coax cable question

[whitedove]

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

 

[RADIOOMAN]

If there are no obvious defects on the new coax and the PL259's were installed properly then check the swr of a known good dummy load.
In other words make sure the dummy load is good before you use it to make this test.
Check it and make sure that it reads 1:1 with as short of lengths of coax as you can manage.
Then put the dummy load where the antenna would be and use your SWR meter inside at the other end to check the SWR.
It should read 1:1.
If it does not then there is something wrong with the coax assembly.

The following is only of interest in the event you experience an undesired result in the preceeding SWR test.
If you want to find more information when you do this test then use a wattmeter.
If you don't have a wattmeter you can use your SWR meter for this test.
Hook up the radio to the WATT METER/SWR METER with a short jumper and then hook up the coax just like you were gonna check the SWR of the antenna only you will have the dummyload hooked up to the far end of the coax.
Adjust the FWD set knob to make the pointer align with the SET mark and then keeping the variable/adjustment knob in the same place take the SWR meter out and hook it between the coax and the dummyload.And then take notice where the pointer is. It should be almost in the same place as it was when you took the first reading inside.
But in either case, wether you have a WATT METER or SWR METER, you are using it for the purpose of indicating the relative amount of loss in the coax.
In the case of the SWR, assuming that the meter scale is relativley linear you can deduce that if the meter shows 1/2 of the first reading (inside) then you have lost approximately 6 db in the coax. ( numbers for illustrative purposes only )
It is most likely that your coax will show only slightly less ( about 92%) which is consistent with the stated loss for your length of coax. (<1db at 30 mcps )
But I am gonna go out on a limb here and guess that your friend somehow misinformed you about the results.
I find it hard to believe that a new piece of coax is the problem.
And, chances are that the antenna was not tuned correctly when it was first installed and with a lower loss coax and a different length of velocity factor the new coax is showing a higher SWR.

 

[whitedove]

Radiooman my friend said my audio sounded the same on both cables. Clean and clear, but while looking at the s meter on his radio it showed I had a 2 s unit stronger signal with the RG 8x than with the CXP1318FX. Afterwards I took the cable to my friend who tested the CXP1318FX cable and told me it is definitely good. He can't explain why the signal was better on the RG 8x. He did tell me RG 213u would work better with an antron 99 than the CXP1318FX.

 

[RADIOOMAN]

Radiooman my friend said my audio sounded the same on both cables. Clean and clear, but while looking at the s meter on his radio it showed I had a 2 s unit stronger signal with the RG 8x than with the CXP1318FX. Afterwards I took the cable to my friend who tested the CXP1318FX cable and told me it is definitely good. He can't explain why the signal was better on the RG 8x. He did tell me RG 213u would work better with an antron 99 than the CXP1318FX.

2 S units is a lot.
Is he able to tell you why the RG-213u would work better with an Antron 99 than the CXP1318FX?
Is the friend that report the 2 S unit signal loss the same friend that tested the CXP1318FX cable?
Do you know by what method he used to test the new coax?
Since I have no clue about your radio I must ask if there is any method by which you can reduce the output of the radio when transmitting?
Back to you

 

[whitedove]

My radio is a yaesu ft 450. I can reduce the power.
The friend who gave me the signal info and tested the cable are the same.
Cable was tested with a paint can looking like dummy load

 

[RADIOOMAN]

I would test the radio with a carrier without any modulation unless you use FM.
It would be best to do the test with a radio upon which no adjustment to the power level is possible. ( just to rule out that factor as a variable)
Maybe if you have a cb radio that has a fixed out put you can find someone to look at their Smeter.
Maybe you could find several people to cooperate in this test.
People that are farther away are better to do the test with.
If you are close to someone and you are giving them S9 they probably won't notice if your signal gets a little stronger.
Did your friend have any explanation why the RG8X would work better with an antron than the new coax?

 

[Captain Kilowatt]

I have to agree with radioman about the results. If you go from crappy RG-58u cable to extremely good LDF-4 Heliax cable you would not see that kind of difference. Not on 11m anyway. VHF perhaps but not on CB.Even looking at the manufacturers specs the numbers do not add up unless there is a problem with one of the cables.

 

[RADIOOMAN]

I have to agree with radioman about the results. If you go from crappy RG-58u cable to extremely good LDF-4 Heliax cable you would not see that kind of difference. Not on 11m anyway. VHF perhaps but not on CB.Even looking at the manufacturers specs the numbers do not add up unless there is a problem with one of the cables.

The test results are 'bassackwards' anyway.
The results are counter-intuitive.
His test indicated that the RG8x gave the stronger Smeter reading of the two cables?!?!?
I think it needs to be retested 'cause the first test results are inconsistent with what is expected.

 

[W5LZ]

By using signal strength readings from his friend it amounts to checking the amount of power being radiated from the antenna. So aside from some almost meaningless difference in the feed line's impedance, and an absolutely meaningless velocity factor difference, there was something like a 12 dB of loss (great deal of variations with calibrating an 'S' meter so make that a 'guess'). I didn't see if any particular mode was used in that difference in 'S' meter readings so allow for the possibility of voice mode being used and the corresponding inaccuracies because of that. Another 'unknown' in that whole thing is the difference (if any) in the feed line length. So what does that leave for a possible source of that loss? Keep in mind that 2:1 SWR. Wanna guess where I'm going with that?
- 'Doc

 

[RADIOOMAN]

By using signal strength readings from his friend it amounts to checking the amount of power being radiated from the antenna. So aside from some almost meaningless difference in the feed line's impedance, and an absolutely meaningless velocity factor difference, there was something like a 12 dB of loss (great deal of variations with calibrating an 'S' meter so make that a 'guess'). I didn't see if any particular mode was used in that difference in 'S' meter readings so allow for the possibility of voice mode being used and the corresponding inaccuracies because of that. Another 'unknown' in that whole thing is the difference (if any) in the feed line length. So what does that leave for a possible source of that loss? Keep in mind that 2:1 SWR. Wanna guess where I'm going with that?
- 'Doc

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.
While I agree that the agreed upon value assigned to a Sunit is supposed to be 6 db in some cases, (some radio manufacturers might have disregarded that standard and decided that thier Smeter shall indicate in 3db/Sunit) it is not a absolute in any case unless it is carefully measured to show that is the case.
We cannot verify or agree what value of db gain the Smeter responds to in this case, we can agree, that 2 Sunits is a lot and is inconsistent with the expected results of the test.

 

[BOOTY MONSTER]

i wonder if the rf gain dial on the RX end was adjusted without being noticed ?

 

[wavrider]

My radio is a yaesu ft 450. I can reduce the power.
The friend who gave me the signal info and tested the cable are the same.
Cable was tested with a paint can looking like dummy load

FT-450 starts folding back at 1.5:1 VSWR, so this test may be correct, so many variables to not make it correct but if the VSWR protection circuit did indeed fold back due to higher VSWR then it is possible.

Seems to me that you have some CMC on your coax, A-99 are famous for that.

Time to wrap a choke at the feed point and try it again

 

[whitedove]

Thank you all for the answers. When I get off work I'm going to try and adjust the tuning rings for swr's a little.

Also I'll take a 4 in. piece of pvc pipe and wrap 20 turns of RG 8x coax on it for a choke to install at the feedpoint?

And the frequency we were testing on was 28.315 usb.

Thanks Whitedove

 

[hookedon6]

Thank you all for the answers. When I get off work I'm going to try and adjust the tuning rings for swr's a little.
And the frequency we were testing on was 28.315 usb.

Thanks Whitedove

I would just cut 8 inches off the antenna

 

[BOOTY MONSTER]

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 ?