Some of you may remember that months ago I asked for help with a long time problem that had every temperature reading take a dip, along with the autopilot on altitude hold, every time the PTT was pushed.  A friend of mine (Doug) had a similar problem with his Cozy Mark IV.

 

It was severe - OIL, OAT, CHT and EGT would all take a plunge with the oil dropping 30 degrees, OAT 14, CHT 200 (causing the cyl chill warning light to come on).  The auto pilot would take the nose down if altitude hold was engaged.  Doug and I had many discussions with David McCluskey at VM and Doug also talked to Bob Nuckolls who suggested we consult with the Air Force's secret hangar people about RFI.  Hmmmpf. David suggested we start by using ferrous toroids on the oil temperature leads and sure enough, the oil temp only dropped 8 degrees after they were applied.

 

Now for the Black Art.

 

First, Doug rewired his two comm antennas (located in his winglets) with RG400 to try to eliminate "line leakage" since the cheaper RG50 is well known to be "leaky".  He also got rid of connectors at the wing roots - this required some pulling and routing.   While leaving a 2 foot loop laying on the fuselage floor, but near the cable channel carrying other low voltage wires, a test was made.  I don't remember what the temperatures did, but every time the transmit button was pushed his alternator field breaker would pop (B&C LR3 Regulator).  Just rerouting the antenna lines outside the wire channel and getting rid of the loop stopped the breaker from popping.

 

Second, let me set up my situation:

 

The Radio Stack - from top down

Monroy traffic alerter

Terra Audio Panel

Garmin 430

Terra Com2 - Terra Transponder

Hobbs meter   - Terra ADF (for listening to Rush)

 

The right side of the panel is full of lights and switches, the ADF indicator, 8 very flat EPI 800 displays and at the far right are two vertical rows of circuit breakers.  Forward of the panel and at the bottom is a large grounded aluminum sheet used as a mounting base.  Forward of the breakers are the fast-on ground connections and on legs above that is a 20-fuse fast-on block.  Forward of the displays and mounted on the plate is the special VM annunciator/IO connector block.  The VM computer sits on legs above that and is surrounded by an aluminum box open fore and aft (aft for wires).  On the top of that box are 3 dimmer circuits and the automatic fuel system brain box. At the forward edge of the plate and in front of the VM computer is the ACK encoder.  Velcroed to the inboard vertical side of the box around the VM computer was the Comant antenna switcher for the lines from COM1 and COM2 and the RG50 cable that runs from there forward, down, under the floor boards and thru the tunnel to the com antenna in the vertical stabilizer.

 

More Black Art!!!!

 

Learning from Doug's wire movements (1st and 2nd in A minor), I unstick the Comant unit and wedge it under all the wires coming out of the Terra audio panel, just above the 430 tray.  I slightly reroute the antenna lines to the box and replace the 2 foot line to the Garmin 430 (the most powerful radio) with RG400.  I go fly with the autopilot on alt hold - its a beautiful day.  I dial in an unused frequency and push the PTT for 5 seconds, 10 seconds 15 seconds.  The oil temp drops 1 degree, the CHT and EGT not at all, the OAT in the Rocky Mountain instruments Micro-encoder does not change, the VM OAT drops only 4 degrees C (who cares? Toroids can be added later) and there is no dive from the autopilot. 

 

If only we could see RFI.

 

I will not move the Comant unit anywhere else and if you touch my antenna leads I will... well, let's just say you  wouldn't be able to give the FBI your finger prints ever again.