---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Wed 12/19/18: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 09:35 AM - 2018 List of Contributors (Matt Dralle) 2. 12:24 PM - myths about gps antennas (kjlpdx) 3. 12:41 PM - Re: myths about gps antennas (GTH) 4. 12:49 PM - FYI - passing the ADS-B validation flight (kjlpdx) 5. 02:02 PM - Re: myths about gps antennas (Charlie England) ________________________________ Message 1 _____________________________________ Time: 09:35:12 AM PST US From: Matt Dralle Subject: Avionics-List: 2018 List of Contributors Dear Listers, The 2018 Matronics Email List and Forum Fund Raiser officially ended a couple of weeks ago and it's time that I published this year's List of Contributors. It is the people on this list that directly make these Email Lists and Forums possible! Their generous Contributions keep the servers and Internet connection up and running! You can still show your support this year and pick up a great gift at the same time. The Contribution Web Site is fast, easy, and secure: http://www.matronics.com/contribution Or, by dropping a personal check in the mail to: Matt Dralle / Matronics 581 Jeannie Way Livermore CA 94550 And finally, I'm proud to present The 2018 Fund Raiser List of Contributors: http://www.matronics.com/loc Thank you again to everyone that made a Contribution this year!! Matt Dralle Matronics Email List & Forum Administrator ________________________________ Message 2 _____________________________________ Time: 12:24:54 PM PST US Subject: Avionics-List: myths about gps antennas From: "kjlpdx" I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90 elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition. so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna. when does being overdriven prove a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length? I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly? Read this topic online here: http://forums.matronics.com/viewtopic.php?p=486445#486445 ________________________________ Message 3 _____________________________________ Time: 12:41:54 PM PST US Subject: Re: Avionics-List: myths about gps antennas From: GTH Le 19/12/2018 21:24, kjlpdx a crit: > I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. Paint could be a problem with *some* conductive paints. > could I use a different antenna than the RAMI brand? Yes. > should I not worry about any of this and just go fly? I suggest you submit your questions to the Aeroelectric List at Matronics. You'll get really knowledgeable info. BTW, as you mentioned the 10' minimum coax length looks like some hangar tale... -- Best regards, Gilles http://contrails.free.fr http://lapierre.skunkworks.free.fr ________________________________ Message 4 _____________________________________ Time: 12:49:12 PM PST US Subject: Avionics-List: FYI - passing the ADS-B validation flight From: "kjlpdx" for what few of us are left using older encoders I have learned thus - they take perhaps more than 5 minutes to warm up [the wire for the warmer circuit is actually a very fine gauge]. with the stratus ESG it will transmit as if you are flying while you are actually still on the ground. this will fail your flight. SO, start out in STANDBY mode. press the function key and cycle thru to see pressure altitude displayed. it will show dashes until the encoder is warmed up and working. you can also cycle the functions to see if the gps has locked into your location yet. if you then press ALT the ESG will display GRND showing you are on the ground, unless you taxi over 15 mph. so, taxi slower [at least for the validation flight] than 15. setting the altimeter to 29.92, 59F, 15C, you can see what the current pressure altitude is. this is what shows, to the nearest 100', on the ESG. I find the stratus user manual needing more info. very little is shown as to what the display should look like during normal flight for instance. it appears you can play with the function button while in flight and not affect the output of the transponder. info displays to the right of the 1200. however, if you want to see gps signal strength it needs to be restarted pressing the function and power buttons in order to bring up diagnostic screens. it starts all over acquiring satellites. I believe the transponder is not transmitting in this mode. correct me if I'm wrong. anyway, thought I might save someone else some stress. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=486447#486447 ________________________________ Message 5 _____________________________________ Time: 02:02:57 PM PST US Subject: Re: Avionics-List: myths about gps antennas From: Charlie England On 12/19/2018 2:24 PM, kjlpdx wrote: > > I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90 elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition. > so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna. > when does being overdriven prove a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length? > I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly? > disclaimer: I'm not an engineer (but I do play with airplanes with a couple of them) Like Gilles said, paint *can* cause problems in some situations. Not just with reception, but also by getting on the connector(s). Trust me; somebody will find a way to paint the entire thing. I'm pretty sure you won't find any antenna mfgr that says it's ok to paint their antenna, because the paint (and the painter) is outside their control. Some antennas are black from the mfgr, so that's obviously ok for them. But if it wasn't black to start with, do you know for a fact that converting it to a 'black body' heat absorber won't affect its performance in the sun? (Another potential reason to restrict painting.) FWIW, the cable isn't 'low impedance'; it's low loss (that usually means that it has lower capacitance per foot). Most aviation stuff is '50 ohm' (impedance) cable, but poorer cables can have higher capacitance per foot, meaning that their actual impedance at different frequencies will vary more over longer lengths than the higher quality, lower capacitance cable. The mfgr knows their device, the frequencies over which it will operate, the capacitance of their chosen cable, and whether everything will stay within their needed limits at a given cable length for all frequencies and signal levels (which can vary quite a bit). You might get away with what you're doing with no issues whatsoever. But you might not. And the mfgr isn't likely to tell you it's ok, because they likely haven't tested the *system* configured the way you configured it. Think about buying a new fuel injector for your Chevy. Would Porsche tell you that it'll work fine in your 911? Charlie --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ------------------------------------------------------------------------------------- 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.