Re: Stumped
Ken, You may have a problem using brass. It will have rather higher resistive loss than copper shielding. Small diameter copper tubing, such as is used to connect (say) a sink's drinking-water dispenser, is probably a better choice. In fact, even copper tape should be a good ad-hoc test, and not too much trouble (other than bleeding all over the floor from cut fingers) to apply. But do make sure whatever you use is terminated properly at the ends off the cable under test. Cheers, Cortland --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped
I used a probe calibrated to 450 MHz. I am going to my local hardware store, they used to carry copper and brass stock tubing, and I am going to try your suggestion. Thank you! -- >From: Cortland Richmond <72146@compuserve.com> >To: Ken Javor , ieee pstc list >Subject: Re: Stumped >Date: Tue, Oct 15, 2002, 3:19 PM > > It looks like you've answered your own earlier question, Ken; yes, you CAN > see a difference between a leaky coax and good coax. I don't know that you > can rely on the usual clamp-on current probe up at 400 MHz, but the > relative difference tells you a good deal. And at 400 Mhz you only need a > few feet for most of the power in shield current -- where the leaks end up > -- to radiate away. You may also have copper losses in the shield -- which > is not designed to carry signal current, remember -- as well as radiation > losses through it. > > However, 20 dB more than very little is not necessarily a lot. You can > measure how much is lost to radiation by repeating your original test, but > this time with a small-diameter - as tight as practical - copper tube > replacing the braid, making an almost perfect shield. The power lost > thorough radiation will no longer be dumped to space, and you should see > that as decreased loss end-to-end. > > Cortland > --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped
It looks like you've answered your own earlier question, Ken; yes, you CAN see a difference between a leaky coax and good coax. I don't know that you can rely on the usual clamp-on current probe up at 400 MHz, but the relative difference tells you a good deal. And at 400 Mhz you only need a few feet for most of the power in shield current -- where the leaks end up -- to radiate away. You may also have copper losses in the shield -- which is not designed to carry signal current, remember -- as well as radiation losses through it. However, 20 dB more than very little is not necessarily a lot. You can measure how much is lost to radiation by repeating your original test, but this time with a small-diameter - as tight as practical - copper tube replacing the braid, making an almost perfect shield. The power lost thorough radiation will no longer be dumped to space, and you should see that as decreased loss end-to-end. Cortland --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped
To try and verify your theory, I set up a signal generator at 100 and 400 MHz, -20 dBm into 50 Ohms. I drove a six foot section of RG-58 with bnc connections, and terminated in a shielded 50 Ohm dummy load. I repeated the same measurement using one of my twisted shielded pairs. I measured "leakage" current by placing a current probe around first the coax and then the TSP, sliding the probe up and down the cable looking for maxima. I did not see a significant difference at 100 MHz, but at 400 MHz there was 20 dB more leakage on the TSP than from the coax. Is it a good assumption that anything I measure with the current probe is essentially lost in transmission? -- >From: Cortland Richmond <72146@compuserve.com> >To: Ken Javor , ieee pstc list >Subject: Re: Stumped >Date: Tue, Oct 15, 2002, 12:59 PM > > Now that I've re-read the message, I see where you are coming from. > > I thought you were looking at common-mode loss of the cable (as a whole, > shield included) *above ground*; you are looking at the center conductor > common mode with respect to the overshield, almost as a coaxial cable > itself. Yes, that seems a reasonable impedance for that configuration. > > Loss is from the conductor and from the dielectric. You have a relatively > large, low-loss conductor -- but due to its high capacitance, I'd expect > dielectric loss to predominate in the setup you are using. > > A question about the braid; you said it appears to be Kapton coated. Could > it be that braid conductors are not making intimate contact with each > other? In that case, radiation loss could still be a large part of what you > saw. > > > > Cortland > --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped
