SHEBA: RF_Communications Messages: 6 Entries..

Date: Wed, 15 Oct 1997 17:03:10 -0600
From: Terry Hock 
To: militzer@shebaship.apl.washington.edu
CC: horst@stout.atd.ucar.EDU
Subject: Re: comm questions from John

Hi John,

How's the weather?

> Tom,    Notes  Monday 13-Oct-97, 20:30 AK
> 
> Communication Problems,  Bad News:
> 
>         A: The line-of-sight to station 2's location was behind the
>         main mast from the antenna.  The survey crew apparently had
>         forgotten to check for that.  As a result we began looking for
>         an alternative antenna location on the mast using the 200'
>         cable and spare antenna we brought.  The places we tried
>         performed worse than the CG installation in terms of 'seeing'
>         stations 1&3.  What we really needed was an installation on
>         top of the rear mast as originally planned, but that should
>         have been done in Quebec and is probably not possible now,
>         certainly not with the cable/spare antenna we brought, which
>         is either bad or has too much loss.  The ship is definitely a
>         hostile environment for the low power freewaves.
> 
>         For now:
>         This evening Pierre (ace elec.tech./eng.) and i moved the stub RG213
>         cable he'd built to the main mast as a jumper from the starboard
>         antenna mount to a point higher on the mast he found
>         as an alternative.  This point has better LOS to all 3
>         station locations, but we haven't made it permanent
>         yet.   Also it is behind the radar, which could be a problem
>         when that is operating.   I don't know how much power/freq. it
>         operates on and whether that might bomb the freewave when it
>         is turned on.   We might be able to move our antenna behind
>         the mast from the radar though.  Anyway, I have seen data
>         coming in from all 4 sleds which is encouraging, and am able
>         to do console operations with each.   Admittedly it is quite
>         'rough' with sta-3 and many characters are dropped.   Sending
>         big blocks of data is more robust.
> 
>         One worry is when breakup begins.   For now, the 3 site are
>         probably 'fixed', but with breakup there's a chance that the
>         station(s) could move outside the antenna look angle although
>         the new location is about as good as we can get on the main mast.
> 
>         To consider:
> 
>         Possibly a crossed yaggi arrangement using a splitter to hit
>         the major quadrants around the mast.  This could be either 2,
>         using the reduced gain back lobe, or else 4 antennas, but the
>         3db loss per splitter is an issue.
> 
>         Tom, please discuss this situation with Terry and Freewave:
>         Could a splitter/crossed yaggi arrangement likely work?
>         Also, we're in international waters where no-one is, can the
>         power be increased of the radios?
> 
>         - Also, access to the rear mast might be more possible in spring
>         and we could measure the distance and build a better cable,
>         mount arrangement for installing then.
>         - Another thought would be to install the yaggis on the PAMs,
>         The risk is rotation moving them out of LOS; i recall the
>         yaggis have 30-deg. beam.  That would require a new mount but
>         that'd not be too difficult.  It may be worthwhile to consider
>         bringing the yaggis up and building a 1" PVC or steel pipe
>         arrangement to clamp the yaggis to.
> 
>         - A higher power radio might be a good idea.  One of the
>         project folks says they use HF (good range, lower data rate)
>         up here and never need worry about licensing.
> 
>         - Final thought (ask terry about this): we could put our GOES
>         radios back in, put on Omni's (maybe the ones we have would
>         work) and maybe send the data to Boulder (the elevation angle
>         is about 5 degrees here to GOES-west) and email status
>         reports to the ship.   One problem is that we don't currently
>         have an access to a GOES-west channel, but i could probably
>         arrange that later this fall.
> 
>   JM
> 

A couple of observations in regards to your questions.  Tom informed me
that the range to the PAM sites is about 2 miles.  The path loss for 2
miles is quite low for what the Freewave radios are designed for, there
should be a SIGNIFICANT margin if the radios are line of sight and in
the 2 mile range. This would be true also if omni directional antenna's
were also used in lie of the yagi antenna's you are currently using.
I think there is some fundamental  problem with the installation besides
the mast blocking the LOS from the antenna.  Are the Freewave radios
outside in the cold temperatures or are they in a environmentally
controlled area at both ends to the RF link.  To increase the power of
the radios would only have a small improvement in performance and
probably not noticeable, the max. power is 1 watt and I assume there
power level is close to that now.  I would be surprised if the power can
be set greater than 1 watt due to FCC certification.  Even though the
FCC does not govern your area, Freewave has no incentive to build radios
for that applications with higher power.  The loss in the RG-213 can be
reduced by about half by using TIME coax, this again would be only a
small improvement.

The best option would be to go to separate antennas with the power
dividers which would certainly increase the loss of the system by 3.5 dB
for a two-way or 7 dB for a 4-way but if true blockage is your problem
then you are fighting a 20 dB problem. 

 I think your problem is more of severe blockage of the RF signal or the
Freeewave radios have a temperature problem.  The other possibility is
that there is some other instrument which is causing interference or
generating noise in the 900 MHz band.

Let me know a few more details about the RF conditions and I will then
call Freewave to get there thoughts on the problem.   Please correct me
if my assumptions are wrong.

