 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
bobair(at)me.com
Guest
|
 Posted: Mon Jan 24, 2011 12:50 pm Post subject: Comm Antenna & SWR Reading: Additional Info |
 |
|
Bob, et al,
Here is some additional information:
To Bob's inquiry "It would be interesting to do an ohmmeter test from center pin on the antenna's connector and ground. If is shows a 'short', I suspect that some sort of matching system is installed.", my ohmmeter showed a complete open between the center pin and the shell of the BNC connector on the antenna base.
To Dj Merrill's questions:
1. The antenna base is about 16" aft of the aft portion of the GlaStar's metal cage steel tubing and about 54" aft of the main gear legs (my 'Star is a taildragger). The bent whip portion of the antenna trails aft, obviously, from the base. We didn't check the SWR while moving the empennage control cables -- they run about 3" - 4" above the antenna base. (But I just installed in the tail cone about 18" above the control cables a magnetometer for a Dynon EFIS and the indicated heading didn't change when I moved the elevator controls if that info is relevant to this discussion.)
2. The antenna base is installed on the exterior surface of the composite fuselage and the ground plane is on the inside surface. They are about 7/16" of an inch apart and, as I mentioned before, electrically bonded by the four stainless machine screws that mount the antenna to the airplane. I haven't researched whether the antenna must be mounted directly on the ground plane -- if so, that will be an issue since some composite surgery will be required that I'd really rather avoid.
3. I didn't see any adjustment on the antenna itself.
Based on the responses, it looks like I've got some more tweaking/testing to do. Specifically:
Re-test the antennas (including the cat's whisker) and their feed lines separately, and then together after I've got the feed lines cut to final length and with their final BNC connectors in place. The RG-400 feed line from the Comm 1 antenna to the Garmin 430W will be about 10' long. I can vary (i.e., lengthen) that length if it will help performance. Is there a rule of thumb in how long to make antenna feed lines for optimum performance?
When re-running the tests, would it make any difference to use a more powerful transmitter than my little hand-held? Or should I stick with what I used originally to eliminate one more variable that might affect the follow-on data?
Thanks for the helpful advice.
Best regards,
Bob
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
 |
deej(at)deej.net
Guest
|
| Posted: Mon Jan 24, 2011 1:15 pm Post subject: Comm Antenna & SWR Reading: Additional Info |
|
|
On 01/24/2011 03:24 PM, Bob Falstad wrote:
| Quote: | Is there a rule of thumb in how long to make antenna feed lines for optimum performance?
|
Typically the longer the cable run, the higher the loss induced by the
cable, so I strive to make the cable runs as short as practical while
still leaving adequate length for maintenance, moving things, etc. An
extra foot or two won't make much difference, but I wouldn't leave an
extra ten feet, for example.
| Quote: |
When re-running the tests, would it make any difference to use a more powerful transmitter than my little hand-held? Or should I stick with what I used originally to eliminate one more variable that might affect the follow-on data?
|
I typically test with a 5 watt handheld. I can see no reason to throw
more power at it. However, it might be worth trying the test with a
different handheld to remove the radio itself as a potential source of
the problem.
-Dj
--
Dj Merrill - N1JOV
Glastar Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Please use Netiquette Guidelines http://tools.ietf.org/html/rfc1855
Kindly TRIM your email replies and post AFTER the relevant text
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
|
| Posted: Tue Jan 25, 2011 10:02 am Post subject: Comm Antenna & SWR Reading: Additional Info |
|
|
Another problem with making the feed line much too long is what to do with
the access. If you coil it up you have just made another electrical tuning
circuit. This can be really bad with unshielded zip wire like used in some
stereo systems.
Noel
--
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
