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Author Topic: Why use a tuner  (Read 18899 times)
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Jerry-n5ugw
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« on: June 02, 2008, 02:27:25 PM »

Just to get others opinion other than mine.
Why should you use a tuner if the tube transmitter will load into the ant. without it. Would you not just be giving away output power into the tuner??
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Steve - WB3HUZ
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« Reply #1 on: June 02, 2008, 02:29:09 PM »

Correct. If no tuner is needed, don't use one.


Just to get others opinion other than mine.
Why should you use a tuner if the tube transmitter will load into the ant. without it. Would you not just be giving away output power into the tuner??
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Jerry-n5ugw
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« Reply #2 on: June 02, 2008, 02:47:51 PM »

I am in the process of aquiring a DX-100, which has a very wide Pi network and I do not thing I need to worry about SWR's if the plate rig will load into the antenna. Thanks HUZ
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« Reply #3 on: June 02, 2008, 03:27:27 PM »

Jerry,

Huz's ideas are correct (of course)  as well as your intended plans.


Here's some more info:

The swr will always be the same on the feedline whether a tuner is used or not. The antenna itself or the feedline does not even know the tuner is there.

The only thing affected is the match between the transmitter and  feedline input.
One exception to this is if the antenna feedline is balanced (like open line) and the tuner will present a balanced to unbalanced transformation to the transmitter. This isolation will help prevent feedline radiation.


As a general rule, the only time to use a tuner is if the transmitter doen't have the tuning range to match power into the antenna (load) or if you are using an openwire fed antenna for multiband (or single band) use.  In this case the open wire will have a high swr on certain bands, but the feedline loss is low.

Using a tuner with a single band coax fed antenna is usually a waste with most pi-network tube rigs.

If the match is so bad (with a coax fed antenna) that a tuner is needed, it is best to work on the antenna to improve the match and not use the tuner at all.

Most solid state rigs have a limited match range, and unless they have a built in tuner, power "foldback" can occur....  but again, if the coax match is way off, fix the antenna first, for best results.

73,

T
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Jerry-n5ugw
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« Reply #4 on: June 02, 2008, 04:20:01 PM »

That's is what I've always beleived and used. The DX-100 has a very wide matching network and should be able to load into the coax fed balen, which I might just get rid of and feed the 450ohm with 50ohm coax direct. I have to use the coax to get it outside the RV to the wire in the trees..
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« Reply #5 on: June 02, 2008, 05:48:15 PM »

That's is what I've always beleived and used. The DX-100 has a very wide matching network and should be able to load into the coax fed balen, which I might just get rid of and feed the 450ohm with 50ohm coax direct. I have to use the coax to get it outside the RV to the wire in the trees..

Sounds good Jerry...

One thing to consider - I know many antenna manufacturers do it, like for the G5RV, but going directly from balanced open wire to unbalanced coax will often cause feedline radiation. It might not be that big of a deal on 75M using a nice square 90 degree feedline angle from the antenna and using a single antenna. (vs: a stack)   But I would consider using a balun with the proper ratio for the coax/opnwire transformation.  I realize you're doing this cuz the open wire cannot be brought into the shack directly. Consider using a plexiglas window or other scheme.

OR, another balun/choke idea:  Take a 4" diameter ABS/PVC plastic pipe and wind about 8-10 turns of your coax run on it, and mount it right at the coax/openwire junction. . This will help choke off any unbalanced currents flowing on the shield.   

For all my coax fed antennas here, I use this simple choke technique.... even for stacks which are highly sensitive to phase shift caused by feedline radiation. Use 5-6 turns for 40M and so forth.

T
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« Reply #6 on: June 03, 2008, 03:18:04 AM »

I agree with all of the comments. Why fiddle with a tuner?
The only tangable positive benefit that I can think of is the filtering that some tuners provide. In other words, your neighbor or wife on the phone upstairs may like the tuner.

If you use primitive transmitters or military surplus transmitters, a tuner can improve harmonic rejection, enable a strange Z output to match 50 Ohms and in the case of poor receivers, it can even improve image rejection. Most of these are moot with commercial ham gear designed for 50 Ohms.

One last thing: Inserting a small tuner between a low power rig and an untuned input amplifier like a G-G 811 job can greatly improve and drive and output power. The Handbook says that it can also improve linearity.

