[mythtv-users] Antenna and signal strength

Brian Wood beww at beww.org
Sun Feb 19 16:14:00 UTC 2006


On Feb 19, 2006, at 7:41 AM, Yan Seiner wrote:

> I am finally ready to do some recording....  But it seems that my  
> signal
> comes and goes.
>
> Sometimes the channels come in crystal clear, at other times I get
> digital breakup (the image tiles heavily).
>
> Since I live in an urban area with stations in close proximity  
> (most of
> my stations are within 5-8 miles) I suspect that my antenna is the
> culprit.  This is not surprising, since the antenna is a highly
> directional yagi that someone was going to throw away, so I got it for
> free, along with the cable.  The cable is a cheap RG-58U cable that  
> has
> been out in the weather for a while...
>
> I got the mast and the antenna, but not the bracket that attaches the
> antenna to the mast, nor the brackets that attach mast to house.
> Apparently the previous owners just stuck the antenna into the end of
> the mast and pointed it straight at the sky.  As a result, I have this
> thing in the attic, sitting on a roll of insulation, probably not the
> best place for it to be.  I can fab up the bracket and mount the mast,
> but first I want to make sure the antenna is functional....
>
> Is there a utility somewhere that will let me measure signal strength
> from the antenna?
>
> Also, any Yagi antenna experts out there that can tell me how to wire
> this thing correctly?  I'll post some pics later with detailed  
> questions....
>

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.

Your cable is probably RG-59 (75 ohm) and not Rg-58 (50-52 ohm).  
There are some 50-ohm antennas made but they are not designed for  
consumer  or normal TV reception use (not that it's a huge  
difference, especially in an urban-grade signal contour).

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.

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.

Your use of the terms "RG-58" and "yagi" lead me to believe you may  
be a ham ???

Lastly, remember the adage "You get what you pay for" :-)


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