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And yes you can stand-by-for-fireworks if you think lightning
protection isn't an issue. Anyone that thinks "floating equipment chassis" (isolated from ground) is a good plan, lives in a place where lighting is something they watch only on the Discovery Channel. 73, Jack Jack Let me assure you, my station is well grounded, Hi! I even have an abnormal passion regarding grounds. My remark was in regarding to a "floating" balanced antenna tuner, which is not grounded anymore than is a balanced line fed doublet. Certainly everything before the tuner is well grounded. I even have a spark gap type lightning protector on the balanced feeds. As far as the debate regarding baluns at the input or output, I would be delighted to be convinced that it either does not matter, or is better at the output..because it makes my life a lot simpler. Right now I am using about 5 feet or so of LMR400 from my unbalanced tuner to a Radio Works remote balun, terminated with 300 ohm transmitting twinlead, feeding a 40 meter doublet. Works like gangbusters. Jim |
In article E6tvd.6659$7p.4476@lakeread02,
Jack Painter wrote: I can't imagine what's possibly gained by 1:1 in front of the tuner v. 4:1 (when applicable, some antennas recommend this, including for twin-lead) after it. The reason I've seen stated, is that many 4:1 balun designs only work "as advertised" if they're working into something fairly close to their design impedances. For example, a 4:1 balun intended to match 200 ohms to 50 ohms, will only provide a 4:1 ratio and good current balance and efficiency when matching impedances fairly close to those. If you put such a balun at the output of a wide-range transmatch, and try to match up a difficult load, then the balun might "see" something like 750-j250 or 25+10j on its "200-ohm" side. The result might be poor current balance on the "balanced" side, or excessively high current flows which would require de-rating the balun's power handling capability. "Voltage" baluns seem to be most vulnerable to this sort of problem. Putting a 1:1 balun on the input side of the tuner, and using a fully-balanced or pseudo-balanced tuner is one way around this, since the balun "sees" only the impedance load for which it was designed. Another approach, often suggested, is to use a 1:1 transmission-line current balun on the output. Using a link-coupled tuner (a classic Matchbox, or a Z-match) is yet another option. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
"chuck" wrote Jack, I do think there's some confusion here. In cases where the balun is a part of the tuner input, the tuner chassis is usually connected directly to the transmitter chassis through the normal coax. You can ground the tuner chassis to an external earth ground if you so wish. Internally, the balanced output of the balun is connected to the "T" components at the input side. The coil, of course is not at chassis rf ground potential, but that is not relevant. It is, however, at DC ground potential (via the balun winding). I don't see any additional lightning issues associated with placing the balun at the tuner input. 73, Chuck Hi Chuck (and Jim), I was unclear on what the benefits would be, hence my questions to Jim (and the Group). But the file I referenced earlier also questioned the benefits, and explained the need for floating the tuner when a Balun i used in front of it, which would be a very bad move if lightning protection was an issue. There would be no ground connection to the tuner, leaving it as a sacrifice gear but inside the shack!. That's not all that uncommon to sacrifice a tuner by the way, but usually seen where the tuner is up in the air at the feedpoint. Marine applications often use this configuration. I don't! Hi! -- 6. Conclusions As noted by Roy Lewallen, W7EL,[2] putting a choke balun on the input of an unbalanced tuner to drive a balanced line is useless. It introduces a ``hot'' tuner case which must be isolated with no benefit over putting the balun on the output. -- I agree that a 4:1 after the tuner (or after coax from tuner to feedpoint where laddr-line begins) is a compromise at best, offering beneficial performance at some frequencies and degradation at others. All a matter of choices I guess, make the decision that's safe (first) and best for your needs after that. As always, I find this group shakes out great comments and explanations. If Roy L wants to add something to this I'm sure we would all be interested. 73, Jack wrote: And yes you can stand-by-for-fireworks if you think lightning protection isn't an issue. Anyone that thinks "floating equipment chassis" (isolated from ground) is a good plan, lives in a place where lighting is something they watch only on the Discovery Channel. 73, Jack Jack Let me assure you, my station is well grounded, Hi! I even have an abnormal passion regarding grounds. My remark was in regarding to a "floating" balanced antenna tuner, which is not grounded anymore than is a balanced line fed doublet. Certainly everything before the tuner is well grounded. I even have a spark gap type lightning protector on the balanced feeds. As far as the debate regarding baluns at the input or output, I would be delighted to be convinced that it either does not matter, or is better at the output..because it makes my life a lot simpler. Right now I am using about 5 feet or so of LMR400 from my unbalanced tuner to a Radio Works remote balun, terminated with 300 ohm transmitting twinlead, feeding a 40 meter doublet. Works like gangbusters. Jim |
