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LDG Z11 Pro II tuner with an Icom IC-761
On 9/28/2011 7:00 PM, Owen Duffy wrote:
I think your question relates to the connections between the LDG and that Molex plug. Was it LDG who supplied the adapter? If so, ask them. Seems a bit silly that would supply the thing without adequate information on how to use it. Owen Well, I did ask LDG and they were kind enough to send me the application note describing the connections. And the more I looked into this the more I realized, "You have an antenna tuner built in into the Icom IC-761." Homer Simpson moment, "Do-oh!" However, the specified tuning range of the internal tuner is 16.7 to 150 ohms. The LDG is specified as 6 to 1000 ohms. A bit more latitude. OK, "How did I get side tracked like this?" Earlier this year I got an MFJ Versa Tuner to use with the doublet antenna. It works fine. But of course, it's manual. (But it does have a 4:1 balun inside.) So I get the LDG in a swap for some goodies. No balun inside. Ok, I ordered an MFJ 4:1 current balun. And those do work a LOT smoother tuning that with the internal 4:1 voltage type the MFJ tuner has. It was while obsessing over the "talk to the radio" cable for the LDG that I realized, "Oh right, this is designed for radios that don't have internal tuners." For example, my Icom IC-726 has the correct interface to talk to the LDG. I do have the matching AT-150 auto-tuner for the IC-726. That is specified the same as the IC-761 tuner. Once the balun gets here, the FIRST thing I'm going to do is to find out if the internal tuner has enough range to deal with my antenna. I just love wild goose chases, because in the end, you usually do learn something useful in the process. Jeff-1.0 wa6fwi -- "Everything from Crackers to Coffins" |
#2
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LDG Z11 Pro II tuner with an Icom IC-761
Jeffrey Angus wrote in
: .... I just love wild goose chases, because in the end, you usually do learn something useful in the process. Yes, there is always a risk of that. The auto tuner can be a path to hiding shortcomings in an antenna system, in search of the holy grail, low VSWR. Whilst you seem critical of the 4:1 voltage balun in the MFJ, it is my perception that they are still the most popular balun. My theory on that is that antenna systems that exhibit extreme impedance can often be 'matched' with that configuration, assisted by the loss in the balun. It is an example of how the device's operation can be misunderstood. There is little doubting the considerable anecdotal evidence that 4:1 voltage baluns work 'better', it is understanding what is meant by 'better' that is revealing. That leads into the question of whether a 4:1 balun is 'better'. If you were selling product, you would concentrate on the things that deliver good VSWR, because that is all that is in the minds of most buyers. Owen PS: for avoidance of doubt, nothing above should be interpreted to recommend a 4:1 voltage balun or a 4:1 balun. |
#3
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LDG Z11 Pro II tuner with an Icom IC-761
On 9/28/2011 7:31 PM, Owen Duffy wrote:
The auto tuner can be a path to hiding shortcomings in an antenna system, in search of the holy grail, low VSWR. This is a 102' doublet with 40' of open wire balanced feed line. Except for the input of the tuner looking like 50 ohms to make the transmitter happy, there is no such thing as "low VSWR" on this type of antenna. Whilst you seem critical of the 4:1 voltage balun in the MFJ, it is my perception that they are still the most popular balun. My theory on that is that antenna systems that exhibit extreme impedance can often be 'matched' with that configuration, assisted by the loss in the balun. It is an example of how the device's operation can be misunderstood. There is little doubting the considerable anecdotal evidence that 4:1 voltage baluns work 'better', it is understanding what is meant by 'better' that is revealing. Actually, the MFJ 949b Versa Tuner has an internal 4:1 voltage balun. The reason for that is simple. One large toroid and you're done. There isn't room inside the case for a 4:1 current balun. If you disconnect the open wire line from the internal voltage balun in an MFJ tuner and replace it with an external current balun you will find that the tuning of the match on the tuner is a lot smoother as opposed to almost erratic. (But still obtainable.) Due to the location of my station on the 2nd floor over looking a covered porch, having a "good RF ground" is not going to happen. The current balun forces the antenna and feed line into a truly balanced condition. No ground needed, other than a proper bonding of all the related equipment to a common reference in the station. The whole purpose of the tuner is to allow the transmitter to see a 50 ohm unbalanced load that it was designed for. Accomplishing that, allows the most power to be transferred to the antenna. The 102' doublet with open wire line seems to do a remarkable job at radiating. (And equally well at receiving.) That leads into the question of whether a 4:1 balun is 'better'. Better than what? A 1:1 balun or none at all, which seems to be the selling point of the G5RV antenna and it's clones. Jeff-1.0 wa6fwi -- "Everything from Crackers to Coffins" |
#4
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LDG Z11 Pro II tuner with an Icom IC-761
Jeffrey Angus wrote in news:j60h8s$ao0$1@dont-
