Test a Balun? - Carolina Windom Problem

[Carl WA1KPD]

Happy Monday,

Several years ago I bought and installed a full size 160-6 Carolina Windom antenna. I was very happy with it's performance and the SWR was low on all bands. General design is layout is below.

This weekend I noticed that the SWR was very high, particularly on the lower bands, and improving as I went up in the bands.

The only different thing I noticed was that a branch had grown over the shorter leg, so I went out and trimmed it. It was at the very limit of my branch trimmer and the sun was in my eyes, Murphy was there and I managed to trim the wire too. No big problem,I soldered it back together .

Anyway, trimming the branch had no noticeable impact. I dragged my dummy load out and hooked it to the end of the coax.. Back to the station and low SWR on All bands, so the coax is good.

Cleaned the PL-259 and SO-239 to eliminate any possible issues.  Checked for continuity in the balun- OK, for what that is worth. Checked for continuity from the balun ladder line to the antenna wires, OK. Checked SWR at shack with same dummy load, OK.

I am beginning to suspect something has gone south with the 4:1 balun. Not a lot of moving parts in there but although sealed, it was subject to being covered in snow this winter and possibly something got in there and cracked a core? However the only way to physically check it would destroy the case so I am trying to find a way to test it, without doing that.

Any thoughts or suggestions. I really liked the antenna and had good luck with it.
 
Thanks and 73
Carl
WA1KPD

[KK4RF]

This should be an interesting topic. I also had a Carolina Windom but mine was for 80 meters and the HF bands. I had some kind of intermittent problem with mine and I suspected water got into the balun. I ended up just taking it down and putting up an 80 meter dipole fed with ladder line. The antenna had worked well before, however, and I liked it.
     Jim Thompson at Radio Works is a very good guy and I'll bet he could give you some ideas on how to test your balun without cutting it open. I'd be curious to see what others think. I still have mine all rolled up in storage and would like to use it again.
     73s, good luck.---Marty, KK4RF---

[W2VW]

10 kw carrier @ 14.3 mhz for about 3 minutes will test it.

After that the antenna can be reconfigured to a single wire feed so you can compare.

Sorry, I can't help myself.

[Jim, W5JO]

An antenna analyzer like the MFJ 259 has a test procedure for them.

[KA0HCP]

I too would suspect water in the balun.

Try drilling a hole in the bottom and see if you get any moisture.

You could then put it in a 120F oven for several hours to drive off the moisture and retest.

[K1JJ]

As a low power initial bench test:


Do you have an MFJ-259B antenna analyzer?     Disconnect the open wire line and put a 200 ohm 1/2 watt carbon resistor across the balun output and connect the MFJ to the coax input. Sweep it 160-10M.  SWR should be less than 1.3:1 or whatever depending on balun quality and setup.  (R 50 ohms, J0)


If the balun passes, then cob together a 100w 200 ohm non-inductive resistor and put it across the balun output.  Sweep the balun 50 ohm input with a 100w rig and swr meter looking for heat, intermittents  and swr abnormalities.



T

[Carl WA1KPD]

As a low power initial bench test:

Do you have an MFJ-259B antenna analyzer?    

Thanks but no, not a piece of equipment I have......
Carl

[WQ9E]

Carl,

I used one of the Radioworks 160 Carolina windoms quite a bit back in the mid/late 1990s.  It worked well but I did have a problem with water getting into either the line isolator or balun, I can't remember which anymore.  It would cause the SWR to go up and you could watch it change over a 30 second unmodulated carrier transmission.  I inverted the offending piece for several days and then resealed it with sealing tar and put a collar with more tar over it and never had another problem for the next several years I used it.

As suggested earlier, I would call Radioworks and get their input.

[Carl WA1KPD]

Tom,
I found this one on sale.....
http://www.ebay.com/itm/SWR-METER-to-Test-CB-Radio-Antennas-Workman-SWR2T-/261317589430?pt=US_Radio_Comm_Meters&hash=item3cd7bdf9b6

[K1JJ]

Tom,
I found this one on sale.....
http://www.ebay.com/itm/SWR-METER-to-Test-CB-Radio-Antennas-Workman-SWR2T-/261317589430?pt=US_Radio_Comm_Meters&hash=item3cd7bdf9b6

And there's three available. What a bargain.   

(It's almost worth sending the guy an email to axe WTF?   He's either made an error or singing "'Scuse me while I kiss the sky.")   

