Re: [A/S] Installing Batwing antenna

["Rick Kunath" <k9ao@xxxxxxxxxxx>]

> One basic difference between the two is that the Winegard has an
> amplifier in the head and the Braund's amplifier is in the wall unit.
> Changing antenna's requires changing the wall unit as well. The Winegard
> puts 12V on the coax cable to the antenna and picks the TV signal off
> the same coax. The Braund can be used with the wall amplifier on or off
> depending on signal strength. The Winegard must be turned on to get much
> of anything. Good but different.
> The installation challenge is the Airstream installed 300 ohm flat lead
> antenna wire. It was good stuff in it's day but 75 ohm coax is better.

It's still "good stuff". 

300-ohm Twinlead has vastly lower loss than any flexible affordable coaxial 
cable made. It is still good stuff and useful over long runs to reduce cable 
attenuation. The difference is negligible with the cable run length in a 
trailer. No need to replace the Twinlead in a working installation because of 
a perceived "improvement". Coaxial cables are immune to losses due to running 
within 3 times the Twinlead conductor spacing over conductive surfaces, and 
if the connectors are installed correctly can, but not always, be more immune 
to common-mode noise pickup. A lot here depends on the quality of the 
termination on each end, and in consumer television receivers this isn't 
always all it should be.

> They just don't work together.
> You have two choices. As mentioned you can run wire along the roof and
> down through the refer vent or you can convert using a little in line
> transformer often called a balun, from Radio Shack or the like.
> The roof connection can be done so that it is inside the roof. The
> inside connection would be in the wall behind the wall unit.

This would work, except that the Winegard apparently needs to feed power to 
the antenna mounted preamplifier via the coaxial feedline. You won't be able 
to do this with baluns in line. The trifilar windings inside the VHF balun 
will look like a short to the DC being applied to the lower end of the 
coaxial feeline to the antenna. You'd need to capacitively isolate the upper 
end of the antenna and re-inject the power up there. 

I'd look for a replacement antenna that has no need for a power feed, and 
retain the existing wall mounted preamplifier if it were me. 

Barring that, I'd suggest doing the extra work and replacing the 300-ohm 
Twinlead with 75-ohm double shielded stranded center-conductor coaxial cable. 
(The standard TV stuff with the solid center-conductor and only a foil shield 
won't handle rotating without breaking.) That way you are free to replace the 
wall amplifier and insert the DC feed plate (DC block), sending the power up 
the coaxial cable, as the per the antennas design requirements.

Rick Kunath
WBCCI #3060