The braid looks pretty tight to me, but since real coax is always coated with opaque insulation, I can't make a direct comparison. If it were a "leaky coax" effect, would I be able to pick that up with a current probe placed around the cable? If I compared the current probe reading from a leaky coax to a good one, could I see the difference that way? -- >From: Cortland Richmond <72146@compuserve.com> >To: Ken Javor , ieee pstc list >Subject: Re: Stumped >Date: Tue, Oct 15, 2002, 12:59 PM > > Now that I've re-read the message, I see where you are coming from. > > I thought you were looking at common-mode loss of the cable (as a whole, > shield included) *above ground*; you are looking at the center conductor > common mode with respect to the overshield, almost as a coaxial cable > itself. Yes, that seems a reasonable impedance for that configuration. > > Loss is from the conductor and from the dielectric. You have a relatively > large, low-loss conductor -- but due to its high capacitance, I'd expect > dielectric loss to predominate in the setup you are using. > > A question about the braid; you said it appears to be Kapton coated. Could > it be that braid conductors are not making intimate contact with each > other? In that case, radiation loss could still be a large part of what you > saw. > > > > Cortland > --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped
Now that I've re-read the message, I see where you are coming from. I thought you were looking at common-mode loss of the cable (as a whole, shield included) *above ground*; you are looking at the center conductor common mode with respect to the overshield, almost as a coaxial cable itself. Yes, that seems a reasonable impedance for that configuration. Loss is from the conductor and from the dielectric. You have a relatively large, low-loss conductor -- but due to its high capacitance, I'd expect dielectric loss to predominate in the setup you are using. A question about the braid; you said it appears to be Kapton coated. Could it be that braid conductors are not making intimate contact with each other? In that case, radiation loss could still be a large part of what you saw. Cortland --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped
I measured impedances of 15 - 25 Ohms. The separation between twisted shielded pair center conductor(s) and shield is the thickness of the center conductors' insulation - very thin. This makes the capacitance higher than for 50 Ohm coax. At the same time the close proximity of center conductors and shield reduces the inductance, relative to 50 Ohm coax, and since the impedance is the square root of the ratio of inductance by capacitance, it seems clear to me that the impedance has to be lower than 50 Ohms. But the impedance is not the major issue here. How am I getting so much loss in the very thin conductor insulation? Or is there another loss mechanism of which I am unaware? -- >From: Cortland Richmond <72146@compuserve.com> >To: Ken Javor , ieee pstc list >Subject: Re: Stumped >Date: Tue, Oct 15, 2002, 2:52 AM > > Ken, a few thoughts. > > Did you account for radiation resistance? You have described not merely a > single-wire transmission line but ALSO, a fairly good antenna. > > The impedance is probably higher than you calculate. A coax cable with the > same ratio of shield radius (height above ground) to inner conductor size > will be higher impedance tan your 15-25 ohms. You have greater spacing -- > the ground isn't concentric -- and the impedance HAS to be higher. > > For all but the lowest frequencies in the range you mention, the chamber > prevents current on the cable from flowing as on a transmission line; its > resonances couple differently to the line than operating over an unenclosed > ground plane. But assuming your matching is correct, you SHOULD see only > a travelling wave on the cable, and current or voltage that does not vary > along the line (except due to loss). If the match is incorrect, you will > have standing waves, and this you can confirm pretty easily with a current > probe. The chamber resonances may obscure this. > > It is possible to find loss in common mode simply by measuring common-mode > current at a peak near one end of a suspended conductor and again at a peak > near the other end. The location of current nodes will depend (outside a > chamber!) on wavelength, but the difference between them over length will > depend on radiation and other losses. > > Cortland > --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped
Ken, a few thoughts. Did you account for radiation resistance? You have described not merely a single-wire transmission line but ALSO, a fairly good antenna. The impedance is probably higher than you calculate. A coax cable with the same ratio of shield radius (height above ground) to inner conductor size will be higher impedance tan your 15-25 ohms. You have greater spacing -- the ground isn't concentric -- and the impedance HAS to be higher. For all but the lowest frequencies in the range you mention, the chamber prevents current on the cable from flowing as on a transmission line; its resonances couple differently to the line than operating over an unenclosed ground plane. But assuming your matching is correct, you SHOULD see only a travelling wave on the cable, and current or voltage that does not vary along the line (except due to loss). If the match is incorrect, you will have standing waves, and this you can confirm pretty easily with a current probe. The chamber resonances may obscure this. It is possible to find loss in common mode simply by measuring common-mode current at a peak near one end of a suspended conductor and again at a peak near the other end. The location of current nodes will depend (outside a chamber!) on wavelength, but the difference between them over length will depend on radiation and other losses. Cortland --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped (screw shaped inner 'coax' conductor, CEM simulation WAS: TSP or FTP ... )
> which means that whatever the impedance actually is, if properly matched, > mismatch losses may be bounded. Base on the significant electrical length per turns, I cannot see how mismatch losses can be 'bounded' especially at 1GHz. Perhaps at a higher frequency for a much shorter electrical length LAMBDA. > If it were "mismatch loss" wouldn't the > loss be strongly frequency dependent in a periodic fashion? The usual type of mismatch losses is indeed periodic, for resons to do with the defined location of the 'mismatch' or 'physical boundary' in the Tx line. This physical boundary remains the same as the electrical length of the cable changes with frequency. > The losses I > measured increased with increasing frequency, and the nature of the increase > was identical to that specified for the RG-XX coaxial types (with larger > magnitude as previously noted). Speaking off the cuff, (I should expect) the twisting profile (number of twist per unit physical length) would translate to number of 'smooth humps/bumps' per electrical length to decrease as frequency increases. :-) Considering the frequency of interest (80MHz-1GHz in IEC 1000-4-3) there may not be a substantial number of twist per electrical length. Due to the nature of the original intend of the insulation, I expect epsilom_r to be 'resonably' constant. We may not have to deal with the uncertainty associated with the dielectric medium. Making a (hazardous ?) guess, at 1GHz (LAMBDA_0 = 30 cm) LAMBDA= 30 cm/sqrt_epsilon_r Assuming epsilon_r =5 (I believe this will not be an unresonable figure), then LAMBDA=13.4 cm I suppose at a twist rate, say 80 t/meters (having no idea about you cable specs, I pull a figure of approx 12 mm pitch :-) it is roughly 11 or so t/LAMBDA. This will probable be closer to be 'distributed' at 100MHz being then 110 t/LAMBDA. (Ken, I need to corrected my statement I made a few min earlier ...) This I suppose needed some kind of MoM simulation to see the loss characteristics. I would like to hear from anyone handy with a CEM code like NEC, but on some hindsight, the proximity effect of the closely spaced conductors may be a problem for NEC. I suppose at the lower frequency the pair of twisted conductor will start to look like a short circuit at 80MHz. Does anyone out there know of a suitable CEM 'code' or technique to simulate the EM behaviour of such a conductor? I think SPICE is out for this kind of cable. regards, Tim Foo --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Stumped (TSP or FTP (Foil screened Twisted Pair) )
The cables in question all used braided shield construction and were aerospace quality. The individual center conductors are insulated, of course, but there is nothing else between the insulated wires and the shield braid. The shield braid itself appears to be Kapton coated. It is indeed true that the twisted pair as a center conductor has an irregular shape relative to a single coaxial conductor. However there is an expression for the characteristic impedance of just such a cable (except for the twist) in the Reference Handbook for Radio Engineers. In my 1953 copy this type of transmission line is termed "wires in parallel - sheath return." It is a complex formula but the point is that even with an irregular center conductor there is a defined transmission line characteristic impedance, which means that whatever the impedance actually is, if properly matched, mismatch losses may be bounded. If it were "mismatch loss" wouldn't the loss be strongly frequency dependent in a periodic fashion? The losses I measured increased with increasing frequency, and the nature of the increase was identical to that specified for the RG-XX coaxial types (with larger magnitude as previously noted). I can send a test data attachment to anyone