Mike WU2D
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« Reply #7 on: June 03, 2008, 09:43:11 AM »

Another advantage of a tuner is to insure that the feed point between the tuner and the TX is 50 Ohms J0. This is handy since most external filters and power meters are designed to work into that impedance and performance will degrade if there is deviation from 50 J0.
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« Reply #8 on: June 03, 2008, 10:59:05 AM »

I can't tune a piano but I can tuna fish   73
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« Reply #9 on: June 03, 2008, 11:18:13 AM »

I agree with all of the comments. Why fiddle with a tuner?
The only tangable positive benefit that I can think of is the filtering that some tuners provide. In other words, your neighbor or wife on the phone upstairs may like the tuner.

If you use primitive transmitters or military surplus transmitters, a tuner can improve harmonic rejection, enable a strange Z output to match 50 Ohms and in the case of poor receivers, it can even improve image rejection. Most of these are moot with commercial ham gear designed for 50 Ohms.

One last thing: Inserting a small tuner between a low power rig and an untuned input amplifier like a G-G 811 job can greatly improve and drive and output power. The Handbook says that it can also improve linearity.

Mike WU2D


Mike, 

Yep, that's three more good reasons for a tuner.   Each has it's own special application.

In fact, right now I'm building up a super clean, near-class-A, solid state FET linear driver. (with the expert guidance of Frank/GFZ)  I plan to use some kind of tuner between the tube amp and this linear IPA for harmonic suppression , flywheel/linearity effect and matching.  (Three of your suggestions rolled into one)   

Clean driver... it should do -45db 3rd IMD or better  vs: the stock -30db 3rd coming out of the 200w  FT-1000D.  I will be using the low level 10mw from the FT-1000D to drive the IPA, which is near -70db 3rd.


Mark/QHQ;  Yes, how true about power meters giving higher/false readings when the Z<>0.  I actually put a 50 ohm to ~50 ohm HB tuner in line last month JUST so I could accurately measure power. The Bird didn't like the Z.  The advantage of not using a tuner is it makes you feel good- like you're running more power than reality...  Wink

BTW, as you know, trying to match 50 ohms to near  40-60 ohms is not easy.  A ~1:1 un-un match is tough.  I was using a series L in with a variable cap to gnd... or a cap to gnd followed by a series L...   Is there a better configuration to match 50 > ~50ohms unbalanced to get rid of Z ?


T



 
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« Reply #10 on: June 03, 2008, 03:36:31 PM »

A T-match tuner (C-L-C) works well for tweaking a coax fed resonant dipole (or array) to 50 + j0 across the band. There are a number of combinations that will give a perfect match, however the combination with the highest amounts of C are best as this will give the lowest Q and therefore lowest loss. I've measured efficiency at > 98%.

I typically start with the variable capacitors fully meshed and adjust the roller inductor for an initial dip in VSWR then alternately adjust all three variable elements for a perfect match while maintaining as high C as possible. Once you get used to the procedure tuneup is quick and easy.     
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« Reply #11 on: June 03, 2008, 04:28:46 PM »

A T-match tuner (C-L-C) works well for tweaking a coax fed resonant dipole (or array) to 50 + j0 across the band. There are a number of combinations that will give a perfect match, however the combination with the highest amounts of C are best as this will give the lowest Q and therefore lowest loss. I've measured efficiency at > 98%.



Hi Jay,

Tnx fer the Dope, OM.  (With a cartoon of a ham shooting a needle in another ham's arm)   

I'll add another C to ground on the other side of L.

As it was, when trying to match, say, 50 ohms,+J25, it was next to impossible to keep R as it was while adjusting  J.

T
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« Reply #12 on: June 03, 2008, 07:36:42 PM »

T

As you've found, an L network has limitations.

I've been using the C-L-C (series C, shunt L, series C) for years to 'tweak in' dipoles, wire beams etc. Comes in handy with the Class-D AM transmitter since there are no tuning elements in the transmitter - just a low-pass filter after the transformer. Although the transmitter operates just fine into a VSWR of 2:1 it's nice to have some adjustment.

Actually, it was an MD administering the 'dope'. No mention if he was a ham or not...



 



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« Reply #13 on: June 03, 2008, 08:25:20 PM »

OK I see -  not an L, but a T....   C series, L shunt, C series making a T network.

I'll try that.

