Eric,
I'm pretty sure that the XR2206, like many of the neat XR chips, is no
longer available, but yes that is a good option if available.
Tom Fowle WA6IVG

On Wed, Nov 25, 2015 at 09:24:20PM -0700, Eric Oyen wrote:
> ok,
> let me chime in here. I had some experience building vco circuits back =
> when I could see to do so.
> 
> the simplest (assuming you can still find them) are the XR-2206 function =
> generator IC (it has a vco built in) and a standard garden variety op =
> amp. use the op-amp on the non-inverting input and use a negative =
> feedback system (run a line through a resistance from output to =
> inverting input). Once the gain level is set, the vco will have =
> sufficient voltage to work with. Properly setup, this has a wide number =
> of applications and can be run on a single 9 volt battery. check with =
> your sighted tech friends and see if they can put this puppy together.
> 
> DE n7zzt Eric
> 
> On Nov 25, 2015, at 8:40 PM, Tom Fowle wrote:
> 
> > richard,
> > How you adapt the directional system depends entirely upon what kind =
> of
> > signal is available from it.
> >=20
> > Let's assume the unit to be modified has a regular old fashioned meter
> > movement  which indicates how well the antenna is aimed at the fox.  =
> If the
> > meter simply reads "higher" when more closely pointed, it's pretty =
> easy.
> >=20
> >  In that case you need a VCO which can look at the voltage across
> > the meter,  usually 50 to 100 Milivolts
> >=20
> > A slightly trickier system uses a so-called "zero center" meter which =
> shows
> > whether you're aimed left or right of the fox. These meters actually =
> measure
> > current in either direction  This would need a bit of fiddling before =
> being
> > applied to a VCO.
> >=20
> >=20
> > There are gobs of such vco circuits available from transistorized ones
> > designed in the 1950s to specialized chips and microcontrollers.=20
> >=20
> > If all you need is a "relative" indication, not the ability to get an =
> exact
> > measurement, I'd suggest the transistorized circuit for its =
> simplicity.
> >=20
> > You and your friend can find many such circuits in plain text format =
> in:
> > The Smith-Kettlewell Technical File
> > https://legacy.ski.org/rehab/sktf/index.html
> >=20
> > Search the magazine for "audio gimmick" circuits or "meter readers" =
> and
> > you'll find more than you'll ever want.
> >=20
> > the only issue for your presumably sighted friend is that the =
> schematics are
> > text discriptions not schematic drawings. Sometimes it's fun to have =
> the
> > sightlings be at a small disadvantage <GRIN>
> >=20
> > If I can help with more specific choice of circuits or related stuff, =
> please
> > email me either on list or directly.
> > Tom Fowle WA6IVG
> >=20
> > On Wed, Nov 25, 2015 at 09:36:41AM -0800, Richard B. McDonald wrote:
> >> Hi!
> >>=20
> >>=20
> >>=20
> >> In a few months, my club is going to do some fox hunting activities.  =
> My
> >> question here relates not so much to making the "antenna" itself per =
> say,
> >> but rather to making an audible tone direction indicator.  I think =
> this
> >> thing is called a "V C O?"  Basically, the V C O causes the pitch of =
> a tone
> >> to change as the direction finding antenna is pointed towards the =
> fox.
> >>=20
> >>=20
> >>=20
> >> A very techy friend of mine in the club is going to build this =
> contraption
> >> for me, including the antenna itself.  He has some ideas.  However, I =
> wonder
> >> what others here on our list have done?
> >>=20
> >>=20
> >>=20
> >> 73,
> >>=20
> >> Richard KK6MRH