Shireen RFC-400 (LMR-400) Coax SWR Issues

[Fizz306]

Hello all!

Maybe you all can read my amazon review, along with my correspondence with Shireen regarding coax issues I'm having. Terrible and erratic SWR across the entire 70cm spectrum.

Of note is the sales rep for Shireen stating I should probably use RG-8 for UHF transmissions rather than their LMR-400 equivalent. Am I bonkers, or does this make no sense?

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-----Original Message-----
From: Sales Team - Shireen Inc [mailto:sales@shireeninc.com]
Sent: Wednesday, January 07, 2015 1:50 PM
To: sales
Subject: Contact Form



Name: Robert Fissel
E-mail: XXXXXXXXXXXXX
Telephone: XXXXXXXXXXXX

Comment: Good afternoon,

I purchased a 500 foot roll of your LMR-400 equivalent from an Amazon reseller (allrfcables). The cable performs well when transmitting from 1.8 MHz through 150 MHz. Unfortunately, the UHF ham bands (420 MHz - 450 MHz) presents concerning issues in regards to SWR.

This coax has been connected to an Arrow Antenna 2m-70cm J-Pole. I have tried replacing the original run of your coax (approx. 40 feet) with another length of your coax, only to find similar SWR issues. Using my Icom radio in the sense of a spectrum analyzer, the SWR would vary widely between 435-450 MHz, from a low of a good 1:1 ratio all the way up to 10:1 or higher. The high peaks of SWR varied between the two different pieces of Shireen coax. When replaced with a length of DX Engineering RG-8 coax for a quick test, the SWR maintained a level 1.1:1 across the whole 70cm band.

Normally I would just stick with this new coax, but at 70cm the losses on non-LMR-400 type coax are higher than I'm willing to accept. I've read nothing but good reviews regarding your coax, and fear that I've received a bad spool.

Please note that I have used a good portion of the roll already for 3 separate HF antennas and the J-Pole previously mentioned, and only noticed the 70cm SWR issues after deploying most of my antennas at home.

Please advise on what Shireen can do to remedy this situation.

Regards,

Rob

--------------------------------------

Dear Robert,

I read your email in detail.. Seems to me that you would need RG8 (with teflon dielectric and solid copper conductor) type cable, instead of LMR400 type.. Our RFC400 or LMR400 cable are made of foam dielectric and copper clad AL as center conductor.. We have been selling our RFC line of cables for more than ten yrs now and never got any complain due to cable quality..

On the other hand it is quite possible that there is impedence mismatch with the antenna that caused VSWR go off. Its hard to guess what caused this problem and how standard RG8 fixed it.. BTW DX engineering is also our customer so most likely you have use our cable too.

Now we can do which ever option you prefer..
1. Take the spool back from you and replace with the new one. Or
2. Issue credit for unused spool, if you prefer to return..

Either way you like, we want you to be 100% satisfied with the purchase.

Thanks
XXXXXXXXXXXXXXXX

--------------------------------

Rob XXXXXXXXXXXXXXX
2:36 PM (4 minutes ago)

to sales
XXXXXXX,

Thanks for the reply. I am puzzled why you suggest to utilize a more lossy cable like RG8 on UHF frequencies over an LMR-400 equivalent. Are you saying that because you're using foam rather than teflon, and copper clad aluminium center conductor is not suitable for UHF+ transmission?

I am also confused because I have used authentic Times Microwave LMR-240 and LMR-400 coax in the past for UHF applications without any issues. My contact at Arrow Antenna strongly believes that this is a coax issue, as he says "if the SWR is not 1.1:1 across the entire 70cm spectrum, the coax is not up to the task."

Side note - it's interesting that DX Engineering's coax is Shireen. I didn't know that at all. Makes me wonder why there is such a drastic difference per foot between DX Engineering and other sellers like allrfcables on Amazon.

Regardless, I'd like to replace the whole spool, as I will most likely replace all the coax for my HF and UHF antennas. How can I go about returning the remaining spool to you for replacement?

Again, I appreciate the prompt reply and assistance.

Regards,

Rob Fissel

----------------------

Amazon Review:

Terrible SWR issues above 70cm/430 MHz, January 7, 2015
By Robert W Fissel
Verified Purchase(What's this?)
This review is from: 500ft spool 400 grade cable, RFC400 (Electronics)
I made this purchase after reading several reviews from sites like QRZ and eHam, where users had great success with this coax. Being nearly $.50 cheaper per foot than traditional Times Microwave LMR-400, I decided to take a chance.

