Re: [AMRadio] Classic Link Coupled Tuner
Hi Brian: Next time we come up there I will be sure to give you some notice. But I had already taken a side trip to Don's, K4KYV, to get rid of some stuff. I was needing to spend some time with the kids there in Searcy. If you are getting a good match and there is no heating then the energy from the XMTR must be getting to the antenna. I would worry too much about it all. But it sounds like you have the same brain disease that I have, CAN'T STAND TO NOT KNOW WHY. I must have spent weeks studying and experimenting with this matching stuff and neutralizing circuits, don't even get me started. HIHI One thing I have found is that the breadboard design is the best for changing and learning and the shot glass can be used for an insulator or to ease the frustration, which comes often for me. While on the subject, I must tell you of an experiment I did some time back (25 years ago). I put a 6AL5 tube in the top box of a Heath Cantenna and lit it up with a 6V lantern battery. Using only one diode, I connected the plate directly to the dummy load and the cathode was by passed to ground with a .01uf ceramic capacitor and then connected to the little RCA jack on the top box. Now I had a decent peak reading RF detector. I just measure the DC on the RCA jack to indicated the peak of the RF voltage (very accurate by the way, but that's another story). I took 60 ft of open wire balanced line made of #12 wire with Phenolic spacers about every foot and stretched it out across the back yard suspended by wood chairs and such. The dummy load RF detector was then attached to the far end. I had the balanced antenna tuner connected to the feed end and a SWR meter between the tuner and the XMTR. I adjusted the tuner so that running 800 watts and with the SWR meter sensit ivity all the way up it showed nothing on the reflective meter. I then took my Simpson meter out to the dummy load and measured the voltage at the output of the 6AL5 RF detector. I of course don't remember the exact voltage but let's say about 250V DC. Then I connected 100 Ft of RG8 to the dummy load and the other end to the SWR meter. The SWR meter still show flat but the RF detector meter showed less voltage, not much less but something like 240V. I thought maybe I have made a slipup somewhere so I when through all the procedures again making sure that I disconnected the battery from the 6AL5 when not measuring so as not to have the filament voltage going down in between measuring. I got the same results each time. So I was finally convinced that the losses in a good tuner are negligible and the looses of coax far exceed the losses of open wire line. John, WA5BXO __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Classic Link Coupled Tuner
Hi John: Love the story John --- an inquiring mind is a treasure. Kindest regards Jim K9AXN - Original Message - From: John Coleman j...@pctechref.com To: Discussion of AM Radio in the Amateur Service amradio@mailman.qth.net Sent: Monday, August 17, 2009 8:52 AM Subject: Re: [AMRadio] Classic Link Coupled Tuner Hi Brian: Next time we come up there I will be sure to give you some notice. But I had already taken a side trip to Don's, K4KYV, to get rid of some stuff. I was needing to spend some time with the kids there in Searcy. If you are getting a good match and there is no heating then the energy from the XMTR must be getting to the antenna. I would worry too much about it all. But it sounds like you have the same brain disease that I have, CAN'T STAND TO NOT KNOW WHY. I must have spent weeks studying and experimenting with this matching stuff and neutralizing circuits, don't even get me started. HIHI One thing I have found is that the breadboard design is the best for changing and learning and the shot glass can be used for an insulator or to ease the frustration, which comes often for me. While on the subject, I must tell you of an experiment I did some time back (25 years ago). I put a 6AL5 tube in the top box of a Heath Cantenna and lit it up with a 6V lantern battery. Using only one diode, I connected the plate directly to the dummy load and the cathode was by passed to ground with a .01uf ceramic capacitor and then connected to the little RCA jack on the top box. Now I had a decent peak reading RF detector. I just measure the DC on the RCA jack to indicated the peak of the RF voltage (very accurate by the way, but that's another story). I took 60 ft of open wire balanced line made of #12 wire with Phenolic spacers about every foot and stretched it out across the back yard suspended by wood chairs and such. The dummy load RF detector was then attached to the far end. I had the balanced antenna tuner connected to the feed end and a SWR meter between the tuner and the XMTR. I adjusted the tuner so that running 800 watts