interested. -- >From: "Wan Juang Foo" >To: Ken Javor , >Subject: Re: Stumped (TSP or FTP (Foil screened Twisted Pair) ) >Date: Mon, Oct 14, 2002, 9:11 PM > > > Ken, > I am only making a guess in the absence of the cable's specifications. Is > your TSP a FTP (Foil screened Twisted Pair) type of cable constructed from > copper wires coated with polyethylene and wrapped by Mylar tape (a > transparent and mechanically tough film) between the TP and the screen? I > think it is just mismatch losses due to the eccentricity of the cable. > Imagine what kind of performance one would expect from a coax with an inner > conductor that exhibit irregular cross sectional radius. > > IMHO, it's the inherent 'mismatch' losses of the 'cable' to CM signal. > Given the inherent twisting (eccentricity) of the conductors within the > 'screen', it is more like a coax with a screw shaped (how would I describe > it???) distribution of Zo along the length of the cable. The TP > configuration in the CM situation should be low loss only to circularly > polarised electromagnetic waves (if there is such a phenomenal in > electromagnetic propagation within a Tx line). For propagation modes of > anything else approaching something that may represent a substantial > fraction of Lambda would be, (or shall I say, should be) presented (or > seen) as a lossy line due to the changing cross sectional characteristic of > a FTP. > >> I expected losses that would be on the same order or lower than >> that associated with off-the-shelf coax types like RG-58. Instead my > losses >> were dramatically higher. > > In terms of CM performance (e.g. input impedance, losses, etc... ), a FTP > due to it's eccentricity, I suppose cannot be compared to a RG-58. I have > come across some FTP with 0.52 mm i.d. copper with a final diameter of 6.1 > mm for the cable. Let me know if this description fits your bill. I have > some information on their fabrication. > > Just another of my 2 ¢ ... > > regards > > Tim Foo > > > > > Ken Javor > >emc-p...@majordomo.ieee.org > ce.com>cc: (bcc: Wan > Juang Foo/ece/staff/npnet) > Sent by: Subject: Stumped > > owner-emc-pstc@majordo > > mo.ieee.org > > > > > > 10/15/02 05:31 AM > > Please respond to Ken > > Javor > > > > > > > > > > > Forum, > > I have made some measurements and gotten results which are at odds with my > intuition. I am wondering if someone out there can shed some light on this > subject. > > I was interested in the losses associated with rf traveling on a twisted > shielded pair cable. The scenario is that a length of this TSP cable is > exposed to an rf environment (as in a test chamber during IEC 1000-4-3 > testing) and then the cable penetrates a bulkhead using a grounded > connector > that provides excellent shield termination, and the cable continues on the > other side in the pristine rf environment of a shielded control chamber, > say > for several meters. The question is, how much rf signal is at the final > destination point vs. at the bulkhead. The concern is common mode, not &g
Re: Stumped (TSP or FTP (Foil screened Twisted Pair) )
Ken,
I am only making a guess in the absence of the cable's specifications. Is
your TSP a FTP (Foil screened Twisted Pair) type of cable constructed from
copper wires coated with polyethylene and wrapped by Mylar tape (a
transparent and mechanically tough film) between the TP and the screen? I
think it is just mismatch losses due to the eccentricity of the cable.
Imagine what kind of performance one would expect from a coax with an inner
conductor that exhibit irregular cross sectional radius.
IMHO, it's the inherent 'mismatch' losses of the 'cable' to CM signal.
Given the inherent twisting (eccentricity) of the conductors within the
'screen', it is more like a coax with a screw shaped (how would I describe
it???) distribution of Zo along the length of the cable. The TP
configuration in the CM situation should be low loss only to circularly
polarised electromagnetic waves (if there is such a phenomenal in
electromagnetic propagation within a Tx line). For propagation modes of
anything else approaching something that may represent a substantial
fraction of Lambda would be, (or shall I say, should be) presented (or
seen) as a lossy line due to the changing cross sectional characteristic of
a FTP.
> I expected losses that would be on the same order or lower than
> that associated with off-the-shelf coax types like RG-58. Instead my
losses
> were dramatically higher.
In terms of CM performance (e.g. input impedance, losses, etc... ), a FTP
due to it's eccentricity, I suppose cannot be compared to a RG-58. I have
come across some FTP with 0.52 mm i.d. copper with a final diameter of 6.1
mm for the cable. Let me know if this description fits your bill. I have
some information on their fabrication.
