ELT turns on with comm transmitting ???

[R&R Sherwood]

A new problem has recently popped up with my ELT, an ACK Technologies model
E-01. I now have 160 flight hours on my Glasair. Occasionally the ELT
starts transmitting when the comm push-to-talk button is depressed. I
must hit the ELT reset button to stop it. The
only change that I have made is the addition of a one foot tall aluminum
structure placed about 8 inches from the ELT antenna. The comm is a King
97A, its antenna is about 4 feet from the ELT antenna. Have any ideas as
to what may be causing this?

Throttle Up,
Russell Sherwood

[[email protected]]

Russell: Some Diamond DA-40s have a similar problem. It seems to be
related to routing of the radio coax near the ELT control wiring. They
came out with a Service Bulletin which is bsically putting a split
ferrite on the control cable near the E-01. Here is the link:


http://80.121.174.62/support/PDF/DA40-180/TM/RSB40-045.pdf

[R&R Sherwood]

Looks like your tip worked....added ferrite toroids and moved the antenna
cable about 6 inches further away.
Thanks,
Russell Sherwood


> wrote in message
ups.com...
> Russell: Some Diamond DA-40s have a similar problem. It seems to be
> related to routing of the radio coax near the ELT control wiring. They
> came out with a Service Bulletin which is bsically putting a split
> ferrite on the control cable near the E-01. Here is the link:
>
>
> http://80.121.174.62/support/PDF/DA40-180/TM/RSB40-045.pdf
>

[[email protected]]

Glad it helped!

Steve

On Feb 28, 7:16 pm, "R&R Sherwood" > wrote:
> Looks like your tip worked....added ferrite toroids and moved the antenna
> cable about 6 inches further away.
> Thanks,
> Russell Sherwood
>
> > wrote in message
>
> ups.com...
>
> > Russell: Some Diamond DA-40s have a similar problem. It seems to be
> > related to routing of the radio coax near the ELT control wiring. They
> > came out with a Service Bulletin which is bsically putting a split
> > ferrite on the control cable near the E-01. Here is the link:
>
> >http://80.121.174.62/support/PDF/DA40-180/TM/RSB40-045.pdf

[[email protected]]

On Feb 28, 6:16 pm, "R&R Sherwood" > wrote:
> Looks like your tip worked....added ferrite toroids and moved the antenna
> cable about 6 inches further away.
> Thanks,
> Russell Sherwood
>
> > wrote in message
>
> ups.com...
>
>
>
> > Russell: Some Diamond DA-40s have a similar problem. It seems to be
> > related to routing of the radio coax near the ELT control wiring. They
> > came out with a Service Bulletin which is bsically putting a split
> > ferrite on the control cable near the E-01. Here is the link:
>
> >http://80.121.174.62/support/PDF/DA40-180/TM/RSB40-045.pdf- Hide quoted text -
>
> - Show quoted text -

Sometimes even that doesn't work. We have an ACK in one of the
airplanes that did that at certain airports, implying that certain
frequencies would trigger it. Ferrites reduced the incidence but
eventually I swapped it out for an ACK from another airplane, and now
they're both happy. The factory said that some were more sensitive
than others.

Dan

[R&R Sherwood]

Today I made the second and third flights since the adjustments.....ELT
triggered once.....much better but not 100%.
I have made a deal with someone to swap our ACKs. Hopefully this will do
the job.
Thanks
Russell Sherwood



> Sometimes even that doesn't work. We have an ACK in one of the
> airplanes that did that at certain airports, implying that certain
> frequencies would trigger it. Ferrites reduced the incidence but
> eventually I swapped it out for an ACK from another airplane, and now
> they're both happy. The factory said that some were more sensitive
> than others.
>
> Dan

[COLIN LAMB]

I do not know the layout of the ELT, but have experience in servicing solid
state devices and reducing interference, so I am responding in general.

I expect that the problem is created because the rf from the transmitter is
being picked up by the control cable of the ELT. That cable is acting as an
antenna. Rf entering into the ELT is rectified by a diode junction (solid
state devices can act as crystal sets). That rectification creates a
voltage which activates the ELT.

The factory specified a ferrite bead to solve the problem. That reduces the
rf getting inside the ELT. If that does not solve the problem, then use
more drastic measures to prevent rf from getting inside the ELT.

Some additional steps that can be taken are:

1. Loop the control cable through the ferrite bead 2 or 3 times. That will
multiply the effectiveness of the ferrite.
2. If you cannot do that, you can simply use 2 or 3 ferrite beads.
3. If the control cable is not shielded, replace it with shielded cable.
4. Add a capacitor across the terminals at the input of the ELT. A .001
ufd (1000 pf) capacitor should help.
5. Moving the comm antenna further away from the wiring.

I have not addressed the certification issue, which should be considered.
My aircraft is experimental and I feel like I have a bit more license to
work on it.

Colin Lamb