A comment about Receiving
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For me, receive capability was an important factor, among others, in the decision to buy an Elecraft. The model is irrelevant to this post. For years, I have been studying comments made about receiving, as opposed to those who think a radio is 'good to the last watt'. Recently, there was a rather lengthy thread about whether a K3 user was having receive problems or not. I'd like to share an experience with the group.
Over the years, I have used coax fed antennas and lived with compromise SWR figures. I wanted an all-band antenna so I recently changed the 80 meter dipole so that it is center fed with homebrew 450 ohm ladder-line to a tuner. I use an MFJ Matchmaker (TM) to 'tune the tuner'. While it puts out a white noise, I tune for minimum S-meter reading. When finished, a quick transmit reveals the SWR. One day while tuning close to optimum at the frequency I was on, and because I receive while I tune, I began to hear a weak CW signal. At first, I thought it had just come on frequency, but as I listened, I realized that the station had been in qso for awhile, but I didn't hear it until I reached optimum resonance with the tuner. I knew a resonant antenna was important, but I was surprised at the difference it could make in receiving. A good receiver is wasted if the signal doesn't get to it. Richard Fjeld, n0ce [hidden email] I'd rather be learning. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Rich,
Yes the tuner acts as a preselector and peaks up the signal. Years ago I wrote W6AM a letter asking him if he used an antenna tuner with his rhombic antennas. He replied that he did use a tuner but not so much to improve the impedance match to the rhombics for transmit, (he had them tuned up pretty well) but to act as a preselector to peak up the signals. He went on to describe his setup, using Collins 75A4 receivers and a Johnson KW matchboxes. He said the big Johnson KW matchbox, not the smaller one, was very effective at peaking up the received signal. I was convinced that the tuner was a a good thing to have in line for receive if he had receive enhancement using the tuner with his big rhombics ! Bob K6UJ On Mar 28, 2011, at 11:05 AM, Richard Fjeld wrote: > For me, receive capability was an important factor, among others, in the decision to buy an Elecraft. The model is irrelevant to this post. For years, I have been studying comments made about receiving, as opposed to those who think a radio is 'good to the last watt'. Recently, there was a rather lengthy thread about whether a K3 user was having receive problems or not. I'd like to share an experience with the group. > > Over the years, I have used coax fed antennas and lived with compromise SWR figures. I wanted an all-band antenna so I recently changed the 80 meter dipole so that it is center fed with homebrew 450 ohm ladder-line to a tuner. I use an MFJ Matchmaker (TM) to 'tune the tuner'. While it puts out a white noise, I tune for minimum S-meter reading. When finished, a quick transmit reveals the SWR. > > One day while tuning close to optimum at the frequency I was on, and because I receive while I tune, I began to hear a weak CW signal. At first, I thought it had just come on frequency, but as I listened, I realized that the station had been in qso for awhile, but I didn't hear it until I reached optimum resonance with the tuner. I knew a resonant antenna was important, but I was surprised at the difference it could make in receiving. A good receiver is wasted if the signal doesn't get to it. > > > Richard Fjeld, n0ce > [hidden email] > I'd rather be learning. > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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How does the preselector know to peak up the RX signal and not also peak up the noise? Dale W4OP > Rich, > > Yes the tuner acts as a preselector and peaks up the signal. > > Years ago I wrote W6AM a letter asking him if he used an antenna tuner > with his rhombic antennas. He replied that he did use a tuner but not so > much > to improve the impedance match to the rhombics for transmit, (he had them > tuned up pretty well) > but to act as a preselector to peak up the signals. He went on to > describe his > setup, using Collins 75A4 receivers and a Johnson KW matchboxes. He said > the > big Johnson KW matchbox, not the smaller one, was very effective at > peaking up the > received signal. I was convinced that the tuner was a a good thing to > have in line > for receive if he had receive enhancement using the tuner with his big > rhombics ! > > > Bob > K6UJ > > > > On Mar 28, 2011, at 11:05 AM, Richard Fjeld wrote: > >> For me, receive capability was an important factor, among others, in the >> decision to buy an Elecraft. The model is irrelevant to this post. For >> years, I have been studying comments made about receiving, as opposed to >> those who think a radio is 'good to the last watt'. Recently, there was a >> rather lengthy thread about whether a K3 user was having receive problems >> or not. I'd like to share an experience with the group. >> >> Over the years, I have used coax fed antennas and lived with compromise >> SWR figures. I wanted an all-band antenna so I recently changed the 80 >> meter dipole so that it is center fed with homebrew 450 ohm ladder-line >> to a tuner. I use an MFJ Matchmaker (TM) to 'tune the tuner'. While it >> puts out a white noise, I tune for minimum S-meter reading. When >> finished, a quick transmit reveals the SWR. >> >> One day while tuning close to optimum at the frequency I was on, and >> because I receive while I tune, I began to hear a weak CW signal. At >> first, I thought it had just come on frequency, but as I listened, I >> realized that the station had been in qso for awhile, but I didn't hear >> it until I reached optimum resonance with the tuner. I knew a resonant >> antenna was important, but I was surprised at the difference it could >> make in receiving. A good receiver is wasted if the signal doesn't get to >> it. >> >> >> Richard Fjeld, n0ce >> [hidden email] >> I'd rather be learning. >> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.894 / Virus Database: 271.1.1/3535 - Release Date: 03/28/11 02:34:00 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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The antenna tuner acts as a pre-selector so to speak, by making the sytem of the antenna, the transmission line, and the radio, resonant, and matched impedence.