and with the SWR meter sensit ivity all the way up it showed nothing on the reflective meter. I then took my Simpson meter out to the dummy load and measured the voltage at the output of the 6AL5 RF detector. I of course don't remember the exact voltage but let's say about 250V DC. Then I connected 100 Ft of RG8 to the dummy load and the other end to the SWR meter. The SWR meter still show flat but the RF detector meter showed less voltage, not much less but something like 240V. I thought maybe I have made a slipup somewhere so I when through all the procedures again making sure that I disconnected the battery from the 6AL5 when not measuring so as not to have the filament voltage going down in between measuring. I got the same results each time. So I was finally convinced that the losses in a good tuner are negligible and the looses of coax far exceed the losses of open wire line. John, WA5BXO __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Classic Link Coupled Tuner
That's a great story John!! Yep, for the time being I'm going to leave the tuner well enough alone... We are building a new house down on my east property smack in the woods. Once the house is complete and ready to move in, I will begin getting my AM rigs back up and running. I've got to move this Gates BC-1T too. It's going to be a booger. it will be the first project after the move to get going on 75 and 160. Searcy is very close to us. Only about 35 minutes from here. Next time you are up, come by and see the new shack. By the way, for all interested, always keep an eye on the lookout for these large old link coupled coils like the one in my photo. Also for the large slip stator caps. You can build a tuner for balanced feedline, 450 ~ 600 ohms, that will far surpass the abuse a modern tuner that uses the toroid baluns can take. I went to ladder line 10 years ago and never went back to coax for any lowband antennas. 73 Brian On 8/17/09, John Coleman j...@pctechref.com wrote: Hi Brian: __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Classic Link Coupled Tuner
Hey Brian, I wanted to just chime-in and tell you that I had the same sort of experience with my big link coupled tuner. I have been concerned that the tap points for the open wire line seemed very near the center of the coil and seemed to result in much less L than what I expected would be the proper setting. It appeared that the amount of coil needed was way too small. I suppose I should have been satisfied that it provided an apparent good match, but I was still concerned about the values being different that what I expected. I'm using a large 4 diam. Cu tubing coil and a link wound from the (insulated) center conductor of poly-type RG-8U coax wound around the center turns. I put a large multi-gang loading type variable cap in series with the link to allow tuning it. The big tuning cap (250 uF) is across the whole coil which is much more L than even what I need for 160M. Anyway...can't argue with successit works! 73, Jack, W9GT --- On Mon, 8/17/09, WA5AM ars.w5...@gmail.com wrote: From: WA5AM ars.w5...@gmail.com Subject: Re: [AMRadio] Classic Link Coupled Tuner To: Discussion of AM Radio in the Amateur Service amradio@mailman.qth.net Date: Monday, August 17, 2009, 12:22 PM That's a great story John!! Yep, for the time being I'm going to leave the tuner well enough alone... We are building a new house down on my east property smack in the woods. Once the house is complete and ready to move in, I will begin getting my AM rigs back up and running. I've got to move this Gates BC-1T too. It's going to be a booger. it will be the first project after the move to get going on 75 and 160. Searcy is very close to us. Only about 35 minutes from here. Next time you are up, come by and see the new shack. By the way, for all interested, always keep an eye on the lookout for these large old link coupled coils like the one in my photo. Also for the large slip stator caps. You can build a tuner for balanced feedline, 450 ~ 600 ohms, that will far surpass the abuse a modern tuner that uses the toroid baluns can take. I went to ladder line 10 years ago and never went back to coax for any lowband antennas. 73 Brian On 8/17/09, John Coleman j...@pctechref.com wrote: Hi Brian: __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Classic Link Coupled Tuner
