[Antennas] Mini Yagis using Coax

Thu Nov 2 02:35:01 EST 2006

Hi all
Some of you might recall my posts not too long ago enquiring about the 
ideal antenna to use to pick up my local airport control tower on VHF. I 
settled on a simple dipole which I've had mounted inside in one of the 
'hot spots' in my study. The reception is weak but very readable at 
best, although on a bad day things do decline quite a bit. I opted for a 
dipole over a discone because of the horizontal gain. Discones are 
generally recommended for aviation use because they are omnidirectional, 
but all the stations I'd be tuning in the overhead position would be no 
more than about 9km away, and with only my roof between them and the 
antenna, it seemed wasteful to go for a true omni.
The indoor dipole is not ideal, and if I were to mount it outside it 
would certainly outperform any indoor antenna of equivalent quality. 
However, circumstances at the moment make an indoor antenna a much more 
feasible option than an outdoor, so I'm trying to improve on it. I've 
read a few articles, in particular this one 
http://www.hamuniverse.com/K4mmg2and6meter.html mentioning that you can 
take advantage of the low velocity factor of certain types of coax to 
build an antenna with shorter elements than you'd normally require. Has 
anyone done this with success?
I'd like to try a 3-element Yagi done this way, but thought I'd see if 
anyone has any experience with shortened Yagis.
Regards
Richard