All of this adds up to minimize losses in a couple of ways. The impedence matching means that the xmission line and antenna are as close to the input impedence of the radio (nominally 50 Ohms these days). If it is not at 50 Ohms then you do not get maximum power in to the rig based on simple simple Ohms law power. A highly simplified way of explaining resonance part of "a resonant antenna" is the act of making sure all of the current is in phase with the voltage so that when the power does get to the reciever, that it is in a useable form to drive things. It is somewhat the reverse or inverse of a good spring and shock absorber system on a car....if you have things wrong, and drive along a rough road with bumps spaced jsut right relative to how fast, then all heck breaks loose; maximim power transferred, and that is a resonant system. If things are not resonant, well, you get a smooth ride in your car, or in the case of your radio, poor reception (and transmission). -ron WT5RZ |
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I believe I understood all of your comment Ron. But as our noise floor at HF is limited by external noise (atmospheric, manmade and galactic) I don't understand how efficiency, within reason, comes into play for a receive antenna. Certainly, for signals above the noise floor, adding in 3 or 10 of attenuation makes no difference in the S/N ratio, and since the preselector cannot discriminate between signal and noise, I still don't understand the mechanism of how a preselector improves S/N unless its BW is better than the BW of the receiver- and I can't imagine that situation either. One of my best low band antennas is a rotatable half sized Flag whose gain runs around 30dB below my sloper. Dale W4OP > The antenna tuner acts as a pre-selector so to speak, by making the sytem > of > the antenna, the transmission line, and the radio, resonant, and matched > impedence. > > All of this adds up to minimize losses in a couple of ways. The impedence > matching means that the xmission line and antenna are as close to the > input > impedence of the radio (nominally 50 Ohms these days). If it is not at 50 > Ohms then you do not get maximum power in to the rig based on simple > simple > Ohms law power. > > A highly simplified way of explaining resonance part of "a resonant > antenna" > is the act of making sure all of the current is in phase with the voltage > so > that when the power does get to the reciever, that it is in a useable form > to drive things. It is somewhat the reverse or inverse of a good spring > and > shock absorber system on a car....if you have things wrong, and drive > along > a rough road with bumps spaced jsut right relative to how fast, then all > heck breaks loose; maximim power transferred, and that is a resonant > system. > If things are not resonant, well, you get a smooth ride in your car, or in > the case of your radio, poor reception (and transmission). > > -ron WT5RZ > > -- > View this message in context: > http://elecraft.365791.n2.nabble.com/A-comment-about-Receiving-tp6216105p6217679.html > Sent from the Elecraft mailing list archive at Nabble.com. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.894 / Virus Database: 271.1.1/3536 - Release Date: 03/28/11 14:34:00 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Dale,
The bandwidth can make a difference - the noise is broadband while the signal is narrowband. If the bandwidth of the receiver input is wide, then a preselector will make a difference because it decreases the total noise that the receiver is handling. Note that many(most) tuners will not produce that pre-selector effect. Only those with a resonant circuit will do that. Most common T-network of L-network tuners create either a high pass or a low pass filter. 73, Don W3FPR On 3/29/2011 9:55 AM, Dale Parfitt wrote: > I believe I understood all of your comment Ron. > But as our noise floor at HF is limited by external noise (atmospheric, > manmade and galactic) I don't understand how efficiency, within reason, > comes into play for a receive antenna. Certainly, for signals above the > noise floor, adding in 3 or 10 of attenuation makes no difference in the S/N > ratio, and since the preselector cannot discriminate between signal and > noise, I still don't understand the mechanism of how a preselector improves > S/N unless its BW is better than the BW of the receiver- and I can't imagine > that situation either. > One of my best low band antennas is a rotatable half sized Flag whose gain > runs around 30dB below my sloper. > > Dale W4OP > >> The antenna tuner acts as a pre-selector so to speak, by making the sytem >> of >> the antenna, the transmission line, and the radio, resonant, and matched >> impedence. >> >> All of this adds up to minimize losses in a couple of ways. The impedence >> matching means that the xmission line and antenna are as close to the >> input >> impedence of the radio (nominally 50 Ohms these days). If it is