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Author Topic: UNUN/Balun  (Read 1959 times)
K2OWK
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Posts: 1061




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« on: November 14, 2012, 04:49:15 PM »

Will a balun or a UNUNs ferrite change enough with temperature to affect frequency response? I am asking this question because the 4 to 1 UNUN I have on my S9 antenna is now covering 80 thru 6 meters, except 40. before the temperature drop I was able to work 40, but not 20, 10 and some of the other frequencies I can now operate. Anyone have any other ideas of what could have happened besides the temperature change?

Thanks.

73s

K2OWK
 
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WX7G
Member

Posts: 6038




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« Reply #1 on: November 14, 2012, 06:35:35 PM »

To see if the issue is balun temperature the balun can be heated with a hair drier. The tuning can be checked before and during heating.
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WB6BYU
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Posts: 13242




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« Reply #2 on: November 14, 2012, 06:41:41 PM »

The balun certainly isn't the first place I'd look, as the resistance required for "reasonable"
matching isn't that critical.  A more likely place would be a connection that shrunk physically
in the cold, or a balun housing (or coax cable) with water in it that froze.

One check would be to remove the balun and see how the antenna matches.
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V47JA
Member

Posts: 108




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« Reply #3 on: November 15, 2012, 06:25:19 AM »

You may want to open-up and your check your "free" LDG Unun, as a bad solder joint can be temperature sensitive. As the LDG Unun is not without problems:  

http://www.eham.net/reviews/detail/4122  
   VS      
http://www.eham.net/reviews/detail/9098

For that matter look at the reviews on any Balun Design Balun's or Unun's , they are great products. And I have no association with Balun Design, other then a very happy user of his products.

As you know, when something is "free", you often get what you pay for.

73,

John
« Last Edit: November 15, 2012, 06:48:29 AM by V47JA » Logged
K2OWK
Member

Posts: 1061




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« Reply #4 on: November 15, 2012, 03:16:46 PM »

WX7G, Excellent idea. I will try heating the UNUN and see what happens. The antenna matches only 40 and 15 without the UNUN as it should. I did remove the UNUN and check the inside for loose connections and bad solder joints. I tightened some connections a little. All the solder joints appeared clean with no cold  solder connections. There was no water or moisture as I had sealed the UNUN as per directions before installing. The only difference is when I installed the UNUN to the radial plate I was only able to get one mounting screw back in, but I doubt this could have been the  initial problem. As long as it keeps working as good as it does I will use it the way it is. I am a strong believer in the saying  "if it ain't broke don't try to fix it." Thanks for some of the recommendations for troubleshotting. If I have a problem again I will try some of these.

I realize this is a cheep UNUN (remember it is free), but it looks OK on the inside and it seems to be OK except for the cheep plastic case, which is fine as I do not have to worry about rust or corrosion.

73s

K2OWK
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K2OWK
Member

Posts: 1061




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« Reply #5 on: November 15, 2012, 04:08:26 PM »

I just found the reason for my problem which leads to another question. If I insert my SWR bridge before my MFJ- 914 Auto Tuner Extender I am able to tune the entire spectrum from 80 thru 6 less 40 meters. If I put my SWR bridge after my 914 extender I can not tune all the bands. There must be a reactants somehow from the SWR bridge. I normally like to keep the bridge at the antenna to see the actual SWR of the antenna, but this will not work with this configuration. It is not a big problem. because all works as it should. I now see the final SWR of my tuned antenna insted of the actual antenna SWR. Anyone have any idea why this is happening.

73s

K2OWK 
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WX7G
Member

Posts: 6038




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« Reply #6 on: November 15, 2012, 07:11:25 PM »

The SWR between the tuner and the antenna does not matter much. It is academic.

It looks like you are using an autotuner and an MFJ-914 Auto Tuner Extender. If the autotuner is your transceiver, no SWR meter should be placed in the circuit. If the autotuner is external to your transceiver the SWR meter should only be placed between the autotuner and the transceiver.
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W5DXP
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Posts: 3581


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« Reply #7 on: November 16, 2012, 05:54:51 AM »

Anyone have any idea why this is happening.

Is the feedline a different total length when the SWR meter is in the circuit?
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K2OWK
Member

Posts: 1061




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« Reply #8 on: November 16, 2012, 02:41:44 PM »

All feed lines are the same length. It is just the location in the circuit of the SWR meter that affects the tuning.

73s

K2OWK
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WB6BYU
Member

Posts: 13242




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« Reply #9 on: November 16, 2012, 05:06:21 PM »

I had a similar problem that turned out to be due to the type of PL-259 on the end
of my jumper cables.  My SWR meter is >30 years old and the contacts had been
spread out slightly:  it made contact deep in the socket with conventional soldered
PL-259 connectors but crimped ones with a tapered tip didn't make reliable
contact.

Everything looked the same, but one combination of jumper cables and equipment
didn't work like the others.

I'd also check the ground connections (shield to shell of connector) as an open
circuit there could cause the symptom you are seeing.
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K2OWK
Member

Posts: 1061




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« Reply #10 on: November 16, 2012, 09:24:34 PM »

I would like to thank everyone for there help. I just installed an MFJ- 949E in conjunction with my MFJ-914. Putting the 949E in the feed thru position allows me to auto tune all the bands except 40 meters. For this band I switch in the 949E and manual tune using the feed thru position on the 914.  This is the best and easiest way to tune all the bands, as I just adjusted the 949E for one band (40 meters) and I do not have to re-tune it as I am only using it on that one band for now. This system works great for me, and I can finally tune all the bands on one antenna. The S9 works great like this, and it seems I can talk to just about anyone I can hear. I am very satisfied. Now to sit back and rag chew. Hope to hear you on the bands.

73s

K2OWK
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