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Author Topic: SWR ON TENNADYNE T8  (Read 1999 times)
W4DEE
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Posts: 4




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« on: December 30, 2013, 08:09:50 PM »

I HAVE OWNED 2 TENNADYNE T 8 AND I CAN NOT GET THE SWR DOWN ON 12 BELOW 2. 5. I HAVE TRIED EVERYHING I CAN THINK OF I AM ABSOLUTLY CERTAIN IT IS PUT TOGETHER CORRECTLY , I READ ALL THE REVIEW AND THERE WAS VERY LITTLE TALK ABOUT SWR . ANY SUGGESTS WILL BE APPRECIATED

DON
W4DEE
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K3SF
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Posts: 52




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« Reply #1 on: December 31, 2013, 06:14:17 AM »

Hi Don

i also have T8..with no issue on 12m...the tuning stub and balun setup are primary areas to investigate

i suggest you look at the following yahoo group
http://groups.yahoo.com/neo/groups/TennadyneAntennas/conversations/messages

lot of discussions on swr issues

you can search thru the messages and see if any fit your situation and if not then just ask ..
when asking for help...the more information you provide the better


Paul K3SF
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K5ACO
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Posts: 9




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« Reply #2 on: December 31, 2013, 06:30:09 AM »

T6 here.  about 1.7 on 12M and lower everywhere else.  Used suggested choke balun at end of boom.  For good measure, put a dozen beads on where cable starts down the mast.

Read about all the "magic" some folks are doing, but found none of it necessary. 
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W5WSS
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Posts: 1725




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« Reply #3 on: December 31, 2013, 07:03:44 AM »

If The design uses a Hot boom and a 1:1 current balun at the feed point then it is OK to route the coaxial line  taped directly to the boom half that is connected to the shield. With the Current balun at the feed point then it can remain at that location without any adverse problems provided the coaxial feed line is grounded to the mast where it exits the cold shield boom half.

This can be done using a UHF barrel splice and clamp for bonding.

This treatment should be used with a hot boom log Periodic.

This technique is anecdotal and might relieve your specific issues relative to 12m.

73
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K3VAT
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Posts: 709




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« Reply #4 on: December 31, 2013, 07:10:58 AM »

I HAVE OWNED 2 TENNADYNE T 8 AND I CAN NOT GET THE SWR DOWN ON 12 BELOW 2. 5. I HAVE TRIED EVERYHING I CAN THINK OF I AM ABSOLUTLY CERTAIN IT IS PUT TOGETHER CORRECTLY , I READ ALL THE REVIEW AND THERE WAS VERY LITTLE TALK ABOUT SWR . ANY SUGGESTS WILL BE APPRECIATED

DON
W4DEE

In addition to the above responses, please see: http://www.w8ji.com/baluns_on_log_perodic_antennas.htm.

GL, 73, Rich,  K3VAT
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K5ACO
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« Reply #5 on: January 01, 2014, 03:37:50 PM »

I do not dispute that the W8JI ideas will work, but did not find it necessary to ground the coax shield at the mast.

The Tennadyne has 2 booms separated by a half inch and the bottom one  is connected to the shield.  I taped coax directly to the boom, did not droop it below the boom as some have suggested.

Results are exactly as would be expected from a LPDA of this size.  ( have T6 here, T8 should play even better)
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W5WSS
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« Reply #6 on: January 01, 2014, 07:59:22 PM »

OK did you fasten the antenna coaxial feed line to the boom half that is serving as the transposed feeder system/support boom shield half?  Because the other half is the center conductor and it will cause problems if it is taped or fastened to that hot half.

The coaxial antenna feed line should not be directly against routed or fastened to the hot half or it will couple to the shield easily through the line outside jacket since the transposing current is along the outer surface of the conductive boom material.

If you have in fact fastened to the proper cold half then be sure it is on the far side away from the hot boom another words use the cold half to block or be directly in between the line and the other side hot section.

Do not run it in the space or natural channel between the halves.

In 1983 I never used a balun for my home made 52 ohm LOG Yagi. I used the regular drip loop and saddle clamp.after first pre forming a 10m mono band air wound coaxial choke The continuous antenna feed line dropped straight away and downwards towards a point on the mast forming a drip loop large enough to rotate the antenna never had any problems with common mode so perhaps you can do the conventional drip loop and this will move the line away from the boom totally.

73 
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WB2WIK
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« Reply #7 on: January 01, 2014, 08:16:43 PM »

I have a T-8.  They don't provide the balun with the antenna; I made mine using 7t of RG-400/U on a 5" diameter form, tie-wrapped to hold its shape, and tie-wrapped to the lower boom only at one point at the very end of the boom so 90% of the balun is just hanging below the antenna in free space.

I let the feedline (RG-214/U in my case) "droop" down below the lower boom, a lot.  It makes a "half loop" about 3-4' below the antenna and then comes back up to meet the mast at the center of the antenna, where it's supported again.  But it blows around in the breeze and isn't close to either boom.

I did that mostly because having visited many "commercial/military" LPDA installations, I saw that's exactly what almost all of them did.  No other reason, really -- I just "copied" what those installations did, figuring there must have been a reason for it.

My VSWR on 12m is 1.3:1 across the 100 kHz band.  Actually, from 14.0 to 29.0 MHz, it never rises above 1.6:1 anywhere.  But at 29.7 MHz it's a bit higher, about 2:1.

I did not cut or modify the "shorting loop" at the back end of the antenna.  Would not have minded doing that, but it just didn't seem necessary.  My T-8 is 55' above ground; height may make a difference.
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W5WSS
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Posts: 1725




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« Reply #8 on: January 01, 2014, 09:10:06 PM »

Hello Steve, Yeah I used RG 214 with that home made 10m Log Yagi (you could not buy one nobody fabricated them commercially then or now). This antenna is the best beam I have used to date! side by side either Mono band quads or yagi's could not compete with this antenna on 10m.

The SWR curve was 1:1 from 28.300 to 28.700 and rose to 1:5:1 at 28.000 and 1:5:1 at 29.000 really a total success.

 The boom was 2" OD 6061-t6 and the 4 log cell elements were mounted on pure 5/8" thick Phenolic flat stock plates for excellent isolation the boom was cold and the reflector and director was directly mounted to the boom using a Wilson element to boom clamps was OK since the centers of the two parasitic elements were at zero voltage  the elements worked as designed.

Anyway as we have both indicated the conventional method of feed line routing should work fine
 with a conventional Log Periodic array.

73
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NY0P
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Posts: 16




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« Reply #9 on: January 02, 2014, 05:51:40 AM »

I had a similar experience on 12m with my t11.  I used their balun but deviated from the instructions by not taping the coax feed to the lower boom.  My coax feed is suspendedabout a foot below the booms.  I suspect this deviation from the assembly instructions is why my standing wave was around 2.5 on 12m.

I was able to bring mine swr down to 1.8 as measured in my shack by shortening the hairpin on the back of the antenna and using a antenna analyzer.  I can now run the legal limit on 12m with  my AL-82 no problem.

Rick


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