If they were only providing the head shield, lots of RF could still have been leaking down the strobe cable.
_____ From: [email protected] [mailto:[email protected]] On Behalf Of William Becks Sent: Friday, May 01, 2009 3:48 PM To: [email protected] Subject: Re: [Repeater-Builder] Computer noise in 2M Repeater Bill, Thanks for responding with the information about the shield kits being supplied by the manufacturer. With this info I will be able to contact them for a price and availability check for our site. I first encountered RFI caused by the early Flashguard units back in the mid 90's. My company had a site with a UHF TDMA rural radio (BETRS) system that suffered high BERT at night. At the time, Flashguard offered a suppression kit to retrofit the strobe housing, but that proved to be virtually ineffective. As a temporary fix, we had gave up channel capacity switching from 16-PSK to 4-PSK modulation. Eventually, we just got rid of the strobe and went with an incandescent beacon lamp system on the tower. Bill ----- Original Message ----- From: Bill Smith <mailto:[email protected]> To: [email protected] Sent: Friday, May 01, 2009 1:37 PM Subject: RE: [Repeater-Builder] Computer noise in 2M Repeater We contacted Honeywell/Flashguard and they sold us the kits. In our situation, we changed to our backup antenna which is 20 feet below the main which is less than 2 feet from the strobe head until the shield kit was installed. The shield housing mounts to the top plate of the tower with the strobe head placed inside. It's hinged to allow service access. The cable shield is a plastic covered metal liquid tight conduit with a fitting that connects to the shield housing to ground it. Sorry I don't have any cost info. Bill _____ From: [email protected] [mailto:[email protected]] On Behalf Of William Becks Sent: Tuesday, April 28, 2009 7:34 PM To: [email protected] Subject: Re: [Repeater-Builder] Computer noise in 2M Repeater Bill, Can you please elaborate on the shield housing used? I have similar noise on my VHF ham repeater caused by the same Flashguard 3000 system. I was able to reduce the noise during night operation by reorientation of the antenna at the expense of a less than optimum radiation pattern. The cellular company that owns the tower doesn't seem to have any problems with the RFI from the strobe lamps, but then they are using panel antennas directed away from the tower and strobe lamps. Thank you, Bill, WA8WG ----- Original Message ----- From: Bill Smith <mailto:[email protected]> To: [email protected] Sent: Tuesday, April 28, 2009 4:33 PM Subject: RE: [Repeater-Builder] Computer noise in 2M Repeater I have experience with several 451 MHz systems getting hammered by noise from the strobe. These were Flashguard 3000 units. During the day when the strobe tubes triggered once it wasn't noticeable. At night when the tubes were retriggered multiple times to lengthen the on time of the flash, it dropped our RX sensitivity by over 30 dB. A spectrum analysis showed noticeable RF from below 50 MHz, peaking around UHF and dropping off around 900 MHz. In this unit, the tubes are about 6 inches long. We installed a shield housing over the entire head and 20 feet down the power cable along with installing toroids on the power feed inside the head. Bill KB1MGH _____ Now. the strobe problem you're describing sounds like a potential horrible electrical problem at the site. In my experience an FM rig shouldn't be greatly affected by a strobe. It also shouldn't be causing a problem/reaction with the WISP gear (it may be causing damage to it!) so I'd definitely find out what is going is going on with the strobe. Good luck! Jacob Suter
