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#61
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Cecil, was it you that mention a "windom balun?"
Ian Jackson wrote in
: .... As a Windom is only likely to be used on the HF bands (and probably mainly on the lower HF bands), I would have thought that a few dB of attenuation would have negligible effect on the SNR. Ian, Ah, the statements in support of mediocrity about. Yes, there is an element of truth in what you say... but looking at it a little further.... On any bands where the external noise is very much greater than the receiver internal noise, small extra antenna loss will not markedly degrade S/N ratio on receive. One of the issues when the feedline participates as an antenna condcutor is that its proximity to noise sources (eg the power wiring of a building) may lead to higher receive noise without increasing signal strength, so feedline participation can degrade S/N by that mechanism. You won't see that called out in Carolina Windom adds which claim feedline participation as an advantage. On the tx side, loss in the antenna system reduces EIRP, and so directly degrades S/N at the other end. So, even on those bands where external noise is very much greater than receiver internal noise, pay attention to antenna efficiency to achieve optimal radiated power to be heard at best S/N. One of the bogus arguments often trotted out is that efficiency is less important with QRP since there is less power to damage a lossy component. Another view is that if you start out with a transmitter that is 10dB or so behind the average transmitter power being used, then why exacerbate the situation when an even lossier antenna system. For a once technically based hobby, we do think up some phony rationale. It is a personal judgement about whether 3dB (mentioned by one poster) or any other number is acceptable in the compromise that is made with all practical antenna systems. Owen |
#62
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Cecil, was it you that mention a "windom balun?"
On Sep 15, 7:24*am, John Smith wrote:
If a mere loss of 10% drops you too close to the sensitivity threshold of your receiver, your ability to pull out a weak signal just suffered the kiss of death ... John, when are you going to give up on this crystal receiver set of yours and get a decent receiver? http://crystalradiosupply.com/conten...%20edition.jpg For me, receiving at anywhere near the 0.13 uV receiver threshold is just too much work. I think they should outlaw any received signal below 1 uV. -- 73, Cecil, w5dxp.com |
#63
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Cecil, was it you that mention a "windom balun?"
On 9/15/2010 12:55 PM, Cecil Moore wrote:
On Sep 15, 7:24 am, John wrote: If a mere loss of 10% drops you too close to the sensitivity threshold of your receiver, your ability to pull out a weak signal just suffered the kiss of death ... John, when are you going to give up on this crystal receiver set of yours and get a decent receiver? http://crystalradiosupply.com/conten...%20edition.jpg For me, receiving at anywhere near the 0.13 uV receiver threshold is just too much work. I think they should outlaw any received signal below 1 uV. -- 73, Cecil, w5dxp.com Darn Cecil, quite peeking! From the crystal silicon in the semiconductors, to the crystaline structure of the metals ... I just can't get away from the darn crystal radios! And, alas, I am afraid, these days, the sensitivity of my receivers front end far exceeds my hearing ... I was just bragging. You caught me! But, I can still remember those days when I could pull out a gnats whisper above ... but then, as I remember, there was far less noise then. Regards, JS |
#64
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Cecil, was it you that mention a "windom balun?"
On 9/15/2010 12:55 PM, Cecil Moore wrote:
... -- 73, Cecil, w5dxp.com quite = quit ... another bad habit in the making. Regards, JS |
#65
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Cecil, was it you that mention a "windom balun?"
In message , Owen Duffy
writes Ian Jackson wrote in : ... As a Windom is only likely to be used on the HF bands (and probably mainly on the lower HF bands), I would have thought that a few dB of attenuation would have negligible effect on the SNR. Ian, Ah, the statements in support of mediocrity about. Yes, there is an element of truth in what you say... but looking at it a little further.... On any bands where the external noise is very much greater than the receiver internal noise, small extra antenna loss will not markedly degrade S/N ratio on receive. One of the issues when the feedline participates as an antenna condcutor is that its proximity to noise sources (eg the power wiring of a building) may lead to higher receive noise without increasing signal strength, so feedline participation can degrade S/N by that mechanism. You won't see that called out in Carolina Windom adds which claim feedline participation as an advantage. On the tx side, loss in the antenna system reduces EIRP, and so directly degrades S/N at the other end. So, even on those bands where external noise is very much greater than receiver internal noise, pay attention to antenna efficiency to achieve optimal radiated power to be heard at best S/N. One of the bogus arguments often trotted out is that efficiency is less important with QRP since there is less power to damage a lossy component. Another view is that if you start out with a transmitter that is 10dB or so behind the average transmitter power being used, then why exacerbate the situation when an even lossier antenna system. For a once technically based hobby, we do think up some phony rationale. It is a personal judgement about whether 3dB (mentioned by one poster) or any other number is acceptable in the compromise that is made with all practical antenna systems. Owen I can't disagree with anything you say. I'm no advocate of the Carolina Windom, and have no plans to use one. From the point of view of receiving (and causing) interference, allowing the feeder to contribute to the antenna radiation is certainly something which one should be circumspect about. The various comments and explanations (here and elsewhere) indicate that can be a bit of an art to ensure that the radiating common-mode feeder currents are restricted to where they ought to be. And while, on receive, a bit of 'unnecessary' loss is usually of little consequence on the lower frequencies, losing transmitter power is not something you want to do, on any frequency (if you can avoid it). But, as always, it is often a balance between performance, convenience, and what you are really trying to achieve with your amateur radio station. -- Ian |
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