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Author Topic: External antenna tuners and ZS6BKW and G5RV antennas  (Read 6743 times)
AK4YA
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Posts: 106




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« on: September 16, 2012, 10:06:02 AM »

Will an external tuner be able to solve 80:1 - 90:1 that the ZS6BKW sees on 15m?  How about the 51:1 - 59.6: it sees on a G5RV at 10m?

Everywhere I read, I hear how much better the ZS6BKW is, but my thoughts are that since I'm getting an external tuner, I don't necessarily want to count out the G5RV if I can use it for 10m with an external tuner.  But I'm also interested in 15m.  Thus my dilemma.

Speaking of external tuners,  do any of them allow you to see the SWR and/or reflected power between the antenna and tuner? I'd also be interested in seeing these figures, and if possible, do it with metering built into the tuner.  Not sure but I suspect that the tuner only gives info on these figures for the link between the amp and the tuner, not the tuner and antenna.

Thanks!
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N4CR
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« Reply #1 on: September 16, 2012, 10:18:24 AM »

If this is your worry, why not build an antenna that doesn't have such limitations. Such as a fan dipole.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
AK4YA
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Posts: 106




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« Reply #2 on: September 16, 2012, 10:22:38 AM »

Im starting from absolutely zero equipment and am spending lots of time on selecting all the equipment for my station, dealing with custom amps and power supplies, RF MPE calcs, and grounding.  So for now, its going to be either a G5RV or ZS6BKW, just to get me on the air on as many bands as possible for now.  More antennas to come later for sure.

Thanks!
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WB6BYU
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« Reply #3 on: September 16, 2012, 10:32:19 AM »

Quote from: AK4YA

Will an external tuner be able to solve 80:1 - 90:1 that the ZS6BKW sees on 15m?  How about the 51:1 - 59.6: it sees on a G5RV at 10m?



There are two issues here, and one has nothing to do with the tuner.

The biggest problem with such a high SWR is NOT matching it, but the losses in the coax
between the tuner and the antenna.

VK1OD's handy transmission line loss calculator is quite useful for looking at such things:
http://vk1od.net/calc/tl/tllc.php

For example, if you had 50' of RG-213 (which is a reasonably short length of good feedline
on HF) and the load impedance at the antenna matching section was 2500 ohms on 15m
(SWR = 50 : 1) then the loss in the coax is 5.4dB.  (It's a bit higher if the load impedance
is 1 ohm, which also gives SWR = 50 : 1.)  At 100 : 1 it can be 8dB.  So, even with a good
short run of coax your losses can be 6 to 8dB in the circumstances you describe for either
the ZS6BKW on 15m or the G5RV on 10m, unless you put the tuner right at the end of the
matching section.

The good news in this, however, is that, because the the coax losses, the SWR at the
rig end is less than 15 : 1.  (The lower the feedline loss, the more radical the load that
the tuner has to match.)  Using W9CF's online tuner simulator available here:

http://fermi.la.asu.edu/w9cf/tuner/tuner.html

we can then get an idea of the expected tuner losses:  at 15 : 1, they would range from
about 0.2 to 0.5dB.   They can be higher than that for higher SWR, and will depend on
both the actual impedance at the end of the matching section and the length of the
feedline.  (Remember that tuners match impedance, not SWR.)


So, if you are running a lengthy feedline from the antenna to your tuner, the limiting
factor will be the coax losses.  With 100' of RG-8X, these can be 10dB or so.  Using
shorter and/or lower loss coax makes it more efficient.

The lower the coax loss, the more extreme the load that the tuner has to match.
Most common tuners are more efficient matching higher impedances than lower ones,
so, for the same SWR, the tuner losses will vary depending on the exact impedance.
With enough coax loss, the tuner shouldn't have a problem matching the antenna.
If the tuner is right at the end of the matching section, the tuner losses will likely
be higher, but the coax losses will be lower.


If you are running high power, you also need to consider that a high SWR reduces
the power handling capability of the coax because the peak voltage and current
are both increased.  I remember one UHF operator who had a short jumper of RG-213
coax in his antenna line right above his operating desk:  when it started to melt and
sag, he knew there was a fault in the antenna system.
« Last Edit: September 16, 2012, 10:36:30 AM by WB6BYU » Logged
WX7G
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Posts: 5975




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« Reply #4 on: September 16, 2012, 10:35:42 AM »

To eliminate the coaxial cable loss issue don't use it. A 100' dipole fed with ladder line to a tuner will get you on 80-10 meters. The MFJ-1777 is such an antenna and sells for $59. I like the MFJ-901B tuner at only $99.
« Last Edit: September 16, 2012, 10:39:02 AM by WX7G » Logged
G0VKT
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Posts: 64




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« Reply #5 on: September 16, 2012, 10:43:15 AM »

I agree. Based on recent experiments the open wire fed doublet is better than my coax fed G5RV.
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N4CR
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Posts: 1662




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« Reply #6 on: September 16, 2012, 11:25:07 AM »

Im starting from absolutely zero equipment and am spending lots of time on selecting all the equipment for my station, dealing with custom amps and power supplies, RF MPE calcs, and grounding.  So for now, its going to be either a G5RV or ZS6BKW, just to get me on the air on as many bands as possible for now.  More antennas to come later for sure.

Thanks!

From what I read, you're probably overthinking your first install. It's not something that you'll do once only in your life and then you are done.

Radio. Get one that works on the bands you like. Stop worrying about getting the ultimate radio on your first install.

RF exposure is unlikely to be an issue for any horizontal antenna that's up high enough to work well.

