Re: [Elecraft] Balun at input or output of tuner
Jim Brown said: Mon, 12 Dec 2011 17:10:36 -0800 I have not attempted to measure the Zo of the bifilar wound chokes I've built using #12 and #14 THHN, but Jerry Sevick, in the last of his books, did wind some using exactly that method and that wire, and he says the Zo of those he wound were about 100 ohms. This is a useful data point. (I've got to rummage through my library to find the Sevick book.) I used a bifilar wound CM choke at the input of the ARRL high-powered tuner described in late editions of The ARRL Antenna Book. It had 12 bifilar turns of #10 AWG Formvar wire on a 24-inch diameter OD Type 43 core. (Nowadays I'd probably use a more optimal Type 31 mix.) In testing the input balun (aka CM choke) 1500 W of RF at 29.7 MHz was applied for 60 seconds. The #10 wire in the balun got warm to the touch (after the RF was shut off!) but the core remained cool, as it should when there are no common-mode currents, only differential-mode current in the bifilar-wound transmission line. Now, #10 wire is roughly the same size as the inner conductor used in RG-213. On 10 meters the majority of loss in the bifilar transmission line wound around the torroid will be I-squared-R conductor loss, rather than additional dielectric losses that come into effect in the VHF and UHF regions. So, I then assume that the matched-line loss in the bifilar-wound transmission line is the same as that for RG-213 at HF so that I can do computations using TLW. I then used the User-Defined Transmission Lines capability in TLW as follows: Frequency = 28.0 MHz; Matched-Line Attenuation, dB/100 Feet = 1.142, Velocity Factor = 0.95; R0 = 100 ohms; Computed X0 = -0.698 ohms. Again, a total length of three feet is assumed for the bifilar-wound transmission line. For a 3000 + j 0 load, TLW reports additional line loss due to SWR (which is 30:1) of 0.416 dB, a power loss in the balun of 137.0 W for a 1500-W transmitter. This level of dissipation in a physically small package will result in catostrophic destruction when the balun is placed at the output of the tuner. For a 3 + j 0 ohm load, the SWR is 33.33:1, and the total line loss is 0.449 dB, amounting to 147.3 W dissipation in the balun -- again, this amount of power in the CM choke balun would surely destroy it. The use a a bifilar-wound transmission line instead of RG-213 has resulted in a slightly greater susceptibility to catosphrophic destruction at low-impedance loads when the balun is placed at the output of the tuner. For a 5 + j 0 load (a 10:1 SWR), the total line loss is 0.274 dB, which for 1500 W is 91.7 W for 1500 W input, or 30.6 W for 500 W RF input. This would be about the limit of safe operation for a CM choke balun placed at the output terminals of an antenna tuner. 73, Dean, N6BV __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Balun at input or output of tuner
Joe: Right on -- certain unnamed baluns had a quite reputation as being RF fuses. But as the suject title above says, I'm still talking about the pros and cons of placing a CM choke balun at the input or at the output of an unbalancing antena tuner to feed balanced lines. Both positions are valid ones, and like most engineering matters there are tradeoffs to both approaches. Some tradeoffs involve significant smoke and flames... ! 73, Dean, N6BV -Original Message- From: Joe Subich, W4TV [mailto:li...@subich.com] Sent: Tuesday, December 13, 2011 11:21 AM To: Dean Straw Cc: j...@audiosystemsgroup.com; elecraft@mailman.qth.net Subject: Re: [Elecraft] Balun at input or output of tuner I used a bifilar wound CM choke at the input of the ARRL high-powered tuner described in late editions of The ARRL Antenna Book. It had 12 bifilar turns of #10 AWG Formvar wire on a 24-inch diameter OD Type 43 core. (Nowadays I'd probably use a more optimal Type 31 mix.) In testing the input balun (aka CM choke) 1500 W of RF at 29.7 MHz was applied for 60 seconds. The #10 wire in the balun got warm to the touch (after the RF was shut off!) but the core remained cool, as it should when there are no common-mode currents, only differential-mode current in the bifilar-wound transmission line. Moving this discussion away from the tuner and to the feedpoint of the antenna ... I would never use a bifilar wound CM choke with a high HF antenna. Years ago I tried to use a well known, third party high power balun on a triband antenna with a reputation for blowing its OEM (fuse) balun. That attempt was spectacularly unsuccessful on 15 meters where the 90-100 Ohm Zo of the bifilar winding coupled with a line length of slightly over 12 feet transformed the normally benign 50 Ohm SWR of the antenna into something that was poor across the entire band. With an