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passive tuners...I'm a convert
I used to think that passive antenna tuners or matching networks
were worthless, but over the weekend I got some real SWL evidence to the contrary. My prime RCVR is a Sat800 refurb hooked to 156 feet of AWG 16 hard drawn stranded, oriented NNW/SSE up about 40 feet between two large trees and fed off center at the 1/3 // 2/3 point with twin RG6U which comes down to a 4:1 balun outdoors at a decent ground (copper ground pipe filled with copper sulfate, steel well casing and cast iron soil pipe bonded together with coax braid.) Coax from the balun goes into the house to the RCVR. One thing about the Sat800 has always bothered me...there's no way to turn the AGC *off*, so the noise floor is always rushing up to blast you in the headphones when you tune between stations. I'd previously not been able to receive anything but a couple of local aero beacons on longwave, nor anything but the Christian megawatt at 3200 on the 90 meter band. I didn't care much about the longwave since the very useful aviation weather Elmira NY on 385 khz was replaced by better service on 162.40 Mhz vhf. Last week, just for fun I made a Hi-Q parallel resonant tank for longwave from a 385 pf variable cap and a 3.850 mh inductor. (82 turns #24 awg wire on a 1.3" audio toroid core) This tunes 520 khz down to 170 khz with a pronounced peak. I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Same thing happened when I picked up a used Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend. The peaks are not as pronounced as the longwave tank, but the 90 meter band yielded a half dozen African stations where previously I'd heard nothing but QRMN. On some frequencies the most dramatic improvement came where the peak in signal strength and the peak in noise came at slightly different settings of the tuner. This to me is evidence that nearby noise sources, even when filtered out of the detector and audio in the receiver are still affecting the AGC line, turning down the effective signal. Seems like an active preselector will help if you can't get an antenna out in the clear, but even if you can, some more selectivity *before* the front end of the receiver can help. I'm a convert. |
In article u, wcm1
@NOSPAM.cornell.edu says... I'd previously not been able to receive anything but a couple of local aero beacons on longwave, nor anything but the Christian megawatt at 3200 on the 90 meter band. I didn't care much about the longwave since the very useful aviation weather Elmira NY on 385 khz was replaced by better service on 162.40 Mhz vhf. Last week, just for fun I made a Hi-Q parallel resonant tank for longwave from a 385 pf variable cap and a 3.850 mh inductor. (82 turns #24 awg wire on a 1.3" audio toroid core) This tunes 520 khz down to 170 khz with a pronounced peak. I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Has anyone bookmarked the longwave site whcih gives freq's, calls and locations? Just for curiousity I'd like to find out where some of these beacons are. PKA 260.9 YGK 263.4 IT (ithaca) 267.0 YQA 272.3 YPP 303.3 ZMX 317.3 CL 345.0 SB 362.2 YMW 366.4 ZQ 372.6 YB 394.4 Y8 401.3 YTA 409.2 BC 414.4 RYS 420.0 |
William Mutch wrote: I used to think that passive antenna tuners or matching networks were worthless, but over the weekend I got some real SWL evidence to the contrary. My prime RCVR is a Sat800 refurb hooked to 156 feet of AWG 16 hard drawn stranded, oriented NNW/SSE up about 40 feet between two large trees and fed off center at the 1/3 // 2/3 point with twin RG6U which comes down to a 4:1 balun outdoors at a decent ground (copper ground pipe filled with copper sulfate, steel well casing and cast iron soil pipe bonded together with coax braid.) Coax from the balun goes into the house to the RCVR. One thing about the Sat800 has always bothered me...there's no way to turn the AGC *off*, so the noise floor is always rushing up to blast you in the headphones when you tune between stations. I'd previously not been able to receive anything but a couple of local aero beacons on longwave, nor anything but the Christian megawatt at 3200 on the 90 meter band. I didn't care much about the longwave since the very useful aviation weather Elmira NY on 385 khz was replaced by better service on 162.40 Mhz vhf. Last week, just for fun I made a Hi-Q parallel resonant tank for longwave from a 385 pf variable cap and a 3.850 mh inductor. (82 turns #24 awg wire on a 1.3" audio toroid core) This tunes 520 khz down to 170 khz with a pronounced peak. I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Same thing happened when I picked up a used Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend. The peaks are not as pronounced as