Wow!! Thanks for all the great ideas, and comments. As is, I think I have a spot tapped that works well, however using such little coil tells me there may be some side effect. No, there is absolutely no heat. Never has, even with full legal limit AM 100% modulated for 10 minutes. I took a photo taken this morning of the tuner here that should give some idea of the size. I put a shot glass in the photo for scale: http://w5ami.net/images/TUNER.JPG The things that come to mind for me are where I am tapping the parallel cap, and my feedline length. As you can see, there is a lot of extra coil beyond where I currently have the taps for 75 meters. That extra coil will never be used on the ham bands. I think I will try tapping the cap out several turns from where the feedline taps are, but not at the ends of the entire coil. I will try this after setting the 75 meter taps at about 22uH and see if there is any indication of resonance. I think having the cap and feedline tap in the same places on the coil is a possible problem. If that doesn't seem to help, I will take a look at my feedline length. 73 Thanks for the help! Brian / wa5am PS: John, sure would have been nice to meet up for a cup of coffee had I known you were close by! On 8/15/09, John Coleman j...@pctechref.com wrote: Thanks Bob Just to add a little something: Someone said earlier, something to the effect, that there may be a non resonate antenna and feed line combination that can cause a lot of trouble. This is very true because then the L and C of the tuner must add or subtract reactance in order to make the whole system resonate. This is often more easily done when you have a lot of capacitance to work with. So having a high Q tank in the tuner has its advantages. John, WA5BXO __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
[AMRadio] Classic Link Coupled Tuner
I'm bumfuzzled... This is not exactly AM, but I use an AM tx with it... Several years ago, I built a large link coupled tuner from parts I managed to get off ebay. A large coil with rotating link in center which came out of a vintage BC transmitter, and a large Johnson split stator variable, about 35 to 475 pF. I breadboarded these two components together and have been using it since on 75 and 40 meters with great results using 450 ohm ladder line to a doublet cut for 75 meters. After I built this, I found tapping points on the main coil that worked well on 75, ultimately giving me a standing wave of near perfect on a given freq. I did that simply by trial and error... About two years ago I purchased an inductance/capacitance meter. Never thought to measure the coil taps on the tuner with it, etc., until yesterday. I disconnected the cap, coil and feedline from one another and checked the inductance of the main coil where I had my 75 meter taps. To my surprize it was only ~7.2 uH!! For the heck of it, I measured the variable in the range it normally is adjusted to and it showed about 220pF. According to formula, my values do have a resonant value near the upper end of 75 meters, and in real life do well around 3.885Mhz with my conditions. Looking at other tuners, homebrew and commercial, it appears most will tap a balanced coil like this at about 22uH and set a capacitance at around 75 pF to get resonance on 75 meters. Since I have plenty of coil on this, I did exactly that and can not get anywhere near where I need to on my tuner. What gives?? As a reference; the lowest SWR I could achive was about 5:1, and there was a noticeable attenuation on rx too. Since I can get it to work just fine with my original 7.2uH tap, it really is no big deal to me, but I am curious why others I've seen use (and can use) a lot more inductance. I know using more C gives better 'Q', but why is my real life parameters so far from the norm, and why will it not tune using the normal parameters of L and C? There must be something not right on feedline length, or the length of the doublet itself, maybe? By the way, the measured inductance of the link coil is about 3uH. One other thing I've noticed is that many seem to indicate the variable is paralleled to the entire length of the coil, not directly to the points where it is tapped for a given band. See this diagram: http://www.possumnet.com/Graphics/Diagram.jpg I don't do this. My variable is is paralleled directly to the feedline taps. 73 Brian / wa5am __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Classic Link Coupled Tuner
HI Brian: Q is usually not a factor at all unless someone wants a narrow bandwidth tuner for some reason. The issue is very likely your feedline length, the only time the feed point looks like the antenna Z is if it is multiples of electrical 1/2 waves long. If multiples of 1/4 wave lengths it will basically invert the antenna Z, IE a high Z will appear as low at the feed point, a low z will appear high. Now, anything in between these lengths also introduces reactance, some conditions producing a large amount that requires rather extream measures to adjust out. I would wager that yours is in that catagory. If you place a second tuning cap in series with the link you will find that adjustments are a little easier, however what you have will work fine if the coupling link can be turned easily.also, usually one would expect to see the cap across