Just another of my 2 ¢ ...
regards
Tim Foo
Ken Javor
cc: (bcc: Wan Juang
Foo/ece/staff/npnet)
Sent by: Subject: Stumped
owner-emc-pstc@majordo
mo.ieee.org
10/15/02 05:31 AM
Please respond to Ken
Javor
Forum,
I have made some measurements and gotten results which are at odds with my
intuition. I am wondering if someone out there can shed some light on this
subject.
I was interested in the losses associated with rf traveling on a twisted
shielded pair cable. The scenario is that a length of this TSP cable is
exposed to an rf environment (as in a test chamber during IEC 1000-4-3
testing) and then the cable penetrates a bulkhead using a grounded
connector
that provides excellent shield termination, and the cable continues on the
other side in the pristine rf environment of a shielded control chamber,
say
for several meters. The question is, how much rf signal is at the final
destination point vs. at the bulkhead. The concern is common mode, not
differential mode. Meaning that the twisted pair can be looked at like
coax, with an identical signal on both inner conductors relative to the
shield. I expected losses that would be on the same order or lower than
that associated with off-the-shelf coax types like RG-58. Instead my
losses
were dramatically higher.
Following is my measurement technique.
---
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Stumped
Forum, I have made some measurements and gotten results which are at odds with my intuition. I am wondering if someone out there can shed some light on this subject. I was interested in the losses associated with rf traveling on a twisted shielded pair cable. The scenario is that a length of this TSP cable is exposed to an rf environment (as in a test chamber during IEC 1000-4-3 testing) and then the cable penetrates a bulkhead using a grounded connector that provides excellent shield termination, and the cable continues on the other side in the pristine rf environment of a shielded control chamber, say for several meters. The question is, how much rf signal is at the final destination point vs. at the bulkhead. The concern is common mode, not differential mode. Meaning that the twisted pair can be looked at like coax, with an identical signal on both inner conductors relative to the shield. I expected losses that would be on the same order or lower than that associated with off-the-shelf coax types like RG-58. Instead my losses were dramatically higher. Following is my measurement technique. I measured the transmission line impedance of the TSP in the following way. I tied the center conductors together. I shorted the center conductors to the shield at one end, and measured the inductance, using an LCR meter. I opened the connection and measured the open circuit capacitance. The square root of the l/c ratio is the characteristic impedance. I built matching networks to get from 50 Ohms to the measured impedances which ranged from 15 - 25 Ohms for a variety of different cables. For each cable, I built two pairs of identical matching networks: 4 each: 50 to RC adapters I used an HP 4195A network analyzer, over a range of frequencies 0.1 - 500 MHz. The set up was as follows. There was 16 dB of pad coming out of the source (including the 6 dB splitter). There was 10 dB of pad at the reference and test ports. Results showed little evidence of vswr. Coming out of the source, there is the 6 dB splitter. Between one port of the splitter and the reference port, I inserted one pair of the matching networks: Splitter output connects to 50 Ohm to RC adapter connects to RC to 50 Ohm adapter connects to reference port. I connected the exact same sequence between the other splitter output and the test port. The network analyzer displayed the dB ratio of the test port signal relative to the reference signal. This would be the difference in loss between each pair of matching networks. If I had built them perfectly, the analyzer should have shown 0 dB difference. Actual differences were under 3 dB. Then I inserted the cable-under-test between the RC connections on the two matching networks in the test port side. The loss associated with cable-under-test (CUT) is the difference between the losses measured with the CUT in place and with the matching networks directly connected. The numbers I got were considerably higher than even a high loss coax such as RG-174. Because real coax uses a much thicker dielectric material than just the insulation around a TSP center conductor, my "gut feel" is that losses should be lower than for 50 Ohm coax. I expect that materials picked to be dielectrics for coax have low loss tangents relative to wire insulation, but I don't have a feel for whether the difference in loss tangents can make up for the extra thickness of the dielectric in real coax. Can any one tell me if either my test set up or my expectations are wrong, and why? Thank you. Ken Javor --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