the longwave tank, but the 90 meter band yielded a half dozen African stations where previously I'd heard nothing but QRMN. On some frequencies the most dramatic improvement came where the peak in signal strength and the peak in noise came at slightly different settings of the tuner. This to me is evidence that nearby noise sources, even when filtered out of the detector and audio in the receiver are still affecting the AGC line, turning down the effective signal. Seems like an active preselector will help if you can't get an antenna out in the clear, but even if you can, some more selectivity *before* the front end of the receiver can help. I'm a convert. With that type of antenna I'd always recommend a tuner. It is an off center fed dipole, and as such will be frequency limited without the use of an antenna tuner. If one wants broadband performance out of a single antenna it is best in most applications to go with a random wire antenna. Steve Holland, MI Drake R7, R8 and R8B http://www.iserv.net/~n8kdv/dxpage.htm |
William Mutch wrote: In article u, wcm1 @NOSPAM.cornell.edu says... I'd previously not been able to receive anything but a couple of local aero beacons on longwave, nor anything but the Christian megawatt at 3200 on the 90 meter band. I didn't care much about the longwave since the very useful aviation weather Elmira NY on 385 khz was replaced by better service on 162.40 Mhz vhf. Last week, just for fun I made a Hi-Q parallel resonant tank for longwave from a 385 pf variable cap and a 3.850 mh inductor. (82 turns #24 awg wire on a 1.3" audio toroid core) This tunes 520 khz down to 170 khz with a pronounced peak. I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Has anyone bookmarked the longwave site whcih gives freq's, calls and locations? Just for curiousity I'd like to find out where some of these beacons are. PKA 260.9 YGK 263.4 IT (ithaca) 267.0 YQA 272.3 YPP 303.3 ZMX 317.3 CL 345.0 SB 362.2 YMW 366.4 ZQ 372.6 YB 394.4 Y8 401.3 YTA 409.2 BC 414.4 RYS 420.0 http://frodo.bruderhof.com/ka2qpg/ Scroll down for looking up US beacons. |
"William Mutch" wrote in message Has anyone
bookmarked the longwave site whcih gives freq's, calls and locations? Just for curiousity I'd like to find out where some of these beacons are. PKA 260.9 YGK 263.4 IT (ithaca) 267.0 YQA 272.3 YPP 303.3 ZMX 317.3 CL 345.0 SB 362.2 YMW 366.4 ZQ 372.6 YB 394.4 Y8 401.3 YTA 409.2 BC 414.4 RYS 420.0 Go to the following site and download WWSU V5.10. It will give you the location and frequency of the NDB station. In addition it will tell you the distance and bearing from your location when you set in your locations co-ordinates. It also offers some nice search capabilities if you only get part of a call. http://members.rogers.com/wiecek6010/files.htm Al KA5JGV San Antonio, Tx. |
I'd like to put in a plug for
www.airnav.com You can look up locations by beacon call letter there (at least US). Also gives lots of info about the originating airport, like VHF freqs, size and services, etc. john kb5ag "Al - KA5JGV" wrote in message ... "William Mutch" wrote in message Has anyone bookmarked the longwave site whcih gives freq's, calls and locations? Just for curiousity I'd like to find out where some of these beacons are. PKA 260.9 YGK 263.4 IT (ithaca) 267.0 YQA 272.3 YPP 303.3 ZMX 317.3 CL 345.0 SB 362.2 YMW 366.4 ZQ 372.6 YB 394.4 Y8 401.3 YTA 409.2 BC 414.4 RYS 420.0 Go to the following site and download WWSU V5.10. It will give you the location and frequency of the NDB station. In addition it will tell you the distance and bearing from your location when you set in your locations co-ordinates. It also offers some nice search capabilities if you only get part of a call. http://members.rogers.com/wiecek6010/files.htm Al KA5JGV San Antonio, Tx. |
N8KDV wrote: William Mutch wrote: In article u, wcm1 @NOSPAM.cornell.edu says... I'd previously not been able to receive anything but a couple of local aero beacons on longwave, nor anything but the Christian megawatt at 3200 on the 90 meter band. I didn't care much about the longwave since the very useful aviation weather Elmira NY on 385 khz was replaced by better service on 162.40 Mhz vhf. Last week, just for fun I made a Hi-Q parallel resonant tank for longwave from a 385 pf variable cap and a 3.850 mh inductor. (82 turns #24 awg wire on a 1.3" audio toroid core) This tunes 520 khz down to 170 khz with a pronounced peak. I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Has anyone bookmarked the longwave site whcih gives freq's, calls and locations? Just for curiousity I'd like to find out where some of these beacons are. PKA 260.9 YGK 263.4 IT (ithaca) 267.0 YQA 272.3 YPP 303.3 ZMX 317.3 CL 345.0 SB 362.2 YMW 366.4 ZQ 372.6 YB 394.4 Y8 401.3 YTA 409.2 BC 