OK, the cutover to HDTV is coming up, and I want to have a good antenna
on the roof long before February, so I'm in need of advice. I'm using a
converter box to feed my current TV set, but rabbit ears don't work well
at all.

I know I need a rooftop antenna, but the available commercial literature
is more hype than help. I'm hoping that someone out there has expertise
on the new antennas being offered for HDTV.

I know this depends a lot on what the signal strengths are at my QTH,
but assuming that all-other-things-are-equal:

* Are flat-panel units worth the price?
* Can I get by with an old VHF-UHF combination antenna?
* What's the tradeoff between feedline length and antenna gain?
* Do masthead preamps perform well, and is the cost and maintenance
worth it?

73,

Bill W1AC

--
Bill Horne

(Remove QRM from my address for direct replies.)

On Mon, 29 Sep 2008 21:57:20 -0400, Bill Horne wrote:

OK, the cutover to HDTV is coming up, and I want to have a good antenna

on the roof long before February, so I'm in need of advice. I'm using a

converter box to feed my current TV set, but rabbit ears don't work wel
l
at all.

I know I need a rooftop antenna, but the available commercial literatur
e
is more hype than help. I'm hoping that someone out there has expertise

on the new antennas being offered for HDTV.

I know this depends a lot on what the signal strengths are at my QTH,
but assuming that all-other-things-are-equal:

* Are flat-panel units worth the price?
* Can I get by with an old VHF-UHF combination antenna?
* What's the tradeoff between feedline length and antenna gain?
* Do masthead preamps perform well, and is the cost and maintenance
worth it?

What market are you in, and how far are you from the local towers?

I would suggest you can get away with an old combination antenna if it's
still in decent shape. You may want to think about replacing the
feedline, it ages less gracefully than the antenna...

My personal experience has been that masthead preamps are pretty reliable
..
However, I'd be slow to use one unless you're in a fringe area. They ca
n
easily overload and make reception *worse*.

In article ,
Bill Horne wrote:

I know I need a rooftop antenna, but the available commercial literature
is more hype than help. I'm hoping that someone out there has expertise
on the new antennas being offered for HDTV.

I know this depends a lot on what the signal strengths are at my QTH,

..... and on whether the channels in your area are all going to be on
UHF, or whether there are some which will still be on VHF high-band,
or even one or more on VHF low-band.

but assuming that all-other-things-are-equal:

* Are flat-panel units worth the price?

As to price I can't say (although there's an open-source design or two
floating around which can be home-fabricated).

Flat-panel designs (bowtie-and-reflector, usually, I think) are
probably decent solutions for UHF-only areas. I don't expect that
their performance on VHF is terribly good, unless they're very large.

* Can I get by with an old VHF-UHF combination antenna?

If you've got a decent ghost-free picture on NTSC with a combo
antenna, chances are probably fairly good that it'll work well enough
for ATSC digital.

If all of your ATSC stations are going to be UHF, you might get better
results with a multi-bay UHF-only antenna... the combo antennas don't
always have a very clean pattern (good front-to-back ratio)

* What's the tradeoff between feedline length and antenna gain?

Well, a longer feedline leads to greater losses, and if your signal is
already at the lower limit of what's acceptable then you'll need to
make up the lack somehow else... higher antenna gain, or a preamp, or
increasing the signal "seen" by the antenna.

There's a definite tradeoff between feedline length and antenna
*height* - raising the antenna will increase the feedline length (and
losses), but may give the antenna a better "view" of the transmitter
antenna and thus a stronger/cleaner signal.

If you're a good distance from the transmitter (more than a few
miles), raising the antenna is often a very good tradeoff...
if you don't, the transmitter antenna may be below the horizon (from
your antenna's point of view) and you'll be depended on diffracted
signal rather than line-of-sight signal. An extra 10' of antenna
height may increase the signal into the antenna by quite a bit more
than the amount you'll lose in 10' of feedline.

* Do masthead preamps perform well,

A lot of cheaper preamp designs are prone to overload if there's a
strong signal nearby (e.g. fire, police, ham radio), and this is
Ungood. Some are prone to instability - they can start oscillating
without warning - and this is Really Ungood.

and is the cost and maintenance
worth it?

That depends very much on your situation.

If many of the stations you're receiving are quite distant, and if you
need a long feedline, and if you've already got a good antenna, and if
you buy a high-quality masthead preamp which is resistant to
strong-signal overload, and if there are no nearby strong-signal
transmitters, then such a preamp may well be worthwhile.

I tend to think that preamps are a decent way to compensate for losses
in the feedline. Unless they're quite good, though (low noise figure
and high overload resistance) they're not a good substitute for
getting enough of a clean signal *into* the antenna - positioning the
antenna better/higher, and using an antenna with more directional gain
are better bets. Remember, a masthead preamp will amplify ambient RF
noise, and multipath reflections just as much as it'll amplify the
desired input signal!

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Fix up your analog signal now and lock it in. If the HD station is up to
par with their analog, you are ready to go. Have you picked up a box yet?

If your current system is more than 5 years old you might have to replace it
all anyway due to deterioration. Use the good coax too. Pay attention to
the db loss fugures at 900 Mhz. Lower is better.

Bill Horne wrote:

* Can I get by with an old VHF-UHF combination antenna?

My advice would be to try it and see. You'll know right away, as
digital reception tends to be pretty much "all or nothing". I had no
problem with my existing antenna when converting to the new signals.

If it ain't broke, don't fix it.

If it is broke, then do a little research to determine what frequencies
you're interested in (VHF, UHF, or both) and how far you are from the
transmitting locations. There are web sites that will help with that.
Given that information, you'll be in a better position to figure out
what you need.

73, Steve KB9X