High Def Forum
Thank you for visiting. This is our website archive. Please visit our main website by clicking the logo above.

OTA/UHF Antenna setup

scrooge39
06-20-2006, 10:03 AM
Recently upgraded TV to a HDTV set. The only antenna I have for OTA is a roof-mounted outside VHF antenna, naturally I am experiencing dropout on the HD channels. There is 300 ohm lead-in (app. 50' in length) from the antenna to a 75 ohm transformer, with the transformer being located at the back of the TV set.
Per antennaweb.org, the HD stations in my area are 12-15 miles away from my house with a 40 degree spread between them.
My plans to try to cure the dropout are as follows:
-Install a CM4221 antenna on same pole as existing antenna.
-Install 300 ohm to 75 ohm transformer at antenna end and use RG-6 coax (app. 50') to an A/B switch
at the TV end. The reason for using an A/B switch is to switch between the VHF and UHF antennas.
I did not want to use a VHF/UHF lead-in "combiner" so as to keep the UHF signal as high as possible.
I will be watching only one VHF HD channel so using the A/B switch won't be an inconvienence as the rest of the HD channels are UHF.

So my question is....will my plans eliminate(or significantly cut down) on the dropout or is there something else I can do?
Any thoughts or comments would be appreciated.

Thanks............Richard

jim5506
06-20-2006, 11:10 AM
I have a UHF yagi reflector (Radio Shack U-75R) that picks up my only VHF digital channel just fine (90-95 signal strength from 3 miles away). You might get lucky and the CM4221 might work for all your stations.

You might look at the CM 4228. It is essentially 2 4221's mounted side by side except if you tie the two reflector grids together it greatly improves the high VHF performance of the UHF antenna (best on channels 10 and 12).

You did not provide your zipcode so I can't look at your channels, but trying to pick up UHF stations on a VHF antenna is a problem.

The 300 ohm lead in is really better for signal transmission than coax, but it is difficult to maintain (frequent replacement required) and it being unshielded (unless you buy the shielded version) it is susceptible to stray RF. JUST a little useless info.

Rick0725
06-20-2006, 07:59 PM
instead of using an a-b switch to combine the uhf and vhf antennas, use a channel master cm 0549 uhf /vhf antenna combiner. They are about $7.50 on line, only .5 db loss, installed at the antenna, and are designed for that purpose.

Even though the towers are less than 20 miles away, I would prefer the cm4228 over the cm4221...even though the cm4221 would be the antenna suggested on paper.

I would also suggest a rotor since it would come in handy in the antenna peaking process...and since you are experiencing drop outs the rotor will help tremendously. using the cm 4221 is a hint that a rotor was not part of the design plan.

http://www.starkelectronic.com/cmjoiner.htm

Also suggest to use rg6 through out the system and use the balum at the antenna instead of runnning 300 ohm cable.