414.4 RYS 420.0 http://frodo.bruderhof.com/ka2qpg/ Scroll down for looking up US beacons. YQA 272 Muskoka, Ontario 45 02 21N 79 16 58W YTA 409 Pembroke, Ontario 45 48 10N 77 13 09W YGK 263 Kingston, Ontario 44 17 48N 76 36 20W YPP 303 Parent, Quebec 47 53 22N 74 40 19W SB 362 Sudbury, Ontario 46 38 53N 80 55 18W YB 394 North Bay, Ontario 46 23 04N 79 28 07W BC 414 Baie-Comeau, Quebec 49 07 04N 68 19 34W ZMX 317 Montreal Mirabel, Quebec (Listed as Janvier) 45 44 29N 73 55 14W YMW 366 Maniwaki, Quebec 46 12 27N 75 57 23W Y8 401 Drummondville, Quebec 45 50 50N 72 23 56W The frequencies I gave is the listed (carrier) frequency. The ones you have listed is the Upper Sideband - which is the way to get the beacons. Hope this helps, Dave |
In article ,
says... "William Mutch" wrote in message Has anyone bookmarked the longwave site whcih gives freq's, calls and locations? Just for curiousity I'd like to find out where some of these beacons are. PKA 260.9 YGK 263.4 IT (ithaca) 267.0 YQA 272.3 YPP 303.3 ZMX 317.3 CL 345.0 SB 362.2 YMW 366.4 ZQ 372.6 YB 394.4 Y8 401.3 YTA 409.2 BC 414.4 RYS 420.0 Go to the following site and download WWSU V5.10. I tried this site and did the download. Interesting looking program , but returns some nonsense values for range and bearings. The map "beacon radar" doesn't correlate with the entered location. It will give you the location and frequency of the NDB station. In addition it will tell you the distance and bearing from your location when you set in your locations co-ordinates. It also offers some nice search capabilities if you only get part of a call. http://members.rogers.com/wiecek6010/files.htm Al KA5JGV San Antonio, Tx. |
In article . edu, wcm1
@NOSPAM.cornell.edu says... In article , says... "William Mutch" wrote in message Has anyone bookmarked the longwave site whcih gives freq's, calls and locations? Just for curiousity I'd like to find out where some of these beacons are. PKA 260.9 YGK 263.4 IT (ithaca) 267.0 YQA 272.3 YPP 303.3 ZMX 317.3 CL 345.0 SB 362.2 YMW 366.4 ZQ 372.6 YB 394.4 Y8 401.3 YTA 409.2 BC 414.4 RYS 420.0 Go to the following site and download WWSU V5.10. Got it working...misconfig to east longitude Cool program. I tried this site and did the download. Interesting looking program , but returns some nonsense values for range and bearings. The map "beacon radar" doesn't correlate with the entered location. It will give you the location and frequency of the NDB station. In addition it will tell you the distance and bearing from your location when you set in your locations co-ordinates. It also offers some nice search capabilities if you only get part of a call. http://members.rogers.com/wiecek6010/files.htm Al KA5JGV San Antonio, Tx. |
"William Mutch" wrote in message l.edu... I used to think that passive antenna tuners or matching networks were worthless, but over the weekend I got some real SWL evidence to the contrary. My prime RCVR is a Sat800 refurb hooked to 156 feet of AWG 16 hard drawn stranded, oriented NNW/SSE up about 40 feet between two large trees and fed off center at the 1/3 // 2/3 point with twin RG6U which comes down to a 4:1 balun outdoors at a decent ground (copper ground pipe filled with copper sulfate, steel well casing and cast iron soil pipe bonded together with coax braid.) Coax from the balun goes into the house to the RCVR. One thing about the Sat800 has always bothered me...there's no way to turn the AGC *off*, so the noise floor is always rushing up to blast you in the headphones when you tune between stations. I'd previously not been able to receive anything but a couple of local aero beacons on longwave, nor anything but the Christian megawatt at 3200 on the 90 meter band. I didn't care much about the longwave since the very useful aviation weather Elmira NY on 385 khz was replaced by better service on 162.40 Mhz vhf. Last week, just for fun I made a Hi-Q parallel resonant tank for longwave from a 385 pf variable cap and a 3.850 mh inductor. (82 turns #24 awg wire on a 1.3" audio toroid core) This tunes 520 khz down to 170 khz with a pronounced peak. A disclaimer: I may be totally wrong about this, but I think what you built is actually more like a sharp-tuned preselector than an antenna tuner, because it's not resonating your antenna system or improving the impedance mismatch, so much as it's favoring signals around the frequency of interest over signals that are outside this range. This would reduce the stress on your receiver's front end by attenuating out-of-band signals. You can verify this (or disprove it) by comparing a signal at say, 15 Mhz with and without your matching network installed. If your HF signals drop in strength, this may explain why reception is so much better with the parallel resonant