This cable appears to perform well on everything below 70cm (430 MHz). After installing multiple HF antennas, and one Arrow Antenna VHF/UHF J-Pole, using up 2/3rds of the spool in the process, I noticed that the SWR on 70cm was erratic and unacceptable, and would vary widely from 1.1:1 up to 10+:1 throughout the 70cm band. Everything below 70cm, when properly matched, showed acceptable SWR. My MFJ antenna analyzer also shows acceptable/expected line loss from 2m down through the HF spectrum.

I cut another length from the same spool, thinking that maybe my PL-259 connectors were bad or maybe it was just a bad run to begin with. Still the same erratic SWR across 70cm. I can only imagine what SWR would be like on higher frequencies. I tried a separate radio with an SWR meter to confirm my IC-7100 wasn't the culprit. Again, the SWR was all over the place across a band with an antenna that should present 1.1:1 across all 20 MHz of spectrum.

I went on to rule everything out in the transmission line from feed point to radio. Used a different lightening arrestor, bypassed my SWR/watt meter, used different coax from arrestor to radio...everything. Still no improvement, the issue here is definitely with the coax.

It's worth noting that I did a quick test with some DX Engineering RG-8 coax, and the antenna showed a solid 1.1:1 across the whole 70cm band.

While the coax performs well on HF, I purchased an LMR-400 equivalent to minimize losses on UHF+ frequencies, in addition to providing superior performance on HF. This has been disappointing to say the least. I hope it's just a bad spool and that either allrfcables (the Amazon reseller whom I purchased through) or Shireen will be able to remedy the situation.

I've contacted Shireen through their website and will advised what type of customer service they provide, and/or if allrfcables reaches out to me with a solution.

 

[N8OHU]

What are you using it for? DO NOT USE FOR A REPEATER, not even for short runs. This goes for any LMR-400, not just from.this particular manufacturer. I hope you do get it straightened out, though.

 

[prcguy]

Something smells fishy here. Who installed the connectors on the coax that is causing the VSWR problem? When you say its erratic, does it change by itself or does it vary over different frequencies?

What is the VSWR on the Arrow J-pole with a very short length of known good coax? BTW, a J-pole will usually have lots of common mode RF on the coax and can show varying VSWR with different cable lengths.

If an antenna has a VSWR problem it will be masked by a long length of lossy coax and will show itself better with the same length of low loss cable, like LMR400.

Try a dummy load in place of the antenna and see what happens. If the VSWR is low and stable then something other than the coax is causing the problem, like the antenna.

I've seen a lot of coax and antenna problems over the years but what you describe is usually the result of damage like someone pinching off the coax in multiple places with Ty-Raps, etc, or the problem is elsewhere.
prcguy

 

[Fizz306]

prcguy,

I installed the connectors on all the coax I've used. I follow this method for the connectors to avoid damaging the insulation with solder. I use a 200w soldering gun to solder the center connector. I've never had an issue in the past using this method.

FWIW, I am not using this for a repeater at all. Just a VHF/UHF J-Pole connected to an IC-7100.

https://www.youtube.com/watch?v=qPlcT9SXNPs

The SWR is erratic meaning it doesn't change by itself on one frequency, but varies over different frequencies. One length of this coax produced SWR spikes upwards of 10:1 all over the band. It would yo-yo between 1.1:1 up to infinity with no rhyme or reason across the band. The next length of the coax I tried produced the same situation of yo-yoing SWR, albeit the SWR spikes occured in different places across the spectrum. In other words, it varies with frequencies. The new length installed has a VSWR of 1.3:1 on the only real UHF repeater I use, but the varying spikes across the spectrum remain. The cable lengths between both tries remain approximately the same.

I do check for continuity and shorts across the whole length of coax prior to installation.

I used a separate piece of RG-8 that I also did the connector installation on. This piece was only 20 feet or so in length, and produced good SWR ratios from 430 MHz up to 450 MHz.

I do use cable ties on the mast to secure 4 lines of this LMR-400 coax, but I don't believe I pulled it too tight or pinched the cable at all.

The idea of a J-Pole's common mode RF causing various VSWR is something that I'm not convinced is the issue here.

Also from Arrow Antenna's webpage:

Connect the Dummy Load to the end of the coax instead of the Antenna. Connect SWR Meter or Antenna Analyzer to the other end.

