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'[ot]: static on a 900 mhz'
2001\06\18@212141 by rad0

picon face
hello,

well this has me baffled...

I have one of those 900 mhz wireless tv transmitter/receiver systems
for putting a tv in the next room without wiring up an antenna, it
duplicates what is on a satelite system and send it to the tv in another
room.


well, it has worked fine except for intermittant interferrance from time to
time
that usually only lasted for a few seconds to a minute or two...

now this type of static has persisted for over a day now

what's going on here?   Am I being jammed by a neighbor with a
microwave oven?  or is it just an unusual electrical storm or condition??

thanks

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2001\06\18@215114 by William Shultz

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face
Hello

Some years back I ran into a similar problem with a similar product. It was
in a commercial building and they were transmitting video from a remote
camera. About 4 times an hour, static would appear on the picture, this
lasted about 2 or 3 seconds then disappeared. We tracked it down using an
old AM radio because it was so susceptible to interference. After an
afternoon of searching we found an air compressor in the basement that was
used for pneumatic HVAC controls. As the pressure switch began to call for
the compressor to run it would chatter, causing all types of RF
interference. You may try this same method of detection but first I would
start eliminating other electronic equipment in the area , unplugging them
one at a time.

Bill N8HKI
{Original Message removed}

2001\06\18@220413 by David VanHorn

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face
At 08:19 PM 6/18/01 -0500, rad0 wrote:
>hello,
>
>well this has me baffled...
>
>I have one of those 900 mhz wireless tv transmitter/receiver systems
>for putting a tv in the next room without wiring up an antenna, it
>duplicates what is on a satelite system and send it to the tv in another
>room.
>
>
>well, it has worked fine except for intermittant interferrance from time to
>time that usually only lasted for a few seconds to a minute or two...
>
>now this type of static has persisted for over a day now
>
>what's going on here?   Am I being jammed by a neighbor with a
>microwave oven?  or is it just an unusual electrical storm or condition??

Microwave ovens run at 2.4 GHz, but then again, so do many of the video
senders.
Does yours have square "paddle" looking antennas? If so, it's 2.4G.

If you're on the 900 meg band, it could be any number of things, from
another part 15 device, to a ham (like me) who runs video at anywhere from
several watts to 1500 watts.  I only run 60W myself.   There are also
industrial and scientific and medical (hence "ISM" band designation) that
uses these frequencies, and they can be pretty large emitters when they are
operating.

The part 15 rules are pretty clear on your options here:
http://www.lwca.org/sitepage/part15/part15_s.txt

You can move or re-orient your antennas, and you can modify the antenna on
the receiver to be more directional, and/or reduce receiver gain. You can't
modify the transmitter or it's antenna in any way.

Another possibility is that your device itself is intermittently defective.

Seriously, I'm not sure what the legal implications are, but I see no
literal problem in say, mounting the unmodified transmitter with it's
unmodified antenna, at the focus of a dish.. It does seem to part company
with the spirit of the law, but it seems in compliance with the word of the
law.. IANAL, YMMV, get a ham licence and play with the big boys :) You get
1500W and gain antennas on both ends.





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2001\06\18@225546 by rad0

picon face
Alright, I must be wrong here...This thing has little square paddles for
antenna...and it is interferred with when I run my microwave...

so it must be this 2.4 ghz, eh?


> Microwave ovens run at 2.4 GHz, but then again, so do many of the video
> senders.
> Does yours have square "paddle" looking antennas? If so, it's 2.4G.
>
> If you're on the 900 meg band, it could be any number of things, from
> another part 15 device, to a ham (like me) who runs video at anywhere from
> several watts to 1500 watts.  I only run 60W myself.   There are also
> industrial and scientific and medical (hence "ISM" band designation) that
> uses these frequencies, and they can be pretty large emitters when they
are
> operating.
>
> The part 15 rules are pretty clear on your options here:
> http://www.lwca.org/sitepage/part15/part15_s.txt
>
> You can move or re-orient your antennas, and you can modify the antenna on
> the receiver to be more directional, and/or reduce receiver gain. You
can't
> modify the transmitter or it's antenna in any way.
>
> Another possibility is that your device itself is intermittently
defective.
>
> Seriously, I'm not sure what the legal implications are, but I see no
> literal problem in say, mounting the unmodified transmitter with it's
> unmodified antenna, at the focus of a dish.. It does seem to part company
> with the spirit of the law, but it seems in compliance with the word of
the
> law.. IANAL, YMMV, get a ham licence and play with the big boys :) You get
> 1500W and gain antennas on both ends.
>
I want something with a lawnmower engine on it !!!

seriously, I'll try the am radio detector method...

I'm guessing this is someone's airconditioner maybe,

the weather couldn't do this could it??

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2001\06\18@231034 by David VanHorn

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At 09:54 PM 6/18/01 -0500, rad0 wrote:
>Alright, I must be wrong here...This thing has little square paddles for
>antenna...and it is interferred with when I run my microwave...
>
>so it must be this 2.4 ghz, eh?

Yes.
They may make some at 5-6G as well, but I've never seen one.

>I want something with a lawnmower engine on it !!!
>seriously, I'll try the am radio detector method...

Unlikely to get results. Few broadband sources like ignition or arcing put
out much energy at 2.4G.
Much more likely, a newer cordless phone.

>I'm guessing this is someone's airconditioner maybe,

Not likely

>the weather couldn't do this could it??

Tropo ducting happens at 2.4G, in fact the biggest contest in ham radio is
coming up soon, and there will be a lot of activity on every ham band there
is.

However, this is another very unlikely candidate. Such signals are usually
weak.