circuit in place. It's my understanding that a substantial antenna like yours will pick up many volts of total RF at a very wide range of frequencies. These components stress your front end, driving it into non-linearity and causing mixing products, some of which will fall within the passband of the LF signal you're trying to hear. This is experienced as a higher noise level. The pre-selector knocks down these out-of-band signals, dramatically reducing the amount of rmixing and thus reducing the background noise level. I'm EXTREMELY skeptical of any claim that impedance matching by itself will make any difference to HF reception once you have more than (say arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal set. :) The reason why is, external noise is so high at HF that increasing the efficiency of energy transfer increases the efficiency of noise transfer just exactly as much as it increases the efficiency of signal transfer, resulting in a net 0 dB change in signal-to-noise ratio. You get higher S-meter readings, but no change in signal readability. Preselection, on the other hand, should never hurt and would help in cases where the receiver is overstressed by total signal levels. This is one possible explanation for your results. Again, I'm not certain this is correct. However, if you notice a big drop in signal level well up the HF spectrum when your network is installed, this would be plausible at least. :) -- Ross I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Same thing happened when I picked up a used Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend. The peaks are not as pronounced as the longwave tank, but the 90 meter band yielded a half dozen African stations where previously I'd heard nothing but QRMN. On some frequencies the most dramatic improvement came where the peak in signal strength and the peak in noise came at slightly different settings of the tuner. This to me is evidence that nearby noise sources, even when filtered out of the detector and audio in the receiver are still affecting the AGC line, turning down the effective signal. Seems like an active preselector will help if you can't get an antenna out in the clear, but even if you can, some more selectivity *before* the front end of the receiver can help. I'm a convert. |
Ross Archer wrote:
A disclaimer: I may be totally wrong about this, but I think what you built is actually more like a sharp-tuned preselector than an antenna tuner, because it's not resonating your antenna system or improving the impedance mismatch, so much as it's favoring signals around the frequency of interest over signals that are outside this range. This would reduce the stress on your receiver's front end by attenuating out-of-band signals. You can verify this (or disprove it) by comparing a signal at say, 15 Mhz with and without your matching network installed. If your HF signals drop in strength, this may explain why reception is so much better with the parallel resonant circuit in place. It's my understanding that a substantial antenna like yours will pick up many volts of total RF at a very wide range of frequencies. These components stress your front end, driving it into non-linearity and causing mixing products, some of which will fall within the passband of the LF signal you're trying to hear. This is experienced as a higher noise level. The pre-selector knocks down these out-of-band signals, dramatically reducing the amount of rmixing and thus reducing the background noise level. I'm EXTREMELY skeptical of any claim that impedance matching by itself will make any difference to HF reception once you have more than (say arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal set. :) The reason why is, external noise is so high at HF that increasing the efficiency of energy transfer increases the efficiency of noise transfer just exactly as much as it increases the efficiency of signal transfer, resulting in a net 0 dB change in signal-to-noise ratio. You get higher S-meter readings, but no change in signal readability. Preselection, on the other hand, should never hurt and would help in cases where the receiver is overstressed by total signal levels. This is one possible explanation for your results. Again, I'm not certain this is correct. However, if you notice a big drop in signal level well up the HF spectrum when your network is installed, this would be plausible at least. :) -- Ross I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Same thing happened when I picked up a used Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend. The peaks are not as pronounced as the longwave tank, but the 90 meter band yielded a half dozen African stations where previously I'd heard nothing but QRMN. On some