not at 50 >> Ohms then you do not get maximum power in to the rig based on simple >> simple >> Ohms law power. >> >> A highly simplified way of explaining resonance part of "a resonant >> antenna" >> is the act of making sure all of the current is in phase with the voltage >> so >> that when the power does get to the reciever, that it is in a useable form >> to drive things. It is somewhat the reverse or inverse of a good spring >> and >> shock absorber system on a car....if you have things wrong, and drive >> along >> a rough road with bumps spaced jsut right relative to how fast, then all >> heck breaks loose; maximim power transferred, and that is a resonant >> system. >> If things are not resonant, well, you get a smooth ride in your car, or in >> the case of your radio, poor reception (and transmission). >> >> -ron WT5RZ >> >> -- >> View this message in context: >> http://elecraft.365791.n2.nabble.com/A-comment-about-Receiving-tp6216105p6217679.html >> Sent from the Elecraft mailing list archive at Nabble.com. >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > -------------------------------------------------------------------------------- > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.894 / Virus Database: 271.1.1/3536 - Release Date: 03/28/11 > 14:34:00 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Hi Don, That is why I mentioned the case of: >I still don't understand the mechanism of how a preselector improves >S/N unless its BW is better than the BW of the receiver- and I can't imagine >that situation either. Now, if you are saying the wideband noise may be desensing or causing IM- I understand. That is one of the reasons we have passive filters up front in a rig. But I still don't understand how a preselector with say 50KHz -3dB BW can improve S/N in a modern communications RX- Dale W4OP > Dale, > > The bandwidth can make a difference - the noise is broadband while the > signal is narrowband. > If the bandwidth of the receiver input is wide, then a preselector will > make a difference because it decreases the total noise that the receiver > is handling. > > Note that many(most) tuners will not produce that pre-selector effect. > Only those with a resonant circuit will do that. Most common T-network > of L-network tuners create either a high pass or a low pass filter. > > 73, > Don W3FPR > > On 3/29/2011 9:55 AM, Dale Parfitt wrote: >> I believe I understood all of your comment Ron. >> But as our noise floor at HF is limited by external noise (atmospheric, >> manmade and galactic) I don't understand how efficiency, within reason, >> comes into play for a receive antenna. Certainly, for signals above the >> noise floor, adding in 3 or 10 of attenuation makes no difference in the >> S/N >> ratio, and since the preselector cannot discriminate between signal and >> noise, I still don't understand the mechanism of how a preselector >> improves >> S/N unless its BW is better than the BW of the receiver- and I can't >> imagine >> that situation either. >> One of my best low band antennas is a rotatable half sized Flag whose >> gain >> runs around 30dB below my sloper. >> >> Dale W4OP >> >>> The antenna tuner acts as a pre-selector so to speak, by making the >>> sytem >>> of >>> the antenna, the transmission line, and the radio, resonant, and matched >>> impedence. >>> >>> All of this adds up to minimize losses in a couple of ways. The >>> impedence >>> matching means that the xmission line and antenna are as close to the >>> input >>> impedence of the radio (nominally 50 Ohms these days). If it is not at >>> 50 >>> Ohms then you do not get maximum power in to the rig based on simple >>> simple >>> Ohms law power. >>> >>> A highly simplified way of explaining resonance part of "a resonant >>> antenna" >>> is the act of making sure all of the current is in phase with the >>> voltage >>> so >>> that when the power does get to the reciever, that it is in a useable >>> form >>> to drive things. It is somewhat the reverse or inverse of a good spring >>> and >>> shock absorber system on a car....if you have things wrong, and drive >>> along >>> a rough road with bumps spaced jsut right relative to how fast, then all >>> heck breaks loose; maximim power transferred, and that is a resonant >>> system. >>> If things are not resonant, well, you get a smooth ride in your car, or >>> in >>> the case of your radio, poor reception (and transmission). >>> >>> -ron WT5RZ >>> >>> -- >>> View this message in context: >>> http://elecraft.365791.n2.nabble.com/A-comment-about-Receiving-tp6216105p6217679.html >>> Sent from the Elecraft mailing list archive at Nabble.com. >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[hidden email] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >> >> -------------------------------------------------------------------------------- >> >> >> >> No virus found in this incoming message. >> Checked by AVG - www.avg.com >> Version: 9.0.894 / Virus Database: 271.1.1/3536 - Release Date: 03/28/11 >> 14:34:00 >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.894 / Virus Database: 271.1.1/3537 - Release Date: 03/29/11 02:34:00 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Don Wilhelm-4
