75 meter loop - a success story dealing with local QRN
I put up a horizontal loop on my lot in town. I needed to reduce the
noise coming from my neighbours and local industry. I had been using a 75 meter dipole. I was enduring an S7 noise level with my dipole. I used 450 ohm window line from one corner of my loop as the feed point to the corner of my home where it transitioned to LM400 coax from a 4:1 balun. I then had 25 feet of this coax coming in through metal siding to my amplifier. This scheme reduced my noise level to S3-4. This felt like a very nice accomplishment. My friends on 75 meters locally here all reported a higher signal level from my transmitter. This was unexpected. I was just trying to deal with the high noise level in my receiver. I used the loop this way for about two years. Next an antenna guru who lived about 80 miles away finally talked me into changing to an open wire feed line with of course air dialectric instead of plastic. This further reduced my noise level. I have no idea why. He did not either, he just knew it worked for him. At this point I am at a normal noise level of S2. I was pretty happy with this. Then a retired engineer in Iowa who owned the same rig as myself, an Icom 751A said that I could improve noise rejection and increase receiver gain by paralleling all the dual gate mosfets in my IF strip with the latest type of high gain Mosfet from Philips in Germany. The number was BF988. I was reluctant to do this because I am 70 years old and do not have the best vision or steadiness of hand. I finally dove in and did it. As he predicted, my receiver gain jumped up and 75 meter stations within about 300 miles from me were pegging my S meter. I was immediately afraid of losing this meter and was sure it would never be able to be replaced. I turned down the internal RF gain pot so that those stations no longer banged my meter against the peg. Now my S meter noise level during the day without lightning is 0. Some days it bounces up to 1. I am so glad I bit the bullet and put in those new transistors. This low noise level makes ham radio so much more enjoyable. I am able to copy mobiles on 75 that I just could not hear before. The other benefit from the loop antenna with the air dialectric feed line is that by dumb luck it made 20, 15, and 10 meters a very good match with no tuner. I have a solid state amplifier and now jumping around these bands chasing DX is really fun. Just one hams journey trying to reduce received noise. A nice part of this story is that there is very little monetary investment in a wire loop antenna. Michael |
75 meter loop - a success story dealing with local QRN
On Sat, 27 Apr 2013 12:44:40 -0500, Fred wrote:
I put up a horizontal loop on my lot in town. I needed to reduce the noise coming from my neighbours and local industry. I had been using a 75 meter dipole. I was enduring an S7 noise level with my dipole. I used 450 ohm window line from one corner of my loop as the feed point to the corner of my home where it transitioned to LM400 coax from a 4:1 balun. I then had 25 feet of this coax coming in through metal siding to my amplifier. This scheme reduced my noise level to S3-4. This felt like a very nice accomplishment. My friends on 75 meters locally here all reported a higher signal level from my transmitter. This was unexpected. I was just trying to deal with the high noise level in my receiver. I used the loop this way for about two years. Next an antenna guru who lived about 80 miles away finally talked me into changing to an open wire feed line with of course air dialectric instead of plastic. This further reduced my noise level. I have no idea why. He did not either, he just knew it worked for him. At this point I am at a normal noise level of S2. I was pretty happy with this. Then a retired engineer in Iowa who owned the same rig as myself, an Icom 751A said that I could improve noise rejection and increase receiver gain by paralleling all the dual gate mosfets in my IF strip with the latest type of high gain Mosfet from Philips in Germany. The number was BF988. I was reluctant to do this because I am 70 years old and do not have the best vision or steadiness of hand. I finally dove in and did it. As he predicted, my receiver gain jumped up and 75 meter stations within about 300 miles from me were pegging my S meter. I was immediately afraid of losing this meter and was sure it would never be able to be replaced. I turned down the internal RF gain pot so that those stations no longer banged my meter against the peg. Now my S meter noise level during the day without lightning is 0. Some days it bounces up to 1. I am so glad I bit the bullet and put in those new transistors. This low noise level makes ham radio so much more enjoyable. I am able to copy mobiles on 75 that I just could not hear before. The other benefit from the loop antenna with the air dialectric feed line is that by dumb luck it made 20, 15, and 10 meters a very good match with no tuner. I have a solid state amplifier and now jumping around these bands chasing DX is really fun. Just one hams journey trying to reduce received noise. A nice part of this story is that there is very little monetary investment in a wire loop antenna. Michael MNI TNX, OM!! We need more first-person reporting like this in r.r.a.a. 73 ES GUD DX JONESY W3DHJ -- Marvin L Jones | jonz | W3DHJ | linux 38.24N 104.55W | @ config.com | Jonesy | OS/2 * Killfiling google & XXXXbanter.com: jonz.net/ng.htm |
75 meter loop - a success story dealing with local QRN
On Sat, 27 Apr 2013 12:44:40 -0500 "Fred" wrote in
article I put up a horizontal loop on my lot in town. I needed to reduce the noise coming from my neighbours and local industry. I had been using a 75 meter dipole. I was enduring an S7 noise level with my dipole. I used 450 ohm window line from one corner of my loop as the feed point to the corner of my home where it transitioned to LM400 coax from a 4:1 balun. I then had 25 feet of this coax coming in through metal siding to my amplifier. This scheme reduced my noise level to S3-4. This felt like a very nice accomplishment. My friends on 75 meters locally here all reported a higher signal level from my transmitter. This was unexpected. I was just trying to deal with the high noise level in my receiver. I used the loop this way for about two years. Next an antenna guru who lived about 80 miles away finally talked me into changing to an open wire feed line with of course air dialectric instead of plastic. This further reduced my noise level. I have no idea why. He did not either, he just knew it worked for him. At this point I am at a normal noise level of S2. I was pretty happy with this. Then a retired engineer in Iowa who owned the same rig as myself, an Icom 751A said that I could improve noise rejection and increase receiver gain by paralleling all the dual gate mosfets in my IF strip with the latest type of high gain Mosfet from Philips in Germany. The number was BF988. I was reluctant to do this because I am 70 years old and do not have the best vision or steadiness of hand. I finally dove in and did it. As he predicted, my receiver gain jumped up and 75 meter stations within about 300 miles from me were pegging my S meter. I was immediately afraid of losing this meter and was sure it would never be able to be replaced. I turned down the internal RF gain pot so that those stations no longer banged my meter against the peg. Now my S meter noise level during the day without lightning is 0. Some days it bounces up to 1. I am so glad I bit the bullet and put in those new transistors. This low noise level makes ham radio so much more enjoyable. I am able to copy mobiles on 75 that I just could not hear before. The other benefit from the loop antenna with the air dialectric feed line is that by dumb luck it made 20, 15, and 10 meters a very good match with no tuner. I have a solid state amplifier and now jumping around these bands chasing DX is really fun. Just one hams journey trying to reduce received noise. A nice part of this story is that there is very little monetary investment in a wire loop antenna. Michael Thanks for that! I had a horizontal 80m loop at my old qth. It worked well but when I moved I didn't recreate it at the new place. I will try now - my new qth is so noisy on the lower bands that operating is just no fun any more. Worth a try! 73 WA2LJW |
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