frequencies the most dramatic improvement came where the peak in signal strength and the peak in noise came at slightly different settings of the tuner. This to me is evidence that nearby noise sources, even when filtered out of the detector and audio in the receiver are still affecting the AGC line, turning down the effective signal. Seems like an active preselector will help if you can't get an antenna out in the clear, but even if you can, some more selectivity *before* the front end of the receiver can help. I'm a convert. I thought your choice of the word "stress" (above) was curious. I've never seen that word used in the context of overloading a receiver's front-end. I'm sure you know that signal overloading doesn't actually damage anything in the radio, so what does "stress" mean to you in this case? Just curious. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
= = = William Mutch wrote in message
= = = ll.edu... I used to think that passive antenna tuners or matching networks were worthless, but over the weekend I got some real SWL evidence to the contrary. My prime RCVR is a Sat800 refurb hooked to 156 feet of AWG 16 hard drawn stranded, oriented NNW/SSE up about 40 feet between two large trees and * This Antenna sounds Long and High Enough. fed off center at the 1/3 // 2/3 point * Sounds 'sort-of-like' a WINDOM (52 Ft & 104Ft) Antenna that is configured with Two un-equal Top Arms 'elements': + 156 Feet = 1WL @ 6.4 MHz & 1/2WL @ 3.2 MHz & 1/4WL @ 1.6 MHz + 104 Feet = 1WL @ 9.7 MHz & 1/2WL @ 4.8 MHz & 1/4WL @ 2.4 MHz + 52 Feet = 1WL @ 19.3 MHz & 1/2WL @ 9.7 MHz & 1/4WL @ 4.8 MHz http://www.packetradio.com/windom.htm with twin RG6U which comes down to a 4:1 balun * Then sounds like a G5RV Down Leg 'elements'. http://www.qsl.net/aa3px/g5rv.htm outdoors at a decent ground (copper ground pipe filled with copper sulfate, steel well casing and cast iron soil pipe bonded together with coax braid.) * The Ground sounds solid enough. * READ: Compilation of "Ground" Messages http://groups.yahoo.com/group/Shortw...na/message/524 Coax from the balun goes into the house to the RCVR. * A Coax Feed-in-Line is always a Good Idea :o) One thing about the Sat800 has always bothered me...there's no way to turn the AGC *off*, so the noise floor is always rushing up to blast you in the headphones when you tune between stations. I'd previously not been able to receive anything but a couple of local aero beacons on longwave, nor anything but the Christian megawatt at 3200 on the 90 meter band. I didn't care much about the longwave since the very useful aviation weather Elmira NY on 385 khz was replaced by better service on 162.40 Mhz vhf. Last week, just for fun I made a Hi-Q parallel resonant tank for longwave from a 385 pf variable cap and a 3.850 mh inductor. (82 turns #24 awg wire on a 1.3" audio toroid core) * Sounds like a fairly good Tuned Circuit for your targeted Longwave Frequency Range. * FWIW: Sounds like what you have may be more of a Longwave Signal "Pre-Selector" then an 'general' Antenna Tuner. * Read - Why:: Baluns -v- Antenna Tuner -v- Pre-Selector -v- Modern Radio/Receivers http://groups.yahoo.com/group/Shortw...na/message/728 This tunes 520 khz down to 170 khz with a pronounced peak. I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! * Again sounds like your basic tuned circuit works for the intended Longwave Band Area. The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! * You may have obtained/gain the same Noise Reduction results by simply using a Lead-in-Line Isolator 1:1 Matching Transformer between the Coax Cable Feed-in-Line and the Receiver. * READ - Wellbrook "Low Noise Antenna" 'design concept' using two components that WellBrook manufactures: the Universal Magnetic Balun (UMB) and the Antenna Feed Isolator. ISOLATOR= http://www.wellbrook.uk.com/longwire.html http://groups.yahoo.com/group/Shortw...na/message/675 NOTE: Please Read Wellbrooks Claims at the bottom of the webpage concerning how the "Isolator" can 'reduce' Noise at Low Frequencies by up to 40 dB. Same thing happened when I picked up a used Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend. The peaks are not as pronounced as the longwave tank, but the 90 meter band yielded a half dozen African stations where previously I'd heard nothing but QRMN. On some frequencies the most dramatic improvement came where the peak in signal strength and the peak in noise came at slightly different settings of the tuner. This to me is evidence that nearby noise sources, even when filtered out of the detector and audio in the receiver are still affecting the AGC line, turning down the effective signal. Seems like an active preselector will help if you can't get an antenna out in the clear, but even if you can, some more selectivity *before* the front end of the receiver can help. I'm a convert. iane ~ RHF .. |