I believe that if HF noise power is tolerated and not spread by RX
non-linearities and the incoming noise substantially exceeds any added RX noise (as in the excellent K3 or K2 design), then the input signal to noise for the portion of the spectrum that IS LISTENED TO at chosen bandwidth IS NOT affected at all by input matching. At VHF this is another story, because it is very easy for the amplification devices to contain the limiting noise. At this point the matching and bandwidth issues become prime. There is no general statement that encompasses this issue for both HF and VHF. 73, Guy. On Tue, Mar 29, 2011 at 12:22 PM, Don Wilhelm <[hidden email]> wrote: > Dale, > > The bandwidth can make a difference - the noise is broadband while the > signal is narrowband. > If the bandwidth of the receiver input is wide, then a preselector will > make a difference because it decreases the total noise that the receiver > is handling. > > Note that many(most) tuners will not produce that pre-selector effect. > Only those with a resonant circuit will do that. Most common T-network > of L-network tuners create either a high pass or a low pass filter. > > 73, > Don W3FPR > > On 3/29/2011 9:55 AM, Dale Parfitt wrote: >> I believe I understood all of your comment Ron. >> But as our noise floor at HF is limited by external noise (atmospheric, >> manmade and galactic) I don't understand how efficiency, within reason, >> comes into play for a receive antenna. Certainly, for signals above the >> noise floor, adding in 3 or 10 of attenuation makes no difference in the S/N >> ratio, and since the preselector cannot discriminate between signal and >> noise, I still don't understand the mechanism of how a preselector improves >> S/N unless its BW is better than the BW of the receiver- and I can't imagine >> that situation either. >> One of my best low band antennas is a rotatable half sized Flag whose gain >> runs around 30dB below my sloper. >> >> Dale W4OP >> >>> The antenna tuner acts as a pre-selector so to speak, by making the sytem >>> of >>> the antenna, the transmission line, and the radio, resonant, and matched >>> impedence. >>> >>> All of this adds up to minimize losses in a couple of ways. The impedence >>> matching means that the xmission line and antenna are as close to the >>> input >>> impedence of the radio (nominally 50 Ohms these days). If it is not at 50 >>> Ohms then you do not get maximum power in to the rig based on simple >>> simple >>> Ohms law power. >>> >>> A highly simplified way of explaining resonance part of "a resonant >>> antenna" >>> is the act of making sure all of the current is in phase with the voltage >>> so >>> that when the power does get to the reciever, that it is in a useable form >>> to drive things. It is somewhat the reverse or inverse of a good spring >>> and >>> shock absorber system on a car....if you have things wrong, and drive >>> along >>> a rough road with bumps spaced jsut right relative to how fast, then all >>> heck breaks loose; maximim power transferred, and that is a resonant >>> system. >>> If things are not resonant, well, you get a smooth ride in your car, or in >>> the case of your radio, poor reception (and transmission). >>> >>> -ron WT5RZ >>> >>> -- >>> View this message in context: >>> http://elecraft.365791.n2.nabble.com/A-comment-about-Receiving-tp6216105p6217679.html >>> Sent from the Elecraft mailing list archive at Nabble.com. >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[hidden email] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >> >> -------------------------------------------------------------------------------- >> >> >> >> No virus found in this incoming message. >> Checked by AVG - www.avg.com >> Version: 9.0.894 / Virus Database: 271.1.1/3536 - Release Date: 03/28/11 >> 14:34:00 >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Don Wilhelm-4
I still don't understand. If signals pass through a 500 Hz roofing filter on the front end of the rig, what effect can wideband noise have on the receiver? This assumes the noise is not strong enough to trigger the radio's hardware AGC, but wideband noise is typically far below that level (about S9+30). Unless the tuner has an extremely high-Q (i.e. like a crystal filter) I don't see how it can help a rig like the K3 with a CW roofing filter. Most tuners' bandwidths are in the order of hundreds of kHz...not hundreds of Hz. 73, Bill W4ZV |
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In reply to this post by Dale Parfitt-3
Dale,