Yep, I know that dude. His call is W1MD.  Jeeves told me so.

Tnx again fer the dope, OM.

T
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« Reply #14 on: June 03, 2008, 10:52:23 PM »

I think the  best way to feed a dipole is to use open wire tuned feeders, with a tuner between the transmitter and feedline.  You can use the same antenna for multiple bands.  It beats putting up a half dozen dipoles, each fed with coax to work a single band.

The selectivity of the tuner and open wire line virtually assure that you won't radiate enough harmonic energy to get a citation.  The system's efficiency will be essentially uniform across any amateur band.
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« Reply #15 on: June 03, 2008, 11:53:36 PM »

I think the  best way to feed a dipole is to use open wire tuned feeders, with a tuner between the transmitter and feedline.  You can use the same antenna for multiple bands.  It beats putting up a half dozen dipoles, each fed with coax to work a single band.


If the room is available, I'd take single band coax choke/balun fed dipoles any day over a multiband antenna tuner set up. I've had both at various times.

Here's my thinking why...   When talking about wire dipoles, we are talking about fixed antennas, no rotary stuff.  A single band 1/2 wave dipole has a predictable, broad, figure 8 pattern with good horizontal coverage except off the sides where there is a null.

The multiband 1/2 wave dipole will have a broad figure 8 on the lowest band only, then on the next higher band a very sharp figure 8, followed by a 4 lobe clover leaf on the next higher band, etc.  The nulls get very deep and frequent on the upper bands, upwards of 20 db+  nulls in various directions.  There is a tendency to be very PW in certain fixed directions.  The 2 db gain only shows up on the 2nd higher band. On the 4th higher band, we have an 8 legged octapus pattern with deep nulls in between.

There's ways to compromise this by making the lowest band  (160M) 3/8 wave so that 40M is a double extened zepp and maintains it's sharp figure 8, but it will still have side lobes and nulls of the side/front.

Another single band  dipole advantage is that the vertical takeoff angle can be controlled. Planning your pattern is more control-able. If possible one would put each dipole at 1/2 wavelength above ground for a clean, single vertical lobe DX pattern, or opt for 1/4 wave high for more local higher angle work.  A multiband antenna is a compromise of height and take off angles.

One advantage of the multiband dipole is no band interaction as with closely spaced single band dipoles. The solution is to put singles at right angles or far apart.

Another advantage of single band dipoles is the quick bandswitching ability with a coax switch.  Multiband antenna tuners take time.

At one time I had five JJ antenna tuners hooked to various antennas and arrays. Now I run three underground CATV hardlines to each tower and use coax exclusively for the last 20 years.

It's really a wash when it comes to losses of each type. 

Actually, I like both systems, but find single band dipoles give me more control of the signal pattern and the hardware is easier to work with.

It all depends on personal taste, like Ford or Chevy...  Grin

T
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Jerry-n5ugw
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« Reply #16 on: June 04, 2008, 06:04:50 AM »

In response to the which tuner comment, I use a Murch 2000b. What a brute.. does a fine job..
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« Reply #17 on: June 04, 2008, 09:45:49 AM »

The multiband 1/2 wave dipole will have a broad figure 8 on the lowest band only, then on the next higher band a very sharp figure 8, followed by a 4 lobe clover leaf on the next higher band, etc.  The nulls get very deep and frequent on the upper bands, upwards of 20 db+  nulls in various directions.  There is a tendency to be very PW in certain fixed directions.  The 2 db gain only shows up on the 2nd higher band. On the 4th higher band, we have an 8 legged octapus pattern with deep nulls in between.

Great explanation Tom. I use a 160 meter half wave with open wire feed and your pattern description is pretty much what I experience when using it on the higher bands. It is most noticeable on 40 meters, where the pattern is complex and it is a roll of the dice when trying to work into certain areas of the compass.

73,

Rob W1AEX
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« Reply #18 on: June 04, 2008, 10:01:47 AM »

The other issue of using a tuner with an older tunable output rig is the 'dance' you can slip into of tuning the transmitter, then the tuner, then having the transmitter out of resonance, and so on. Took me a while (and some advice from an OT) to understand tuning the transmitter into a dummy load, then tuning the ant/SWR with the tuner. With a coax-fed dipole, it was a PITA, and unneeded.


