Amps
[Top] [All Lists]

Re: [Amps] RF in Vehicles

To: "Mark Bitterlich" <markbitterlich@embarqmail.com>, <amps@contesting.com>
Subject: Re: [Amps] RF in Vehicles
From: "Carl" <km1h@jeremy.qozzy.com>
Date: Fri, 21 Apr 2017 21:14:13 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Mark, do you have access to or build a RF sniffer that can be run along the wiring and coax to detect hot spots? The sensitivity will likely have to be very poor or have switchable attenuation and then feed into a VNA or SA.

I had to spend 6 days on the USS Carl Vinson, CVN-70, in 82 to locate and fix the ships RF getting into the computers and work stations. That was my first serious field experience with ferrites and the fix was done in 3 days. The rest was a "sea cruise" as I was also a USNR CWO2 and had a ball with the chiefs. Catapulted off and flew home from PR.

Carl


----- Original Message ----- From: "Mark Bitterlich" <markbitterlich@embarqmail.com>
To: "Mark Bitterlich" <markbitterlich@embarqmail.com>; <amps@contesting.com>
Sent: Friday, April 21, 2017 6:39 PM
Subject: Re: [Amps] RF in Vehicles




Carl, the transmitter ranges from 60 MHz, to 500 MHz. David, the reason for
that much power is that it is used for jamming.   Bob Moody, it is
impossible to radiate this transmitter on the ground.  There are serious
HERP and HERO issues.  Ron, same answer.  Can't transmit it on the ground.
Further, the power source is a Ram Air Turbine.  The transmitter has been
checked on a bench and operates normally.  The antenna and feedline have
been checked with a VNA, but not under load, which of course makes them
suspect.  They were replaced.  Same problem.  Jim, the electronics are
pretty well designed.  Yes, I agree that the RF is coupling to the wiring
(thus my point when I presented this true condition) but in a way that is
not obvious and not easy to troubleshoot.  My comment was also intended to
make the obvious connection that RF outside can easily become RF "inside"
even with a properly designed antenna, ground plane and feedline. Amazingly enough, this problem occured at the exact same time as the "RF in vehicles"
subject line appeared, so I thought I would mention it.

Interestingly enough, at 1-10 GHz, at the same or higher power level, there
are no issues with the generator.

The length of the wiring from the transmitter enclosure to where it enters
the aircraft is about 12 inches or less.  It is also extremely well
shielded, and also has been replaced.  The grounds for these shields have
not been extensively tested, only with a standard ohm meter. Using a bridge
to check it down to milliohms is being done.

I am not permitted to redesign the aircraft.

Mark


----- Original Message ----- From: "Carl" <km1h@jeremy.qozzy.com>
To: <qrv@kd4e.com>; <amps@contesting.com>
Sent: Thursday, April 20, 2017 9:07 PM
Subject: Re: [Amps] RF in Vehicles


RF can flow on both sides of the aircrafts skin and it appears you have a typical common mode issue. If you would be a bit more specific about the frequency, since VHF/UHF covers from 30 mHz to 3 gHz, a solution can be suggested.

Carl


----- Original Message ----- From: <qrv@kd4e.com>
To: <amps@contesting.com>
Sent: Thursday, April 20, 2017 7:14 PM
Subject: Re: [Amps] RF in Vehicles


He was speaking in shorthand.

Of course the radio is the "source" of the RF.

Presuming that the coax is properly connected to the radio, the
radio is properly grounded, and the antenna is resonant then the
problem would seem to be that something is coupling the RF from
the antenna into the wiring to the Supervisory Control Panel ...
or, the RF is somehow getting back though the power supply line.

If the antenna is non-resonant, for some reason, then the coax
can unintentionally become part of the antenna system ...

1KW at VHF/UHF is a ton of RF anywhere - but in the closed system
of an aluminum container - wow. You don't have to misplace much
of that power to cause mischief.

Given your altitude I wonder about the need for so much RF power,
but that's your business.

Just one non-engineer Ham's thoughts ...

73, DavidC KD4E

So I have this airplane. Not a Cessna 150, but not a B-52 either. Jet with with about 30 KW available as the power source. The transmitter consists of a phased combiner with four PA stages adding up to well over a KW in the VHF/UHF range. The antenna is a basic monopole that uses the complete mounting base as a ground plane. This arrangement is mounted on the aircraft centerline. The aircraft itself makes a fairly good Faraday Shield in that it has a solid surface of aluminum that is overlapped and bonded to the internal structure. Never-the-less, there are several wiring bundles that connect to this transmitter assembly for command and control that are fed inside of the aircraft and thus by-pass the "Faraday Shield".

When the transmitter is turned on, one of the internal generators in the aircraft immediately turns off. The generator is a 3 phase 115 VAC 400 Hz model that uses an internal permanant magnetic generator at 40 volts AC 800 Hz, that is in turn regulated to control the field of the generator. This is controlled by a Supervisory Control Panel that controls the field and also monitors for over/under voltage and frequency.

Clearly the Supervisory Control Panel is being impacted by RFI thus shutting the generator down.

The comment was: "This makes no sense. Unless something is very wrong with the radio, there should be no RF on power or control wiring. From an EMC point of view, the ANTENNA and it's counterpoise (metallic parts of the vehicle) are the source of RF, NOT the radio. Clearly, whoever at Toyota wrote this doesn't have a clue."

Ok, so what's wrong with this airplane?

Mark Bitterlich
WA3JPY

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps


---
This email has been checked for viruses by AVG.
http://www.avg.com

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps


_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps

<Prev in Thread] Current Thread [Next in Thread>