L-Band Antenna Suppression Line 1

[sb1786]

Hello All,

I am trying to install on an A310 a communications antenna using L-Band frequency. I've been told that a suppression line system should be installed in order to avoid this antenna from interfering with important systems such as DME, VHF, TCAS etc. Unfortunately, I wasn't given more details than that so I am wondering what is a suppression line, what does it do and how you install it?

 

[FieldTeam]

The suppression line would be a discreet coming from the RT of your system to the RT's of the TCAS, TACAN..... that would inhibit the associated RT from receiving during the transmit mode.

 

[debodine]

FieldTeam is correct. It has been a few years since I did design work in that area (ok MORE than a few years) but as I recall in the old analog days the pulse was a positive 28 VDC pulse 0.5 microseconds in length that was sent by an L band transmitting unit (typically a DME Unit) to an L band receiving unit (typically an ATCRBS transponder) which would warn the ATCRBS transponder to shut down the receiver input to protect it from possible stray high energy RF from the DME transmitter.

The ATCRBS transponder also sends a suppression pulse to the DME unit for the same purpose when the ATCRBS transmits and the DME receiver needs protection.

Physical separation of the two sets of antennas was still good practice but the suppression pulse was necessary for complete protection.

DME transponders transmit on a channel in the 962 to 1150 MHz range and receive on a corresponding channel between 962 to 1213 MHz. ATCRBS transponders transmit on 1090MHz and receive on 1030MHz.

You can see that the two ATCRBS frequencies fall in the DME range, so depending upon which DME channel was selected then the possibility of interfere existed.

The equipment you are installing should have details of the operating frequencies in the installation manual and should give guidance on how to hook up an incoming and/or outgoing suppression pulse.

As an example, look at page 9 of this installation manual I found on the Internet for a typical ATC transponder:

http://volkslogger.de/cms/images/stories/manuals/01.0200.11e vt01inst_rev1.3.pdf

You will note a clear definition of both the incoming and outgoing suppression pulse criteria. Elsewhere in the manual it will define which pin or set of pins provides the suppression input/output.

Hope this is not TMI but instead helps you to understand the reasoning behind the suppression pulse issue.

debodine

 

[sb1786]

Debodine,

This is exactly what I was looking for an explanation.