Check the SWR on all frequencies. SWR should be 1.0:1 on all frequencies. If the SWR is not 1.0:1 or if the SWR varies with frequency, then the Coax is Not up to the task.

------

I don't have a dummy load (I know, shame on me) to test, but didn't think to obtain one to try this test considering the alternative RG-8 I used produced different (and appropriate) results. I can try and pick one up and see what kind of difference it makes once the snow melts and I can get up on the roof.


All this being said, does this sound indicative of bad coax?

 

[prcguy]

If the center conductor wandered around inside the dielectric or the cable was pinched in several places it could cause VSWR problems at specific frequencies. In the case of a pinched cable, the problem will usually first show up at some frequency based on how far the pinch is from one end of the cable then the problem will repeat at multiples of that frequency.

I've never encountered a cable that was so far out of spec on the center conductor placement that it caused any problems. If that were a problem it should be visible when you cut the coax in small chunks and the center conductor will be in different places along its length. However that may not be as bad as a pinched cable because where the center conductor is closer to the shield on one side its also farther from the other side and the impedance may not change radically.
prcguy

prcguy,

I installed the connectors on all the coax I've used. I follow this method for the connectors to avoid damaging the insulation with solder. I use a 200w soldering gun to solder the center connector. I've never had an issue in the past using this method.

FWIW, I am not using this for a repeater at all. Just a VHF/UHF J-Pole connected to an IC-7100.

https://www.youtube.com/watch?v=qPlcT9SXNPs

The SWR is erratic meaning it doesn't change by itself on one frequency, but varies over different frequencies. One length of this coax produced SWR spikes upwards of 10:1 all over the band. It would yo-yo between 1.1:1 up to infinity with no rhyme or reason across the band. The next length of the coax I tried produced the same situation of yo-yoing SWR, albeit the SWR spikes occured in different places across the spectrum. In other words, it varies with frequencies. The new length installed has a VSWR of 1.3:1 on the only real UHF repeater I use, but the varying spikes across the spectrum remain. The cable lengths between both tries remain approximately the same.

I do check for continuity and shorts across the whole length of coax prior to installation.

I used a separate piece of RG-8 that I also did the connector installation on. This piece was only 20 feet or so in length, and produced good SWR ratios from 430 MHz up to 450 MHz.

I do use cable ties on the mast to secure 4 lines of this LMR-400 coax, but I don't believe I pulled it too tight or pinched the cable at all.

The idea of a J-Pole's common mode RF causing various VSWR is something that I'm not convinced is the issue here.

Also from Arrow Antenna's webpage:

Connect the Dummy Load to the end of the coax instead of the Antenna. Connect SWR Meter or Antenna Analyzer to the other end.

Check the SWR on all frequencies. SWR should be 1.0:1 on all frequencies. If the SWR is not 1.0:1 or if the SWR varies with frequency, then the Coax is Not up to the task.

------

I don't have a dummy load (I know, shame on me) to test, but didn't think to obtain one to try this test considering the alternative RG-8 I used produced different (and appropriate) results. I can try and pick one up and see what kind of difference it makes once the snow melts and I can get up on the roof.


All this being said, does this sound indicative of bad coax?

 

[Robinsmark]

In 30+ years of installing antennas, my money is on a BAD COAX CONNECTION. 9 times out of 10 thats what it is. You may also have gotten water in there if you did not used a gum type coax seal. Thats what I used on commercial 2 way sites when I did that type of work years ago. You MUST keep water out at all costs. I would take the advice of the previous poster and borrow a dummy load and place it in place of the antenna, then see what the SWR looks like. LMR400 is not the easiest coax to work with, but it has far less loss than RG8. The poster who earlier suggested not using for repeaters is correct, but it should be ok for what you are doing. 73!

Borrow a dummy load if you can and try what the other poster has suggested.

 

[Fizz306]

Thanks for the advice, Robinsmark.

I can rule out water being an issue, as the second attempt with a fresh piece of coax immediately exhibited the same issues. I'm also using quality silicone type coax seal on all outdoor connections.

Out of all my accumulated equipment, I'm embarrassed to say that a dummy load isn't an item I have. I'll be heading to KJI next week to pick one up and once the snow falls, head up on to the roof and test the coax.

I appreciate all the advice, and look forward to resolving the issue soon!