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DAVE : Wind yer coil of at least a hundred turns of magnet "war"
around a 1" PVC pipe segment (when I was a KID I used a lacquered toilet paper core) and take taps off it every 2-5 turns (arbitrary) and use the selector switch to derive signal from the taps that give you the best performance (it will vary per band) The capacitors are from old garage sale radios and may not even be needed This accomlishes what you have already proven with your work, that certain frequencies can be canceled out by selection of signal inductor-load.in series with your antenna The capacitors merely help you tune it in more making a tank circuit that resonates with the frequency you're "working" I did perhaps the same thing by winding 100 turns of magnet war on a salvaice ring torid core from a ttransistor powwer supply off a dead computer...The antenna went to 1 end of this 100 turns and the other end was grounded. On top this hundred turns I wound 25-40 turns and ran on end of THAT winding to my radio's antenna IN connector and the other end to the radio's ground You have just made a 4:1 balun...which all in one almost does what the couple above does...no adjustment tho Or you can do the quick and dirty trick with a TV 300 ohm to 75 ohm coupler, connecting the 300 ohm end to the antenna and ground as above, and the 75 ohm connectors to your radio's antenna and ground You wont notice the difference Yodar Dave wrote: The antenna does indeed seem to be working great, and the radio is not operating too shabily either as it is only the "background noise" I am trying to reduce. I hooked a 100 mH RF choke up to it with good results, and am planning on adding another one or two similar devices in an effort to cut down on higher frequency interference. Question: how would I ground this antenna? I have a grounding rod right outside the window, but don't know what to hook it too. The negative battery terminal? This radio does have an external antenna input, but that has a plastic ring around the outside. Open to suggestions. And thanks for the input RE purchasing a new/used tuner. dave ... Private wrote: Dave, I have been in a very similar situation. I used almost an identical antenna and had fantastic results. The radio likely does not have sufficent filtering in this case (Antenna is likely working great). I would start by ensuring the antenna has a good ground connection to the radio. An antenna tuner/preselector would defantely help. Purchasing a new or used amateur radio tuner (i.e. MFJ) 1.8Mhz-30Mhz would be the easiest option. Adding capacitors separetely could work, but from experience is a challenge to achive an workable solution for all frequencies. Homac "Dave" wrote in message ... I recently hooked up a thirty-six foot (plus or minus a couple of feet) piece of four-stranded wire with alligator clip to the internal "whip" antenna of my portable shortwave receiver, for the extra performance such a device offered. It works so well that I now cannot usually use my "DX" setting because of all the background noise (sounds like hundreds of other broadcasts vying for attention.) I don't know the frequency source of all this background noise, but would like to filter out as much of it as I can. One manufacturer of a similar "wind-up" antenna adds a capacitor to the wire in order to lower the resonance frequency of the wire. If I were going to try something similar (adding a capacitor, in series) in an attempt to bring the resonance of the wire down into the 30 MHz range, what size (roughly) capacitor should I use? Should I just try a few with different ranges, or does anyone here have any suggestions? TIA Cross-posted between sci.electronics.basics and rec.radio.shortwave Dave |
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