In a message dated 31/03/05 19:42:07 GMT Daylight Time, [EMAIL PROTECTED] writes:
Not inexpensive, but works well: http://www.dci.ca/ Specifically: http://www.dci.ca/?Section=Amateur We installed one of the 2M units on our repeater to eliminate bandpass and to give a DC ground to our preamp on our repeater system. It was intolerant of the energy from Lightning. One of these solved all our problems. Looks like the specs say > -72dBm @ 135Mhz on the 2Mhz wide unit. The 4Mhz wide unit is better documented, and shows > -89dBm @ 126 Mhz. That should knock down any nastys that will get your 6m XV-50. Have been using the DCI-145-2H, 4 section helical filter since 1999 on the local 2m repeater GB3LD which I hold the license. Without this we would be swamped by pagers in particular located on ours and adjacent masts. The normal bandpass and notches found in the repeater duplexer whilst they are efficient in preventing energy from it's own TX entering the RX, work relatively poorly in keeping out energy from external sources. Notch filters are only really successful when a single fixed frequency is involved. The bandpass filter on the repeater worked so well that I ended up buying one for my shack when 153 MHz pagers were installed close to the home location. For these devices to work you need to have a bandpass filter of this type on the receiver that is being affected and not the TX that is causing the interference, unless the TX output purity is sufficiently poor to warrant this. In other words if the 6m receiver is being affected, a 6m bandpass filter is needed and not really much use in installing one on the 2m TX. Bandpass filters incur a penalty in that they are lossy and usually mean a loss of about 1dB in the case of the 2m unit and greater at UHF. If it is installed in the common antenna feed of the TX/RX mean the same loss on TX power. All too often the designers of normal every day amateur receivers for VHF/UHF skimp on the selectivity of the front end to achieve a better sensitivity and the price is blocking or even damage if the local field strengths from other sources are too high. By comparison commercial 2 way radios by virtue of performance regulations are far superior in the selectivity stakes, quite often using miniature helical filters at the front end to achieve the performance. Good bandpass filters are expensive, but if transmitters on other frequencies are causing a problems, are a necessary evil. Bob G3VVT Keeper GB3LD/GB3LF _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
