Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hplsla!tomb
From: tomb@hplsla.HP.COM (Tom Bruhns)
Newsgroups: sci.electronics
Subject: Re: direction finder
Message-ID: <5170037@hplsla.HP.COM>
Date: 2 Jun 89 15:25:59 GMT
References: <11269@megaron.arizona.edu>
Organization: HP Lake Stevens, WA
Lines: 39

prem@crackle.amd.com (Prem Sobel) writes:
>In article <11269@megaron.arizona.edu> wendt@arizona.edu (Alan Lee Wendt) writes:
>>I'd like to build a direction finder that my wife (who's blind)
>>can use to find the house.  Something with a range of 2 miles or
>>so, that could be left on all the time at the house and a small
>>battery-operated hand buzzer that would stop buzzing when lined
>>up with the direction of the house.
>>
>>Help me get my wife her instrument license.  What frequencies
>>are available for this kind of use?  Anybody have any designs
>>for bits of this?
>
>Since city blocks are not radial, it might be useful for there to also
>be an audible distance measurement, but that is VERY expensive. For
>direction a system similar to the aircraft VOR system might be useful
>(again unfortunately very expensive), which sends an omnidirectional
>radio pulse out at the same time it uses a phased array to sweep a
>beam around at a known rate. The receiver measure the time between the
>omnnidirectional and swept beam to give angle to transmitter.

But VOR gives more information than requested:  the person does not
need to know that she is N, S, E, or W of the house, only in which
direction the house is.  That's easier.  If you have a beacon 
transmitter at the house and a receiver with an antenna with a single
sharp null (cardiod pattern), you have what the original poster wants.
I have no idea about frequencies, etc.  How about calling your local
FCC field office?  There have been some articles in ham magazines
on direction-finding within the last couple years that might be
useful; try _Ham_Radio_ magazine and QST.  I recall an article on the
"Double Duckie" antenna that has a sharp null - but the null is in
two directions.  Even so, it's fairly easy to resolve the ambiguity.
By nature of its operation, the antenna puts essentially FM modulation
on a CW signal, so you could broadcast a CW sig and she could hear the
modulation and turn the antenna to null it...
>
>If power levels are below a certain level (100 milliwatts I believe)
>or the signal is on on certain allowable experimental frequencies
>(above VHF) then no license is needed.
>----------