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Measurements of Commercial transmitters causing QRM to ham bands.



Hello from Chris NN0V in Hiawatha, Iowa.
I have been reading the Amsat mail list for a year or two and find much
of it quite interesting. So here's some stuff I wanted to bounce off
you guys -lucky those of you that live in the rural areas. Thats where 
I'm moving next.

How many of you live near town and get QRM from cell and pager?
It's terrible here. 

On VHF its mainly the 158.7 and 163.25.
Weak signals seem mixed with computer whines on numerous frequencies.
The unlucky will have images right on top of satellite downlinks.
On UHF  either cell band A and B mix with each other and with 929-932
high power pagers.
PCS towers are putting 1 meg wide spread spectrum in downconverters for S band.

Some of the 435-437 downlinks are wiped out by water telemetry and repeaters in
the 458-460 band at an image frequency. I think one of them is right on
top of the AO27 downlink.

Every time I go by a cell tower the noise is so strong it either squelches
my radios out or covers the desired signal with a mix of paging and cell calls.
So much for weak signal work around here. Yeah I know filter them out
-kind of hard to do without some heavy mods to portables. The filter would
be bigger than the radio. Also it defeats the ability to tune to different
bands easily. Its just that I dont think they need such strong signals
and that they could be adjusted to much lower levels especially in the
hot zones under these towers. Remember the paranoia about RF radiation
causing cancer? Time to bring that up again, what about the people in
that 1/2 mile zone under these cell towers? Time to get ahold of the
zoning board. Oh well I guess I'm not too afraid of that.

Recently an article appeared in our newspaper how pagers, cellphones
and the upcoming iridium as well as ATC from airports is beginning
to interfere with the radio telescops used by the NRO.
One of the 82' telescopes is 15 miles south of here in North Liberty, Iowa.
It recieves all the radiotelescope bands from 300 MHz up to millimeter wave.
They ask us 'What if you are on your cellphone and we miss the real long
distance call from the galaxy because of the interference? The racket from
cellular telephones and pagers is making it hard for powerful radio telescopes to explore outer space -AP 3/4/98.

That got me to thinking how much pager and cell junk I have desensing and
mixing in my recievers here -Just how strong are these things?
I set up a 900 MHz 1/4 wave mag mount  and put it on the roof of a van.
I went around town with a spectrum analyzer and found cell towers and pagers
runing -10 to -30 dbm in the zones 0.25 to 0.75 miles from their towers.
This seems to drop to -40 line of sight at 1 mile and -50 in dips.
Unless cellphones are really junky that looks like 50-60 db s/n to me.
The pagers were as much as -5dbm within a mile of their towers.
The new 929-932 band has some pagers licensed for 3.5KW in this area.
Remember how in amateur radio we are supposed to use the minimum power needed
to communicate? Well these radio operators just turned it all the way up
and left it there. Oh yeah they have a licence to do so but I question
this is of any benefit to them and a detrement to anyone else.
I called the engineer up on B system here and asked him to think long and
hard about what they are doing here. I use the 902-928 band for links
and its rendered that band very junky. I've had to add bandpass filters 
to the older radios and I cant really do that to portables.
I've had to pump the power up on transmitters.

I found out that there are power controlled base stations available
that they could use (turns the 100 watts erp down for a phone that is 
running close to the tower) which would help alot if they would put it in.
The cell engineer seemed cooperative and said he would call headquarters
about it. Motorola does provide this option. 
Also they can change antenna types and just plain old turn it down.
I dont see the sense in running 100 watts if the portable phones are running
0.6 watts.


I think the FCC should add field strength limitations effective for
FM broadcast, Cell and pagers. The way the installations are put in 
around here, they just do whatever they want and now we have these 
zones of interference around every one of the cell and pager towers.
--------
If you have the same problem be sure and let me know
direct email not through this list server.
The cell engineer was asking me who else did I know with this same problem.
I could use your help and help you with what ever info that can be exchanged. 
Complaints just hit delete; sorry; I got a pretty thick skin after being
on the internet for a couple of years.

If this note goes over poorly here perhaps I'll try
in rec.radio.scanner too.

-Chris in Iowa -uses mainly Mir packet, and used to use RS satellites,
shuttle sarex when its up, and mode A satellite. 
I also have a 9 foot dish on S band recieve, have picked up Dove OK on it.




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