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Tom,
It should be obvious when somebody asks how to find VF by using an HF antenna analiser he is interested, like every other radio amateur, in the HF value of VF. If you agree with the table in the other posting, which gives VF vesus frequency, and you are aware VF decreases with frequency, then how come you didn't realise you had taken the value of 0.665 out of its HF context. All my figures are correct. ---- Reg '''''''''''''''''''''''''''''''''''''''''''''''''' '''''''''''''''''''''''''' ''''''''''''''' "Tom Bruhns" wrote in message m... "Reg Edwards" wrote in message ... "Tom Bruhns" wrote "Reg Edwards" The velocity factor of ALL solid polyethylene coax cable, regardless of impedance, is 0.665 ================================ And this comes from someone who I could swear posted not long ago a table that had velocity factors for solid polyethylene cable that were significantly different from this magic number? ... Freq Ro jXo Angle VF ------ ------ ------ ------ ------ 50 Hz 967 -965 -44.95 0.034 1 kHz 220 -213 -44 0.151 10 kHz 80 -58 -36 0.41 100 kHz 56 -9.3 -9.5 0.59 1 MHz 52.4 -2.4 -2.7 0.63 10 MHz 50.7 -0.76 -0.86 0.65 100 MHz 50.2 -0.23 -0.27 0.66 Smith Chart calculations begin to be inaccurate around 2 MHz and below. So do SWR meters. |
Tom,
It should be obvious when somebody asks how to find VF by using an HF antenna analiser he is interested, like every other radio amateur, in the HF value of VF. If you agree with the table in the other posting, which gives VF vesus frequency, and you are aware VF decreases with frequency, then how come you didn't realise you had taken the value of 0.665 out of its HF context. All my figures are correct. ---- Reg '''''''''''''''''''''''''''''''''''''''''''''''''' '''''''''''''''''''''''''' ''''''''''''''' "Tom Bruhns" wrote in message m... "Reg Edwards" wrote in message ... "Tom Bruhns" wrote "Reg Edwards" The velocity factor of ALL solid polyethylene coax cable, regardless of impedance, is 0.665 ================================ And this comes from someone who I could swear posted not long ago a table that had velocity factors for solid polyethylene cable that were significantly different from this magic number? ... Freq Ro jXo Angle VF ------ ------ ------ ------ ------ 50 Hz 967 -965 -44.95 0.034 1 kHz 220 -213 -44 0.151 10 kHz 80 -58 -36 0.41 100 kHz 56 -9.3 -9.5 0.59 1 MHz 52.4 -2.4 -2.7 0.63 10 MHz 50.7 -0.76 -0.86 0.65 100 MHz 50.2 -0.23 -0.27 0.66 Smith Chart calculations begin to be inaccurate around 2 MHz and below. So do SWR meters. |
So, Reg, I note that (1) YOUR table shows more variation in VF over
the HF ham bands (especially so if you allow it to be extended down to the 1.8MHz ham band, which I assume the MFJ analyzer would cover) than the three significant digits of 0.665 would allow (the table showing only 0.65 at 10MHz, and I suppose you'd go for about 0.64 at 2MHz, maybe even 3.5MHz), (2) your posting in this thread of 0.665 did NOT qualify the VF as being HF only, and (3) my posting DID say something that SHOULD have indicated to you and anyone else who read it that I was thinking beyond the bounds of HF with respect to large VF variation. I'd STILL say there are instances where one should not assume 0.665 for solid polyethylene at HF. There are instances where 0.64 and 0.665 are different enough to want to get the right value. You're welcome to get all bent out of shape over that if you wish. Cheers, Tom "Reg Edwards" wrote in message ... Tom, It should be obvious when somebody asks how to find VF by using an HF antenna analiser he is interested, like every other radio amateur, in the HF value of VF. If you agree with the table in the other posting, which gives VF vesus frequency, and you are aware VF decreases with frequency, then how come you didn't realise you had taken the value of 0.665 out of its HF context. All my figures are correct. (As we noted at the time of the original posting, the numbers in the table are rough approximations...certainly they're correct as approximations...) ---- Reg '''''''''''''''''''''''''''''''''''''''''''''''''' '''''''''''''''''''''''''' ''''''''''''''' "Tom Bruhns" wrote in message m... "Reg Edwards" wrote in message ... "Tom Bruhns" wrote "Reg Edwards" The velocity factor of ALL solid polyethylene coax cable, regardless of impedance, is 0.665 ================================ And this comes from someone who I could swear posted not long ago a table that had velocity factors for solid polyethylene cable that were significantly different from this magic number? ... Freq Ro jXo Angle VF ------ ------ ------ ------ ------ 50 Hz 967 -965 -44.95 0.034 1 kHz 220 -213 -44 0.151 10 kHz 80 -58 -36 0.41 100 kHz 56 -9.3 -9.5 0.59 1 MHz 52.4 -2.4 -2.7 0.63 10 MHz 50.7 -0.76 -0.86 0.65 100 MHz 50.2 -0.23 -0.27 0.66 Smith Chart calculations begin to be inaccurate around 2 MHz and below. So do SWR meters. |
