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Author Topic: Your Preference & Why: Log Periodic vs. Trap Multi-Band Beam?  (Read 7336 times)
WA2OLZ
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Posts: 64




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« on: October 01, 2012, 09:25:55 AM »

I am seeking your expertise and experience to help me decide on my next HF antenna. All inputs are certainly welcome and I especially appreciate real world comparisons of others who may have traveled the same road. There’s a tremendous amount of Internet lore about the pros and cons, often spiced with liberal doses of theory and prejudice with little actual trial by fire. I also am falling victim to the marketing hype of the manufacturers and want to avoid that trap!

My Situation:
Currently running a Kenwood TS-480SAT through an LDG AT-100Proll tuner to a Force-12 3-CSS beam on the roof of the house (~35' AGL). A Collins KWM-2A will be joining the party after being tweaked and tuned by a Collins guru. All ops are barefoot and I expect will stay that way for the foreseeable future.

All operations are SSB.

There is no opportunity to install a tower.

I am not a serious DX hound or involved in contests. My operation is a casual one in which I enjoy conversation and the challenge of getting through a pileup to contact that ‘rare’ one.

The Objective:
My objective is to get increased gain on all bands between 10 and 20 meters, including WARC. Improved front-to-back and/or front-to-side are also desirable.

Six meters coverage would be a side benefit but not all that important to me.

The maximum antenna boom length should be eighteen feet or less. This is more an XYL and neighborly restriction than a physical one.

The Contestants:
The short list (I think) is down to the Mosley TA-53M and the Tennadyne T8 Log Periodic.

This is certainly not an exclusive list and others would be considered.

Yes, cost IS a consideration also!

All input, as I stated earlier, is welcome!

Thanks and 73
Jack – WA2OLZ
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WD5GWY
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Posts: 392




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« Reply #1 on: October 01, 2012, 09:49:13 AM »

I don't currently own a beam(too old to climb towers anymore  Cry  ). But, in the past I have used Mosley(TA-33Jr) and Hygain(TH-11DX) beam antennas. Both were good and worked well for me. Neither one worked on the new bands.
I have read good things about the Force 12 antennas and looked (drooled actually) at them at HAMCOM in Plano,TX (hamfest). They seem to be very
well built. Had you thought of looking into one of their later models?
  I was wondering one thing. Are you using your auto tuner to work the WARC bands with your current beam antenna? While that may work, I would think performance would suffer quite a bit. (just curious)
Anyway, wish I could offer you some good ideas on which way to go.
Good luck.
james
WD5GWY

(oh, I know about XYL's not liking big antennas. Had to tell one years ago
if she wanted to be an ex-YL that she should keep up the complaining. She stopped............ and six years later she became an ex-YL )
 
 
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WX7G
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Posts: 5973




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« Reply #2 on: October 01, 2012, 10:00:06 AM »

Based on the gain specs (appear to be free space gain) the Mosley has higher gain. However, the Mosley gain may be specified at the optimum frequency in a band while the Tenadyne gain may be constant across any band.

Mosley gain specs:
10 meters   7.9 dBd
12 meters   7.1
15 meters   6.9
17 meters   6.7
20 meters   6.5

Tenadyne gain spec:
13-32 MHz  6.1 dBd   



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N4UM
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Posts: 468




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« Reply #3 on: October 01, 2012, 10:31:54 AM »

I've probably owned a half dozen trapped beams over the years (TH-2, MP-33, TA-33, CL-33, TET 4 El, TH6-DX etc.) but only owned one LP (The Tennedyne T-8).  I was always looking for a better antenna and when I got the T-8 I think I found it. The T-8 was totally hassle free and went thru several hurricanes with no problems.  The trapped beams were always creating hassles - water in the traps etc.  As I got older and less enthusiastic about climbing towers I came to appreciate "hassle free" more and more.  I now live in an HOA and am unable to have any sort of outdoor antenna but I have very fond memories of my T-8.  Hassle free has gotta be worth at least a couple DB!
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NR9R
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Posts: 151




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« Reply #4 on: October 01, 2012, 01:58:03 PM »

Unfortunately you can't really do any comparisons with manufacturer specs and gut-feeling antenna reviews are even worse.

There are a few good on-air experiments with multiband directional antennas that are very insightful:
1) HF TRIBANDER PERFORMANCE - TEST METHODS & RESULTS by N0AX and K7LXC
2) Quads vs Yagis Revisited by N6NB appearing in Ham Radio Magazine, May 1979.

The tests compare various types of multiband designs to various monoband yagi designs.  I have walked away with a few basic conclusions from these tests:

1) Three bands (10, 15 and 20m) seems to be about the limit for trapped yagi designs that provide measureable gain and f/b over a dipole.  Designs with trapped WARC elements stuck between the triband elements appear to bring the performance close to a rotatable dipole.   

2) Yagis covering the 10-20m amateur bands with a compact boom length (less than 20 ft) struggle to achieve the performance of a LPDA or two element yagi of the same boom length.  This seems true regardless of how many elements for a given band can be squeezed on the boom.  People who have opted for a forward staggered design, used by Force-12 and Optibeam, with two active elements on each band have realized this limitation.  In other words, one must let go of the idea of achieving anything close to 6dBd of gain (1 S unit) with a compact broadband yagi with fixed element lengths.