T

[w8khk]

Better bid soon, before someone outbids you.  These things must be scarce as hen's teeth to command that kind of dough..

On second thought, maybe an MFJ 259B, or even a 269, might be a slightly better investment.

I believe Tom's first suggestion to be the best.  If you load the balun with 200 ohms non-reactive resistor, and test the SWR from the shack, you may confirm that the coax and the balun are performing as designed, both at low power and the normal operating power level.  If that test indicates a problem, focus on the balun.  If it performs as expected, examine the remainder of the antenna and feed at the load side of the balun.

GL on getting it operational.  Weather and trees are unpredictable.  But in the long run, the antenna will prevail!

[Carl WA1KPD]

load the balun with 200 ohms non-reactive resistor, and test the SWR from the shack, you may confirm that the coax and the balun are performing as designed, both at low power and the normal operating power level.  If that test indicates a problem, focus on the balun.  If it performs as expected, examine the remainder of the antenna and feed at the load side of the balun.

Interesting results. Looks like the balun is bad


Removed leads, attached resistor. SWR flat on all bands, but then began to rise. Realized I had forgotten to drop power- 50 watts into a 2 watt carbon. It is now a 400 ohm resistor….

Replaced resistor- SWR higher than it should be but inconsistent. Went out, replaced antenna for SWLing. Checked SWR after about 20 minutes and discovered low SWR on all bands. But then it began climbing.

I think something is going on in the balun when it is used. It is supposed to be rated for 1KW and thee tests are being run at 50 watts…

Thanks for the help!

Carl
WA1KPD

[W2VW]

The balun is probably only good for its rating into a 200 ohm resistive load.

Makes a good case for testing one at the multi kilowatt level.

I feel bad for anyone on the balun business

[WQ9E]

Carl,

Put your balun in a bag of dry rice for 2 or 3 days and then retest, I bet it is full of moisture.  If that is the problem either dry and reseal or get a replacement from RadioWorks. 

My balun had a noticeable temperature rise on 75 meter AM when fed by a Valiant.  I replaced the Carolina Windom with a full wave 75 meter horizontal loop when I acquired my Desk KW.

[WD5JKO]

http://www.arraysolutions.com/Products/baluns.htm#4:1 balun

some worthy alternatives at Array Solutions


Jim
wd5JKO

[Carl WA1KPD]

OK latest update.

I got a new balun from  DX Engineering, a COM-BAL-41130T. which had very good reviews on eham. Unfortunately that is not the cure.
I spent the better part of the day trimming all branches that came close to the antenna since it was installed.

Checked coax to balun again with 50 ohm dummy load, FB there. Checked for continuity between the top and bottom of the ladder line. No problem there.

I did put the Bird in line and I see that the Flex is not giving me accurate SWR readings. But even with the Bird, 160 is 4:1 across the band and 75 is 1:1 at 3.5 and up to 5:1 at 3885. My recollection is that when I first put it in 3 years ago it was pretty low and flat across the bands. So much so I stopped using my tuner as the tuner in the 756 could handle it without any problem.

As you may recall, I trimmed some close branches last week that had grown in and accidentally cut the short leg with the trimmer. In repairing I probably lost about 2-3 inches. I guess my next step is to proportionately trim the long leg. Its possible I have fixed the issue and am seeing the result of that. There is really nothing else that can be wrong.

Long and frustrating day. I welcome anymore thoughts.


Carl
/KPD

[WQ9E]

Carl,

I went back and checked my notes packed with mine out in the barn and it was the line isolator that caused problems with mine.  It was full of water.  This is the part that is 22' down from the balun/"dedicated matching unit" (as Radioworks calls it).

Check your line isolator.  This is also the part on mine that became noticeably warm even at moderate AM power.  I see now that they no longer rate the antenna for AM/RTTY use at all so depending upon the power level you have been using you may have melted the coax in the line isolator.

[Carl WA1KPD]

Thank you Rodger,

The way mine is set up the OCFD is fed by 22' feet of 300 ohm then goes into the 4:1 balun. The output of the balun is 50 ohms and goes straight to feedline coax. This design does not have a line isolator.
So there is only one transformer and it is now replaced with a brand new one rated for the power...

Odd.
Carl

/KPD

[AB2EZ]

Carl

Can you clarify:

When you cut the short side, did you cut it right at the end insulator... and just reattach the cut wire to the insulator (losing a few inches of wire)

or

Did you cut the short side at a distance from the end insulator... and splice the two wires back together (losing a few inches in the splicing operation)?

