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Author Topic: Trapped EFHW info  (Read 5125 times)

caulktel

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Trapped EFHW info
« on: June 11, 2017, 06:58:42 PM »
Hi all,

I normally use EFHW antennas for all my portable ops with a 28ft fiberglass pole, but they are all mono band, so I got this idea to make a multi band 20,40 meter EFHW using these traps from, http://www.sotabeams.co.uk/pico-traps-kit-pair/ I understand how to tune the traps, but I'm not clear on how to determine where to place the trap on the wire. I assume being as I want to use it on 20 and 40, that it needs to be approximately 66 feet long total length, but where do I insert the 20 meter trap, at 33 feet? I have done a lot of searching, but have not found a definitive answer on how to figure it. Do I build the 20 meter section first with the trap at the end and tune it to length, then add the 40 meter section? Any help would be appreciated.

Joel
N6ALT 

Jon_Garfio

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Trapped EFHW info
« Reply #1 on: June 12, 2017, 02:10:08 AM »
The best performance that you can get on a EF antenna is using a complete half wave lenght, without traps.

However, if you want a multi-band end fed best choice is use a linked wire.



This is my opinion.


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gil

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Re: Trapped EFHW info
« Reply #2 on: June 12, 2017, 03:27:43 AM »
Quote
However, if you want a multi-band end fed best choice is use a linked wire.

Yes. I do like traps though because you can change bands without taking your antenna down...

Gil.

RadioRay

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Re: Trapped EFHW info
« Reply #3 on: June 12, 2017, 08:13:20 AM »
EFHW antennas are half wave > or multiples of half wave < and so they work on their harmonics.  So, if your lowest band is 40, it should also work on 20 using the same length of wire with no traps needed.  I do that here with my 80 m EFHW, it also tuned forty and twenty.  Naturally, on twenty meters the radiation pattern becomes mildly directional along the axis of the wire, but that can be desirable.


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caulktel

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Re: Trapped EFHW info
« Reply #4 on: June 12, 2017, 09:49:01 AM »
Ray, thanks for the info. I'm presently using a 40 meter EF 0n 20 with a tuner, but the performance is not as good as a cut to length antenna. I can switch between the two in my shack and there are signals that pop up up that can't even be heard on the 40 meter wire with the tuner, so I'm hoping a properly tuned trap would be better. I have never used them before, but like Gil, I would rather not have to take my antenna down to change bands.

Joel
N6ALT

gil

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Re: Trapped EFHW info
« Reply #5 on: June 12, 2017, 01:02:27 PM »
For a longer than half wave end-fed the performance won't be as good if the antenna is vertical, though you can get lucky... With a horizontal antenna you can actually have gain because of directivity. Just know where your main lobes are...
Gil

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cockpitbob

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Re: Trapped EFHW info
« Reply #6 on: June 12, 2017, 11:15:42 PM »
Like Ray said, a 66' length of wire will work on 40 and 20.  It will also work on 15 meters since it is 1.5 wavelengths long at 21MHz.  That's the beauty of what our founding ham fathers did.  Many bands are harmonically related.

Check out myantennas.com.  He sells a line of EFHW antennas that are multiband with one piece of wire and no traps.  His secret sauce is the wideband transformers in the match box.

Traps are good if you want 30M capability.  I made a 40/30/20 EFHW using 20M and 30M traps.  Cutting the wire is tricky.  Here's the process I used.
1. Hoist just a 34' piece of wire into the air and trim to 20M. 
2. Attach a 20M trap to the end and add 13' of wire, hoist back up and trim the new piece to the 30M band.  Expect to trim a lot off since the current flows through the trap's inductor which acts like a loading coil, so the overall length will be shorter than the expected 468/10.1MHz.
3. Attach the 30M trap, add wire and trim the new end to the 40M band.  Again, the added wire will be shorter than expected.

Note that the traps must already be tuned on the bench to the desired frequency.
« Last Edit: June 13, 2017, 02:38:21 PM by cockpitbob »

caulktel

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Re: Trapped EFHW info
« Reply #7 on: June 13, 2017, 06:33:33 PM »
Thanks Bob, that was the exact information I was looking for.

Joel
N6ALT

Lamewolf

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Re: Trapped EFHW info
« Reply #8 on: June 21, 2017, 08:50:17 AM »
Hi all,

I normally use EFHW antennas for all my portable ops with a 28ft fiberglass pole, but they are all mono band, so I got this idea to make a multi band 20,40 meter EFHW using these traps from, http://www.sotabeams.co.uk/pico-traps-kit-pair/ I understand how to tune the traps, but I'm not clear on how to determine where to place the trap on the wire. I assume being as I want to use it on 20 and 40, that it needs to be approximately 66 feet long total length, but where do I insert the 20 meter trap, at 33 feet? I have done a lot of searching, but have not found a definitive answer on how to figure it. Do I build the 20 meter section first with the trap at the end and tune it to length, then add the 40 meter section? Any help would be appreciated.

Joel
N6ALT

Use a 64:1 transformer to feed an end fed half wave for 40 meters and it will work 20 an 15 meter also without a tuner and without traps !

Lamewolf

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Re: Trapped EFHW info
« Reply #9 on: June 21, 2017, 08:53:38 AM »
I already posted a diagram of the 64:1 transformer in a thread here: http://radiopreppers.com/index.php/topic,1292.0.html  in case you want to build one.

Lamewolf

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Re: Trapped EFHW info
« Reply #10 on: June 21, 2017, 09:55:02 AM »

gil

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Re: Trapped EFHW info
« Reply #11 on: June 22, 2017, 03:06:43 AM »
Great link Lamewolf, thanks.

Gil.

caulktel

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Re: Trapped EFHW info
« Reply #12 on: June 24, 2017, 01:02:12 PM »
 Lamewolf, that's the same transformer I use on all my EFHWs. Works great on all bands.

Joel
N6ALT

cockpitbob

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Re: Trapped EFHW info
« Reply #13 on: June 25, 2017, 10:22:34 PM »
One additional comment on trapped EFHWs.  That 40/30/20 antenna I made is super convenient, but it doesn't perform as well on 20 as my 63' long wire.  The 63' wire is resonant on 40 and 20, so on 20 my antenna is 63' long, while with the trapped antenna only uses that first 32' piece of wire.  20 has half the wire in the air, and it's lower to the ground.

caulktel

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Re: Trapped EFHW info
« Reply #14 on: June 30, 2017, 01:21:09 PM »
Well my trapped EFHW was a epic failure. After getting the 20 meter section perfectly tuned with the trap on the end of the wire, I added the 40 meter section. 20 was still fine but the 40 meter section was too long and resonating at about 6.8Mhz, so I started cutting it to get it in band, well that messed up the 20 meter side, so I had to add a foot to it to get it back in tune, then 40 was out again, so I cut some more off the 40 meter side, then the whole antenna became messed up. 20 was resonate in 2 places, neither of which were in the ham bands and 40 was no longer resonate at all. It got so hot outside, I packed up and went home:-( I don't know if I want to try this again, I may just stick with mono band EFHW antennas. Bob, are you saying a 63' wire is resonate on 40 and 20 without a tuner? I have used it that way, but always needed a tuner on 20.

Joel
N6ALT