ANTENNA AND SWR QUESTION

[Unit 75]

I purchased a SHOCKWAVE 5/8 ground plane antenna and put it up on the tower (50' up). I'm using Times Microwave LMR-400 coax (100') to run to the shack.
I tuned the antenna for use on 27.385MHz as I ONLY talk on CH38 LSB) using a AA-230 ZOOM RigExpert antenna analyzer. The SWR was 1.06:1 on channel 38 (which is excellent). The antenna system was awesome for about 2 months. A couple of days ago I checked my SWR (using the RigExpert analyzer) and it showed a very high SWR (over 3:1) and it also showed the infinity symbol on the screen. I did a continuity check between the center conductor and the ground collar of the coax and had an audible beep.
So...I purchased some new coax (again, Times Microwave LMR-400) and installed it. Once I was done, I checked the SWR with the same analyzer and it read 1.06:1
Now here is the thing....I have an awesome match of 1.06:1 (showing no infinity symbol now) but I still have an audible beep for continuity showing between .49 and .50 ohms...but an excellent match. Does this have to do with the antenna design?? I do not get the audible beep when I do the same check on the LMR-400 coax going to my 5 element beam. Any insight would be appreciated.

 

[357magnum]

My thoughts ? A few on here " I " would PM , My antenna guru Marconi or Mogv (? ) comes to mind . Just me they should see your post but I would Pm just in case . Marconi is my " Go To " man . jmo

 

[Unit 75]

Thank you, sir.

 

[BJ radionut]

The ground plane has a DC short for lightning protection.
That's why showing shorted with VOM.
Depending on the type of match the beam has, may or may not show a DC short, most do but?
If analyzer shows good then I'll say your good.
The other coax may have gotten contaminated with water or connector went bad. Place a dummy on the end and check with tester see if it shows good or bad.
All the Best
Gary

 

[Unit 75]

Cool. I do run a amp...so I just wanted to be sure not to blow anything up before I put it back inline. The SWR was taken with the amp out of the connection. Just from the analyzer to the antenna.
The beam is a Antenna Specialists M-134 Mariner using a Gamma match system with a SWR of 1.16:1 on channel 38.
I don't recall any of my previous antennas with the coax hooked to them doing this...Just the Shockwave. That is why I was concerned and thought perhaps it had something to do with the design seeing it utilizes the trombone matching system...but like you said...the match is good.
I was thinking the original coax may have taken on some water as the PL259 connectors seem to be ok when just checking the coax run by itself. No shorts or discontinuities. THank you very much for your reply in the matter. It puts me a little more at ease
-75

 

[Tallman]

The is an item called a "Balun" used for impedance matching. They always read as a DC short. RF does not act the same as DC.

 

[Unit 75]

Yes, I understand RF is AC. What was confusing me was my other antennas did not do that...Just the Shockwave

 

[Marconi]

75, I only read your question above.

Sorry, I have no suggestions for your Shockwave problem, but keep us posted if you find out what happened.

 

[Unit 75]

Thanks, Marconi. I will.

 

[Marconi]

I do not get the audible beep when I do the same check on the LMR-400 coax going to my 5 element beam. Any insight would be appreciated.

75, its been a while now. Have you determined what happened with your Shockwave? Did you try testing the original coax after you replaced it?

You told us you changed the coax and that fixed the problem. That would immediately suggest to me that the coax was probably faulty. One or both of the connectors could be installed badly, or the coax had physical damage. Thus I have no idea how you ever got it working fine in the beginning. Who installed the connectors and were they soldered or crimped?

You compared and evaluated your problem to your beam that works fine. Your testing result differences could have been due to a difference in the matching designs for these two different antennas.

Can you describe your beam antenna or post the instruction manual?

 

[Unit 75]

Thanks for the follow up. It ended up being faulty LMR-400 feed line. I purchased the LMR-400 on eBay new. 100' ready made with (heat-shrinked crimped ends). The antenna system worked great for about 8 months or so before I noticed the SWR issue. (I have meters inline all the time) I did test the connectors and they were fine. What happened was water saturation into the feed line. I didn't find this out until I cut it open and found the shielding corroded. So I cut out the bad parts and made patch cords out of the rest The continuity on the shockwave (DC) for lightning protection and static reduction (part of the design). The 5 element beam I used in comparison was the Antenna Specialists M-134 which utilizes a gamma matching system. All is good now. I have new LMR-400 and I even brought the ground plane down off the tower and mounted it on my 10' test fixture. Then used my RigExpert AA-230 Zoom antenna analyzer and set the Shockwave up for R=50, X=0 for 27.3850MHz where the antenna is now resonant. I was very fortunate to get the pure resistive impedance of 50 ohms at resonance. But it is now back up on the tower working awesome!!

I only talk on 38 LSB. That is why I set the Shockwave up on that frequency.

Thank you, Marconi.