Terry

P.S.  Let's not yet think of using GOES transmitters yet.

From militzer@spows.spo.ca  Thu Oct 16 20:20:09 1997
From: John Militzer 
Subject: Re: comm questions from John
To: hock@ucar.edu
Date: Thu, 16 Oct 1997 20:18:22 -0800 (AKDT)
Cc: horst@stout.atd.ucar.edu, militzer@spows.spo.ca (John Militzer)

Hi Terry,

> How's the weather?

	Cold, now windy now, but it sure can be (really miserable in
	25m/s at -15 or more...can't hardly wait until winter
	arrives).  We do have some icing on the sensors, etc.  I'm
	beginning to believe we should cover our omni's (on the remote
	stations) with plastic/poly tube similar to what the
	Coast-Guard did for our base station antenna.  Any comments or
	experience?


> I think there is some fundamental  problem with the installation besides
> the mast blocking the LOS from the antenna.  Are the Freewave radios
> outside in the cold temperatures or are they in a environmentally
> controlled area at both ends to the RF link.

	The freewaves are inside the ship and inside the electronic's
	box that is inside the insulated Thermal Generator (TEG) Box at the
	stations.   I've noted that the temps as reported by the
	barometer also inside that electr. box have gone quite high,
	as much as 40-50C.  Since that, I removed some insulation from
	the TEG boxes and the temps. have been closer to 25-30.
	Yes I think that was a problem.
 
> A couple of observations in regards to your questions.  Tom informed me
> that the range to the PAM sites is about 2 miles.  The path loss for 2
> miles is quite low for what the Freewave radios are designed for, there
> should be a SIGNIFICANT margin if the radios are line of sight and in
> the 2 mile range. This would be true also if omni directional antenna's
> were also used in lie of the yagi antenna's you are currently using.

	Note, we're using the 5db gain omni's on both ends.
	I agree about the path-loss and margin, or at least that's
	what i thought previously.   One of the problems appears to be
	ground plane.  The ice doesn't conduct very well, so we're
	stuck with the 4 prongs on the antenna alone.  Here's an
	interesting one: after moving the antenna on the ship, we got
	some improvement in LOS for the area (which permitted us to
	set up the 3rd site where the scientists wanted it, otherwise
	it would have been directly behind the 10'dia.mast), but the
	apparent problems with one station persisted.  I went to that
	station yesterday.  All connections were OK, and I removed the
	box insulation (noted below) to help reduce the temp in the
	box.  However I did notice that the sled's metal tow-bar was
	in the upright position, seemingly in the path of the lower
	1/4-1/3 of the antenna, so I lowered it out of the way.  The
	link with that station has definitely improved but it's still
	not perfect (note, all of the data messages are making it to
	the base).  I'm thinking that maybe an improved ground plane
	would help.  That could maybe be alum. foil, or a plate
	attached to the flat lid of the TEG box, or a jumper wire put
	through a hole drilled in the ice to make it to seawater.  The
	second idea doesn't seem necessary, but the bouy folks here
	do this commonly and have reported good noise reduction for
	sensors at least using this technique.  Any ideas.

> for that applications with higher power.  The loss in the RG-213 can be
> reduced by about half by using TIME coax, this again would be only a
> small improvement.
> 
	The cable the Coast Guard used for the installation was along
	the lines of TIME, and we used a short 15' section of 213 to
	splice over to the new higher railing location for the
	antenna.
	This is working definitely better but we're on the main mast
	where there's lots of other RF.  I'll bring some photos back
	to show you the installation.

>  I think your problem is more of severe blockage of the RF signal or the
> Freeewave radios have a temperature problem.  The other possibility is
> that there is some other instrument which is causing interference or
> generating noise in the 900 MHz band.
> 
	The elec. tech. who was here said their stuff in the 900 is
	down (cellular, etc.)

> P.S.  Let's not yet think of using GOES transmitters yet.
> 
	I tend to agree.

12/18 ~01:00gmt
	Brushed frost off PAM antenna mounted on ship.  Twisted 4 rods at 
	base of antenna so they were symmetrical again, not skewed.

	Tested RF communication quality to Baltimore.  Still lousy.  Has 
	always been bad, but seems to have gotten worse in last few days.

1/6 00:30gmt
	Swung ship PAM base antenna and its bracket from starboard side to 
port side on its bracket.  Rear mast is now less in line with antenna and 
Baltimore.  Baltimore communications still not as good as other sites, but 
much improved.  If need be, could probably install longer bracket.

At 1045 AKST, 7 Mar I climbed to the top mast and realigned the base antenna.
Previously it pointed to the port.
It was realigned to point starboard/half aft
Afterwards a communications check was made: Fla ok, Atl ok, Bal ok

Last week I asked the ship's tech to check out the base antenna after we had
lost the data link during the rain.  He didn't find anything wrong then, but
yesterday he was up on the mast and checked the N connector between the ship's
heliax and the NCAR antenna cable. The connector was full of water.  He dried
and taped it back up.  This should help out on those rainy days.

dmc