antenna supporting more than three bands, it is likely that the transformer effect would impact at least one band! 73, ... Joe, W4TV On 12/13/2011 1:43 PM, Dean Straw wrote: Jim Brown said: Mon, 12 Dec 2011 17:10:36 -0800 I have not attempted to measure the Zo of the bifilar wound chokes I've built using #12 and #14 THHN, but Jerry Sevick, in the last of his books, did wind some using exactly that method and that wire, and he says the Zo of those he wound were about 100 ohms. This is a useful data point. (I've got to rummage through my library to find the Sevick book.) I used a bifilar wound CM choke at the input of the ARRL high-powered tuner described in late editions of The ARRL Antenna Book. It had 12 bifilar turns of #10 AWG Formvar wire on a 24-inch diameter OD Type 43 core. (Nowadays I'd probably use a more optimal Type 31 mix.) In testing the input balun (aka CM choke) 1500 W of RF at 29.7 MHz was applied for 60 seconds. The #10 wire in the balun got warm to the touch (after the RF was shut off!) but the core remained cool, as it should when there are no common-mode currents, only differential-mode current in the bifilar-wound transmission line. Now, #10 wire is roughly the same size as the inner conductor used in RG-213. On 10 meters the majority of loss in the bifilar transmission line wound around the torroid will be I-squared-R conductor loss, rather than additional dielectric losses that come into effect in the VHF and UHF regions. So, I then assume that the matched-line loss in the bifilar-wound transmission line is the same as that for RG-213 at HF so that I can do computations using TLW. I then used the User-Defined Transmission Lines capability in TLW as follows: Frequency = 28.0 MHz; Matched-Line Attenuation, dB/100 Feet = 1.142, Velocity Factor = 0.95; R0 = 100 ohms; Computed X0 = -0.698 ohms. Again, a total length of three feet is assumed for the bifilar-wound transmission line. For a 3000 + j 0 load, TLW reports additional line loss due to SWR (which is 30:1) of 0.416 dB, a power loss in the balun of 137.0 W for a 1500-W transmitter. This level of dissipation in a physically small package will result in catostrophic destruction when the balun is placed at the output of the tuner. For a 3 + j 0 ohm load, the SWR is 33.33:1, and the total line loss is 0.449 dB, amounting to 147.3 W dissipation in the balun -- again, this amount of power in the CM choke balun would surely destroy it. The use a a bifilar-wound transmission line instead of RG-213 has resulted in a slightly greater susceptibility to catosphrophic destruction at low-impedance loads when the balun is placed at the output of the tuner. For a 5 + j 0 load (a 10:1 SWR), the total line loss is 0.274 dB, which for 1500 W is 91.7 W for 1500 W input, or 30.6 W for 500 W RF input. This would be about the limit of safe operation for a CM choke balun placed at the output terminals of an antenna tuner. 73, Dean, N6BV __ Elecraft
[Elecraft] Balun at input or output of tuner
Balun at Input or Output of Antenna Tuner? Dean Straw, N6BV (Senior Assistant Technical Editor, Retired) December 12, 2011 I have been lurking on the Elecraft Reflector monitoring the animated discussion about where to place a balun -- at the input or the output of a tuner. I was going to jump into the discussion after I read comments claiming that a balun at the input of an unbalanced tuner feeding a balanced transmission line (and balanced antenna) simply doesn't work. On Dec. 8 Alan Bloom, N1AL, wrote such an elegant analysis that I didn't have to. If I might paraphrase Alan, the stress across the balun due to unwanted common-mode current is the same whether the balun is placed at the input or at the output of an unbalanced antenna tuner network. Other investigators have come to the same conclusion and have argued that the complexity of floating the antenna tuner components doesn't warrant installing the balun at the input of the antenna tuner. As Alan pointed out, when a balun is placed at the input of the tuner, the differential-mode currents/voltages are well controlled, since the tuner's input impedance when tuned is 50 ohms. When the balun is placed at the output of the tuner, the differential-mode currents/voltages are determined by whatever impedance the load happens to be at the shack-end of the transmission line feeding the antenna. And that impedance can range very widely. For my own curiosity, I wanted to get a handle on the amount of loss incurred by the differential-mode loss (i.e., the loss inside the coax) for a common-mode choke constructed with coaxial cable. (Google Jim Brown, K9YC's excellent paper A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing Revision 5a, 5 Jun 2010. The section on transmitting