AeroElectric-List Digest Archive

Thu 08/07/14


Total Messages Posted: 2



Today's Message Index:
----------------------
 
     1. 04:51 PM - Re: Hall effect sensor (Robert L. Nuckolls, III)
     2. 09:29 PM - Re: Half wave copper foil dipole transponder antenna (MikeRV6-A)
 
 
 


Message 1


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    Time: 04:51:14 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Hall effect sensor
    At 03:42 PM 8/6/2014, you wrote: Bob et al. I have a VMS 1000 engine instumentation system that presently uses a hall effect sensor on the main alternator "B" lead to measure current for the display. I'm now installing an auxilliary alternator on the vacuum pad which ties into the same starter contactor to battery contactor lead as the main alternator, a la Figure Z-12. Questions: Is it feasible to route the starter contactor to battery contactor lead through the VMS hall effect sensor to monitor either alternator's current? What is the possible effect during engine start, (current going in the opposite direction ), on the sensor which is marked for a particular wire/current direction? You can run BOTH b-leads through the single hall-sensor which will then measure TOTAL current for both alternators or, obviously, current on each functioning alternator independently. Don't run starter current through the hall-sensor. It won't damage it but it probably WILL super-excite any retentive tendencies and leave you with a non-zero reading when indeed there is no current to be measured. Bob . . .


    Message 2


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    Time: 09:29:15 PM PST US
    Subject: Re: Half wave copper foil dipole transponder antenna
    From: "MikeRV6-A" <mikerv6a@ao-cs.com>
    Transponder uplink frequency is 1030 MHz, downlink frequency is 1090 MHz. So wouldn't we be building a transponder dipole with each leg about 2.75 inches (or so) long? The 6.25 inch per leg dimension would fit an operating frequency close to 450 MHz. Mike RV6A Corvallis, OR > At 02:23 PM 8/5/2014, you wrote: >> >>I hope this isn't a duplicate, but I was unable to find sufficient >>info on this topic in the archives. >> >>I have successfully built and tested several copper foil/tape comm >>antennas for my Cozy MkIV and would like to build a transponder >>antenna the same way. >> >>Will the following work for a Mode S transponder: >> >>1. Vertically oriented 1/2 wave dipole. > > yes . . . > >>2. 1/2" copper tape with ferrites > > not particularly useful at VHF, useless > at uhf > >>3. Each leg 6.25" long > > Yeah . . . about that. Suggest you look over the > Bob Archer SA-005 descriptions and pictures > on the 'net. > > http://tinyurl.com/mdho4z8 > > Bob uses double sided ECB material to craft an > antenna and matching section all in one piece. > As you can see . . . his 'dipole' is rather > wide . . . which yields a low SWR over a rather > wide frequency range . . . not that you NEED > the bandwidth . . . but the wider elements makes > their length less critical. > > Here's Bob's narratives on transponder > antennas. > > http://tinyurl.com/lwgonmx > > Suggest you consider a dipole of at last 1/2" > wide material . . . 1" wouldn't hurt. Assembled > onto a sheet of plexiglas and attached to the > feedline with a Pawsey stub balun. > > http://tinyurl.com/lnjhmem > > http://tinyurl.com/lxzlpky > > The 'thing' about ferrite beads strung onto the > feedline has been popularly circulated through > many venues but there are caveats . . . > > First, the torroid material must be a pretty > good performer at the frquency of interest . . . > NO torroid materials I'm aware of are suited > for service at 1000mHz. > > Second, the inductance presented by a coil of > wire on a core varies as the SQUARE of the > turns on the core. Effective use of torroid > cores as de-coupling baluns calls for MULTIPLE > turns on one core. This picture shows 7 passes > of wire through the core for an effective > inductance 47x that of a single pass. > > > [] > > > Hence, one would need to string 47 single > cores onto the coax as a string of beads to > equal the effectiveness of one core wound with > seven turns . . . but generally useful only > at 200mHz and below. > > There used to be a commercial vhf comm antenna > offered that used the multi-turn torroid de-coupling > philosophy. I think it was called the "airwhip" . . . > don't find anything about the company now . . . > it's been a few years. > > Now that I have ready access to an EMC lab, > any antenna you'd like to fabricate as > a shippable assembly could be mailed to me > for a quick look-see in the lab. > > > Bob . . .




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