the entire coil if it is not too large, then it could have taps for the cap as well as the feedline. It is also common to see two caps, both isolated from each other and ground, connected to taps on the coil, with the feed points connected to the caps. IE each of the caps appear as in series with the feeders. This is used to feed a low Z load, probably what you have. You system will do fine, but it probably is a little critical to initally adjust. with a BC coil the losses are probably small. I assume the is no detectable heating in the coil at all. I have used these tuners since the 1950s and they work great, used to use the BW plug in coils, tapped for each band. Now I have gotten lazy and use a Johnson KW matchbox, The best antenna matching device ever made, in my opinion. Always found that a high Z was easier to match. 73 Bernie W8RPW - Original Message - From: WA5AM ars.w5...@gmail.com To: Discussion of AM Radio in the Amateur Service amradio@mailman.qth.net Sent: Saturday, August 15, 2009 6:05 AM Subject: [AMRadio] Classic Link Coupled Tuner I'm bumfuzzled... This is not exactly AM, but I use an AM tx with it... Several years ago, I built a large link coupled tuner from parts I managed to get off ebay. A large coil with rotating link in center which came out of a vintage BC transmitter, and a large Johnson split stator variable, about 35 to 475 pF. I breadboarded these two components together and have been using it since on 75 and 40 meters with great results using 450 ohm ladder line to a doublet cut for 75 meters. After I built this, I found tapping points on the main coil that worked well on 75, ultimately giving me a standing wave of near perfect on a given freq. I did that simply by trial and error... About two years ago I purchased an inductance/capacitance meter. Never thought to measure the coil taps on the tuner with it, etc., until yesterday. I disconnected the cap, coil and feedline from one another and checked the inductance of the main coil where I had my 75 meter taps. To my surprize it was only ~7.2 uH!! For the heck of it, I measured the variable in the range it normally is adjusted to and it showed about 220pF. According to formula, my values do have a resonant value near the upper end of 75 meters, and in real life do well around 3.885Mhz with my conditions. Looking at other tuners, homebrew and commercial, it appears most will tap a balanced coil like this at about 22uH and set a capacitance at around 75 pF to get resonance on 75 meters. Since I have plenty of coil on this, I did exactly that and can not get anywhere near where I need to on my tuner. What gives?? As a reference; the lowest SWR I could achive was about 5:1, and there was a noticeable attenuation on rx too. Since I can get it to work just fine with my original 7.2uH tap, it really is no big deal to me, but I am curious why others I've seen use (and can use) a lot more inductance. I know using more C gives better 'Q', but why is my real life parameters so far from the norm, and why will it not tune using the normal parameters of L and C? There must be something not right on feedline length, or the length of the doublet itself, maybe? By the way, the measured inductance of the link coil is about 3uH. One other thing I've noticed is that many seem to indicate the variable is paralleled to the entire length of the coil, not directly to the points where it is tapped for a given band. See this diagram: http://www.possumnet.com/Graphics/Diagram.jpg I don't do this. My variable is is paralleled directly to the feedline taps. 73 Brian / wa5am __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net
Re: [AMRadio] Classic Link Coupled Tuner
Brian, I believe the problem is your connection. The Capacitor is NOT connected across the feedline points. It should be connected across the coil ends OR as much of the coil as is needed to resonate on the band in use. A high L(inductance and a low C(capacitance) will give a broader tuning of the coupler. Use the second capacitor in series with the link as it makes the adjustment simpler. With a SWR bridge in the coax to the coupler start with the coil taps about 1/3 of the turns out from the center towards the ends of the coils. Put 20-30 Watts RF into the coupler and adjust both capacitors for the lowest SWR. Now move both coil taps out a couple of turns and readjust. If the SWR goes lower than the first time repeat the coil tap adjustment in the same direction until you reach 1:1. If the SWR went up from the first tap setting it means the taps were moved in the wrong direction. For a parallel tuned coupler (like your drawing) think of the tuned circuit as an adjustable impedance transformer (which it is). At the center of the coil it starts at 50 ohms. The outer ends of the coil where the capacitor is connected is very high