"starman" wrote in message ... Ross Archer wrote: A disclaimer: I may be totally wrong about this, but I think what you built is actually more like a sharp-tuned preselector than an antenna tuner, because it's not resonating your antenna system or improving the impedance mismatch, so much as it's favoring signals around the frequency of interest over signals that are outside this range. This would reduce the stress on your receiver's front end by attenuating out-of-band signals. You can verify this (or disprove it) by comparing a signal at say, 15 Mhz with and without your matching network installed. If your HF signals drop in strength, this may explain why reception is so much better with the parallel resonant circuit in place. It's my understanding that a substantial antenna like yours will pick up many volts of total RF at a very wide range of frequencies. These components stress your front end, driving it into non-linearity and causing mixing products, some of which will fall within the passband of the LF signal you're trying to hear. This is experienced as a higher noise level. The pre-selector knocks down these out-of-band signals, dramatically reducing the amount of rmixing and thus reducing the background noise level. I'm EXTREMELY skeptical of any claim that impedance matching by itself will make any difference to HF reception once you have more than (say arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal set. :) The reason why is, external noise is so high at HF that increasing the efficiency of energy transfer increases the efficiency of noise transfer just exactly as much as it increases the efficiency of signal transfer, resulting in a net 0 dB change in signal-to-noise ratio. You get higher S-meter readings, but no change in signal readability. Preselection, on the other hand, should never hurt and would help in cases where the receiver is overstressed by total signal levels. This is one possible explanation for your results. Again, I'm not certain this is correct. However, if you notice a big drop in signal level well up the HF spectrum when your network is installed, this would be plausible at least. :) -- Ross I coupled it very loosely (2 1/2 turns) to the coax near the RCVR and was astounded at the difference in reception. Around 0500Z I logged 15 different aero beacons at between 260 and 420 khz ! The tuned circuit didn't bring the signal levels up...it took the noise floor DOWN ! Same thing happened when I picked up a used Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend. The peaks are not as pronounced as the longwave tank, but the 90 meter band yielded a half dozen African stations where previously I'd heard nothing but QRMN. On some frequencies the most dramatic improvement came where the peak in signal strength and the peak in noise came at slightly different settings of the tuner. This to me is evidence that nearby noise sources, even when filtered out of the detector and audio in the receiver are still affecting the AGC line, turning down the effective signal. Seems like an active preselector will help if you can't get an antenna out in the clear, but even if you can, some more selectivity *before* the front end of the receiver can help. I'm a convert. I thought your choice of the word "stress" (above) was curious. I've never seen that word used in the context of overloading a receiver's front-end. I'm sure you know that signal overloading doesn't actually damage anything in the radio, so what does "stress" mean to you in this case? Just curious. Stress, an in overall signal levels taxing the ability of one or more of the linear amplification stages to remain in their linear regions. Even a little bit of non-linearity allows spurious mixing products (e.g. intermod) to occur. Anythinng that knocks down the total signal level, especially if it's only signals you don't want to listen to, will reduce that "stress". Yes, it is a curious usage, but I'm just copying a usage I saw elsewhere wrt. dynamic range. -- Ross -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Ross Archer wrote:
"starman" wrote in message ... Ross Archer wrote: A disclaimer: I may be totally wrong about this, but I think what you built is actually more like a sharp-tuned preselector than an antenna tuner, because it's not resonating your antenna system or improving the impedance mismatch, so much as it's favoring signals around the frequency of interest over signals that are outside this range. This would reduce the stress on your receiver's front end by attenuating out-of-band signals. You can verify this (or disprove it) by comparing a signal at say, 15 Mhz with and without your matching network installed. If your HF signals drop in strength, this may explain why reception is so much better with the parallel resonant circuit in place. It's my understanding that a substantial antenna like yours will pick up many volts of total RF at a very wide range of frequencies. These components stress your front end, driving it into non-linearity and causing mixing products, some of which will fall within the passband of the LF signal you're trying to hear. This is experienced as a higher noise level. The pre-selector knocks down these out-of-band signals, dramatically reducing the amount of rmixing and thus reducing the background noise level. I'm EXTREMELY skeptical of any claim that impedance matching by itself will make any difference to HF reception once you have more than (say arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal set. :) The reason why is, external noise is so high at HF that increasing the efficiency of energy transfer increases the efficiency of noise transfer just exactly as much as it increases the efficiency of signal transfer, resulting in a net 0 dB change in signal-to-noise ratio. You get higher S-meter readings, but no change in signal readability. Preselection, on the other hand, should never hurt and would help in cases where the receiver is overstressed by total signal levels. This is one possible explanation for your results. Again, I'm not certain this is correct. However, if you notice a big drop in signal level well up the HF spectrum when your network is installed, this would be plausible at least. :) -- Ross I thought your choice of the word "stress" (above) was curious. I've never seen that word used in the context of overloading a receiver's front-end. I'm sure you know that signal overloading doesn't actually damage anything in the radio, so what does "stress" mean to you in this case? Just curious. Stress, an in overall signal levels taxing the ability of one or more of the linear amplification stages to remain in their linear regions. Even a little bit of non-linearity allows spurious mixing products (e.g. intermod) to occur. Anythinng that knocks down the total signal level, especially if it's only signals you don't want to listen to, will reduce that "stress". Yes, it is a curious usage, but I'm just copying a usage I saw elsewhere wrt. dynamic range. -- Ross After reading your original post again, I see that you were using 'stress' to mean any signal level that causes the front-end of the receiver to operate outside it's design limits, particularly with regard to linearity. I too am skeptical of the value of impedance matching or antenna tuning if the receiver is already getting the signal levels it needs to operate above the local noise floor. However one of the benefits of impedance matching for certain antenna types like the inverted-L is you can also achieve an effective RF ground for the coax shield when the matching transformer (unun or balun) is located close to the ground. This allows for a short (effective) ground connection from the common end of the transformer windings to ground. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"snip" However one of the benefits of impedance matching for certain antenna types like the inverted-L is you can also achieve an effective RF ground for the coax shield when the matching transformer (unun or balun) is located close to the ground. This allows for a short (effective) ground connection from the common end of the transformer windings to ground. That would be a side benefit. The main reason for this grounding arrangement is that the valley I live in gets wicked lightning storms. I think that by having the entire antenna operating at DC ground with the low resistance of the twin RG6 braids entirely outdoors and directly to earth ground would reduce the possiblity of a direct lightning strike on or near the antenna conducting enongh current past the grounded balun to ignite the house where the leadin enters. |
"starman" wrote in message ... Ross Archer wrote: "starman" wrote in message ... Ross Archer wrote: A disclaimer: I may be totally wrong about this, but I think what you built is actually more like a sharp-tuned preselector than an antenna tuner, because it's not resonating your antenna system or improving the impedance mismatch, so much as it's favoring signals around the frequency of interest over signals that are outside this range. This would reduce the stress on your receiver's front end by attenuating out-of-band signals. You can verify this (or disprove it) by comparing a signal at say, 15 Mhz with and without your matching network installed. If your HF signals drop in strength, this may explain why reception is so much better with the parallel resonant