If the room is available, I'd take single band coax choke/balun fed dipoles any day over a multiband antenna tuner set up. I've had both at various times.


You sold me on that idea a few years back Tom, when I queried the group about feedline radiation and you explained the benefits of multiple coax-fed dipoles. Your answer is still under the 'Latest articles' section, and a good read. In my case, open wire line wasn't feasible due to the twists and turns required to get behind the house and up to the ant.

Other than using one ant for multiple bands, what benefit does open wire line really offer beyond the coolness factor? I love the look of it running across a bead board ceiling on beehive standoffs, along with the glass feed-thru insulators. Some kind of caged dipole or similar buzzardly ant will be employed at the new location, but only for the fun factor. The results from wire arrays used by G and Tina are just too convincing to ignore.

 
 
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« Reply #19 on: June 04, 2008, 10:25:52 AM »

Not to steal Jerry's thread, but I have often wondered if using a fan dipole arrangement with an open wire feedline might help clean up the pattern. Something like the attached picture, or perhaps with 40 meter elements added as well. Would this give a cleaner figure 8 pattern on each upper band that is added?

Thanks,

Rob W1AEX


* Open Wire Fan Dipole.jpg (5.78 KB, 669x256 - viewed 416 times.)
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« Reply #20 on: June 04, 2008, 11:15:38 AM »

Quote by Rob W1AEX:

"Not to steal Jerry's thread, but I have often wondered if using a fan dipole arrangement with an open wire feedline might help clean up the pattern. Something like the attached picture, or perhaps with 40 meter elements added as well. Would this give a cleaner figure 8 pattern on each upper band that is added?"

Hi Rob,

Yes, a fan dipole fed with coax is some improvement over the the multiband dipole when considering a more controlled pattern, but still not as good as a single bander. You would think that the legs resonant on the given frequency would take all the power. However, if you model it, you will find that the other legs DO have a small influence with distortion of the pattern somewhat. It all depends on the band and legs, but it certainly is a great way to maintain a reasonable figure 8 and reasonable match across many bands.  Of course, the height is a compromise and most guys will opt to put it up as high as possible favoring the lower bands.  On 160 and 75M, height is good...  even on 40M, putting a dipole at 60' will give both high and low vertical angles, so it not a bad deal at all.


Other than using one ant for multiple bands, what benefit does open wire line really offer beyond the coolness factor? I love the look of it running across a bead board ceiling on beehive standoffs, along with the glass feed-thru insulators. Some kind of caged dipole or similar buzzardly ant will be employed at the new location, but only for the fun factor. The results from wire arrays used by G and Tina are just too convincing to ignore.

Todd,

Yep!

I was thinking I would get beat up for suggesting that a coax fed dipole is as good as openwire.... Grin  But you hit the nail on the head.  There's no doubt that the COOLEST antenna for 160 and 75M operation is an open wire fed dipole with a HB antenna tuner.  Hands down. It looks so good and performs really well. Low loss, totally balanced, band excursion, etc.  I love it!  It's like riding into a Harley biker club with a Harley vs: a Moto Guzzi.  And there's times when we prefer to use openwire... for two half waves in phase, high impedance wire phased arrays, etc.

But I'm here to say that in the end, there is very little difference in signal performance between a properly tuned coax fed dipole (with a choke balun) and an open wire fed system. The pattern control advantages of the single band dipole mentioned in my last post are important to some and not to others.

** My point of all this is really for the newcomers. I often hear beginning AMers on the air acting like running a coax fed dipole is like running a stock, restricted ricebox on AM.  Second class. Some mention they want to rip down the coax as soon as possible and put up open wire, expecting a big signal increase. Some cannot run openwire into the shack because of XYL or other obstacle reasons and feel POed about it.  Well don't despair if that's you. You have good company....

Below is a list of some of the sharpest hams on AM. Each has a rock crushing signal. Most COULD run openwire if they wanted, (and some do both) but run single band, coax fed dipoles on 160 and 75M.  My point is that in the end, there is little difference between the two systems, performance-wise. Each ham needs to figure out which hardware and bands he wants to use and go with it.

