---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Mon 10/08/07: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:40 PM - comm tx causing avionics fluctuations (Tom Goddard) 2. 07:51 PM - Re: comm tx causing avionics fluctuations (Charles Reiche) 3. 08:01 PM - Re: comm tx causing avionics fluctuations (Ron Quillin) 4. 10:07 PM - Re: comm tx causing avionics fluctuations (John Rippengal) ________________________________ Message 1 _____________________________________ Time: 05:40:33 PM PST US From: "Tom Goddard" Subject: Avionics-List: comm tx causing avionics fluctuations 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 9:04 AM ________________________________ Message 2 _____________________________________ Time: 07:51:17 PM PST US From: "Charles Reiche" Subject: Re: Avionics-List: comm tx causing avionics fluctuations As impossible as it sounds I once installed a noise free wx-1000+ system into a glassair that was already well thought out and had a single point ground very close to the battery negative lead. Try and find someone with a MJF or other make antenna analyzer and check that the ground plane and antenna connections out of the back of the radio case look like a good low SWR antenna. Also if this is transmitting into rg-58 antenna coaxes, you might think of upgrading the whole ship with rg-142 or rg-400 double shielded coax. This would help greatly if the real problem is RF power leaking out of a poorly shielded coax. You could try shielding the EGT box with MU metal if thats where it is being affected. It might be coming into the box on the lead wires themselves. Check your engine mount to grounding system resistance. Everyone will tell you that idea numbers are 3 Milliohms but thats really hard to achieve in the amateur built community, crap even the production stuff with foberglass and mesh ground planes like cirrus or socata (the roof). Good luck Charles Reiche ----- Original Message ----- From: Tom Goddard To: avionics-list@matronics.com Sent: Monday, October 08, 2007 8:38 PM Subject: Avionics-List: comm tx causing avionics fluctuations 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 ________________________________ Message 3 _____________________________________ Time: 08:01:42 PM PST US Subject: Re: Avionics-List: comm tx causing avionics fluctuations From: Ron Quillin At 17:38 10/8/2007, you wrote: >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) This still may not be a real change. Meters, especially inexpensive ones, in an RF field can rectify the RF energy and add it to actual DC voltage as displayed. One would not expect to see a rise in bus with additional load applied, unless perhaps there was some disturbance to the regulator. Same observed change with engine/alternator/generator off? Do you have a 'scope available you could use to monitor the bus(s) and see if you observe a change? Ron Q. ________________________________ Message 4 _____________________________________ Time: 10:07:14 PM PST US From: "John Rippengal" 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 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message avionics-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Avionics-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/avionics-list Browse Digests http://www.matronics.com/digest/avionics-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.