like 12-15,000 ohms. Between these two points you can find any value between the two. What you are doing by connecting the capacitor across the feed points is always having your feedline connectecd to the highest impedance on the tuned circuit. Now before anyone jumps all over my explanation of the impedances here I know that the statement is not absolutely technically correct but about 90% and it will serve to make the whole thing understandable to someone whom is just starting out with this type of coupler. This type of coupler is one of the handiest things around. If you need a coupler to match anything this is it. Brian once you get the hang of it which will come quickly you won't even try anything else Good Luck 73 Gerald D. (Jerry) Stockinger K9GOZ WA5AM wrote: I'm bumfuzzled... This is not exactly AM, but I use an AM tx with it... Several years ago, I built a large link coupled tuner from parts I managed to get off ebay. A large coil with rotating link in center which came out of a vintage BC transmitter, and a large Johnson split stator variable, about 35 to 475 pF. I breadboarded these two components together and have been using it since on 75 and 40 meters with great results using 450 ohm ladder line to a doublet cut for 75 meters. After I built this, I found tapping points on the main coil that worked well on 75, ultimately giving me a standing wave of near perfect on a given freq. I did that simply by trial and error... About two years ago I purchased an inductance/capacitance meter. Never thought to measure the coil taps on the tuner with it, etc., until yesterday. I disconnected the cap, coil and feedline from one another and checked the inductance of the main coil where I had my 75 meter taps. To my surprize it was only ~7.2 uH!! For the heck of it, I measured the variable in the range it normally is adjusted to and it showed about 220pF. According to formula, my values do have a resonant value near the upper end of 75 meters, and in real life do well around 3.885Mhz with my conditions. Looking at other tuners, homebrew and commercial, it appears most will tap a balanced coil like this at about 22uH and set a capacitance at around 75 pF to get resonance on 75 meters. Since I have plenty of coil on this, I did exactly that and can not get anywhere near where I need to on my tuner. What gives?? As a reference; the lowest SWR I could achive was about 5:1, and there was a noticeable attenuation on rx too. Since I can get it to work just fine with my original 7.2uH tap, it really is no big deal to me, but I am curious why others I've seen use (and can use) a lot more inductance. I know using more C gives better 'Q', but why is my real life parameters so far from the norm, and why will it not tune using the normal parameters of L and C? There must be something not right on feedline length, or the length of the doublet itself, maybe? By the way, the measured inductance of the link coil is about 3uH. One other thing I've noticed is that many seem to indicate the variable is paralleled to the entire length of the coil, not directly to the points where it is tapped for a given band. See this diagram: http://www.possumnet.com/Graphics/Diagram.jpg I don't do this. My variable is is paralleled directly to the feedline taps. 73 Brian / wa5am __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in
Re: [AMRadio] Classic Link Coupled Tuner
Brian, The bumfuzzlement is being caused by something that your calculations don't have the ability to deal with. All your other tuners do NOT use link coupling! The commercial tuners are usually an outboard PI-Network. Although the UT-2000 is a T-Network. The link coupling does this in a manner different than a PI or T, in that the link coupling has that little quantity of the field that the coupling depends upon. I do NOT have numbers to perform a mental gymnastic exercise, although I have had the experience of using the three of them. The link coupled is much like the BC-610 PA Coil with its rotating link. It actually can be set to different coupling positions and STILL achieve resonance by retuning the variable capacitor. Bob - N0DGN WA5AM wrote: I'm bumfuzzled... This is not exactly AM, but I use an AM tx with it... Several years ago, I built a large link coupled tuner from parts I managed to get off ebay. A large coil with rotating link in center which came out of a vintage BC transmitter, and a large Johnson split stator variable, about 35 to 475 pF. I breadboarded these two components together and have been using it since on 75 and 40 meters with great results using 450 ohm ladder line to a doublet cut for 75 meters. After I built this, I found tapping points on the main coil that worked well on 75, ultimately giving me a standing wave of near perfect on a given freq. I did that simply by trial and