email.me: On 9/28/2011 7:31 PM, Owen Duffy wrote: The auto tuner can be a path to hiding shortcomings in an antenna system, in search of the holy grail, low VSWR. This is a 102' doublet with 40' of open wire balanced feed line. Except for the input of the tuner looking like 50 ohms to make the transmitter happy, there is no such thing as "low VSWR" on this type of antenna. Well to "make the transmitter happy" is jsut the new language for low VSWR. ... There isn't room inside the case for a 4:1 current balun. But there is probably room for an effective 1:1 Current Balun. If you disconnect the open wire line from the internal voltage balun in an MFJ tuner and replace it with an external current balun you will find that the tuning of the match on the tuner is a lot smoother as opposed to almost erratic. (But still obtainable.) Ok, so in your experience, you haven't yet come across a load that could be matched with the voltage balun, but not with an external current balun. Due to the location of my station on the 2nd floor over looking a covered porch, having a "good RF ground" is not going to happen. The current balun forces the antenna and feed line into a truly balanced condition. Ideal conditions like "forces" and "truly balanced" don't often exist in the real world. It would be of more interest if you had measured and reported the differential and common mode current at various frequencies. The whole purpose of the tuner is to allow the transmitter to see a 50 ohm unbalanced load that it was designed for. Accomplishing that, allows the most power to be transferred to the antenna. The Yes. It is the meaning of "most" that is relevant. Most doesn't need to mean 100%, or close to it, you make compromises for frequency agility and multiband use, but "most" is often unknown. Perhaps some DX QSL cards can substitute. 102' doublet with open wire line seems to do a remarkable job at radiating. (And equally well at receiving.) Yes, they can be a good antenna, but it is not a no-brainer. For example, a correspondent recently reported problems with just such a thing on 40m. Turns out his feed line length was such that at 800W into the feed line, the voltage between the wires was some 4000+V and was causing flashovers in a 3kW rated ATU. In this case, I recommended that since he could not lengthen or shorten the feed line enough, that he shorten the antenna so solve the problem. He had previously smoked up a CWS Bytemark 5kW rated current balun on 80m with another antenna, caused by unlucky feed line length. That leads into the question of whether a 4:1 balun is 'better'. Better than what? A 1:1 balun or none at all, 1:1. 4:1 reduces the voltage impressed on the ATU components, which is good for high impedance loads, and poor for low impedance loads. There is no simple thing that always works best on a random set of loads (which is the case for many multi band antennas). which seems to be the selling point of the G5RV antenna and it's clones. Perhaps to some. There is good argument for use of a balun with a G5RV and not-balanced transmitter. Varney conceded that in one of his later articles. Most people who are adament about what Varney did or did not describe have not read his articles. Antenna manufacturers are not a good source of factual information. Owen |
#5
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LDG Z11 Pro II tuner with an Icom IC-761
On 9/28/2011 8:54 PM, Owen Duffy wrote:
Jeffrey wrote in news:j60h8s$ao0$1@dont- email.me: On 9/28/2011 7:31 PM, Owen Duffy wrote: The auto tuner can be a path to hiding shortcomings in an antenna system, in search of the holy grail, low VSWR. This is a 102' doublet with 40' of open wire balanced feed line. Except for the input of the tuner looking like 50 ohms to make the transmitter happy, there is no such thing as "low VSWR" on this type of antenna. Well to "make the transmitter happy" is jsut the new language for low VSWR. You're missing the point. The "Holy Grail" is low VSWR at the antenna. Obviously having the tuner present a nice resistive 50 ohm load to a transmitter designed to be loaded with a resistive 50 ohm load is a "Good thing(tm)". But with a random length, i.e. non-resonant, antenna, VSWR at the antenna is not a meaningful term. ... There isn't room inside the case for a 4:1 current balun. But there is probably room for an effective 1:1 Current Balun. But my point was MFJ chose to use a voltage balun for two reasons. They're cheaper and they still work to a fashion. Ok, so in your experience, you haven't yet come across a load that could be matched with the voltage balun, but not with an external current balun. Not yet. If it matches at all with one, it will match with the other. The difference being that the current balun results in much less erratic/sudden/critical tuning of the antenna tuner itself. Due to the location of my station on the 2nd floor over looking a covered porch, having a "good RF ground" is not going to happen. The current balun forces the antenna and feed line into a truly balanced condition. Ideal conditions like "forces" and "truly balanced" don't often exist in the real world. It would be of more interest if you had measured and reported the differential and common mode current at various frequencies. Um, actually, yes they do. That's the whole point of a current mode balun. The whole purpose of the tuner is to allow the transmitter to see a 50 ohm unbalanced load that it was designed for. Accomplishing that, allows the most power to be transferred to the antenna. The Yes. It is the meaning of "most" that is relevant. Most doesn't need to mean 100%, or close to it, you make compromises for frequency agility and multiband use, but "most" is often unknown. Perhaps some DX QSL cards can substitute. As an example then. How about working RA3DA in a pileup competing with the "big guns" in New York running at or above the legal limit? Sure I didn't get him on the first call, but I did it running under 100 watts and into a $25 antenna. 