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</head><BODY BGCOLOR="white" ><div><SPAN style="font-size:10pt;">I KNEW there was another reason I put a steel roof on my carport! (16' x 30')<br /> -- 73 --<br /> J. Gary Bender, WS5N<br /> Fence Lake, New Mexico USA<br /><br /></span></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> One question,what constitutes a large ground plane?</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> Is it 12"or 12'? Is it a multiple of the vertical whip?</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> Good question. Most people think that four 1/4 wave radials make a ground</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> plane. But if you model a 1/4 wave vertical over 1/4 wave radials, all you</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> get is the exact pattern of a DIPOLE. The radials are just providing a</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> "groundplane" to complete the electrical part of the antenna and give a good</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> match. They do not affect the pattern at all.</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> I modeled verticals over 6' or larger ground planes and only found that you</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> get the added "reflection" gain when the ground plane starts getting that</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> big or more. I wish I had time to use EZNEC to show the added gain</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> (skyward) versus the size of the ground plane. And how "radials" (above</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> actual ground) have nothing to do with the "pattern".</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> SO, the bigger the better. It should be worth 2 to 3 dB if you could make</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> it very large...</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> This is the page in question:</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> <a href="http://aprs.org/aprs-satellite-igate-antennas.html">http://aprs.org/aprs-satellite-igate-antennas.html</a></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> Bob, WB4aPR</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> On 6/19/2015 3:57 PM, Robert Bruninga via aprssig wrote:</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> Subject: APRS Satgate Antenna page</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> Since the ideal APRS Satellite IGate OMNI antenna is exactly the opposite</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> of</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> the typical terrestrial IGaate antenna, I prepared the following WEB page:</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> <a href="http://aprs.org/aprs-satellite-igate-antennas.html">http://aprs.org/aprs-satellite-igate-antennas.html</a></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> It shows how a vertical ¼ or ¾ wave VHF omni equals the performance of a</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> full OSCAR class array (over half the sky) but does it with no moving</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> parts.</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> It makes up for the weak-signal horizon part of the sky by there simply</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> being more omni-IGates. The APRS-IS cloud with all of its IGates is</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> probably one of the largest spatially distributed satellite receiver</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> system</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> in the world (?).</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> But with people used to the 10W transmitter on the ISS, just a few IGates</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> can capture just about every packet from the ISS horizon to horizon on a</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> whip. But with the 14 dB weaker signal from PSAT, we need more SatGates</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> to</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> make up for their smaller skyprint. For the USA we need more than a dozen</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> such Omni-SATgates.</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> To see the significance of the weaker downlink from PSAT, look at the</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> successful IGates on the <a href="http://pcsat.aprs.org">http://pcsat.aprs.org</a> page compared to the IGates</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> that hear the ISS packets on <a href="http://ariss.net">http://ariss.net</a> Both are listening on</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> 145.825 and passing along every packet they hear. But only TRACKING</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> IGates</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> or good vertical gain satgates hear PSAT. And since we want these running</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> 24/7/365, we do NOT expect people wearing out motors when an omni will do</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> fine (if we have enough).</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> The page also shows how every SATgate with a HIGH and terrestrial type</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> antenna actually creates a DEADZONE around it, effectively blocking any</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> nearby user heaerd direct from appearing on any of the APRS-IS cloud</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> satellite web pages. Hence, Omni-satgate antennas should be low to</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> everything surrounding it w hile still seeing the sky above 30 degrees.</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> If your TH-D7 HT is just sitting there, not in use 99% of the time, then</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> just hook it to a vertical whip and let it be an IGate. With the low</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> antenna it will also probably be safe from all weather lightening too.</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> Put</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> the UHF side on 435.350 and turn up the speaker. When PSAT PSK31 comes</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> into</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> view, you can watch the PSK31 activity as a bonus!</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>></SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> Bob, WB4APR</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> _______________________________________________</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> aprssig mailing list</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> aprssig@tapr.org</SPAN></div>
<div><SPAN style="font-size:10pt;color:maroon;">>> <a href="http://www.tapr.org/mailman/listinfo/aprssig">http://www.tapr.org/mailman/listinfo/aprssig</a></SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> _______________________________________________</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> aprssig mailing list</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> aprssig@tapr.org</SPAN></div>
<div><SPAN style="font-size:10pt;color:navy;">> <a href="http://www.tapr.org/mailman/listinfo/aprssig">http://www.tapr.org/mailman/listinfo/aprssig</a></SPAN></div>
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