Transponder interferes with fuel flow

Still building-- haven't flown yet. I've got a red cube fuel flow sender supporting a GRT engine monitor. A Trigg tt22 transponder mounted remotely behind the panel. The antenna for the transponder in mounted in the floor about 4 inches aft of the firewall. When the transponder is on, the FF indicator reads .3 gph with the engine shut off. When transponder is off it reads zero as it should. Must be getting Rf interference from the transponder. Any Ideas on how to fix it. My ideas are:
1. calibrate the ff with transponder on.
2. try a shielded wire gong to the red cube.
3. leave it as is and see how accurate it is when I fly.

- I really don't have a good place to move the transponder antenna without it encroaching on the com antennas.

Shield the wire. It sounds as if the wire is picking up pulses from the transponder and counting it as fuel flow. Not ideal.

Don

You may try moving away from any metal structures.

I'd try using a shielded, twisted pairs cable for the red cube, but first, make sure your RG-400 (not -58!) transponder coax is physically separated from the red cube wires. Look carefully at the transponder antenna connection to see that the coax cable's shield is properly attached to the BNC connector, and that the antenna itself is properly grounded to the airframe.

Try moving the plane outside and then test it to see if it still interferes with the fuel flow. Might be caused by too much RF energy bouncing off the walls etc.

My 2 cents

Hi,

I've worked with FPV Rc flying where I'm using 2.4 and 1.3 ghz signals along with spinning a high kv motor. I have found tha using a ferrite ring usually fixes any rf interference, it's a cheap and easy fix.

Fertile ring

Thanks for the tip. I never heard of a ferite ring before, but I googled it and it appears inexpensive and cheap. It looks like I would wind wire(s) through the ring. Would it be ok to run all three wires through the same ring?

Instruct

Run all the wires you think have interference from an outside source.you can even run them multiple times.

I'm not claiming to be a pro at using these nifty devices, but I'm sure you can find great resources online to assist in installing.

Wait a second, I guess we're all online aswell.... That's so weird having someone online recommending to go somewhere else online!?

Good luck my virtual friend.