Hello, I am the builder and keeper of a two metre repeater "GB3VT" here in the UK and the repeater has now been operational for the past 30 years. In 1994 it was necessary to vacate the original site, but a few months later we located a new site and in 1995 the repeater was again operational.
However with the repeater now operational at the new location, the equipment was exhibiting a problem that was not experienced at the original site and the problem consisted of a mix caused by a Medium Wave AM transmitter on 603KHz, the said effect was mainly during the evening and hours of darkness. Our new site is a private residence, no tower, no guy wires and nothing obvious to cause any possibility of RF rectification, just a colinear aerial on a pole attached to a brick garage. But because it is a private residence and naturally being extremely grateful to the owners for allowing access to their property, I felt it imperative to keep the number of site visits to an absolute minimum. With this in mind I decided to make three changes to the Repeater Equipment Installation and all three said changes were to be implemented at the same time. Now whether it was a combination of all the three changes or perhaps just one I really can not say, but thankfully the mixing problem stopped. I added the following hardware: 1/ A Two Stage (air spaced) Bandpass Filter bolted directly to the equipment cabinet between the aerial feeder termination of the Eight Cavity Duplexer output and the aerial feeder. 2/ A substantial and efficient Mains Supply Filter bolted directly to the equipment cabinet. 3/ Using the Ferrite Core from an old television line output transformer, I wound as many turns as possible of the coax feeder between the Duplexer and the Bandpass Filter (now reduced to RG58/U) around the Ferrite Core allowing just the one layer of turns. >From that day on, now some 15 years ago, the mix stopped and with all fingers >crossed it stays that way. Yes it would be interesting to know exactly which one of the three actions proved the cure, or perhaps it was indeed a combination of all three, but then, if it aint broke, why fix it? 73, Geoff, G8DZJ. ~~~~~~~~~~~~~~~ ----- Original Message ----- From: lpcoates To: [email protected] Sent: Monday, April 26, 2010 4:06 AM Subject: [Repeater-Builder] Interference from local 600 kHz radio station. Hi We have a local AM radio station on 600 kHz. Their transmitter site is about 10 miles from the center of the city. From what I've found on the web, they run 25,000 watts during the day and 8,000 watts at night. On at least one of our repeaters we're finding that this is mixing with the output of repeater to create a phantom signal exactly on the input. We're not sure whether the mixing is happening inside the repeater or in something in the environment near the repeater. We've confirmed this is the source of the problem on one repeter and supect it on another. Has anyone had experince with a loacl AM station on 600 kHz? We're looking for way to combat the interference. Thanks Bruce - VE5BNC ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.814 / Virus Database: 271.1.1/2834 - Release Date: 04/25/10 07:31:00
