[Elecraft] EFHW

Sun Feb 12 00:53:37 EST 2017

10% efficient is for a “short” end fed antenna and a ground rod or similar.
Something near a quarter wave and a typical one or two wire counterpoise is much better.
It doesn’t take much effort to get to 50% efficient with a quarter wave or longer wire, and a few short radials.
After that, there are diminishing returns for a given amount of effort.  The BC 120 radial, half wave long ground systems are a good example.  
And, as QRP and mobile operators have shown, contacts with a 10% efficient antenna system do happen!

73,
Rick  K7MW

> On Feb 11, 2017, at 9:19 PM, Kevin - K4VD <kevin at k4vd.net> wrote:
> 
> So what we are saying here is that all the local and DX QSOs we make from
> a picnic bench with an end fed or random wire thrown up in a tree and a
> short or no counterpoise doesn't really happen or, at best, is a fluke. The
> end fed is only 10% efficient (did I get that right) and most of our QRP
> signals are going to heat worms. Pretty hopeless situation I guess. I
> might have to just stick with the local repeater and Google Hangouts for
> communications.
> 
> Or, for those of you that are thinking the situation isn't so hopeless,
> grab your portable antenna, head out to the campsite, throw your wire up in
> the tree and I'll catch you on the air. Let's warm up the worms.
> 
> 73,
> Kev
> 
> 
> On Sat, Feb 11, 2017 at 11:54 PM, Ron D'Eau Claire <ron at cobi.biz> wrote:
> 
>> Ha, ha!!! Well put Wes!
>> 
>> Some mountain portables erect low "horizontal" antennas on the side of a
>> steep mountain. The result is a very low angle of radiation because, even
>> though the main lobe is "straight up" from the mountainside from the
>> antenna, the slope puts that lobe at a fairly low angle relative to the
>> earth.
>> 
>> 73, Ron AC7AC
>> 
>> -----Original Message-----
>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Wes
>> Stewart
>> Sent: Saturday, February 11, 2017 8:02 PM
>> Cc: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] EFHW
>> 
>> It is with some reluctance that I smack this whole EFHW tarbaby, but here
>> goes.
>> Comments in no particular order:
>> 
>> 1)  A resonant antenna (even one that is self-resonant), e.g. one with a
>> non-reactive feedpoint, isn't necessarily "efficient."  A
>> quarter-wavelength monopole over lossy earth leaps to mind.
>> 
>> 2)  A non-resonant antenna isn't necessarily inefficient.  The ever
>> popular G5RV isn't resonant on the band of interest (20M) but when fed
>> appropriately, was as efficient as a resonant dipole.
>> 
>> 3)  Consider a BC band 1/2 wavelength vertical antenna.  Does the station
>> designer say, "Well, this EFHW doesn't really doesn't need much of a
>> counterpoise, so I'll just throw a 100' long wire on the ground and call it
>> good enough?"  No, he install 120 radials that are even longer than the
>> ones he would use under a 1/4 wavelength monopole.  Devoldere in "Low-Band
>> DXing, Chapter 9, Section 4.3 says: "Here comes another surprise. A
>> terrible misconception about voltage-fed verticals is that they do not
>> require either a good ground or an extensive radial system.'"  Later in the
>> same section he says, "Therefore it is even more important to have a good
>> radial system with a voltage-fed antenna such as the voltage-fed T or a λ/2
>> vertical. These verticals require longer radials to do their job
>> efficiently compared to current-fed verticals."
>> 
>> 3)  When you backpacking mountain goats say, "Hey my wire isn't a
>> vertical, it's mostly horizontal", I say, if your radio is sitting on a
>> boulder or the ground, it's a vertical and your wire-on-the-ground
>> counterpoise proves it.
>> 
>> Wes  N7WS
>> 
>> 
>> 
>> On 2/11/2017 2:33 PM, Ron D'Eau Claire wrote:
>>> All efficient antenna systems are "resonant" (jX=0) but the shorthand
>>> often used is "resonant" to mean "self resonant". That is true of any
>>> 1/4 wavelength long radiator (again our common shorthand is usually
>>> "1/4 wave
>>> wire") or any multiple thereof worked against ground. It is also true
>>> of any half wave length radiator or any multiple thereof. (Note that
>>> these are electrical lengths, taking into account any surroundings
>>> including the radiator itself.)
>>> 
>>> While self-resonant antennas do not present a reactive load to the
>>> source of RF power, the value of R, the resistance, may vary widely.
>>> There is nothing magic about the 50 ohm load most of our transmitters
>> are designed for.
>>> 
>>> However, a half wave radiator fed at the center presents a resistive
>>> value near 50 ohms when fed at typical heights above ground (in free
>>> space it is
>>> 75 ohms). Half wave antennas became very popular after WWII because
>>> 50-ohm coaxial feed line became abundant and cheap on the "surplus"
>>> market and Hams were taking steps to deal with needing to avoid
>>> interfering with the rapidly growing number of TV sets in nearby
>>> homes, including the Ham's own living room.
>>> 
>>> In the following decades, greater and greater demands on harmonic
>>> suppression have led to Ham transmitters with output filters
>>> specifically designed for a 50 ohm load instead of being able to match
>>> a wide range of load impedances.
>>> 
>>> So we have now moved the wide-range output network that was in
>>> Grandpa's Ham transmitter out of the transmitter and into what we call
>> an "Antenna Tuner".
>>> But, of course it does not "tune" an antenna at all. It's just a
>>> matching network to be sure the transmitter is delivering power to a
>>> load close to 50 ohms and non-reactive.
>>> 
>>> 73, Ron AC7AC
>>> 
>>> -----Original Message-----
>>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
>>> Wes N7WS
>>> Sent: Saturday, February 11, 2017 12:44 PM
>>> To: Charlie T, K3ICH
>>> Cc:elecraft at mailman.qth.net
>>> Subject: Re: [Elecraft] EFHW
>>> 
>>> jX = 0
>>> 
>>> Sent from my iPhone
>>> 
>>>> On Feb 11, 2017, at 1:29 PM, Charlie T, K3ICH<pincon at erols.com>  wrote:
>>>> 
>>>> Define "resonance".
>>>> 
>>>> Chas
>>>> 
>>>> -----Original Message-----
>>>> From: Elecraft [mailto:-bounces at mailman.qth.net] On Behalf Of Fred
>>>> Jensen
>>>> Sent: Saturday, February 11, 2017 2:40 PM To:elecraft at mailman.qth.net
>>>> Subject: Re: [Elecraft] EFHW
>>>> 
>>>> Ummm ... A full-wavelength wire is not resonant?
>>>> 
>>>> 73,
>>>> 
>>>> Fred ["Skip"] K6DGW
>>>> Sparks NV DM09dn
>>>> Washoe County
>>>>> -----Original Message-----
>>>>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf
>>>>> Of Lynn W. Taylor, WB6UUT
>>>>> Sent: Friday, February 10, 2017 12:13 PM To:elecraft at mailman.qth.net
>>>>> Subject: Re: [Elecraft] EFHW
>>>>> 
>>>>> Just a reminder, folks.
>>>>> 
>>>>> If it's not a half-wave, then it's a non-resonant wire.
>>>>> 
>>>>> 
>> 
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>> 
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to ron at cobi.biz
>> 
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>> 
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to kevin at k4vd.net
>> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to k7mw78 at gmail.com