circuit in place. It's my understanding that a substantial antenna like yours will pick up many volts of total RF at a very wide range of frequencies. These components stress your front end, driving it into non-linearity and causing mixing products, some of which will fall within the passband of the LF signal you're trying to hear. This is experienced as a higher noise level. The pre-selector knocks down these out-of-band signals, dramatically reducing the amount of rmixing and thus reducing the background noise level. I'm EXTREMELY skeptical of any claim that impedance matching by itself will make any difference to HF reception once you have more than (say arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal set. :) The reason why is, external noise is so high at HF that increasing the efficiency of energy transfer increases the efficiency of noise transfer just exactly as much as it increases the efficiency of signal transfer, resulting in a net 0 dB change in signal-to-noise ratio. You get higher S-meter readings, but no change in signal readability. Preselection, on the other hand, should never hurt and would help in cases where the receiver is overstressed by total signal levels. This is one possible explanation for your results. Again, I'm not certain this is correct. However, if you notice a big drop in signal level well up the HF spectrum when your network is installed, this would be plausible at least. :) -- Ross I thought your choice of the word "stress" (above) was curious. I've never seen that word used in the context of overloading a receiver's front-end. I'm sure you know that signal overloading doesn't actually damage anything in the radio, so what does "stress" mean to you in this case? Just curious. Stress, an in overall signal levels taxing the ability of one or more of the linear amplification stages to remain in their linear regions. Even a little bit of non-linearity allows spurious mixing products (e.g. intermod) to occur. Anythinng that knocks down the total signal level, especially if it's only signals you don't want to listen to, will reduce that "stress". Yes, it is a curious usage, but I'm just copying a usage I saw elsewhere wrt. dynamic range. -- Ross After reading your original post again, I see that you were using 'stress' to mean any signal level that causes the front-end of the receiver to operate outside it's design limits, particularly with regard to linearity. I too am skeptical of the value of impedance matching or antenna tuning if the receiver is already getting the signal levels it needs to operate above the local noise floor. However one of the benefits of impedance matching for certain antenna types like the inverted-L is you can also achieve an effective RF ground for the coax shield when the matching transformer (unun or balun) is located close to the ground. This allows for a short (effective) ground connection from the common end of the transformer windings to ground. And in my experiments, it's a major advantage in reducing local noise pickup, when the coax shield is connected to a ground rod and into the ground. Just keep in mind that many impedance-matching tuners do not isolate RF input and RF output from each other. They might not serve as well as a transformer would in for noise pickup reduction? -- Ross -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Ross Archer wrote:
"starman" wrote in message After reading your original post again, I see that you were using 'stress' to mean any signal level that causes the front-end of the receiver to operate outside it's design limits, particularly with regard to linearity. I too am skeptical of the value of impedance matching or antenna tuning if the receiver is already getting the signal levels it needs to operate above the local noise floor. However one of the benefits of impedance matching for certain antenna types like the inverted-L is you can also achieve an effective RF ground for the coax shield when the matching transformer (unun or balun) is located close to the ground. This allows for a short (effective) ground connection from the common end of the transformer windings to ground. And in my experiments, it's a major advantage in reducing local noise pickup, when the coax shield is connected to a ground rod and into the ground. Just keep in mind that many impedance-matching tuners do not isolate RF input and RF output from each other. They might not serve as well as a transformer would in for noise pickup reduction? Does Palomar's so called 'Magnetic Longwire Balun' isolate the RF input and output? It may be an auto-transformer design with a low impedance tapped secondary. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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