[Antennas] Simple Question

Wed Nov 8 16:36:29 EST 2006

C Whitaker wrote:
> de WB2CPN
>> Since no comments have been made, here goes:
>> RG-58 is lossy at that frequency, so keep the run
> short unless you can get a better coax. The length
> your 1/2 wave balun must be calculated to include
> the Velocity of the coax it made of. Try .66 for
> starters, but it's in the book, as someone is going

Sorry, I forgot to mention in my reply that I based my measurements on a 
Velocity Factor of 0.66 for the balun.
> to tell you. You didn't say if the half of the dipole
> that you removed was the half fed direct, or the
> half fed via the balun. 

Either. It doesn't seem to matter.
> Also, be aware that the
> bandwidth of your setup is going to be very narrow,
> so tune around and see if you find a freq that works
> better. 

What's interesting here is that there are two transmitters I'm trying to 
pick up. Both located within a few metres of each other, both vertically 
polarised and using the same transmitter power. One is the ATIS on 
129.7MHz (continuous voice transmission, which makes a great test 
pattern) and one is the tower on 120.6MHz. I can get a strong signal on 
the ATIS, but the tower is complete rubbish inside. You'd tend to assume 
that is due to narrow bandwidth, but the VOR which is located about 2KM 
from the TX site on 113.4MHz also comes through at a reasonable strength 
in certain locations inside.
> And, "inside the house" has
> to consider the way the house is built. Metal and
> stone, or thin wood. Is the transmitter on the
> same side of the house as where the antenna is
> hung? Questions, yes, but there are the things
> budding antenna engineers have to think about.
> Let us know how you make out.

I do appreciate the need for detail in any kind of scientific situation.
The house is brick, presumably reinforced with metal inside. The 
transmitter isn't on the same side. There is one room to get through 
before going outside in a straight line to the transmitter. I've been up 
in the attic for a few tests, but the signal up there is virtually 
non-existent.
It seems there are two sets of antenna rules affecting me. The set that 
applies outside are all the conventional rules. If i remove one dipole 
element, the signal worsens, directional antennas behave in a 
directional manner, and in general, everything you read about antenna 
design works out there. The rule set that applies inside seems to bear 
no resemblance to traditional antenna theory. Single-sided dipoles 
behave better than whole ones and directional antennas make little or no 
difference. I'm not suggesting the laws of physics don't apply inside my 
house. Clearly there is some something strange happening to the RF 
signal which is causing things to be the way they are. I'm just trying 
to tap into what it is so I can let it work for me.
Richard