102' doublet with open wire line seems to do a remarkable job at radiating. (And equally well at receiving.) Yes, they can be a good antenna, but it is not a no-brainer. For example, a correspondent recently reported problems with just such a thing on 40m. Turns out his feed line length was such that at 800W into the feed line, the voltage between the wires was some 4000+V and was causing flashovers in a 3kW rated ATU. In this case, I recommended that since he could not lengthen or shorten the feed line enough, that he shorten the antenna so solve the problem. He had previously smoked up a CWS Bytemark 5kW rated current balun on 80m with another antenna, caused by unlucky feed line length. See above. Why is it that hams seem to think they absolutely need to run 800 (or more) watts of power? That leads into the question of whether a 4:1 balun is 'better'. Better than what? A 1:1 balun or none at all, 1:1. 4:1 reduces the voltage impressed on the ATU components, which is good for high impedance loads, and poor for low impedance loads. There is no simple thing that always works best on a random set of loads (which is the case for many multi band antennas). All I've said is that this appears to work perfectly for me. In the time honored tradition of Usenet "Your mileage may vary." which seems to be the selling point of the G5RV antenna and it's clones. Perhaps to some. There is good argument for use of a balun with a G5RV and not-balanced transmitter. Varney conceded that in one of his later articles. Most people who are adament about what Varney did or did not describe have not read his articles. Antenna manufacturers are not a good source of factual information. You're hear equally unsubstantiated claims about how well an off center fed Windom antenna works with no tuner as well. Jeff-1.0 wa6fwi -- "Everything from Crackers to Coffins" |
#6
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LDG Z11 Pro II tuner with an Icom IC-761
On Wed, 28 Sep 2011 21:22:55 -0500, Jeffrey Angus
wrote: But my point was MFJ chose to use a voltage balun for two reasons. They're cheaper What is the price differential in winding one wire outside the core, instead of winding it inside the core? Such "savings" accrue only in the production run of millions of units. and they still work to a fashion. If both sides are unbalanced - you mean that fashion? MFJ is not making a killing on this particular poor winding (OK, call it historical inertia) practice, and their market for these internal BalUns is dipoles, not monopoles. 73's Richard Clark, KB7QHC |
#7
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LDG Z11 Pro II tuner with an Icom IC-761
Richard Clark wrote in
: .... MFJ is not making a killing on this particular poor winding (OK, call it historical inertia) practice, and their market for these internal BalUns is dipoles, not monopoles. Hi Richard, I see MFJ getting mention, and whilst they may deserve a bit of a flogging for some things, I spring to their defence on this occasion. MFJ make the claim "More hams use MFJ-949s than any other antenna tuner in the world!" and gauging from questions in online fora, they are indeed popular, the claim may be correct. The MFJ949E uses a Ruthroff voltage balun. I have measured the balun losses in my '949E, and they are as I discussed in the general case earlier, quite high on high impedance loads. Anyone with a rudimentary knowledge of balun design would understand that, but there are those who apparently live in an ideal who would refute it. The simple explanation is that most loss in practical ferrite cored baluns usually results from losses in the core material. The losses in the core material are related to flux density, which in a Ruthroff voltage balun is roughly proportion to the differential voltage, and in a Guanella current balun is roughly proportional to common mode current. There is no reason to think that these two different types of baluns would have identical losses. The MFJ949E could easily be reconfigured as a Guanella 1:1 balun by changing its end connections, but that does not make it an optimally designed current balun. I haven't done it, and so cannot comment further. I cannot see how the cost of manufacturing it wired as a current balun would be any different. I think that it is the buyers who determine the market, and savvy sellers cater to the buyer's wants. While anecdotal evidence abounds that 4:1 voltage baluns match up extreme loads better, and users mostly arent't interested in finding the root cause of the problem and fixing it, voltage baluns will be seen by most buyers and savvy sellers as the solution. A good demonstration of the credibility of anecodotal evidence is the massive online support for the Array Solutions 4:1 Ruthroff voltage balun / ZeroFive unloaded vertical combination. The configuration drives high common mode on the coax feed line. (I should note that the sellers recommendation has recently changed to an unun.) MFJ is no doubt one of the savvy sellers. They do BTW have some higher end ATUs with 1:1 current balun, as does the Ameritron label for those who want a current balun. My own view is that achievement of highest choking impedance in a current balun is assisted by minimising stray capacitance to 'ground', so I would prefer to put a current balun in a non-conductive box, outside the ATU, on a foot of coax to the ATU. (This is one reason why I haven't tried converting my '949E to current balun connection, the windings are quite close to grounded metal and I expect stray capacitance to ground is higher than desirable.) Owen |
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