott]

2 hours ago, Sshannon said:

Used to be able to go to Radio Shack. 

Then turned in to "cell phone shack." Then went bankrupt. I did hear they might be coming back in a few areas.

I also remember going to Lafayette and Olson Electronics as a kid. They're gone too. Heath Kit is kaput. Lots of kids, and adults, got their first exposure to electronics building their stuff.

[Sshannon]

8 minutes ago, Lscott said:

Then turned in to "cell phone shack." Then went bankrupt. I did hear they might be coming back in a few areas.

I also remember going to Lafayette and Olson Electronics as a kid. They're gone too. Heath Kit is kaput. Lots of kids, and adults, got their first exposure to electronics building their stuff.

There’s actually a Radio Shack in Bozeman that never closed. From their ads it appears they mostly sell RC cars. 

[WRXB215]

2 hours ago, Lscott said:

I did hear they might be coming back in a few areas.

Physical locations and online.

https://www.retail-insight-network.com/news/radio-shack-is-coming-back/?cf-view

https://www.amazon.com/stores/RadioShack/RadioShack/page/428CD7AB-87FF-4B6C-B5C3-96B7B297DFC4

[Lscott]

1 minute ago, WRXB215 said:

Physical locations and online.

https://www.retail-insight-network.com/news/radio-shack-is-coming-back/?cf-view

https://www.amazon.com/stores/RadioShack/RadioShack/page/428CD7AB-87FF-4B6C-B5C3-96B7B297DFC4

I hope it doesn't mutate in another cell phone store. At the end the local Microcenter computer store had more electronics parts for robot builders in one section than Radio Shack had in the whole store.

[Santiam]

Now that I have the SWR figured out I deployed my portable repeater back  to compare it against the copper J-Pole I had there last week . Working like a champ and I can hit it at many fars...I changed out the KMR-400 coax which I learned was not the best choice for repeaters with M&P Ultraflex 10.. So far so good... Not always a handy tree to hang it..

[WRUU653]

On 3/4/2024 at 7:51 AM, Sshannon said:

Used to be able to go to Radio Shack. 

Still have a few here thankfully. The closest is run by a local Ham.It’s good to try and use local people over Amazon when you can so these places are still here next year.