Jack Painter wrote:
As always, I find this group shakes out great comments and explanations. If Roy L wants to add something to this I'm sure we would all be interested. I think you gentlemen have pretty well covered the basics. I'll just encourage everyone to read Kevin's (W9CF) excellent treatment at the URL posted by Jack a short while ago. Roy Lewallen, W7EL |
Yes, moving a current balun to a position before the tuner is a
"useless" exercise but it doesn't render the balun "useless" -- it's equally effective at the input as at the output (provided that the tuner case is floated if the balun is at the input). To answer your question about why not use one at the input and output, I recommend against using one at the input because the case of the tuner has to be floated for one at the tuner input to be effective. This has some potential safety implications. If you want to use two baluns in order to increase the common mode impedance, I suggest putting them both at the output. And for maximum effectiveness, space them about a quarter wavelength apart at the most troublesome band. Roy Lewallen, W7EL Cecil Moore wrote: Jack Painter wrote: 6. Conclusions As noted by Roy Lewallen, W7EL,[2] putting a choke balun on the input of an unbalanced tuner to drive a balanced line is useless. The choke on the input is *still* in series with the common-mode current and is still performing the choking function. Moving the balun to the input doesn't relieve the stress on the choke but it also does NOT render the choke non-functional as the word "useless" implies. -- 73, Cecil http://www.qsl.net/w5dxp -----------== Posted via Newsfeed.Com - Uncensored Usenet News ==---------- http://www.newsfeed.com The #1 Newsgroup Service in the World! -----= Over 100,000 Newsgroups - Unlimited Fast Downloads - 19 Servers =----- |
Roy Lewallen wrote:
To answer your question about why not use one at the input and output, I recommend against using one at the input because the case of the tuner has to be floated for one at the tuner input to be effective. Sorry, that's NOT true for remote autotuners. When I was remote autotuning my elevated-radial vertical, the autotuner was 20 feet from the antenna and 65 feet from the shack. Field strength improved the most with chokes on the input AND output. -- 73, Cecil http://www.qsl.net/w5dxp -----------== Posted via Newsfeed.Com - Uncensored Usenet News ==---------- http://www.newsfeed.com The #1 Newsgroup Service in the World! -----= Over 100,000 Newsgroups - Unlimited Fast Downloads - 19 Servers =----- |
Hm, that's interesting. Was the tuner case floating? Did you try putting
both baluns at the input or both at the output for comparison? And how much did the field strength improve and how did you measure it? Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: To answer your question about why not use one at the input and output, I recommend against using one at the input because the case of the tuner has to be floated for one at the tuner input to be effective. Sorry, that's NOT true for remote autotuners. When I was remote autotuning my elevated-radial vertical, the autotuner was 20 feet from the antenna and 65 feet from the shack. Field strength improved the most with chokes on the input AND output. -- 73, Cecil http://www.qsl.net/w5dxp -----------== Posted via Newsfeed.Com - Uncensored Usenet News ==---------- http://www.newsfeed.com The #1 Newsgroup Service in the World! -----= Over 100,000 Newsgroups - Unlimited Fast Downloads - 19 Servers =----- |
Roy Lewallen wrote:
Hm, that's interesting. Was the tuner case floating? Did you try putting both baluns at the input or both at the output for comparison? And how much did the field strength improve and how did you measure it? The tuner case was tied to a ground rod at the base of the antenna support. In the last version, the radials were up at 20 ft. I didn't try it without a choke on the input but adding a choke to the output improved the ground level field strength at ~200 yards by a little over one dB on 40m, if memory serves me right. I can't locate my notebook at the moment. The field strength was measured using a Palomar FS-1 and ferrite rod pickup antenna. The choke on the output appeared to slightly reduce the received noise which is the problem I was chasing at the time. I never could get the received noise down to an acceptable level compared to my horizontal dipole so the vertical is gone. -- 73, Cecil http://www.qsl.net/w5dxp -----------== Posted via Newsfeed.Com - Uncensored Usenet News ==---------- http://www.newsfeed.com The #1 Newsgroup Service in the World! -----= Over 100,000 Newsgroups - Unlimited Fast Downloads - 19 Servers =----- |
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