[KL7AA] balanced terminated folded dipoles

[Jim Movius]

Greetings,

The folded dipoles such as the ones described in the links and the B&W 
commercial version are OK as receiving antennas because most receivers have 
so much gain and produce very low level internal noise that the losses in 
the resistor do not impair receiving.  The undesired external noise is 
attenuated the same amount as the desired received signal, so received 
signal to noise ratio is unaffected by the terminating resistor.

Transmitted signal is another matter.  For instance, at a height of 50' over 
soil conditions typical here in the interior, at a frequency of 3.9 MHz, 
EZNEC PRO calculates that the antenna gain for the terminated dipole 
is -5.12 dBi, down 10 dB from a G5RV at + 4.96 dBi, a slightly longer 
antenna at 102 feet.  What this means that 10 watts to the G5RV will radiate 
the same signal as 100 watts to the terminated folded dipole, 100 watts to 
the G5RV will radiate the same signal as 1000 watts to the terminated 
dipole, etc.  Loss of 90% of the transmitted power in a resistor (read dummy 
load) may be acceptable for military applications where a broad band, no 
antenna tuner required, easy to use in tactical situations antenna is 
preferred.

My view is that as a receiving antenna the terminated dipole is fine, but as 
a transmitting antenna it is not advisable.

73,

Jim, KL7JM

----- Original Message ----- 
From: "John Lynn" <johnlynn at gci.net>
To: "Robert AL2B Rowley" <al2b at alaska.net>
Cc: "Pierre Loncle" <ploncle at mtaonline.net>; <nl7sk at gci.net>; "'KL7AA Mail 
list'" <kl7aa at mailman.qth.net>
Sent: Thursday, October 01, 2009 9:38 PM
Subject: [KL7AA] balanced terminated folded dipoles


> Robert
> As promised, here are a couple of links you may find interesting about
> terminated folded dipoles.  I have had a commercial one up temporary in 
> the
> back yard and it works well.
>
> http://www.buxcomm.com/catalog/index.php?main_page=page&id=5
>
> http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fd.html
>
>
> John Lynn
> 7013 Trafford Avenue
> Anchorage, Alaska 99504
> Telephone 907-337-1091
> Facsimile 907-338-4791
> Email johnlynn at gci.net
> or KL7CY at arrl.net
> gridsquare BP51df
> 61-13-18N 149-45-00W
>
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