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High SWR


WRKH870
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I’ve been trying to build a base station. Bought a HYS UHF Yagi Portable Installation Outdoor Antenna Base Stations 9dBi UHF 70cm/UHF 400-470 MHz, and LMR400 coax. 
 

I have a telescopic mast and originally put everything together just to see what kind of range I would have with the antenna at 15’. My SWR reading was at 1.5. I only bought 30’ of LMR 400. When I pulled the mast out I had almost 35’ so went online and bought 50’ of what I thought was going to be LMR400. 

When I received the 50’ of coax, it was  MFD-400 which I can tell is slightly smaller in diameter and more flexible than the LMR-400. So I decided to use it anyway. The MFD-400 runs from the antenna to the wall..then a lightning arrestor...then LMR-400 runs through the wall to my radio, BTECH GMRS 50x1. The antenna was raised to about 32’. 
 

I plugged in my Surecom SW102 and my SWR reading is 2.95 on two different frequencies. The only thing I did to the new cable was cut it to length and solder the tip of a new PL-259 connector.  The one thing that stands out to me is that I’m using two different types of coax. Could that be my issue?  I did not mess with the tuning adjustment on the antenna since the original SWR reading was 1.5. 
 

Any ideas what my problem is/problems are?

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I can't find any ready reference to an "MFD-400" coax, but did find MPD-400. That is 50 ohm "Superflex" coax.

You mentioned soldering the tip of the coax to a new PL-259 connector. Did you check to ensure that the braid is making good electrical contact with the shell of the connector?

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I’ve been trying to build a base station. Bought a HYS UHF Yagi Portable Installation Outdoor Antenna Base Stations 9dBi UHF 70cm/UHF 400-470 MHz, and LMR400 coax. 
 
I have a telescopic mast and originally put everything together just to see what kind of range I would have with the antenna at 15’. My SWR reading was at 1.5. I only bought 30’ of LMR 400. When I pulled the mast out I had almost 35’ so went online and bought 50’ of what I thought was going to be LMR400. 

When I received the 50’ of coax, it was  MFD-400 which I can tell is slightly smaller in diameter and more flexible than the LMR-400. So I decided to use it anyway. The MFD-400 runs from the antenna to the wall..then a lightning arrestor...then LMR-400 runs through the wall to my radio, BTECH GMRS 50x1. The antenna was raised to about 32’. 
 
I plugged in my Surecom SW102 and my SWR reading is 2.95 on two different frequencies. The only thing I did to the new cable was cut it to length and solder the tip of a new PL-259 connector.  The one thing that stands out to me is that I’m using two different types of coax. Could that be my issue?  I did not mess with the tuning adjustment on the antenna since the original SWR reading was 1.5. 
 
Any ideas what my problem is/problems are?

If the antenna performs fine with limited or no cable between the meter and antenna, but not well with a different cable, connectors and adapters then the issue lies with the components being used when the value is poor, not the antenna. Quality of lightning arrestors, adapters, cable connectors and damaged cable are all candidates for being the cause of your change. Make sure connectors are tight, and installed correctly. Try taking SWR readers with different combinations of connectors, adapters, with and without the LA to find out which combination(s) leave you with a low SWR and which ones give you an elevated SWR.


Michael
WRHS965
KE8PLM
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2 hours ago, n4gix said:

I can't find any ready reference to an "MFD-400" coax, but did find MPD-400. That is 50 ohm "Superflex" coax.

You mentioned soldering the tip of the coax to a new PL-259 connector. Did you check to ensure that the braid is making good electrical contact with the shell of the connector?

I’m sorry. Yes MPD-400. As you can tell I’m new at this. Yes the braid was well into the top of that portion of the connector and I tried not to disturb the braid while screwing it on. 

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3 hours ago, mbrun said:


If the antenna performs fine with limited or no cable between the meter and antenna, but not well with a different cable, connectors and adapters then the issue lies with the components being used when the value is poor, not the antenna. Quality of lightning arrestors, adapters, cable connectors and damaged cable are all candidates for being the cause of your change. Make sure connectors are tight, and installed correctly. Try taking SWR readers with different combinations of connectors, adapters, with and without the LA to find out which combination(s) leave you with a low SWR and which ones give you an elevated SWR.


Michael
WRHS965
KE8PLM

Thank you Michael. When I had the antenna at about 14’, I had the same lightning arrest, about 30’ of the LMR-400. So the LMR-400 made up all of the coax I used. 
 

The only difference when I raised the mast to 32’ was the MPD-400 that ran from the antenna to the lightning arrestor and the PL-259 connector I placed at the end of the MPD-400 connecting to the lightning arrestor. MPD Digital Installed the PL-259 connector on the top end that connected it to the antenna. 
 

Hope I’m explaining it clear enough. Thanks for spending your time to help. 
 

Lee

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Thank you Michael. When I had the antenna at about 14’, I had the same lightning arrest, about 30’ of the LMR-400. So the LMR-400 made up all of the coax I used. 
 
The only difference when I raised the mast to 32’ was the MPD-400 that ran from the antenna to the lightning arrestor and the PL-259 connector I placed at the end of the MPD-400 connecting to the lightning arrestor. MPD Digital Installed the PL-259 connector on the top end that connected it to the antenna. 
 
Hope I’m explaining it clear enough. Thanks for spending your time to help. 
 
Lee

So if I understand correctly, everything from the lightning arrestor to the antenna is what is different? New cable, plus either a connector you applied to the coax or an adapter you applied to adapt the cable to the arrestor.

I recommend breaking this down and testing one thing at a time.

Take your radio and SWR meter outside. Connect the SWR meter directly to the coax that feeds the antenna (no lightning arrestor, no adapter) and see what you get? If it is not good, try your piece of LMR400 between SWR meter and antenna. If it is better with the LMR400 you have an issue with the new piece of coax you are using. If you are using N-Connector to PL259 adapters, you might have a cheap/bad adapter. I have had a number of them that were horrible. If you applied the connector to the cable itself, human error and lack of experience is common issue.

Bottom line, you really need to work the issue starting from the antenna using the shortest possible piece of coax and add in one piece at a time and check SWR each step until you find the item or combination that is failing you. Easier said then done I know if you are short on cable, adapters and other test equipment.

I would also make sure all is working well with antenna down low before raising antenna up, first for convenience, second so you learn what the difference is in performance between when the antenna is low and when it is up. Environmental factors can and do affect antenna SWR performance. It would be good for you to know what the difference is in your situation when everything is 100% the same, except elevation.

If you need help, you can contact an amateur radio club nearby, big cities can have many dozens of them. I am certain that if you shared your issue with someone at the club they would connect you with a member that would gladly come over with some added test equipment, adapters, and cable at no charge to help you diagnose your problem. I would do that in a heart beat if you were in my area. Just need to ask.


Michael
WRHS965
KE8PLM
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The original SWR reading may have been "good" because the coax or a connector absorbed the reflected power.  You may now be seeing the true SWR of the antenna.  

Just one of several possiblities 

While that could be true, since that same piece of coax is still being used in part of the circuit the items added are the probable candidates.

Cases like this are what make a portable antenna analyzer so, so beneficial. Regardless, still takes trial and error measurements until the culprit(s) are found.

Regards


Michael
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KE8PLM
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As others have said.....Check your antenna SWR with just a foot or two of coax if you can.  Minimal loss coax will show the true SWR of the antenna but higher loss coax will hide a bad SWR.  It can make a bad antenna "look" good (but not work good)

If the SWR looks worse with longer or higher loss coax you probably have a connector problem... or the coax is not 50 ohms.

 

Vince

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