So, Reg, I note that (1) YOUR table shows more variation in VF over
the HF ham bands (especially so if you allow it to be extended down to the 1.8MHz ham band, which I assume the MFJ analyzer would cover) than the three significant digits of 0.665 would allow (the table showing only 0.65 at 10MHz, and I suppose you'd go for about 0.64 at 2MHz, maybe even 3.5MHz), (2) your posting in this thread of 0.665 did NOT qualify the VF as being HF only, and (3) my posting DID say something that SHOULD have indicated to you and anyone else who read it that I was thinking beyond the bounds of HF with respect to large VF variation. I'd STILL say there are instances where one should not assume 0.665 for solid polyethylene at HF. There are instances where 0.64 and 0.665 are different enough to want to get the right value. You're welcome to get all bent out of shape over that if you wish. Cheers, Tom "Reg Edwards" wrote in message ... Tom, It should be obvious when somebody asks how to find VF by using an HF antenna analiser he is interested, like every other radio amateur, in the HF value of VF. If you agree with the table in the other posting, which gives VF vesus frequency, and you are aware VF decreases with frequency, then how come you didn't realise you had taken the value of 0.665 out of its HF context. All my figures are correct. (As we noted at the time of the original posting, the numbers in the table are rough approximations...certainly they're correct as approximations...) ---- Reg '''''''''''''''''''''''''''''''''''''''''''''''''' '''''''''''''''''''''''''' ''''''''''''''' "Tom Bruhns" wrote in message m... "Reg Edwards" wrote in message ... "Tom Bruhns" wrote "Reg Edwards" The velocity factor of ALL solid polyethylene coax cable, regardless of impedance, is 0.665 ================================ And this comes from someone who I could swear posted not long ago a table that had velocity factors for solid polyethylene cable that were significantly different from this magic number? ... Freq Ro jXo Angle VF ------ ------ ------ ------ ------ 50 Hz 967 -965 -44.95 0.034 1 kHz 220 -213 -44 0.151 10 kHz 80 -58 -36 0.41 100 kHz 56 -9.3 -9.5 0.59 1 MHz 52.4 -2.4 -2.7 0.63 10 MHz 50.7 -0.76 -0.86 0.65 100 MHz 50.2 -0.23 -0.27 0.66 Smith Chart calculations begin to be inaccurate around 2 MHz and below. So do SWR meters. |
My figures are correct to a better accuracy than can be determind by a cheap
and nasty antenna analyser. Now go away, leave the newsgroup in peace, and stop your childish nitpicking. |
My figures are correct to a better accuracy than can be determind by a cheap
and nasty antenna analyser. Now go away, leave the newsgroup in peace, and stop your childish nitpicking. |
Clearly, if I had an o-scope and a waveform generator, I wouldn't be farting
with this analyzer!! :) "Tim Shoppa" wrote in message om... "Jason Dugas" wrote in message ... I'm interested in measuring the velocity factor of some coax I have (more of an exercise than necessity). In order to do this, the MFJ-259 Operations ... What would be a good way of making this connection? Do you have a scope and a pulse generator? If so, just make a simple TDR (Time Domain Reflectometry) setup to measure the reflection from a un-terminated or shorted far end of the cable. You will get much more accurate results with substantially less effort. Don't get me wrong, the MFJ-259 is a good instrument. It's just that TDR is so quick and easy and unambiguous for propogation delay measurements. Tim. |
Clearly, if I had an o-scope and a waveform generator, I wouldn't be farting
with this analyzer!! :) "Tim Shoppa" wrote in message om... "Jason Dugas" wrote in message ... I'm interested in measuring the velocity factor of some coax I have (more of an exercise than necessity). In order to do this, the MFJ-259 Operations ... What would be a good way of making this connection? Do you have a scope and a pulse generator? If so, just make a simple TDR (Time Domain Reflectometry) setup to measure the reflection from a un-terminated or shorted far end of the cable. You will get much more accurate results with substantially less effort. Don't get me wrong, the MFJ-259 is a good instrument. It's just that TDR is so quick and easy and unambiguous for propogation delay measurements. Tim. |
Clearly, if I had an o-scope and a waveform generator, I wouldn't be farting
with this analyzer!! :) Hi Jason, did you get the email response I sent you? 73 Gary N4AST |
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