3) It is difficult to design multiband yagis with fixed element lengths that maintain the same forward gain and f/b over the entire amateur band.  For instance, some designs have great performance in the SSB portion of the band and turn into rotatable dipoles in the CW portion.  This is where the LPDA design stands out.  It may not have the gain or f/b of an optimized 2 element yagi but at least it maintains some performance over a dipole throughout the entire band. 

A unique solution to all of the drawbacks I've mentioned is the Steppir antenna, which comes at the sacrifice of some mechanical robustness.  It is pretty deceiving though to think that the tiny 2 element Steppir should meet or exceed the performance of an impressive looking 9 element Optibeam or LPDA.

My advice is to go for the LPDA or Optibeam if you need the antenna to survive the elements and choose a Steppir if you are willing to do some maintenance every few years.

Hope this Helps.

   
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WX7G
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Posts: 5973




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« Reply #5 on: October 01, 2012, 03:46:53 PM »

Here is the same question at QRZ.COM: http://forums.qrz.com/archive/index.php/t-326197.html






« Last Edit: October 01, 2012, 04:25:23 PM by WX7G » Logged
N4JTE
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Posts: 1155




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« Reply #6 on: October 01, 2012, 04:24:32 PM »

Confused, tower not an option, whats the log peridoc gonna sit on , did i miss something?
Bob
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N4JTE
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Posts: 1155




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« Reply #7 on: October 01, 2012, 04:36:08 PM »

Okay reread, top of roof maybe 35 above ground but what? 6 ft above roof? save your money on the log these suckers need height not to mention a good support to play well. For the money I would be disappointed with the constraints your dealing with, not sure your gonna get that ahah moment after clearing out your checking account, hi.
Bob
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N4JTE
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Posts: 1155




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« Reply #8 on: October 01, 2012, 04:38:42 PM »

Last thing, sorry too much free time stuck in hotel; there is no such thing as a trap wire multiband beam, best case just a good old dipole. I'm done good luck.
Bob
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WX7G
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Posts: 5973




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« Reply #9 on: October 01, 2012, 04:47:44 PM »

Why would a log periodic need to be higher than a Yagi-Uda?
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WA2OLZ
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Posts: 64




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« Reply #10 on: October 01, 2012, 05:40:16 PM »

I don't know where to start.. you guys are fantastic!! I really appreciate the support, input, information, etc. Excellent. Anyone else following the thread MUST follow the link provided by W7XG ( http://forums.qrz.com/archive/index.php/t-326197.html).

Thanks to all of you I have definitely decided to get a T8, TA-53M and a TA-54 - it just depends on what time it was and whose input I read last  Wink It proves there are different types of antennas for good reason. Many of those reasons iterated above. The Log Periodic was almost declared  the winner (for me) until I asked the original question. Now I am back where I started.

A couple of specific responses:
I am 68 years old and don't even go on the roof either, never mind towers. That is what grandkids are for!
The tuner is used on WARC with the Force-12. It works, but I'm sure the loss is major. I have nothing with which to compare it though.
I considered the new model Force 12 antennas. Those with full band coverage have boom lengths exceeding my self-impose max.
I had a TET 4 element many years ago. It was a great beam! I wish they were still available in the US.
The SteppIR is ruled out as I do not like the idea of mechanical moving parts at the antenna end.
My rotor is a Ham-IV located in the attic. There are concentric black pipes going through the roof to the beam. (See page #50: http://archive.org/stream/73-magazine-1986-09/09_September_1986#page/n50/mode/1up)
Do Log Periodics need to be higher above ground than Yagis? That would be a deal breaker if so.


Keep the replies coming, folks - this is great!
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ZL1BBW
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Posts: 371




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« Reply #11 on: October 01, 2012, 05:42:49 PM »

I would go for the Log every time, traps generally = losses, definitely a high maintenance item.

 
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
WB6BYU
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Posts: 13143




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« Reply #12 on: October 01, 2012, 06:09:36 PM »

But trap losses aren't as bad as some advertisers (who may use lossier methods instead
of traps) often make them out to be.

And while log periodic beams are capable of good performance over a wide bandwidth,
many ham products suffer from trying to use too few elements on too short of a boom
to really see the results.  For a short boom, a parasitic array is likely to have better
gain because not all of the LP is used on every band.

In the end, it all comes down to trade-offs...
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W5WSS
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Posts: 1688




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« Reply #13 on: October 01, 2012, 06:23:12 PM »

The T8 is an balanced antenna fed with a unbalanced coaxial cable.
The LOG Periodic benefits from a good 1:1 current balun installed upon the boom as close to the feed point as possible, and if you are not adding the balun then in either case
ground the coax feedline shielding to the boom very close to the balun/or feedpoint using a UHF barrel splice and saddle clamp.
This will reduce common mode displacement currents. and preserve overall performance.
When common mode is relieved the Log Periodic will exhibit optimal pattern development, directivity, front to back ratio,front to side ratio, frequency respone. Gain is a function of TAO and Sigma design parameter and sets the active region within the transposed dipoles 6 dbi sounds about right for this antenna model design.
The difference between today's trap beams and log periodic or even Log Cell periodic multiband beams is not really in the overall performance as compared on the air as is the longevity and reliability.
I like Log periodic for multi band work.
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W8JI
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Posts: 9304


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« Reply #14 on: October 01, 2012, 08:26:44 PM »

If you buy one of those logs, read this before you install it.

As shipped they have terrible balance.

http://www.w8ji.com/baluns_on_log_perodic_antennas.htm
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