> Likewise, a HIGH-PASS filter cutting off just
> below channel 7 (174 MHz) will be the ideal situation. This would also
> reject two meter ham signals. I don't know if such filters are readily
> available in the marketplace.
Excellent suggestion, Jim. Microwave Filters, Inc. produces such a filter
with a HPF function and can be ordered with a knee at the lower edge of Ch.
7. Their model 3378 would work well between the antenna and DTV receiver --
or between antenna and a mast-head preamp.
http://www.microwavefilter.com/lowhighpass.htm
Wingard makes a reasonably good preamp with DTV in mind
http://www.winegard.com/kbase/upload/WC-809%20_HDP-269.pdf
> "Non-linearity will be a potential problem in digital TV preamps. If
you are out in the weak-signal sticks, overload and non-linear response
aren't as likely to be a problem, but in areas close to the transmitters it
could be. You can have too much of a good thing with digital TV."
Agreed. I ended up removing my preamp from a small mast-mounted bat-wing
antenna where the DTV stations are 10 miles away. I would first attempt
signal capture without the preamp, and only add it if one or more stations
cannot be decoded. Many DTV sets have built-in signal strength meters. Not
that they are lab-quality instruments by any means, but they do a good job
of letting you know if the received signal level is within an acceptable
signal-strength window.
Also, in my case, the stations I am trying to decode are not all in the same
geographic area. Accordingly, one may find that a compromise must be struck
when aligning a directional antenna . I ended up pointing the antenna
mid-way between two antenna farms. In the analog world, that probably would
have resulted in visual problems, but the industry is now on 6th-generation
8-VSB chip-sets and they do a remarkable job of decoding, even in the
presence multipath and low signal strength.
Paul, W9AC
----- Original Message -----
From: <Jimk8mr@aol.com>
To: <rfi@contesting.com>
Sent: Wednesday, June 03, 2009 11:28 PM
Subject: Re: [RFI] Mast-mount TV Pre-Amp -- Avoiding RFI & Overload?
> Two things to consider:
>
> 1. After the digital transition next week, there will be very few
> stations left on channels 2-6. If there are none on these channels in your
> area,
> you can get by with a smaller antenna (element length), which will reduce
> pickup at HF and 6 meters. Likewise, a HIGH-PASS filter cutting off
> just
> below channel 7 (174 MHz) will be the ideal situation. This would also
> reject two meter ham signals. I don't know if such filters are readily
> available in the marketplace.
>
> 2. Non-linearity will be a potential problem in digital TV preamps. If
> you are out in the weak-signal sticks, overload and non-linear response
> aren't as likely to be a problem, but in areas close to the transmitters
> it
> could be. You can have too much of a good thing with digital TV.
>
>
> 73 - Jim K8MR
>
>
>
>
>
>
> In a message dated 6/3/2009 11:15:18 P.M. Eastern Daylight Time,
> doc@kd4e.com writes:
>
> Actually, a digital signal is either real good or it is real
> gone.
>
> Here in the fringe area we need help to get the signal strength
> we need for a consistent signal lock.
>
> If I could find a mast-mount pre-amp which includes
> bandpass and low-pass filters, to keep non-TV signals
> out, then it should do a good job.
>
>
>> WA3GIN wrote:
>> THEY ARE ALL JUNK
>> WITH DIGITAL YOU MAY NOT NEED A PREAMP
>
>
>
>
> **************We found the real ‘Hotel California’ and the ‘Seinfeld’
> diner. What will you find? Explore WhereItsAt.com.
> (http://www.whereitsat.com/#/music/all-spots/355/47.796964/-66.374711/2/Youve-Found-Where-Its-At?ncid=eml
> cntnew00000007)
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