coax cable question

[Marconi]

I have an Antron 99 I'm using for 10m. I put it up using some rg 8x coax I had on hand. The swr's are great all across the band. About a year later I decided to upgrade the coax hoping to get a little better performance. I decided to get 100 ft. of CXP1318FX (RG8/U Size) Double Shld, Flexible, Low Loss, UV/DB Jkt = to LMR-400-UF, Belden 9913F. After installing the cable I did some on air comparisons with a friend. First with the CXP1318FX and then with the rg 8x. I did not tell him I was swapping out cables only that I was testing something. He told me my signal was 2 s units stronger the second time we talked. I explained to him I had swapped cables and told him with the rg 8x that my swr's were below a 1.5 with the CXP1318FX they were close to a 2. I was going to adjust the tuning rings to get try and get the swr's down, but he told me they were not that high and it would not make any difference in my signal. He said rg 213u would have been a better choice coax for this type of antenna and said I should leave the 8x cable on it. I have tested the CXP1318FX cable with an ohm meter and it is good. I would appreciate any thoughts you have.
Thanks Whitedove

whitedove, some years ago I bought 50' of coax from Cable Experts. When I got it, it produced a high SWR as you describe.

I then checked the cable by hand, inch by inch, to see if I could see something wrong. At some point I could feel a lump in the coax. It was a few inches long. I called CX's and they said to return the coax, and they replaced the cable.

They said the cable had a hand made manufacturing splice in it that allows them to fill out 500' spools some times at the end of runs. In such case they indicate on that spool that it has a splice, but sometimes that notice is over looked when cuts are made later...while filling shorter cable orders.

Check your cable by hand.

BTW, it is always a good idea to check all feed lines for wattage through-put before installations, as noted above. I keep a record to compare coax over time. I had a 100' feet of RG8x that had clear coat outer covering hooked to an A99 that was up for over 10 years. At some point I noticed the antenna had a very low noise level, a very broad <2.0:1 bandwidth, and my signals to locals and DX contacts was lower that my neighborhood neighbors running about the same watts. I checked the through-put with a 20 watts in I saw 2 watts out. In operations I never noticed this slow decline in performance. I discovered that were signs of water in my feed line at some point in the past, I saw mold looking discoloration thru the clear coat.

Whitedove I don't think this is your problem, but it may be worth noting for others who use an antenna like the A99, Imax, where the feed point can allow water to go straight into your coax, even with a weep hole in the connector. Water can run right down the wires and these SO239 connectors are no where near water tight.

 

[whitedove]

4-5 even wraps is optimal for 11 meters (27 MHz).

http://www.worldwidedx.com/cb-antennas/62990-coax-choke-info.html

20 wraps is good for 9-13 MHz .
BTW , since you're using a real ham radio ........ do you also have a tuner in the coax line ? or are you just using the one the one in the yaesu ? also , did you get similar results comparing @ other bands/frequencies ?

I never checked the other ham bands as I was only using it for 10m. The radio will not tx on 11m. Thanks Guys. I'll check the coax by hand and try the choke if that is good.

 

[whitedove]

Waverider said "Time to wrap a choke at the feed point and try it again."

I had an 18 ft piece of RG8x coax laying around and a 4 in. piece of pvc coupling about 2 to 3 in. wide. I rolled the coax around the pvc and fastened it with several zip ties. It came out to about 12 turns of coax. I also put a piece of pvc on the mast to mount the choke to isolate it from the mast and provide strain relief. I hooked one end at the antenna feed point the other end to the CXP1318FX coax. I hooked it up to my radio and Wow! My swr's are totally flat on 10m,
12m, 15m, 17m, and they are also great on certain portions of 6m around 51.000 though I don't know how well it will talk on 6m.
Thanks Waverider, Radiooman, and everyone else for the great advice.
Whitedove

 

[RADIOOMAN]

Waverider said "Time to wrap a choke at the feed point and try it again."

I had an 18 ft piece of RG8x coax laying around and a 4 in. piece of pvc coupling about 2 to 3 in. wide. I rolled the coax around the pvc and fastened it with several zip ties. It came out to about 12 turns of coax. I also put a piece of pvc on the mast to mount the choke to isolate it from the mast and provide strain relief. I hooked one end at the antenna feed point the other end to the CXP1318FX coax. I hooked it up to my radio and Wow! My swr's are totally flat on 10m,
12m, 15m, 17m, and they are also great on certain portions of 6m around 51.000 though I don't know how well it will talk on 6m.
Thanks Waverider, Radiooman, and everyone else for the great advice.
Whitedove

I am not sure if we answered all the questions that were present with this thread, but it seems like you are satisfied with the results you have obtained.
I, myself, was concentrating on the more obvious aspects of the details associated with this thread.
I am surprised that this turned out the way it did.
Got to give all the participants credit here; Seems like different posters had different ideas, but I think it is due to that fact, that you were able to come to a resolution for your problem.
Had it not been for the contribution of those involved we might still be stumbling around trying to figure this out.
I would like to give my thanks to those that participated with this thread.

 

[hookedon6]

...I had an 18 ft piece of RG8x ...Wow! My swr's are totally flat on 10m, 12m, 15m, 17m,...

okaaaaaaay,:blink: hope it works out for you

 

[W5LZ]

Radiooman,
"It was not indicated in his post that there was any change in any of the conditions of the antenna; Antenna is a unchanging variable in his test."

You're right, but then there was no indication that there wasn't a change in feed line length, or those other thingys. Have you ever replaced a feed line and used exactly the same length, I can't say that I have (not talking abut inches, but feet). That opens the possibility that the feed line length did/does have an influence on those SWR readings and the resulting reception report. Do you see the possibilities with that?
And then by adding 18 feet of feed line to the antenna system it's suddenly 'flat' over several bands. That indicates that the feed line length IS making a difference in the SWR readings which also indicates that the antenna is tuned incorrectly. A very rough form of conjugate impedance matching, right?
If it sounds too good to be true... Now do you see where I was going with it?
- 'Doc