[Elecraft] EFHW

Ron D'Eau Claire ron at cobi.biz
Sun Feb 12 12:13:13 EST 2017 

I purposely overlooked the obvious error that broadcast band antennas are 1/2 wave length long. How many BCB stations has anyone seen with a free-standing transmitting tower between 400 and 1000 feet high?

Most BCB (0.5 to 1.6 MHz) antennas are 1/8 wavelength high (or less) which necessitates an extensive ground system. Even so an efficiency of 10% or less is not surprising. 

A half wave radiator a decent distance from the earth is much, much more efficient, no matter how it is fed (end, center, off-center). 

73, Ron AC7AC

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Rick Dettinger
Sent: Saturday, February 11, 2017 9:54 PM
To: Kevin - K4VD
Cc: Elecraft Reflector Reflector
Subject: Re: [Elecraft] EFHW

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.
>>>>> 
>>>>> 
>> 
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>> 
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