Here's some AMers using coax fed dipoles on 160, 75 and sometimes 40M:

Chuck, K1KW
Gary, W2INR,
Tina, W1IA
Steve,WA1QIX
Frank, WA1GFZ
Todd, KA1KAQ
Rob, W1AEX
Steve, WB3HUZ
Bob, K1KBW
Rich, K1ETP
Joe, WA2PJP
Tom, W8JI

There's so many more I've missed.  (add yourself to the list)

My point is, if you're new at the game, be proud of running a coax fed dipole on AM. You've got good company.... Grin

Better yet, find some free CATV hardline and run it out to the field and make the last run up to the flatop using flexible RG-213.
A remote coax switch in the field will allow switching the hardline to other coax fed antennas.


T
   
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« Reply #21 on: June 04, 2008, 11:31:11 AM »

I actually run both. I guess it is your choice. A coax fed antenna is easy to use and there are no issues in dealing with open wire line. The down side is frequency coverage. A 75 meter dipole has a fairly high SWR at 3700 when cut for 3.885 but it is usable as long as you use a tube rig that can handle it.
High power I try to stay below 1.5 to 1 VSWR. This would be a choice for any phased array.
My 160 meter antenna is fed with open wire line. I tune it with a tuner and it works find. In a pinch it will work all bands with an adjustment at the tuner.
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« Reply #22 on: June 04, 2008, 11:40:25 AM »

I actually run both. I guess it is your choice. A coax fed antenna is easy to use and there are no issues in dealing with open wire line. The down side is frequency coverage. A 75 meter dipole has a fairly high SWR at 3700 when cut for 3.885 but it is usable as long as you use a tube rig that can handle it.

With many AMers using both 3700 and 3885 these days, Rob/AEX's dipole fan idea starts to make good sense for a single band dipole.  That swr could be kept very low using  legs cut for 3885 and another set for 3700.

T
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« Reply #23 on: June 04, 2008, 12:28:29 PM »

I've actually had pretty good luck going from 3885 down to 3725 without even touching the tuner on my 200' flat-top. That's a good thing, becuase the tuner is in the Junkyard Dawghouse, 80' away from the Junkyard Dawg. Sure, it's a real narrow sweet spot, indicative of heavy reactance, but the 4-250 pulls 275-300 mA cathode current with 50 mA on the screen, just about perfect for 1650 V B+.

I've been one to advocate open-wire fed dipoles, but never told anyone they'd have an increase in performance on the band it's cut for. Tom's right, they won't. The added bands certainly make it worth the effort, though.

Some setups just aren't well suited to open-wire feeding, however. If the shack sits at or near the end of the ant, you're bound to get coupling between the ant and feedline. Such would be the case for me if I were to run a balanced line all the way to the shack, which is part of the reason I have the tuner sitting at the base of the antenna.

One would instinctively think that a balanced feed results in some amount of gain because both legs are tied to the RF source (or sink), rather than one leg tied to ground potential; but it doesn't really work that way. You can't really empirically test the difference either, because addition of a balanced feedline to an antenna changes the antenna's characteristics dramatically.

All in all, I guess my vote is to use a link-coupled tuner to feed a balanced line from coax if you reasonably can. It's not a question of right vs. wrong to me, it's just the most efficient transfer of RF from one unbalanced impedance to another balanced impedance. It's just one out of a hundred effective methods to get on the air.

Not a necessity as much as a nicety.

My $0.02.

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« Reply #24 on: June 04, 2008, 12:47:08 PM »

The other issue of using a tuner with an older tunable output rig is the 'dance' you can slip into of tuning the transmitter, then the tuner, then having the transmitter out of resonance, and so on.

That's definitely an acquired skill.  I use variable link coupling, so my procedure is to run the link out to only minimal coupling, and dip the final.  Then adjust the antenna tuner for any noticeable peak.  If there is none, increase the coupling by running the link in a little, and try again.  Once a peak is found, run in the link to full loading, re-dip the final, and re-adjust the tuner for maximum coupling.  Once the proper setting is found, running the link in and out should have minimal effect on the final amp plate dip.  Set it for proper coupling, and transmit.

I normally do this in "tune" mode, at reduced plate voltage.

Once you get the knack of it, it becomes easy to intuitively adjust plate tuning, coupling and tuner setting in 3-4 adjustments, all within about 15 seconds.  If you are tuning up on an ongoing QSO, it is better to QSY just out of the passband, to a clear frequency, do the tuning, then QSY back to the QSO frequency.  Nothing is more irritating than a tuner-upper right on top of an ongoing QSO.
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