error... About two years ago I purchased an inductance/capacitance meter. Never thought to measure the coil taps on the tuner with it, etc., until yesterday. I disconnected the cap, coil and feedline from one another and checked the inductance of the main coil where I had my 75 meter taps. To my surprize it was only ~7.2 uH!! For the heck of it, I measured the variable in the range it normally is adjusted to and it showed about 220pF. According to formula, my values do have a resonant value near the upper end of 75 meters, and in real life do well around 3.885Mhz with my conditions. Looking at other tuners, homebrew and commercial, it appears most will tap a balanced coil like this at about 22uH and set a capacitance at around 75 pF to get resonance on 75 meters. Since I have plenty of coil on this, I did exactly that and can not get anywhere near where I need to on my tuner. What gives?? As a reference; the lowest SWR I could achive was about 5:1, and there was a noticeable attenuation on rx too. Since I can get it to work just fine with my original 7.2uH tap, it really is no big deal to me, but I am curious why others I've seen use (and can use) a lot more inductance. I know using more C gives better 'Q', but why is my real life parameters so far from the norm, and why will it not tune using the normal parameters of L and C? There must be something not right on feedline length, or the length of the doublet itself, maybe? By the way, the measured inductance of the link coil is about 3uH. One other thing I've noticed is that many seem to indicate the variable is paralleled to the entire length of the coil, not directly to the points where it is tapped for a given band. See this diagram: http://www.possumnet.com/Graphics/Diagram.jpg I don't do this. My variable is is paralleled directly to the feedline taps. 73 Brian / wa5am __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Classic Link Coupled Tuner
Brian: In a link coupled assembly the coupling actually has an effect on the Q, the effective load. But increasing the Q of a parallel tank (less coil more capacitance) will increase the coupling. Using taps on the coil for the antenna connections reduces the coupling while increasing the Q. The fewer turns there are between the antenna connections the greater the Q of the tank but less voltage is coupled to the antenna. The coupling between the link and the main tank increases because the Q of the main tank went up as it was loaded less. The voltage across the ends of the main tank will go up as the taps are moved towards the center. You can get a different run of coupling by tuning the link in parallel instead of series. But this will double the voltage across the link capacitor. You can get yet another run of different coupling factors by using a swinging link. It all boils down to this: The tuner should be adjusted so that there is no L or C reactance at the antenna terminals. Then the coupling is adjusted to pull the current from the rig so that Erf/Irf = desired Z-load (generally 50 ohms). If the Q of the circuit is not high enough you will not be able to couple enough energy out of the XMTR to draw enough RF current to get the desire E/I (LOAD resistance) low enough. If the Q is too high in the wrong place then the circulating currents in the tanks of the tuner will either have high loss or begin arcing. If it aint getin hot and it aint arcin then it's OK. There always a number of ways to do it. BTW: I was in your neck of the woods a couple of weeks ago visiting with Kids in Searcy and drove out to the Peti-Jean park. I guess we must have gone right by you place. 73 John, WA5BXO -Original Message- From: amradio-boun...@mailman.qth.net [mailto:amradio-boun...@mailman.qth.net] On Behalf Of WA5AM Sent: Saturday, August 15, 2009 5:06 AM To: Discussion of AM Radio in the Amateur Service Subject: [AMRadio] Classic Link Coupled Tuner I'm bumfuzzled... This is not exactly AM, but I use an AM tx with it... Several years ago, I built a large link coupled tuner from parts I managed to get off ebay. A large coil with rotating link in center which came out of a vintage BC transmitter, and a large Johnson split stator variable, about 35 to 475 pF. I breadboarded these two components together and have been using it since on 75 and 40 meters with great results using 450 ohm ladder line to a doublet cut for 75 meters. After I built this, I found tapping points on the main coil that worked well on 75, ultimately giving me a standing wave of near perfect on a given freq. I did that simply by trial and error... About two years ago I purchased an inductance/capacitance meter. Never thought to measure the coil taps on the tuner with it, etc., until yesterday. I disconnected the cap, coil and feedline from one another and checked the inductance of the main coil where I