[BC] Isotron AM Antennas

[Cowboy]

On Thursday 19 February 2009 08:57 pm, wmroradio at bellsouth.net wrote:
>  I've been reading up on the Isotron Antenna's that are tuned to the AM 
>  Commerical Band.  

>   For the money (if this works, like they say) would this be a good 
>   "stand-by" antenna for a 1 KW AM daytime station if your main tower went 
>   down?   

 I like the description "elevated dummy load" as being fairly accurate.

 For the money, it's terrible.
 For free, it's not terribly worse than other free options.
 ( but *is* worse )

 This is based on the very old logic that *if* you can couple 1kW into
 a 2 inch dipole on AM, how much power is radiated ?
 Answer: All of it !

 The trick is coupling power into that 2 inch dipole.
 This "antenna" attempts to do that, by making part of the
 coupling network, that coil and plates, part of the antenna, in which case
 the answer becomes "all of it, minus that in circuit losses" which in the
 case of the isotron is most of it.

 I once built a 150 kHz beacon antenna out of a 6 foot coil of litz wire
 top loaded, over a 600 foot radial system.
 That worked fairly well, or somewhat better than expected as far as
 radiation efficiency. As far as bandwidth, it was almost zero.

 SO, probably the isotron can radiate your carrier "fairly well" as long
 as you don't try to modulate it at all.
 Assuming, of course, that you accept 100 watts radiated, and 900 watts
 dissipated as heat, as being "fairly well."

-- 
Cowboy