[mythtv-users] Antenna and signal strength

[Brian Wood]

On Feb 19, 2006, at 11:31 AM, Yan Seiner wrote:

> Brian Wood wrote:
>
>> On Feb 19, 2006, at 7:41 AM, Yan Seiner wrote:
>>
>>
>>
>> You don't mention if you are trying to receive ntsc or atsc signals.
>> If the latter azap will show you the Bit Error Rate, which is more or
>> less directly related to the signal strength. I'm not aware of a
>> utility to measure analog signal level, but if all your signals are
>> coming form the same transmit site the aiming would be the same for
>> all of them.
>>
>>
>>
>>
> Yes.  the leg that's giving me trouble is RG-59U.  The other leg  
> (on the
> other side of the splitter) is run in brand-new RG-6 and it has  
> markedly
> better reception.

RG-6 is a 72-75 ohm coax cable that has less loss than RG-59. Most  
CATV systems have gone to RG-6 since their high-end frequencies are  
getting so high (a length of cable that has 10db. loss at 50Mhz. will  
have 20db. loss at 220Mhz, and it gets worse from there up.

<Trivia>

Incidently, in case you're interested, "RG" stands for "Radio,  
Government", as it was the govt. that came up with the initial  
standards (British govt. I believe). 52 ohms is the base impedance of  
a quarter-wave vertical antenna, and 72 ohms is the center impedance  
of a half-wave dipole. For arcane mathematical reasons 52 ohms is  
better for RF power transmission and 72-ohms for least-loss signal  
transmission.

</Trivia>

>
>> You describe the antenna as a "yagi". I hope it is a modified yagi
>> design known as a "log-periodic". A true yagi has a very narrow
>> frequency range and is normally designed for a single channel, while
>> the log is a wide-band design intended to receive the entire VHF or
>> UHF band.
>>
>>
>
> It's one of those directional Yagi look-alikes:
>
> http://www.kyes.com/antenna/antennatypes/uhfcorneryagi.gif

A combination corner reflector/log-periodic yagi design, very common  
for UHF antennas.
>
>
>> Also, if this is a VHF-only antenna and you are trying to receive UHF
>> stations it may not work all that well. UHF stations are very
>> susceptible to multi-path and blockage so the mere fact that the
>> transmitters are close is no guarantee of good reception. NYC was one
>> of the earliest CATV markets due to poor reception even though 99% of
>> residents lived within 5 miles of the transmitters.
>>
>>
> The other way around, it's a UHF only antenna.  This could have
> something to do with the fact that I can't receive channel 7 at all,
> although it's local.

It would be a very poor antenna indeed at 175Mhz. (Ch. 7 is 174-180).  
It would function basically on the "put up some metal" principle.

>
>> Your use of the terms "RG-58" and "yagi" lead me to believe you may
>> be a ham ???
>>
>>
> No, not really.  I know enough about broadcast to be truly  
> ignorant.  I
> am somewhat better aquainted with wireless networking, thus I know  
> Yagi
> quite well.
>
I thought that high-tech in the WiFi world was a Pringles can ??


>> Lastly, remember the adage "You get what you pay for" :-)
>>
>>
> Well, I know.  But my SO (*S*he who must be *O*beyed) blew the  
> budget on
> the TV and didn't think about all the other stuff needed to make it
> happen.  So we're trying to do this on the cheap.  Eventually I'll  
> have
> to spend some $$$ on a Winegard and a nice amp to split the signal....
> But for now, it's being done on the cheap, with a castaway antenna and
> some $3 passive splitters.
>

I can certainly relate to that. In urban-grade contours you have to  
be careful of overloading amplifiers though.