baluns starts on page 25. Photos of typical coaxial CM transmitting chokes appear on page 29.) By the way, like Jim Brown, K9YC, I prefer the name common-mode choke rather than the term balun, whether it is used at the input or at the output of an unbalanced tuner feeding a balanced transmission line and balanced antenna. I shall use the abbreviation CM choke in the rest of this paper. I assumed that the CM choke consisted of three feet of RG-213 wound through ferrite torroids of the appropriate material and size to achieve K9YC''s target common-mode impedance of 5000 ohms. At that choke impedance the effects of unwanted common-mode current would be low and the effect of differential-mode loss could be explored from a conventional transmission-line perspective. A quick review: a CM choke exhibits two main modes: (1) an impedance to common-mode currents flowing on the outer surface of the coaxial shield and (2) the effect of differential-mode currents/voltages - that is, matched-line loss and the additional loss due to SWR of a three-foot length of RG-213. My tool of analysis is my own TLW program, but there are other programs out there that can do the analysis. I assumed that the load presented to the output terminals of the common-mode choke balun at the output of the tuner was 3000 + j0 ohms at 28 MHz. This amounts to an SWR of 60:1. TLW says that the total transmission-line loss in the three feet of RG-213 under these conditions is 0.373 dB. This is comprised of 0.034 dB of matched-line loss if the RG-213 were matched and an additional loss due to the 60:1 SWR of 0.339 dB. A total loss 0.373 dB doesn't sound like much, but when you pump 1500 W into such a tuner this translates into a lot of watts in a confined space. For 1500 W into the input of the CM choke, 123.5 W must be dissipated safely in the three feet of RG-213. This is 41.2 W per foot and at that level the RG-213 would get very warm and could even melt, especially if the choke were confined in a small box with no circulation of cooling air. Times Microwave has a convenient calculator on their web site, where the power-handling capability of various types of coaxes may be calculated. 100 feet of RG-213 is rated to handle 2.02 kW at 28 MHz with a 1:1 SWR. For a matched line there would be no hot spots along the line due to SWR. The average power-handling capability of RG-213 is thus 2020 W divided by 100 feet, or 20.2 W per foot. Interestingly enough, this short length of coax transforms the 3000 + j 0 load to 1.72 - j 47.3 ohms at the output terminals of the tuner, making the task of the antenna tuner a little more difficult at such a low resistance level. If this 3000-ohm load were presented to a tuner with the CM choke at the input, the loss would be the matched-line loss only of 0.034 dB, which is a power loss of 11.7 W for 1500 W input to the tuner. The same kind of TLW analysis can be done for a low-impedance load of 3 + j 0 ohms, for an SWR of 16.67:1. For a CM choke balun at the output of a tuner this results in an additional loss due to SWR of 0.402 dB and a total loss of 0.436 dB. This is a power loss of 143.3 W in the three feet of RG-213, meltdown city again. While we're
[Elecraft] FW: KRX3 MAIN input
Dear Frank: I just finished installing my KRX3 and had exactly the same problem. I traced it to a poor solder connection on the small PCB called the SUBIN module. The 3-dB Splitter transformer T1 lead number 1 was not soldered properly to terminal 1 on the PCB. This meant that the MAIN input was not getting through. Simply re-soldering the connection brought operation to normal. 73, Dean Straw, N6BV You said: Message: 15 Date: Wed, 24 Dec 2008 15:18:33 +0100 From: Frank R. Oppedijk f.opped...@avista.nl Subject: [Elecraft] K3 Subreceiver ANT selection doesn't work - always uses the AUX antenna To: elecraft@mailman.qth.net Message-ID: 200812241418.mboeif4v043...@smtp-vbr6.xs4all.nl Content-Type: text/plain; charset=us-ascii; format=flowed Hi, I've just installed my KRX3. All went okay. Although I do have a KAT3 installed, I chose the subreceiver's alternative antenna to be the BNC one. If I've understood correctly, pressing BSET followed by ANT allowes me to switch the subreceiver's input between the main receiver's antenna and the BNC antenna. But, irrespective of whether I've selected MAIN or AUX, the subreceiver always uses the AUX antenna. Any clues as to what could be wrong? 73, Frank PA4N Dean Straw, N6BV n...@arrl.net ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[K3] RE: [Elecraft] in-band-IMD test
