[otadtvman]

Hi ADTech,

Thanks for the reply.

Originally Posted by ADTech

To date, I am unaware of any 7-51 combo antennas that may be on the market.

A Google shopping search does provide results for "7 to 51 antennas". However, I suspect that some of these models may actually be 7 to 69 antennas that are being advertised as "7 to 51".

Originally Posted by ADTech

Please keep in mind that rescaling an existing 14-69 UHF antenna to cover 14-51 more effectively will cause the antenna to grow by about 20% for similar performance. As many legacy UHF designs peak strongly at the high end of the UHF band (700 MHz or more), the re-scaling moves the gain curve lower in the UHF band and the narrowed bandwidth allows for greater efficiencies.

I understand that a yagi will peak strongly at the high end of the UHF band:

01-18-08

Originally Posted by ghostie

But I then go to this page and notice that they don't recommend yagi antenna's because of the cutover:
"Note also that now is not a good time to buy a Yagi antenna. Present Yagi antennas are optimized for channel 69. But beginning on 2/17/09, 51 will be the highest channel, and a new generation of Yagi antennas cut for channel 51 will be the most desirable. For the next few years Yagi buyers must pay close attention to the frequency specs."
- http://www.hdtvprimer.com/ISSUES/erecting_antenna.html

Why is this an issue? Sure, channel 52-69 won't be utilized, but is there anything wrong with a standard channel 2-69 yagi antenna after the cutover?

01-18-08

Originally Posted by HDTVChallenged

In the real world, it's probably not a big issue. If the antenna works ok now, it's not going to suddenly crap out when chs 53-69 go way.

OTOH, a pure UHF yagi is designed so that the are most sensitive at the highest frequency (Ch69 currently), the sensitivity decreases (sometimes dramatically) as the frequency decreases. Most real world "yagi" designs include a rear reflector that helps offset the loss at lower frequencies. A lower tuning frequency will result in less gain "loss" at ch14 and perhaps a slightly better gain at ch51.

Edit:

Why tune to the highest frequency you ask? Because the antenna gain rapidly drops to zero dB or less above the tuning frequency.

However, why does rescaling for 14-51 cause the antenna to become ~20% larger.

Thanks