Kingsley,
Where I lost you:
People like to have 5V USB charging points for their ipads etc. fed from
a 12V cigar lighter socket. These are very cheap and very noisy
switchers; interfere badly with AM radio like our COM. Mitigation
involves a filter on their 12V input and on their 5V output. Even so a
cheap switcher radiates and degrades radio reception.
If what we hear is the charging of the capacitor the source should be
the input power lines or the (transformer in) the box, not the output
wiring to the strobe.
With the box located at the bagage bay station it would then seem
strange that the antenna in the tail would be affected and an antenna
near the panel (although lower quality) not at all.
Maybe some more experimentation with antennas would be useful: 1. moving
a test antenna from panel to tail via the bagage bay 2. replacing the
tail dipole with a 50 ohm dummy load.
Jan
On 12/23/2015 11:24 PM, Kingsley Hurst wrote:
> RON I do have twisted pair power supply lines to the strobe power
> supply thanks.
> PETE Thanks for that tip . . . . . LED Strobe will be considered if
> all else fails.
> JAN Comments / answers embedded below . . . .
> Thank you all
> Kingsley
> *From:* Jan de Jong <mailto:jan_de_jong@casema.nl>
> *Sent:* Wednesday, December 23, 2015 7:36 PM
> *To:* europa-list@matronics.com <mailto:europa-list@matronics.com>
> *Subject:* Re: Europa-List: Strobe noise in radio
> I don't know what you mean when you say "chew chew"?
> *It is hard to describe a noise in words . . . Chew Chew is the best
> I can come up with Im afraid.*
>
> Does it appear when receiving radio or always?
> *Always whenever the radio is turned on. Volume of the noise can be
> controlled with the Vol control.*
> The "chew chew" could be the power supply charging its capacitor after
> each discharge?
> *Think you are right on the mark here Jan . . . . the noise
> immediately follows the flash and it does sound like the power supply
> charging its capacitor.*
>
> How did you prove that it is radiation coupling to the antenna?
> *1 Disconnected the power wires to the strobe unit to isolate the
> unit from the rest of the aircraft wiring and then supplied power from
> a second battery direct to the strobe unit. Made absolutely no
> difference to the noise.*
> *2 Disconnecting the aerial from the back of the radio completely
> eliminates the noise as does connecting an aerial from a hand held radio.*
>
> 5V USB switchers are made to behave in the presence of AM radio mainly
> by a filter on the input (2 capacitors and an inductor).
> *Sorry but you have lost me here.
> *
> Thanks again
> K
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