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2001\06\18@235825 by Dale Botkin

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On Mon, 18 Jun 2001, David VanHorn wrote:

> Seriously, I'm not sure what the legal implications are, but I see no
> literal problem in say, mounting the unmodified transmitter with it's
> unmodified antenna, at the focus of a dish.. It does seem to part company
> with the spirit of the law, but it seems in compliance with the word of the
> law.. IANAL, YMMV, get a ham licence and play with the big boys :) You get
> 1500W and gain antennas on both ends.

...but lose the ability to send pretty much anything on TV over the link
without violating FCC regs.

Now, the question remains...  is this a problem, or a solution?  8-)

Dale
--
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On my desk I have a workstation...

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2001\06\19@005739 by David VanHorn

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At 11:01 PM 6/18/01 -0500, Dale Botkin wrote:
>On Mon, 18 Jun 2001, David VanHorn wrote:
>
> > Seriously, I'm not sure what the legal implications are, but I see no
> > literal problem in say, mounting the unmodified transmitter with it's
> > unmodified antenna, at the focus of a dish.. It does seem to part company
> > with the spirit of the law, but it seems in compliance with the word of the
> > law.. IANAL, YMMV, get a ham licence and play with the big boys :) You get
> > 1500W and gain antennas on both ends.
>
>...but lose the ability to send pretty much anything on TV over the link
>without violating FCC regs.
>
>Now, the question remains...  is this a problem, or a solution?  8-)

Depends on your point of view..
:)

I have one of these, constantly sending vid to a TV in the bedroom.
When I leave the office, I put the cable box on the local wx radar.
If I get a wake up call, then I snap on the TV and catch a weather update
while I get dressed.

I'm pretty sure the feds would consider the dish trick a violation, but I'm
not sure a court would agree with them.
It would be legal, for example, to put the device anywhere on your desk,
including that point where the foil insulation panels in the walls create a
corner reflector.. Now, have you modified the device?  No.... :)
What about putting it inside air conditioning ducts, that might be large
enough to function as waveguides at 2.4G?

I do wonder though, why these guys always want to modify the transmitter
for more power when often (especially in this case) making the receiver
more DEAF would probably be a better solution.   You can always do anything
you like to the receive side!


--
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I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here
in my signature line, but due to the inability of sysadmins at TELOCITY to
differentiate a signature line from the text of an email, I am forbidden to
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2001\06\19@013332 by rad0

picon face
> I do wonder though, why these guys always want to modify the transmitter
> for more power when often (especially in this case) making the receiver
> more DEAF would probably be a better solution.   You can always do
anything
> you like to the receive side!
>

I'm want to try to make the receiver paddle receive less....

I've tried wrapping aluminum foil around it, that didn't seem
to have any effect,

how could I make a screen that only lets the antenna receive
from the direction where the transmitter is placed??

what I think I need is to block everything from all directions
except this one direction where the transmx is sitting...

thanks

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2001\06\19@014056 by David VanHorn

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>
>I've tried wrapping aluminum foil around it, that didn't seem
>to have any effect,
>
>how could I make a screen that only lets the antenna receive
>from the direction where the transmitter is placed??
>
>what I think I need is to block everything from all directions
>except this one direction where the transmx is sitting...

Exactly.

The antenna in the paddle is a patch.
One way to do it, would be to mod the circuit in the receiver, and add
attenuation, say 6-10dB, and try that.
It will be more critical of aiming, but may take out the interference.

There are loop yagi designs on the web that will help make it more
directional.


--
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I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here
in my signature line, but due to the inability of sysadmins at TELOCITY to
differentiate a signature line from the text of an email, I am forbidden to
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2001\06\19@045921 by Alan B. Pearce

face picon face
>what's going on here?   Am I being jammed by a neighbor with a
>microwave oven?  or is it just an unusual electrical storm or condition??

perhaps your neighbour has bought a similar system and is wondering why his
has static from yours?

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2001\06\19@102444 by michael brown

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> I do wonder though, why these guys always want to modify the transmitter
> for more power when often (especially in this case) making the receiver
> more DEAF would probably be a better solution.   You can always do
anything
> you like to the receive side!

This is the key difference between ham radio and commercial radio theory.
Hams use low power, good antennas and sensitive receivers.  Commercial
theory says "pump up the power" to overcome the poor antennas and crummy
receivers. <grin>

michael
>
> --
> Dave's Engineering Page: http://www.dvanhorn.org

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2001\06\20@170159 by Peter L. Peres

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> attenuator

BTW you can roll your own attenuator by spraying colloidal graphite spray
on a piece of semigloss cardboard of suitable size. This can be pasted
directly on top of the indoor antenna. A 4B graphite pencil may also do
the trick. Its effect will be small wrt. the graphite cardboard. ;-)

Peter

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2001\06\20@170222 by Peter L. Peres

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> how to make (more) directional receiver

As Dave van Horn has said, you can make a 90 degree corner reflector using
kitchen aluminium foil spanned on two rectangular frames. However, the
paddle is roughly equivalent with several dipoles in a flat (zero) phased
array. Therefore using a medium size serving tray (metal) placed on the
side away from the transmitter of the paddle, and parallel to it, at down
to 2.5cm (lambda at 2.4 GHz is about 10 cm), may bring results. You can
later duplicate this using kitchen aluminium foil and a cheap picture
frame or cardboard box wall. The distance and angle of the reflector will
be critical.

Has anybody got problems with insulating foil in the walls insulating
rooms from each other at 900 MHz and 2.4GHz ? I don't know much about
this, I have always lived in masonry or wooden structures, and so do all
the clients.

Peter

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