Separately, are you sure that the old balun was 4:1 (and not 6:1)?

Stu

[Carl WA1KPD]

Did you cut the short side at a distance from the end insulator... and splice the two wires back together (losing a few inches in the splicing operation)?

Separately, are you sure that the old balun was 4:1 (and not 6:1)?

Stu

Hi Stu
The cut was about 10 feet from the feedpoint insulator, and I just checked, the previous balun was a 4:1 current balun.
Thanks
Carl

[AB2EZ]

Carl

Okay on the clarifications.

I'm wondering if the splice might have a high resistance through it... even if it has good mechanical integrity.

Best regards
Stu

[Carl WA1KPD]

It should be OK.. I wrapped and soldered it well. But who knows? I can always replace that leg.

[WQ9E]

The way mine is set up the OCFD is fed by 22' feet of 300 ohm then goes into the 4:1 balun. The output of the balun is 50 ohms and goes straight to feedline coax. This design does not have a line isolator.
So there is only one transformer and it is now replaced with a brand new one rated for the power...

Odd.
Carl

/KPD

Carl,

Sorry I overlooked your earlier diagram.  Looking at your post #15 was that test run from your radio room with all of the usual stuff in line (or at least the normal coax run)?

Contaminated coax will often change characteristics during a test since the contamination increases loss and heating.  The same behavior can happen because of a coax connector that is either contaminated or has a poor connection.  When I was a new ham installing my first homebuilt quad antenna a brand new Amphenol coax connector caused me to waste a lot of time chasing a SWR problem.  This SO-239 had just under 500 ohms resistance from center to shell, apparently something went wrong with the insulating material.

A couple of other tests to consider:

1.  with the coax disconnected at both ends what does it measure between center and shield?
2.  short the coax at the station end and then measure resistance between center and shield at the other end.  Twist/manipulate the coax near the connector while doing this.  If nothing found repeat this test with the short at the balun feed end and the measurement at your station.

3.  If you haven't already done so test swr with the ATU and its cabling removed.  Suspect any coax switch, relay etc. in the path.

[Carl WA1KPD]

I'll give the resistance measurement a try. I also found a program that uses the Flex system to automatically develop a plot of SWR. on each band. I'm going to use that too. Since it does not require the antenna tuner in the Flex, I will bypass that and eliminate one more item. This weekend I intend to replace the short leg on the chance that joint is bad. It soldered up very nicely with the Weller, and as I said the problem was there before.

I also ordered some new 300 ohm twin lead today. It is a long sht but some critter gnawed at the twin lead plastic. Never broke it, connections are good very slight distortion of lead but at this point for $15.......

Again, thanks and it will be interesting to see what this turns out to be. It worked fine and now for some unknown reasons it does not.

73

Carl
/KPD

[AB2EZ]

Carl

Is this antenna a product that you can provide a brand/product number for?

I'm trying to understand (in some detail) the function played by the length of 300 ohm twin lead in this application. I'm pretty sure that its principal purpose is to achieve the desired low SWR... on all of the ham bands... although it will affect the radiation pattern... as is the case for all Carolina Windom antennas.

More specifically:

The Carolina Windom antennas described on the Radio Works web site, and the OCFD antennas described/discussed on other web sites I've looked at, employ a vertical section as a "radiating element". In the antennas I looked at, this radiating element is the outside of the shield of the section of 50 ohm coax that runs between the 4:1 balun at the feed point and a line isolator (that blocks common mode current flow).

The balanced line (twin lead) can also support common mode current (i.e. equal currents flowing in the same direction in both conductors)... and the balun serves the function of a common mode current isolator... i.e. to block the common mode current in the ladder line from continuing toward the transmitter over the outside of the shield of the 50 ohm coaxial cable on the other side of the balun... so I guess that's what is going on.

But, I'm also wondering why this antenna employs the combination of 300 ohm twin lead and a 4:1 balun. Most of the information that I found on the web indicates that the feed point impedance of an OCFD is 200 ohms... at least at the frequency where the two legs add up to a half wavelength. Perhaps the particular length of 300 ohm twin lead in combination with the 4:1 balun enables a lower SWR to be obtained across all of the ham bands in a multi-band application, than would be obtained with 200 ohm balanced line. Maybe its just that 200 ohm balanced line it not available in the form of twin lead.

Stu