had my 75 meter taps. To my surprize it was only ~7.2 uH!! For the heck of it, I measured the variable in the range it normally is adjusted to and it showed about 220pF. According to formula, my values do have a resonant value near the upper end of 75 meters, and in real life do well around 3.885Mhz with my conditions. Looking at other tuners, homebrew and commercial, it appears most will tap a balanced coil like this at about 22uH and set a capacitance at around 75 pF to get resonance on 75 meters. Since I have plenty of coil on this, I did exactly that and can not get anywhere near where I need to on my tuner. What gives?? As a reference; the lowest SWR I could achive was about 5:1, and there was a noticeable attenuation on rx too. Since I can get it to work just fine with my original 7.2uH tap, it really is no big deal to me, but I am curious why others I've seen use (and can use) a lot more inductance. I know using more C gives better 'Q', but why is my real life parameters so far from the norm, and why will it not tune using the normal parameters of L and C? There must be something not right on feedline length, or the length of the doublet itself, maybe? By the way, the measured inductance of the link coil is about 3uH. One other thing I've noticed is that many seem to indicate the variable is paralleled to the entire length of the coil, not directly to the points where it is tapped for a given band. See this diagram: http://www.possumnet.com/Graphics/Diagram.jpg I don't do this. My variable is is paralleled directly to the feedline taps. 73 Brian / wa5am __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio
Re: [AMRadio] Classic Link Coupled Tuner
Thank you John! You said it in terms that I wasn't dealing with at the time. I was still working on my first cup of coffee, and being pestered by a 13 1/2 year old ShiTzu, that wanted a snack and another run outside to take care of business. sigh Makes it hard to keep the thought train running in the right direction. The effects of link coupling are significant. You've pointed it out VERY well! I haven't used a swinging link since building a 4-1000 amp with the info from Eimac. Mostly I deal with rotating links. Bob - N0DGN John Coleman wrote: Brian: In a link coupled assembly the coupling actually has an effect on the Q, the effective load. But increasing the Q of a parallel tank (less coil more capacitance) will increase the coupling. Using taps on the coil for the antenna connections reduces the coupling while increasing the Q. The fewer turns there are between the antenna connections the greater the Q of the tank but less voltage is coupled to the antenna. The coupling between the link and the main tank increases because the Q of the main tank went up as it was loaded less. The voltage across the ends of the main tank will go up as the taps are moved towards the center. You can get a different run of coupling by tuning the link in parallel instead of series. But this will double the voltage across the link capacitor. You can get yet another run of different coupling factors by using a swinging link. It all boils down to this: The tuner should be adjusted so that there is no L or C reactance at the antenna terminals. Then the coupling is adjusted to pull the current from the rig so that Erf/Irf = desired Z-load (generally 50 ohms). If the Q of the circuit is not high enough you will not be able to couple enough energy out of the XMTR to draw enough RF current to get the desire E/I (LOAD resistance) low enough. If the Q is too high in the wrong place then the circulating currents in the tanks of the tuner will either have high loss or begin arcing. If it aint getin hot and it aint arcin then it's OK. There always a number of ways to do it. BTW: I was in your neck of the woods a couple of weeks ago visiting with Kids in Searcy and drove out to the Peti-Jean park. I guess we must have gone right by you place. 73 John, WA5BXO __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Classic Link Coupled Tuner
Thanks Bob Just to add a little something: Someone said earlier, something to the effect, that there may be a non resonate antenna and feed line combination that can cause a lot of trouble. This is very true because then the L and C of the tuner must add or subtract reactance in order to make the whole system resonate. This is often more easily done when you have a lot of capacitance to work with. So having a high Q tank in the tuner has its advantages. John, WA5BXO -Original Message- From: amradio-boun...@mailman.qth.net [mailto:amradio-boun...@mailman.qth.net] On Behalf Of rbethman Sent: Saturday, August 15, 2009 12:20 PM To: Discussion of AM Radio in the Amateur Service Subject: Re: [AMRadio] Classic Link Coupled Tuner Thank you John! __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
