Re: [amsat-bb] Re: [bod] Fwd: 70 cm band plan???

["Andrew Bachler" <Andrew_Bachler@xxxxxxxxxxxxx>]

This is actually a very easy problem to solve.  Look at § 97.205 (b).  Any
ATV repeater with a receive input on 434.000 MHz  violates the FCC rules.

Andy  N9AB

----- Original Message -----
From: Arthur H Feller <w4art@AMSAT.Org>
To: <07141939@msn.com>
Cc: <amsat-bb@AMSAT.Org>; <amsat-officers@AMSAT.Org>;
<ldanna@teamvideo.com>; <ldanna@news.teamvideo.com>; <ldanna@home.com>
Sent: Tuesday, December 14, 1999 3:56 AM
Subject: [amsat-bb] Re: [bod] Fwd: 70 cm band plan???


> Hi, Gene!
>
> Robin Haighton, VE3FRH, asked me to take a shot at answering your call for
> help.  Let me see what I can do.
>
> As I understand it, the heart of the problem is summed up in these two
> paragraphs.
>
> > >The second group is proposing a second ATV repeater for 70 cm. They
have
> > >selected a frequency pair which includes a wide-band  TV (fast-scan,
full
> > >color) input frequency at 434.000 MHz. The local ATV activity with a 6
MHz
> > >bandwidth would/could prevent weak signal reception from satellites. I
am in
> > >a turmoil here!!! I've asked the second group to change the input
frequency
> > >with no avail.
> > >
> > >I have heard that "ARRL or the FCC" has indicated a band-plan for 70
cm, but
> > >no one here seems to be paying attention to my thoughts. The second ATV
> > >group is preparing to request "frequency coordination" from "T-MARC"
 the
> > >local repeater coordinator). I have attended the annual T-MARC meeting
today
> > >and they indicated little or no objection to the requested 434.000 MHz
input
> > >frequency. I need some help here to convince all that "a bad choice is
in
> > >the making".
>
> Some thoughts for you.
>
> ARRL does have a suggested band plan which is published in several places
> including the repeater directory, last I checked.  Within this band plan
> are some local options which are considered by the frequency coordinating
> committee.  And, there is the band from 435-438 MHz for the
> amateur-satellite service.
>
> FCC respects local frequency coordinators for repeaters and auxiliary
stations.
>
> However, every amateur radio operator signs away the right to any specific
> frequency as a condition of application.  Sharing is the order of the day.
>
> Now, there are some technical considerations.  First, is the ATV power
> spectrum.  While the total bandwidth of an ATV signal may be on the order
> of 6 MHz, the power spectrum in not uniform.  Most of the energy in common
> vestigial sideband NTSC color tranmissions is concentrated at three
> points.  One is at about 1.25 MHz from the bottom of the 6 MHz "channel"
> for the visual carrier and it's most significant sidebands.  The vast
> majority of the sideband energy is most likely to occur within about +/- 1
> MHz of the visual carrier.  The other two are the color subcarrier at
about
> 3.58 MHz above the visual carrier and the aural (sound) carrier at 4.5 MHz
> above the visual carrier.  What's important here is that, while the power
> from an ATV station in the band 435-438 MHz is not zero, it may be low
> enough to be tolerable.
>
> How can you tell what will be tolerable?  This is a normal exercise in
> checking compatibility.  You'll have to look at your own station with its
> directional antenna, where the antenna is likely to be pointing, and the
> signal you'll be receiving and transmitting.  (Yes, transmitting!  You may
> be a source of interference to the ATV repeater.)  Then, repeat the
> exercise for nearby ATV stations.  (You may have to go a ways to find one
> as they're not all that common even in our neighborhood.)  Keeping in mind
> the power within the bandwidth of your receiver, figure out how the power
> received from the unwanted station will compare to the signal you want to
> receive.
>
> Clearly, if you have an ATV station next door, you're much more likely to
> have a problem.  But, as mentioned, that isn't too likely.
>
> Just run the numbers and see how it comes out.  The ATV repeater folks
> should be doing the same thing as they will have to deal with you as a
> source of interference as well.
>
> Then, there's the time factor.  Neither you nor nearby ATV stations will
or
> should be on the air 100% of the time.  So, there may be more sharing
> opportunities here.
>
> Would it be wiser for the ATV'ers to look to wider bands like 902-928 MHz
> or 1240-1300 MHz or other bands?  Sure.  These bands could stand some
> heavier use to help justify their existence in the minds of those who look
> at such things.  Probably so.  But, do the ATV'ers have to look beyond the
> 420-450 MHz band?  No.  Not at all.
>
> The resolution of this problem is most likely to be by means of mutual
> enlightened self interest.  Both you and the ATV group need to find a way
> to get along.  Technically, that may well be possible.  You'll both have
to
> run the numbers taking into account frequency, power density, receive
> bandwidth, time, space, and other relevant factors.  T-MARC may be able to
> lend a hand.  (I'm sending a copy of this to a friend who is a member.)
>
> This may not be the answer you were seeking.  But, I believe it's
> realistic.  I hope it helps.
>
> 73, art.....
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