In a message dated 03/04/05 12:11:33 GMT Daylight Time, [EMAIL PROTECTED] writes:
There have been several schematics using such technics over the last 20 years. Most of them use a seperate short antenna, feeding the signal pase shifted into a combiner which combines the main Antenna Signal with the phases shifted extra antenna signal. This construction can reduce a lot of man made noise. I remember there was a commercial available stand alone unit sold by a small english company. ------------------------------------------- The Antenna interference cancelling unit in the UK was from SEM a company in the Isle of Man (GD). No longer seem to be in business. There is one from MFJ still on the market and believe a model may have come from a company called NIR (now part of Timewave? cannot find any info on the Timewave web site) though could be wrong on this latter unit. I built my own from a design from G4WMX for a "Null Steerer" that was circulating in the UK in 1989. I can remember my late father in law Ted, G3UUA building one at the time and was impressed with how well it worked, taking his S9 level of interference out totally. About two years back when suffering from local electrical interference I had a go at building the same unit. There is a PCB produced by Geoff Steedman, M0BGS available now as well as a kit of parts to populate the bare PCB. For the kit of parts with PCB, I paid £25 (US$47 approx). Built it up into a diecast box and have it permanently in the RX antenna feed. Easy for me as I have a separate TX/RX on the QRO rig. Alternately has PTT switch feed to enable it to be used in the antenna feed of a 100W HF transceiver. With a suitable auxiliary antenna it can null out quite high levels of local interference, the limiting factor being the amount of wanted signal also picked up by the auxiliary antenna. With the power off the unit is totally bypassed. The downside with mine is that with the unit active, the wanted signal is attenuated somewhat and even more when nulling out interference. The upside is that it can still make a vital difference in hearing signals buried under local interference. I believe Geoff, M0BGS has modified more recent PCB to add an emitter follower to the outgoing main antenna feed to offset through losses. Will have to try to modify my PCB to add this. I have the scanned circuit and notes somewhere in my PC for the original unit before the emitter follower was added. If anybody wants to have a go at constructing this device and needs the info, contact me direct. Bob, G3VVT _______________________________________________ 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
