PTT & Tacho

daveb

Member
Joined
Jun 23, 2004
Messages
88
Location
Melbourne, Australia
Aircraft
Open frame 582, Long-EZ
Total Flight Time
Gyros 460+ Sailplanes 920+ GA 80+
Had a surprise today when I looked at the tacho and saw 7000rpm for a second or so. :eek: I didn't hear my new 582 change in pitch yet I saw what I saw and 6100rpm is about MAX on my set up.

Turns out when I use the PTT I get 1000 extra on the tacho. This didn't happen with the old 582 and the same radio configuration.

Any thoughts on what why this is?

Dave
 
Dave,

Sounds like a cheap way to get more power. :)

Sorry I can't offer you anything more helpful. ;)

Rob
In Scarborough, Queensland
 
Dave, I think that the new antenna so close to the tach will be the problem.

Aussie Paul.:)
 
Paul,

Analog or digital tach pickup? If it's creating an analog voltage using magnets crossing a coil, there's a diode somewhere downstream turning the voltage into DC to feed the gauge. The strong radio signal will be picked up and rectified along with it, boosting the reading. If it's a digital, it could be getting in a couple different ways.

Yes...keeping the antenna away from the tack pickup and wiring would be a good first step. If you antenna is not resonant or not well matched to the impedance of the radio and/or cable, you can get radio frequency energy backing up the DC power hot lead into places it doesn't belong. Poorly matched antennas have sometimes caused EFI and CDI systems to act erratically, sometimes stalling engines when the PTT is keyed.
 
Back
Top