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ISS Signal strength, Beam or Dipole

ISS Amateur Radio Status: February	2, 2004

ISS Signal strength,  Beam or Dipole:

By Miles Mann WF1F,

MAREX-MG News	www.marexmg.org

Manned Amateur Radio Experiment

Hi everyone.  During a recent pass of the ISS with packet running I made
some manual notes on the signal strength of the received down link and
compared the data between two different antennas. I used a Beam and a
stock vertical antenna for the testing and of course the beam won.  Here
are some of the approximate results.

Transceiver an Yeasu 736R, all preamps off, 
Kantronics KPC-9612  TNC (Squelch detect)
S-Meter, Non-calibrated, approximately 6db per S-unit.

Antenna #1
Beam 22 element Circular polarized.
Equivalent Element gain 9.75 dBd
LMR 600 UF, 80 Feet, 1.0 dB loss at 145.800
Estimated gain 8.75 dBd

Antenna #2
Omni Vertical, dual half waves, stacked
Equivalent Element gain 3 dBd
BurryFlex coax, 50 feet, 1.2 dB loss at 145.800
Estimated gain 1.8 dBd

Minute	Beam		Omni		Difference	Elevation 		Distance
	S-Unit		S-Unit		S-Units	above horizon		KM
18:35	signals not recorded							1800
18:36	2-3		0-1		2			5-10		1600
18:37	9+(10)		0-2		8+			15-20		1200
18:38	9+(10-20)	3-5		7+			20-40		800
18:39	9+(20-40)	2-5		11+			40-80		600
18:39.70 ISS directly over head at 86 degrees				350
18:40	9+(20-40)	3-9+(10)	5+			80-40		500
18:41	9+(10-20)	3-9+(10)	3+			40-20		700
18:42	9+(10-20)	1-3		9+			20-10		1100
18:43	7-9		1-3		6+			10-5		1700
18:44	2-3		0-2		1			5-1		1900

Analysis Vertical:
During the first and last three (3) minutes of the pass, the Vertical
was able to hear ISS, however it was not able to decode very many
packets.  Signals needed to get above the S2 Range before packets were
decoded reliably.  

During minutes 18:40 and 41 the signals on the Vertical climbed up to
S9+10dB.  There were two deep signal fades.  The are two reasons for the
deep signal fades.  The first is the antenna polarity.  During every 10
minute ISS pass, there will be two instances where your antenna and the
ISS antennas are momentarily cross polarized.  The cross polarization
will cause a very deep signal fade (20 -30 dB in signal drop).  These
signal fades usually only last 20-30 seconds then signal levels begin to
return to normal.
Another reason for one of the fades is because the Space Station passed
directly over my house and was in the Null spot directly above my
Vertical antenna (specifically 86 degrees elevation).

Each day, ISS will pass in range of your location 4-6 times per day. 
Some passes will be better than others.  It looks like stations running
small antennas with 0-3 dBd of gain will have a 4-8 minute window of
reliable packet access.  Your actual results may vary.

Analysis Beam:
The Gain difference between the two antennas is approximately 7 dBd. 
Which means that I should see at least a 1 S-unit difference when
switching between the two antennas.  When I take signal checks on Earth,
testing against mid scale repeaters, I see approximately a 1.5 S-Unit
difference in signal strength (close to what I would expect).  

During the ISS pass I was a little surprised to see such a much larger
difference between the Vertical and the Beam.  Most of the big
difference is because the Circular polarized beam helps compensate for
the constantly rotating signals coming from the Space Station. The
Vertical antenna will suffer a bit from a mismatch antenna alignment
between your Earth antenna and the ISS antennas.
Another aspect of the Beam which helped Boost its performance is the
fact that the beam antenna was computer controlled in both Azimuth and
Elevation.  The Beam was pointing its main receiving lob directly at the
space station at all times.

These numbers I recorded are just approximate.  It would be interesting
if someone had the hardware to actually generate some better numbers
with computer plotting and better recording tools, hint hint.

Kep plot of the track off ISS as it approached Boston Mass,
                               3. ISS
UTC Date  Time Azim/Elev  	Distance Direction  Nearest City..
02Feb2004 1834  234/   0   	79.2 km South of  Gulfport, MS
02Feb2004 1835  234/   2   	56.0 km  ENE  of  Prichard, AL
02Feb2004 1835  234/   4   	25.1 km  East of  Montgomery, AL
02Feb2004 1836  234/   7    	1.5 km  NNE  of  East Point, GA
02Feb2004 1836  234/  10   	37.6 km  WNW  of  Greenville, SC
02Feb2004 1837  234/  14   	76.1 km  West of  Winston-Salem, NC
02Feb2004 1837  233/  19   	15.8 km  WNW  of  Lynchburg, VA
02Feb2004 1838  233/  26   	13.5 km  WNW  of  Dale City, VA
02Feb2004 1838  232/  37   	11.9 km North of  Wilmington, DE
02Feb2004 1839  229/  55    	5.5 km  ESE  of  Greenwich, CT
02Feb2004 1839  197/  83    	8.2 km  NNW  of  Woonsocket, RI
02Feb2004 1840   64/  63   	90.0 km  ESE  of  Portland, ME
02Feb2004 1840   59/  42   	93.2 km  WNW  of  Yarmouth, NS
02Feb2004 1841   58/  29   	89.6 km  East of  Saint John, NB
02Feb2004 1841   58/  21   	46.4 km North of  New Glasgow, NS
02Feb2004 1842   57/  15  	78.1 km North of  Sydney, NS
02Feb2004 1842   57/  11  115.1 km  East of  Channel-Port-aux-Basques,
02Feb2004 1843   57/   8   71.2 km   SW  of  Gander, NF
02Feb2004 1843   57/   5  164.7 km  East of  Gander, NF
02Feb2004 1844   57/   3  324.2 km  ENE  of  Saint John's, NF
02Feb2004 1844   57/   1  519.8 km  ENE  of  Saint John's, NF
--------------------------------end of

Packet and Voice tips:
I have posted information on how to access the ISS station, for both
Voice and Packet operations. The ISS packet system with the Kenwood D700
had been active daily since Mid December 2004


Marexmg Web page

Information on the crew's activities aboard the Space Station, future
launch dates, as well as Station sighting opportunities from anywhere on
the Earth, is available on the Internet at: 


73 Miles WF1F MAREX-MG

Until we meet again

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