Peter,
The WAAS antenna is much more sensitive to interference because the pre-amp has much higher gain than the non WAAS antenna (I think an extra 7-9 DB). Interference on 121.5 can be caused by the ELT re-radiating the energy, but so can interference from a Com unit on that frequency. In my case, it was the latter. I replaced my 121.5 ELT with a 406 MHz unit thinking it was the cause of my issue. I had already inserted a notch filter in the Com antenna line. As it turned out, the energy was not radiating from the antenna, ELT, or coax. KX155/165 units are also known to leak energy thru the display. A simple test is the one described in my post, place an anti-static bag over the face and if the source of the interference is thru the display, it will magically disappear. A small strip of the anti-static bag placed behind the display of a KX155/165 will eliminate this source of interference.
Interesting...
I have read that the KX155/165 are much worse on the 13th harmonic than the "A" versions, but the "A" still did it.
I had an opportunity to open a used 155A on the bench and had a look inside to see if one could fit the TED resonant cavity filter in there. There was no room inside at all. Not even for a 0.5" x 1.5" item like that filter.
The build quality of the "A" seemed to be very competent, with RF gaskets everywhere. I don't think it would leak through the front. Maybe King learnt their lesson by then (late 1990s).
A long time ago I flew an aircraft that had a Skymap and a separate bit of kit called a 'love-bug', this drove a standard ILS indicator allowing you to fly a pseudo ILS to any GPS coordinates. If nothing else this was a pretty useful training aid. Is this the same type of thing that the newer GPS units allow you to do?
Yes; this is not unusual, but it needs a working GPS system.
But to have a panel mounted indicator for it would be most unusual and PROB99 illegal 
Is there any panel mount GPS which can display a pseudo ILS on the CDI, to any user waypoint? I know hendhelds can do it...
The Skymap 2 and 3C units don't have a pseudo ILS feature anyway.
Is this getting more and more frequent? Today I got “attacked” on the south shore of Lac Léman (Geneva), out of a sudden all GPS receivers in my airplane (including handhelds, tablet, phone) lost reception. ATC did not know anything about it.
I’ve had it a few weeks ago at some other place, in total about 5 times this year (3x overhead Cairo 
). It seems to be getting a lot more widespread. Still freaks me out because I get like 10 alarms at the same time although it is a complete non-event because I have my heading, I have ATC with radar in 99% of the cases and there are ground navigation aids.
Does Shorrick have a credible alibi for today 1100Z?
You are sure it has nothing to do with your devices/installation?
5 devices going out at the same time, 3 of which are not installed in the cockpit? Reception going away suddenly and coming back simultaneously on all devices?
The only aircraft installed device that could create such radiation is the DME which I keep turned off all the time. I’ve seen it attenuate the GPS signal but not cause a loss of reception. Static charging on the airframe? Would first knock out VHF.
I cannot rule out an on board radiation source but what would that be?
I got one over Athens, going Milos-Skiathos this week. Lasted about 15 mins. ATC didn’t know anything but I suspect the particular ATCO did not understand “jamming” (or any other bit of conversational English). Greek ATCOs normally speak good English.
I asked for a vector and got it just about the time I dialed in the SKP VOR (I was cleared DCT SKP) and was ready to use that. Whether SKP was within its DOC, at about 70nm, FL100, is a good Q, but the CDI wasn’t flagged.
Candidates for self interference are 11th or 13th subharmonic of 1575MHz, plus some DME settings apparently unrelated to anything (I posted on this here a long time ago).
Achim, That’s really strange …. wow. Did you try to find something online?
If that was an onboard radiation source that made all these devices quit you would probably have been fried :-) (You already have children, right? :-))
An on board GPS antenna can become a transmitter and jam all the remaining units on the aircraft. This is more common with a WAAS antenna because of the higher gain. It is not uncommon.
