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05-24-2011, 10:38 PM
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Join Date: May 2007
Location: salem Oregon
Posts: 1,023
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Rich, Glad to see you are flying. Hey got a question for you. How do you like the Catto prop? Is it quiter and smoother than the 2 bladers?
Ron in Oregon 9A
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05-25-2011, 10:58 AM
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Join Date: Aug 2007
Location: Chico (KCIC) , CA
Posts: 264
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This seems like a great thread to ask a question I have been pondering. I'm about to start a panel upgrade. I currently have a Comant CI - 2680-206 (VHF /XM) mounted on the top. I'm installing a 430 as the primary com and a King KY-97a as the secondary. I picked up a Comant CI-122 to mount on the bottom. My question is this. I've been told the bottom is the best place for you primary radio and the top is better for your secondary. I want the best antenna on the 430 as primary. THe CI-2680 is high dollar, but does that make it better? Or is it just that the xm adds to the $$$$$? What would be best pared with what?
Last edited by GEM930 : 05-25-2011 at 11:05 AM.
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05-25-2011, 11:32 AM
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Join Date: Feb 2006
Location: San Diego, CA, U.S.A.
Posts: 770
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The following comments are partly speculation on my part. If someone better informed has factual/experiential information, that would be most welcome.
Combo (VHF comm) + (anything) antennas will tend to be more expensive because:
a) Combo antennas are a low-volume specialty item.
b) Extra measures in design, manufacturing, and testing have to be taken to ensure that VHF comm transmission won't induce significant interference onto the other half of the combo. This may include built-in filters, etc.
So a more expensive combo antenna is not necessarily a better comm antenna than a less expensive plain comm antenna. In fact, even between different plain comm antennas, price is probably not a good indicator of antenna quality.
As for top vs. bottom mounting, it seems like a top-mounted comm antenna may do better during ground operations, and a bottom-mounted comm antenna may do better in flight, simply due to a less obstructed line-of-sight. So as to which should be used for the primary vs. secondary radio, well, it depends on your preferred method of juggling your two radios. But presuming that at least in flight you tend to use the primary, then that would support the argument that the primary should get the bottom-mounted antenna.
But other factors could also come into play. Bottom-mounted antennas tend to be of the bent-whip style, primarily for ground clearance reasons (they also tend to have lower aerodynamic drag). All else being equal, a bent-whip antenna will likely not perform as well as a straight whip due to a higher VSWR as well as being further from the correct (vertical) polarization. But all else is not equal, so as they say, your mileage may vary.
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05-25-2011, 12:36 PM
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Join Date: Mar 2007
Location: Livermore, CA
Posts: 167
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Is there any reason to not mount the comm antenna to the bottom of the wings? Just curious as to why no one does it.
-Chris
__________________
Chris
RV-8 Wings
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05-25-2011, 01:52 PM
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Join Date: May 2005
Location: Tuttle, Oklahoma
Posts: 2,563
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Quote:
Originally Posted by CMW
Is there any reason to not mount the comm antenna to the bottom of the wings? Just curious as to why no one does it.
-Chris
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Well, I am not an expert by any means, but my thoughts on wing mounting are that the fuselage location would not require as much cable to run to the antenna. There are also issues with getting the cable through multiple ribs, the spar, etc. when running out to the wings. It is a simpler installation to run to the belly of the plane instead.
My .02.
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05-25-2011, 02:15 PM
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Join Date: Jan 2010
Location: Tybee Island, GA
Posts: 664
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i had the same issue with the KX155 and SL 40 in my belly mounted antennas....Check your antenna mounting for poper installation. I also noticed that any oil between the antenna base and fuselage, will create exactly the same problems as described! my.02
__________________
Mitch V.
Semi-Retired in Tybee Island GA
2007 MX2 Nigel Lamb EX RBAR MX2 (Current)
2020 MX2 New Kit Position (Sold at OSH to Team RV Member)
2009 Team Rocket F1 (Sold)
2008 MXS Green Slime"(Sold)
2007 MX2 Patches" (Sold)
1999 Giles 202 "Primal Fear/Perucho" (Sold)
1965 PA32-260 "God Bless America" (Sold)
2003 RV6 "Airhawk One" (Sold)
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05-25-2011, 05:59 PM
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Join Date: Mar 2007
Location: Livermore, CA
Posts: 167
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Under wing mounting
I agree the fuselage may be a simpler installation, but people run cabling for wing tip antennas. I'm just curious if there is a technical reason no one mounts the standard bent whip antenna to the bottom of the wing. It seems like it might give you better spacing between antennas especially on the tandem RVs.
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Chris
RV-8 Wings
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05-26-2011, 05:53 AM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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Quote:
Originally Posted by CMW
Is there any reason to not mount the comm antenna to the bottom of the wings? Just curious as to why no one does it.
-Chris
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Hi, Chris! I've often recommended it on this forum, but I think it's too radical for most. It gives the most separation when using two antennae, and from gear legs, prop, and other stuff, and it gives the best counterpoise (ground plane) area for best distance. But there are very few true experimenters, so you're not likely to see anyone doing it. If you were to decide on this type of installation, be sure to use a really low loss cable such as Andrew FSJ1-50A, which cost about $1.00 less per foot than RG-400 but has more expensive connectors. This cable is known among hams as the premo cable to use. Best!
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05-26-2011, 06:41 AM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,768
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There is no reason not to mount the antenna on the wings other than the minor ones previously pointed out. i.e running of the cable.
Another consideration is that the wings are "stressed skin", so be sure you are not making them weaker by just drilling holes willy-nilly without proper enforcement.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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05-26-2011, 08:46 AM
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Join Date: Mar 2005
Location: Bellevue, NE
Posts: 686
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Quote:
Originally Posted by CMW
Is there any reason to not mount the comm antenna to the bottom of the wings? Just curious as to why no one does it.
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The guy who developed the MotoPod (iirc) did just this since that big motorcycle pod took up all the real-estate on the fuselage, he had to mount his comm antennas on the wing.
Just an example,
-Jim
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