---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Mon 03/08/10: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:05 AM - In line filter (Dave Lammers) 2. 09:14 AM - Re: In line filter (Doug McNutt) 3. 02:25 PM - Re: In line filter (Kelly McMullen) 4. 05:49 PM - GA7 RPM Gauge Urgently Required (Shaun Wilkinson) 5. 05:49 PM - Re: In line filter (Kelly McMullen) ________________________________ Message 1 _____________________________________ Time: 07:05:22 AM PST US From: Dave Lammers Subject: Avionics-List: In line filter Hi, does anyone on the list know where to purchase an in-line (BNC/BNC) low-pass filter to pass 243 mhz, and reject the GPS carrier of 1.5 Ghz and above? It turns out that my comm radio causes the ring diodes in the output of my ELT to resonate and retransmit at frequencies that saturate and shut down the GPS reciever front end. I don't want to move antennas (already 4 feet apart) and think that a simple low pass filter in the ELT antenna line will do. I can easily make one but would rather just purchase one already packaged. Thanks Dave Lammers ________________________________ Message 2 _____________________________________ Time: 09:14:52 AM PST US From: Doug McNutt Subject: Re: Avionics-List: In line filter At 08:42 -0600 3/8/10, Dave Lammers wrote: > >Hi, does anyone on the list know where to purchase an in-line (BNC/BNC) low-pass filter to pass 243 mhz, and reject the GPS carrier of 1.5 Ghz and above? >It turns out that my comm radio causes the ring diodes in the output of my ELT to resonate and retransmit at frequencies that saturate and shut down the GPS reciever front end. >I don't want to move antennas (already 4 feet apart) and think that a simple low pass filter in the ELT antenna line will do. I can easily make one but would rather just purchase one already packaged. >Thanks Huh?? Some things you say just are not clear. Your 121.5/243 MHz ELT had better not be transmitting when you poke a mic key on a comm transmitter. Ring diodes? Are you talking about the diodes in a double-balanced mixer? I suppose something like that could be used in an ELT to create the harmonic of 121.5 that it needs but I haven't seen one that does that and it would more likely be done before a non-linear final amplifier. The GPS carrier is generated only by the satellites. The receivers are only receivers and radiate nothing at 1.5 GHz. Some might have a local oscillator for heterodyning but the level would be quite low. 121.5/243 is dying and is already not being monitored by satellites. Are you planning to replace it with a 409 MHz version. As for a filter about 20 feet of RG-58 will attenuate pretty well at 1.5 GHz and still pass 121.5 MHz. -- --> Halloween == Oct 31 == Dec 25 == Christmas <-- ________________________________ Message 3 _____________________________________ Time: 02:25:58 PM PST US From: Kelly McMullen Subject: Re: Avionics-List: In line filter ELT transmit sections are not isolated in any way and do resonate harmonically when energized by strong RF signal in same spectrum. Especially the early ones. It takes very little harmonics to overwhelm the front end of a GPS. While a com receiver needs something better than -40db signal for you to perceive it, GPS receivers operate with -150 db signal, so a tenth of a watt output of a 5th or higher order harmonic from an ELT will easily overwhelm the GPS receiver. I had ELT harmonics(excited by a dozen TV broadcast antennas within 5 miles) overwhelming both com receivers to break squelch with loud static when all 3 antennas were top-side on the airframe. Moved com 2 antenna to the belly and problem went away. I knew it was the ELT because the same flight with ELT antenna disconnected had no problems. Reconnecting ELT antenna and they came right back. Doug McNutt wrote: > > > Huh?? Some things you say just are not clear. > > Your 121.5/243 MHz ELT had better not be transmitting when you poke a mic key on a comm transmitter. > > Ring diodes? Are you talking about the diodes in a double-balanced mixer? I suppose something like that could be used in an ELT to create the harmonic of 121.5 that it needs but I haven't seen one that does that and it would more likely be done before a non-linear final amplifier. > > The GPS carrier is generated only by the satellites. The receivers are only receivers and radiate nothing at 1.5 GHz. Some might have a local oscillator for heterodyning but the level would be quite low. > > 121.5/243 is dying and is already not being monitored by satellites. Are you planning to replace it with a 409 MHz version. > > As for a filter about 20 feet of RG-58 will attenuate pretty well at 1.5 GHz and still pass 121.5 MHz. ________________________________ Message 4 _____________________________________ Time: 05:49:38 PM PST US From: "Shaun Wilkinson" Subject: Avionics-List: GA7 RPM Gauge Urgently Required Dear All, Ive been given the avionics-list info in the hope that you/somoene might be able to help me. I have a Grumman Cougar 1979 serial number GA7-0105 in the UK. It went for its annual and someone has stolen the rpm guage along with a few other items. I have replaced everything but the rpm guage. I cant get the annual finished till i have one !!! I will pay for your services along with the part and mailing Can anyone help in any way at all. Kind regards Shaun Wilkinson Shaun Wilkinson Owner Cloud 9 Aviation (UK) Cloud 9 Aviation (CZ) Leeds Flying School Yorkshire Flight Training Cloud 9 Air Taxi Cloud 9 Travel Offices in: UK and Czech Private and Commercial Pilot Training UK and European Air Taxi and Charter Full Turn-key service providers bespoke to clients needs Head Office: Leeds Flying School, Coney Park Estate, Leeds & Bradford Airport, Leeds S19 7XS, England, UK Tel: +0044 7535301757 +0044 1642714505 Visit: http://www.cloud9aviation.net Visit: http://www.leedsflyingschool.com CONFIDENTIALITY This e-mail is intended only for the use of the addressees named above and may be confidential or legally privileged. If you are not an addressee you must not read it and must not use any information contained in nor copy it nor inform any person other than Cloud 9 Aviation Limited or the addressees of its existence or contents. If you have received this email and are not a named addressee, please delete it and notify admin@cloud9aviation.net ________________________________ Message 5 _____________________________________ Time: 05:49:45 PM PST US From: Kelly McMullen Subject: Re: Avionics-List: In line filter I believe you can get them from avionics shops. 1st generation ELTs that came out in the '70s are worst for this, and will even interfere with your com radios, often breaking squelch with static if near strong FM/TV transmitters. 2nd generation ELTs from the 90s have better suppression, and I believe the 406 units are supposedly even better. With your GPS, be sure you aren't getting interference directly from your com or nav radios. Most, including King and Narco have specific frequencies that cause GPS interference when tuned to those frequencies..does not require transmit, just being tuned to receive the frequencies will shut down GPS reception. Avionics shops that install IFR certified units are supposed to specifically test all of those frequencies and install notch filters if any of them cause any interference. Dave Lammers wrote: > > Hi, does anyone on the list know where to purchase an in-line (BNC/BNC) > low-pass filter to pass 243 mhz, and reject the GPS carrier of 1.5 Ghz > and above? > It turns out that my comm radio causes the ring diodes in the output of > my ELT to resonate and retransmit at frequencies that saturate and shut > down the GPS reciever front end. > I don't want to move antennas (already 4 feet apart) and think that a > simple low pass filter in the ELT antenna line will do. I can easily > make one but would rather just purchase one already packaged. > Thanks > Dave Lammers > > > > ------------------------------------------------------------------------------------- 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.