Push to Talk causes fuel flow to drop

[Mazerbase]

I've recently been having a drop in fuel flow indication when I use the PTT. I have 2 Dynon systems but it is only happening with one on a SeaRey with an HDX800 (installed in April but the problem is only the last couple weeks. I also have 2 red cube transducers (supply and return). I've read about the PTT and EGT issue but noting about fuel flow. Anybody already faced and resolved this issue? Thanks.

David

 

[Rhino]

I've never heard of PTT interfering with anything, including EGT. It's just a ground, so it's hard to imagine it could. However, PTT does activate other things that could potentially be causing problems, headsets, radios, intercom, etc. PTT also does not go through the EFIS, which makes this even more strange. I would suspect a problem with an audio connection on that one EFIS, to start. You might try swapping them, just as an experiment.

 

[Mazerbase]

Can't. This is an HDX800 and the other is a D1000T.

 

[GKC Aviation]

I'm looking at a Glassair which has interesting problems.
Transmit on Com#1, the EGT's all rise about 50 degrees, release the PTT and they go back to normal.
Transmit on Com#2, the altitude drops about 40 ft, release the transmit and it goes back to normal.
The builder used the old RG-58 coax, and bundled it tight in the wiring looms.
It's obviously interfering with the EMS and ADARS wiring. Going to be quite a job to pull it all and replace with RG-400, and reroute out of the wiring looms.

 

[Rhino]

What's going through the RG-58? PTT is just a ground. Are you referring to the radio antenna cables?

Mazerbase, does this happen with only one radio, or both? What kind of intercom or audio panel do you have?

 

[GKC Aviation]

What's going through the RG-58? PTT is just a ground. Are you referring to the radio antenna cables?

It's the actual transmit of the radios when PTT is keyed.

He could fault find by turning off one radio, then the other to find which com is causing it.

 

[Rhino]

Or swapping them, if they're identical. He could also swap antenna cables. I usually suspect this is an antenna or antenna cable/connection issue. It usually is, especially when it starts doing it out of nowhere. Antennas go bad, water gets in, builders often use cheap cable and connectors.... The list goes on and on. This one gets interesting because he says it only happens with one EFIS. But the EFIS has nothing to do with PTT, so I assume he's referring to the EGT indication. But swapping stuff helps isolate and focus the troubleshooting effort.

 

[Mazerbase]

I only have one radio and I'm not referring to the EGTs. It does transmit fine. Now it seems to be intermittent and on longer transmissions.

 

[Rhino]

PTT does not go through the EFIS, so this points even more toward an RF problem with the radio/antenna/cables. However, voltage variations have been known to cause fluctuating readings on some rare occasions. If you don't want to chase down an RF issue, you could check system voltage on the EFIS to see if it changes significantly when you transmit. You might also try swapping the EFISs, to see if the problem moves with them.

 

[jakej]

I've never heard of PTT interfering with anything, including EGT. It's just a ground, so it's hard to imagine it could. However, PTT does activate other things that could potentially be causing problems, headsets, radios, intercom, etc. PTT also does not go through the EFIS, which makes this even more strange. I would suspect a problem with an audio connection on that one EFIS, to start. You might try swapping them, just as an experiment.

Just had to answer Rhino - actually there was a time when the Dynons would show, sometimes significant, ‘spikes’ in the EMS when transmitting- this was ’fixed‘ by using filtered dsub connectors & then new screens had better resistance to RF/EMI since then. So, yes the PTT action can cause issues.

 

[Mazerbase]

And, as I've mentioned, I only have the one EFIS.

 

[jakej]

Mazer - have you tried unplugging the return line unit ? Swap the units too & do the same ‘test’ when engine running on the ground out in the open ?
Also, there is this however it’s different to your situation but could/may still apply , FYI —-
The insulated wire (white covering) is too stiff & bending it to a desired position when installing the FF unit can & does stretch the wiring internally resulting in intermittent ops - no need to ask how I know . Careful use of a heat gun to soften the wires before bending works really well.
I’ve also noticed that there is some resin? added to the new later purchased cubes - for reinforcing? - where the wires exit.

 

[Rhino]

Just had to answer Rhino - actually there was a time when the Dynons would show, sometimes significant, ‘spikes’ in the EMS when transmitting- this was ’fixed‘ by using filtered dsub connectors & then new screens had better resistance to RF/EMI since then. So, yes the PTT action can cause isThe radio being keyed by th

That wasn't caused by ground from a PTT. It was caused by the radio transmitting in response to the PTT, or maybe an intercom/com panel. That's what I was pointing out in post #2. The ground from the PTT does not cause the problems. It's the downline actions somewhere else that are keyed by the PTT that cause the problems, RF or voltage related. The solutions you mention are basically related to what I was referencing in post #9. Methinks we may be talking about the same thing, and we're just getting hung up on semantics.

But since I only have a vague memory of those past problems, do you recall if they were ever with the HDX systems? I seem to remember that just being in the 100 series systems, but my memory stinks lately, and i don't want to trust it. I trust your expertise more.

 

[Rhino]

...no need to ask how I know ...

LOL! I know! I know!

Been there, done that, too many times!

 

[wilhelmfp]

I had #2 CHT drop whenever I keyed PTT. I recrimped leads to the CHT sensor and problem is gone.

 

[jakej]

That wasn't caused by ground from a PTT. It was caused by the radio transmitting in response to the PTT, or maybe an intercom/com panel. That's what I was pointing out in post #2. The ground from the PTT does not cause the problems. It's the downline actions somewhere else that are keyed by the PTT that cause the problems, RF or voltage related. The solutions you mention are basically related to what I was referencing in post #9. Methinks we may be talking about the same thing, and we're just getting hung up on semantics.

But since I only have a vague memory of those past problems, do you recall if they were ever with the HDX systems? I seem to remember that just being in the 100 series systems, but my memory stinks lately, and i don't want to trust it. I trust your expertise more.

Yeah, semantics, however being clearer about the act of transmitting causing possible RF issues may explain it better for the inexperienced/less knowledgeable? My memory is that the issue re RF causing ‘spikes’ etc was more pronounced with the SV Classics & remote mounted EMS-220 etc. ‘Filtered’ dsub connectors were used as an interim measure until the improvement were made.

 

[Rhino]

Yeah, semantics, however being clearer about the act of transmitting causing possible RF issues may explain it better for the inexperienced/less knowledgeable?

Fair enough. Point taken.

My memory is that the issue re RF causing ‘spikes’ etc was more pronounced with the SV Classics & remote mounted EMS-220 etc. ‘Filtered’ dsub connectors were used as an interim measure until the improvement were made.

Thanks.