Avionics-List Digest Archive

Wed 10/10/07


Total Messages Posted: 1



Today's Message Index:
----------------------
 
     1. 10:58 AM - Re: comm tx causing avionics fluctuations (Roger Roy)
 
 
 


Message 1


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    Time: 10:58:28 AM PST US
    From: "Roger Roy" <Savannah174@msn.com>
    Subject: Re: comm tx causing avionics fluctuations
    John I'll sing that praise forever. I was having a lot of problems same as a lot of what's being talked about with a MicroAir M-760 I went on Ebay and got a brand new one for $14.00 and was able to trouble shoot my faulty BNC at the antenna in minutes, that saved me hours of troubleshooting the system, so a SWR meter should be in every homebuilder tool box. RJ ----- Original Message ----- From: John Rippengal<mailto:j.rippengal@cytanet.com.cy> To: avionics-list@matronics.com<mailto:avionics-list@matronics.com> Sent: Tuesday, October 09, 2007 1:05 AM Subject: Re: Avionics-List: comm tx causing avionics fluctuations You have been given good advice by Tim Hedding; why don't you follow it? Anyone installing their own radios should have a cheap 2 metre band VSWR meter and use it. The other remote possibility is that you have your antenna in the wrong place. The only place for a comm antenna in a plastic aeroplane is in or near the tail or in the winglet in canards. I take it also that all your negative power grounds are separate wires from each instrument and they go back to a single ground buss near and connected with a heavy lead to the battery/alternator ground. Similarly the positive 12/14v leads are run (via a breaker) from one central positive buss also near the battery/alternator. And finally that the positive and ground leads to each instrument run together. John Does any one have experience with comm tx causing transient changes in their engine analyzers egt/cht and voltages in glasairs or other fiberglass airframes? As we continue to debug our panel this problem is now up for a solution. I have heard that it may be "antenna standing wave reflections"? Our vert servo on the TruTrak is affected during Tx as well. We assumed that the other systems being affected were due to the close proximity of the comm antenna coax and the aircraft charging system as they all run through the center console of our Glasair III for a short distance in close proximity. Maybe I am wrong and it is more to do with the Standing Wave Reflection? Our other bugs caused by the comm. Tx are: 1. transient voltage rise on both buses from 14.1 to 14.6 (this is a real voltage change measured by and external meter) 2. egt and cht values decrease by 300 and 100 degrees F respectively (these are obviously not real temp changes) 3. Ray Allan trim and flap indicators flicker (the trim and flaps don't actually move) The following is something Tim Hedding of B&C alternators sent me: 1. Check the transmitting antenna systems for SWR. Check that the antenna, transmission line and transmitter output are of the same impedance and that the connections and ground planes are good. Use an SWR bridge or antenna analyzer to check the antenna system matching / efficiency. There must be some other glass airplanes out there that have seen some of these quirks. Tom Tom Goddard 100 Miner Lane Grand Pre, N.S. B0P 1M0 9026702511 Cell 9025427315 Fax 08/10/2007 9:04 AM http://www.matronics.com/Navigator?Avionics-List<http://www.matronics.com /Navigator?Avionics-List>




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