I think this is mixing up 1/2 wave radiators and 1/4 wave radiators.
To be resonant, a 1/4 wave wire needs another 1/4 wave "counterpoise" -
think of a center fed dipole - it has 1/4 wave on each side whether one
side is a monopole (vertical) and the other 1/4 wave is an elevated
radial or buried radials of indeterminate length, or whether it is a
dipole with the center in the air.
A 1/2 wave radiator fed at the end theoretically does not need any
counterpoise, but in practice it does - but only needs to be about 0.05
wavelength long.
Refer to some antenna books (the ARRL has a good one) or the ARRL
Handbook for good information about basic antennas.
73,
Don W3FPR
On 12/29/2016 10:30 AM, Fred Moore wrote:
With an end fed 1/4 wave you only need a counterpoise that is about .05
wave length. it can be the coax or another counterpoise. Although a
counterpoise has some effect on radiation pattern of a quarter wave
radiator, it is minimal. You won't see much improvement in performance
by going above .05 wave length.. it's not worth the trouble to increase
the counterpoise length.. Fred
On 12/29/16 9:01 AM, mjisted wrote:
Looking at your text message on the elecraft board. About a half wave
length ...here is a question for you. I'm going to put up a half
wavelength of wire for the 5 mhz band. ..hyendfed can I use a quarter
wave length of counter point as a radiator ground plane. ..
The. ..G0MVP.
[email protected]
Sent from Samsung Mobile
-------- Original message --------
From: Fred Moore
Date:29/12/2016 13:04 (GMT+00:00)
To: [email protected]
Subject: Re: [Elecraft] Small QRP antenna
Don,
Thank you very much, for pointing out a very common issue that gets
mixed up into discussions. Your point is so valid the random wire
always seems to get mixed into the 1/2 wave discussion for some
reason.. and should never be mixed together. you are absolutely
correct.. thanks again regards.. Fred
On 12/29/16 12:33 AM, Don Wilhelm wrote:
Scott,
If the radiator is not a half wave long, it is not a "half wave".
Yes, a random length wire may work, but please do not call a random
length a half wave - the length of a half wave is quite specific.
Similarly, a quarter wavelength is a specific length at a particular
frequency.
73,
Don W3FPR
On 12/28/2016 11:20 PM, K9MA wrote:
The counterpoise for an end fed half wave (or multiple) really doesn't
have to be anywhere near a quarter wave long.
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