Hello, Alexander: Yes, please send me that pdf. For your information, I am sending a pdf of an article I wrote in December 1995 QST magazine describing modifications to the AGC system of the ICOM IC-765 to reduce in-band IMD. This illustrates how a Fast time constant can create unwanted in-band IMD. This article was why the ARRL Laboratory started making detailed in-band IMD tests for receivers after December 1995. Thanks 73, Dean, N6BV Senior Assistant Technical Editor, ARRL (Retired) -Original Message- From: e72x (via Nabble) [mailto:[EMAIL PROTECTED] Sent: Thursday, November 13, 2008 1:28 AM To: Dean Straw Subject: Re: in-band-IMD test The Audio mod is a very simply! You just need to add simple two resistor pararell on KIO3 module and replace one RFI choke! If anyone need mode just send me mail and I will forward pdf direct ! 73, E72X, Alexander: Sorry but I don't read Russian. What were the K3's AGC settings for the IMD measurements? At a large input signal (S9+50 dB), using a Fast AGC time constant will often result in poor IMD for conventional receivers using analog type of AGC systems. I don't know the details of the K3's AGC system, however. Have you tried the S9+50 dB input signal with the Slow AGC setting? 73, Dean Straw, N6BV Alexander Ponomarenko-5 wrote: GA for all K3 users. So many guys has talks about perfect audio sound of K3. So many talks about analog K3 sound on e-ham. But how it possible if K3 have the so bad in-band IMD? You can read about in-band-IMD-measurements in russian here: http://forum.cqham.ru/viewtopic.php?t=17119postdays=0postorder=ascst art=0 -- This email is a reply to your post @ http://n2.nabble.com/in-band-IMD-test-tp1491448p1493383.html You can reply by email or by visting the link above. -- View this message in context: http://n2.nabble.com/in-band-IMD-test-tp1491448p1494755.html Sent from the [K3] mailing list archive at Nabble.com. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [K3] [Elecraft] in-band-IMD test
Alexander: Sorry but I don't read Russian. What were the K3's AGC settings for the IMD measurements? At a large input signal (S9+50 dB), using a Fast AGC time constant will often result in poor IMD for conventional receivers using analog type of AGC systems. I don't know the details of the K3's AGC system, however. Have you tried the S9+50 dB input signal with the Slow AGC setting? 73, Dean Straw, N6BV GA for all K3 users. So many guys has talks about perfect audio sound of K3. So many talks about analog K3 sound on e-ham. But how it possible if K3 have the so bad in-band IMD? You can read about in-band-IMD-measurements in russian here: http://forum.cqham.ru/viewtopic.php?t=17119postdays=0postorder=ascstart=0 -- View this message in context: http://n2.nabble.com/in-band-IMD-test-tp1491448p1492342.html Sent from the [K3] mailing list archive at Nabble.com. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] K3 RF Feedback Problem
Lyle: Is remove of L4 on the front panel board and L7 on the KIO3 audio board official Elecraft modifications? I'd hate to void my warranty by messing with something that isn't official. Thanks, Dean Straw, N6BV Lyle Johnson wrote: I bit the bullet and removed L4 and L7 this morning. It is not difficult; they are both on the back of the front panel board. L4 on the front panel board is related to the issues some folks are having when using the front panel mic connector with various audio routers. It can be shorted with a jumper from pin 8 of the mic jack to ground. L7 on the KIO3 audio I/O board can also be bypassed for the same reasons when using the rear panel mic jack in similar installations. L7 on the front panel board is for reduction of noise from the RS232 serial port lines and should definitely not be bypassed! 73, Lyle KK7P ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com -- View this message in context: http://n2.nabble.com/K3-RF-Feedback-Problem-tp1442033p1481790.html Sent from the Elecraft mailing list archive at Nabble.com. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] K3 RF Feedback Problem
Thanks, Lyle. 73, Dean, N6BV -Original Message- From: Lyle Johnson (via Nabble) [mailto:[EMAIL PROTECTED] Sent: Monday, November 10, 2008 11:52 AM To: Dean Straw Subject: Re: [Elecraft] K3 RF Feedback Problem Is remove of L4 on the front panel board and L7 on the KIO3 audio board official Elecraft modifications? Bypassing these two inductors will not impact your warranty. 73, Lyle KK7P ___ Elecraft mailing list Post to: [EMAIL PROTECTED] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com -- This email is a reply to your post @ http://n2.nabble.com/K3-RF-Feedback-Problem-tp1442033p1481946.html You can reply by email or by visting the link above. -- View this message in context: http://n2.nabble.com/K3-RF-Feedback-Problem-tp1442033p1481971.html Sent from the Elecraft mailing list archive at Nabble.com. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
