---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 07/23/17: 6 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:54 AM - Re: 1.57542 GHz Filter (Robert L. Nuckolls, III) 2. 09:37 AM - Re: 1.57542 GHz Filter (Alec Myers) 3. 10:14 AM - Re: AeroElectric-List Digest: 3 Msgs - 07/22/17 (speedy11@aol.com) 4. 01:23 PM - Re: 1.57542 GHz Filter (Robert L. Nuckolls, III) 5. 02:48 PM - ADS-B Out Antenna (Charles Brame) 6. 03:04 PM - Re: 1.57542 GHz Filter (Eric Page) ________________________________ Message 1 _____________________________________ Time: 08:54:12 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 1.57542 GHz Filter At 09:28 PM 7/22/2017, you wrote: >I've tried the filters and they didn't make any difference. What symptoms suggested that the filter was, perhaps, necessary? Bob . . . ________________________________ Message 2 _____________________________________ Time: 09:37:08 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: 1.57542 GHz Filter I'm sorry - I should have given more detail. The GPS reports zero satellites in view and takes itself offline during, and for a few seconds after, any transmission on either VHF COM radio on one of a select few frequencies: 121.175MHz I think is one of them. It=99s an old GPS and not a new problem. I=99ve put a fair amount of resource into trying to fix it some while ago, but not found a resolution. The inline filters didn=99t make any difference. > On Jul 23, 2017, at 11:53 AM, Robert L. Nuckolls, III wrote: > > At 09:28 PM 7/22/2017, you wrote: >> I've tried the filters and they didn't make any difference. > > What symptoms suggested that the filter > was, perhaps, necessary? > > Bob . . . > ________________________________ Message 3 _____________________________________ Time: 10:14:35 AM PST US From: speedy11@aol.com Subject: AeroElectric-List: Re: AeroElectric-List Digest: 3 Msgs - 07/22/17 Thanks to all for your advice. I will install without and add later if needed. Thank you, Stan Do not archive Time: 12:44:12 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 1.57542 GHz Filter At 01:10 PM 7/22/2017, you wrote: >In the Garmin installation manual, it says the following: > >"The GPS antenna is lass susceptible to harmonic interference if a >1.57542 GHz filter is installed on the COM transceiver antenna output." > >Does anyone know of anyone who had to do this? > >Getting ready to install a GTN650 in my RV-8 so trying to anticipate >potential problems. > >Thanks, > >Stan Sutterfield These were found useful on some makes of comm transceivers that had unhappy amounts of harmonic radiation on or near GPS frequencies. I don't now recall the brands/models of radio involved but as I do recall, it was just a select few. Try it without the filter. It's easy to add later if indeed you do need it. It's simply inserted into the transceiver coax feedline 4-70-54-Inline-Gps-Notch-Filter-Bnc I doubt you will find it necessary. Bob . . . ________________________________ Message 4 _____________________________________ Time: 01:23:05 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 1.57542 GHz Filter At 11:35 AM 7/23/2017, you wrote: >I'm sorry - I should have given more detail. > >The GPS reports zero satellites in view and >takes itself offline during, and for a few >seconds after, any transmission on either VHF >COM radio on one of a select few frequencies: >121.175MHz I think is one of them. It=99s an old >GPS and not a new problem. I=99ve put a fair >amount of resource into trying to fix it some >while ago, but not found a resolution. Understand. Some background on cross-system interference issues may be helpful . . . When one runs the DO160/MIL-STD 461/462 gauntlets, it is incumbent on the manufacturer of a new product to measure and document extraneous emissions to be sure they are below tolerable limits for other systems. We know that its difficult if not impossible to drive all potential interference emission to zero but the design goals call for reducing them to insignificance. I.e. the victim system's performance is not degraded. Emacs! A fairly recent edition of DO160 offers these testing limits for radiated emissions. Note those 'notches' in the allowable emissions plot. They are centered over specific ranges of spectrum where RECEIVERS of itty-bitty signals would like to have a clear shot at detecting the information on those frequencies. Note the notches cover vhf nav/comm, uhf nav/comm, transponder/ tcas and gps bands. Not sure what service is being protected up round 5 ghz . . . The energy levels allowed are the sum total of energies radiated from all components of a device and associated cables when laid out on a copper-top table like so. Emacs! All this is fine and dandy for potential antagonists that are NOT designed to radiate buckets of energy on purpose . . . i.e. transmitters. Tests for bkackbox/harness radiation are generally no big deal . . . I've never failed one. Then there are transmitters. By nature, they're intended to radiate signal levels on the order of 130 dBuv/m at 3 meters from an antenna. Given that 'extraneous' emission limits at GPS frequencies are on the order of 85 dBuv/m LOWER, this means that the 13th harmonic (121 mHz x13 = GPS) power has to be on the order of 1 times 10^-8 lower than the fundamental. Modern designs have no problem achieving this goal but there's a goodly number of legacy comm equipment that was designed and qualified before GPS became the backbone of aerial navigation. GPS signals are exceedingly weak . . . generally at or below atmospheric noise. The predictable nature of the incoming signal makes if possible to digitally sift useful data out of what would otherwise be noise. If adding the notch filter didn't fix the symptoms, then perhaps the interference isn't being radiated from the antenna . . . there have been cases of incompatible appliances were the interference was getting out of the enclosure (i.e. wouldn't pass the bench test as described above). Will your gps interference symptom repeat on the ground? You might try dummy loading the transceiver and see if the interference goes away. Oops, just noticed that it repeats on two separate transmitters (same brand/model?) How far apart are your comm and GPS antennas? Bob . . . ________________________________ Message 5 _____________________________________ Time: 02:48:37 PM PST US From: Charles Brame Subject: AeroElectric-List: ADS-B Out Antenna I recently purchased a uAvionix Echo ADS-B Out device for my RV-6A. The instructions say to position the ADS-B Out antenna at least 3 feet from my existing transponder antenna. I will be forced to locate the new antenna in the aft fuselage with at least a 15-20 foot cable - not an ideal situation for me. Is there really a significant reason for the distance requirement for the ADS-B Out antenna? How about proximity to a VHF antenna? Charlie Brame RV-6A N11CB San Atonio ________________________________ Message 6 _____________________________________ Time: 03:04:45 PM PST US Subject: Re: AeroElectric-List: 1.57542 GHz Filter From: Eric Page On Jul 23, 2017, at 1:22 PM, Robert L. Nuckolls, III wrote: > Not sure what service is being protected up round 5 ghz . . . Probably 802.11a WiFi systems. In the U.S., four channels between 5.180 and 5.240 GHz, and five channels between 5.745 and 5.825 GHz. Might be other stuff as well; that's in an Industrial, Scientific and Medical (ISM) band. 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