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Author Topic: Emergency Amateur Radio Club Hawaii = END FED 6–40 Meter Multibander  (Read 4458 times)

Offline KC8AON

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Re: Emergency Amateur Radio Club Hawaii = END FED 6–40 Meter Multibander
« Reply #15 on: November 07, 2014, 18:04:17 UTC »
Hello OM´s

The Hawaiian enfed has nothing more than a 1/9 UNUN transformer . I build several of these antenna´s but the efficiency is pitiable and can not  be compared with the Dutch antenna´s for a unun type antenna is never resonant  on ham bands and gives a lot of stress at your qrp receiver frontend.

BTW a unun should be build on a FT140- 43 type toroid......
Have fun

73 John

I'm just wondering how you think the unun type antenna puts stress on the receiver frontend ?  Also, I wonder why you state that they are never resonant on the ham bands ?  I have built several ununs for use with an end fed half wave and they had an swr of 1:1 with the proper length wire attached.  I use an FT114-43 core with 30 turns of #20 magnet wire with one end of the turns to ground and the other to the antenna wire, then a tap at the 4th turn from the ground end and use that to connect to the 50 ohm feed line to the radio.  Use the formula 468/freq in MHz to find the length of wire to use and then fine tune the length of wire to obtain the lowest swr.  This is more of an impedance transformer but it is for feeding an unbalanced hi Z load making it a unun.

Offline VE2TH

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Re: Emergency Amateur Radio Club Hawaii = END FED 6–40 Meter Multibander
« Reply #16 on: November 18, 2014, 03:01:13 UTC »

Hello all,

GM0LVI said: I'm surprised the Hawaiian balun doesn't incorporate a binding post for a counterpoise.

Concerning the EARCHI end-fed antenna, I read something new in their product.

Link: http://www.earchi.org/92011endfedfiles/Endfed6_40.pdf

With photos of the balun, with the second wing nut for a ground. Plus photo détails of the balun, winding etc.-

FROM THEIR PDF. DOCUMENT:

Best performance is achieved with a coax of 16’ or longer with the coax shield providing the counterpoise function. Additional counterpoise is usually not required in this design, although the lower wing nut provides a convenient counterpoise connector if needed. The end fed antenna system works well in horizontal, sloper, and vertical configurations.

I can confirmed, it works much better and it is more easy to find a very low SWR on 40/20/10 meters.

When portable, as a counterpoise I use a chain link fence when available, or when camping I use the water tap on the campground. It works like a champ. Or the automobile ground, Under the car.-

I always hooked up the balun to the pic-nic table, and the other end of the wire to a tree.

If no trees, I use my 32 feet/10 meters telescopic fiberglass pole from T-MAST CO.

Do not forget, to:  have fun everyday,

72 Michel

I love QRP/QRPp & CW

Offline KC8AON

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Re: Emergency Amateur Radio Club Hawaii = END FED 6–40 Meter Multibander
« Reply #17 on: November 25, 2014, 17:03:14 UTC »
By happy accident, I found this design and I'm glad I did:

http://www.earchi.org/92011endfedfiles/Endfed6_40.pdf


I made one using stuff I had in the junk box and it works fb. There are no new ideas here but the design is a great combination of known principles
Disadvantages
(1) It needs around 5m of coax feed.

Vic


Thats because the coax shield is also used as a counterpoise, but just rememeber, the closer the antenna is to a half wave in length for a given frequency, the less a counter poise is important.  In fact, a properly matched end fed half wave needs no counterpoise at all !  But then its basically just a single band antenna.