The effect of a pre-selector will depend a lot on the particular receiver design. The Elecraft receivers have all active receiver stages after the bandpass, so I would not expect a pre-selector would make any improvement, but I have had several older receivers where it would make a difference - most were tube type and had broad selectivity in the first stage. There was a time when pre-selectors were available for receivers, but that was way back when dirt was young. 73, Don W3FPR On 3/29/2011 12:35 PM, Dale Parfitt wrote: > > Hi Don, > That is why I mentioned the case of: > >I still don't understand the mechanism of how a preselector improves > >S/N unless its BW is better than the BW of the receiver- and I can't > imagine > >that situation either. > Now, if you are saying the wideband noise may be desensing or causing > IM- I understand. That is one of the reasons we have passive filters > up front in a rig. > But I still don't understand how a preselector with say 50KHz -3dB BW > can improve S/N in a modern communications RX- > Dale W4OP > >> Dale, >> >> The bandwidth can make a difference - the noise is broadband while the >> signal is narrowband. >> If the bandwidth of the receiver input is wide, then a preselector will >> make a difference because it decreases the total noise that the receiver >> is handling. >> >> Note that many(most) tuners will not produce that pre-selector effect. >> Only those with a resonant circuit will do that. Most common T-network >> of L-network tuners create either a high pass or a low pass filter. >> >> 73, >> Don W3FPR >> >> On 3/29/2011 9:55 AM, Dale Parfitt wrote: >>> I believe I understood all of your comment Ron. >>> But as our noise floor at HF is limited by external noise (atmospheric, >>> manmade and galactic) I don't understand how efficiency, within reason, >>> comes into play for a receive antenna. Certainly, for signals above the >>> noise floor, adding in 3 or 10 of attenuation makes no difference in >>> the S/N >>> ratio, and since the preselector cannot discriminate between signal and >>> noise, I still don't understand the mechanism of how a preselector >>> improves >>> S/N unless its BW is better than the BW of the receiver- and I can't >>> imagine >>> that situation either. >>> One of my best low band antennas is a rotatable half sized Flag >>> whose gain >>> runs around 30dB below my sloper. >>> >>> Dale W4OP >>> >>>> The antenna tuner acts as a pre-selector so to speak, by making the >>>> sytem >>>> of >>>> the antenna, the transmission line, and the radio, resonant, and >>>> matched >>>> impedence. >>>> >>>> All of this adds up to minimize losses in a couple of ways. The >>>> impedence >>>> matching means that the xmission line and antenna are as close to the >>>> input >>>> impedence of the radio (nominally 50 Ohms these days). If it is not >>>> at 50 >>>> Ohms then you do not get maximum power in to the rig based on simple >>>> simple >>>> Ohms law power. >>>> >>>> A highly simplified way of explaining resonance part of "a resonant >>>> antenna" >>>> is the act of making sure all of the current is in phase with the >>>> voltage >>>> so >>>> that when the power does get to the reciever, that it is in a >>>> useable form >>>> to drive things. It is somewhat the reverse or inverse of a good >>>> spring >>>> and >>>> shock absorber system on a car....if you have things wrong, and drive >>>> along >>>> a rough road with bumps spaced jsut right relative to how fast, >>>> then all >>>> heck breaks loose; maximim power transferred, and that is a resonant >>>> system. >>>> If things are not resonant, well, you get a smooth ride in your >>>> car, or in >>>> the case of your radio, poor reception (and transmission). >>>> >>>> -ron WT5RZ >>>> >>>> -- >>>> View this message in context: >>>> http://elecraft.365791.n2.nabble.com/A-comment-about-Receiving-tp6216105p6217679.html >>>> >>>> Sent from the Elecraft mailing list archive at Nabble.com. >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:[hidden email] >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: http://www.qsl.net/donate.html >>> >>> -------------------------------------------------------------------------------- >>> >>> >>> >>> >>> No virus found in this incoming message. >>> Checked by AVG - www.avg.com >>> Version: 9.0.894 / Virus Database: 271.1.1/3536 - Release Date: >>> 03/28/11 >>> 14:34:00 >>> >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[hidden email] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > > -------------------------------------------------------------------------------- > > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.894 / Virus Database: 271.1.1/3537 - Release Date: > 03/29/11 02:34:00 > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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On 3/29/2011 4:53 PM, Don Wilhelm wrote
> > There was a time when pre-selectors were available for > receivers, but that was way back when dirt was young. Be careful Don, you're talking about my childhood and I *can* remember when dirt was young :-) Fred K6DGW Auburn CA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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