Grounding is absolutely not necessary for an antenna to radiate and receive. There are three kinds of grounds, safety, rf and lightning. The most important one (safety) is already in your house at the outlet. You may never need an RF ground if your antenna is balanced. Lightning grounds are area specific so I can't really comment on it but it's not a must have for your first station. You can unhook the cable and throw it outside in a pinch.

There's lots of easy and inexpensive options for antennas. If you're going to eliminate them from the start why ask us?

Fan Dipole.  Build it yourself, no tuner needed. Build, erect, trim in a day. Done. Works great.
All band doublet fed with parallel line feeder. Tuner needed. Build, erect in a day. Done. Works great.
Trapped Vertical. Install radial field, install antenna, work DX. (A little more effort but a very good antenna to have in your tool kit)

Any of them would beat the pants off of a less suitable antenna pressed into service on the wrong band. It seems as if you have already eliminated these as impossible to start with. My opinion is that any of them would be better to start with.

As with all antennas, getting them up high in the air and clear from your living space is what is hard, what usually costs money and what REALLY makes them work well. That's a much more important topic than which wire you'll haul up into the air or which radio you'll hook it to.

A crappy radio hooked to a properly installed antenna high up in the air will work circles around the best radio in the world hooked to a height limited or highly compromised antenna.

Spend 90% of your time and money figuring out how to get the best antenna you can afford as high as possible in the air. Spend the other 10% getting a radio that works hooked up to it.
« Last Edit: September 16, 2012, 11:31:14 AM by N4CR » Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
K3VAT
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Posts: 705




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« Reply #7 on: September 16, 2012, 02:52:38 PM »

Im starting from absolutely zero equipment and am spending lots of time on selecting all the equipment for my station, dealing with custom amps and power supplies, RF MPE calcs, and grounding.  So for now, its going to be either a G5RV or ZS6BKW, just to get me on the air on as many bands as possible for now.  More antennas to come later for sure.  Thanks! 

From what I read, you're probably overthinking your first install. It's not something that you'll do once only in your life and then you are done.
...
A crappy radio hooked to a properly installed antenna high up in the air will work circles around the best radio in the world hooked to a height limited or highly compromised antenna.

Spend 90% of your time and money figuring out how to get the best antenna you can afford as high as possible in the air. Spend the other 10% getting a radio that works hooked up to it.

This is sound advice on ALL points!  The only change that I'd suggest is the last paragraph where I'd change the "...90% ... money on antenna [system] ..." to a more realistic 50% antenna system, 50% everything else. 

GL, 73, Rich, K3VAT
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AK4YA
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Posts: 106




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« Reply #8 on: September 16, 2012, 04:27:04 PM »

ok, you have about sold me.  are there any auto tuners with a coax input from the amp and a balanced output that work HF+6m?  Are there any balanced wattmeters that measure fwd, reverse, and vswr available?
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N4CR
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Posts: 1662




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« Reply #9 on: September 16, 2012, 07:01:35 PM »

ok, you have about sold me.  are there any auto tuners with a coax input from the amp and a balanced output that work HF+6m?  Are there any balanced wattmeters that measure fwd, reverse, and vswr available?

How much power?

Which antenna?
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
AK4YA
Member

Posts: 106




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« Reply #10 on: September 16, 2012, 07:14:06 PM »

300 watt solid state amp based on BLF175 fets in AB.  According to the spec sheet the FET can withstand VSWR of 50:1.  Possibly going with the recommended 102ft all band doublet with a 45ft mast, with the ends at 25ft.  Id need right at 100 feet of ladderline to feed down the 45ft mast and then to the corner of the house the equipment is in.

Hopefully this wont require a regular meter doubled up with baluns on each side.
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N4CR
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Posts: 1662




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« Reply #11 on: September 16, 2012, 10:29:45 PM »

MFJ-976 is a good balanced only tuner.

PALSTAR BT1500A is pricey but very nice.

Or if you want a more multi-purpose Pi match tuner, there is:

MFJ-989D is what I have. (well, I have a 989C) It's a standard Pi tuner with a built in balun and balanced outputs for ladder line. Also has a built in dummy load and can switch multiple antennas.

All of the above have a built in SWR meter.

Of course, there are dozens of others. Be aware that a 300 watt tuner doesn't mean you can run 300 watts into a terrible mismatch. Typical full rated power is limited to tuning a 3:1 match max. Which is why you should get one rated for a LOT more power than you plan to run.

Unless you don't mind replacing burned out parts occasionally

If you want to shop eBay, look for a Johnson Matchbox. The 300 watt model will handle a kilowatt nicely. The big one will handle whatever legal you throw at it. I think I paid $100 for mine but I shopped for quite a while waiting for a deal to arrive.

And also, you need to understand that there are REAL balanced tuners and Pi tuners with a Balun. They are not the same. There is usually less tuning loss associated with a real balanced line tuner, although I've never noticed much difference between the Johnson Matchbox and the MFJ-989C.

Big components are what makes tuners efficient. Tiny matching components equal more loss, so don't look for something that looks delicate. Because it will be delicate and will also be more lossy.

If you have the room, 135' is a better length for 75/80 meters.

You also may find that 100' of ladder line is a difficult length on some bands. I have found that 93 feet was much easier to match on all bands. I recall that another good length is 112 feet. If it's not, Cecil will be around to correct me on that real soon now...

One last thing. SWR meters go before the tuner, not after. So even if you buy a Johnson Matchbox, the SWR meter goes in the coax leading to the tuner.
« Last Edit: September 16, 2012, 10:34:04 PM by N4CR » Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
N4CR
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Posts: 1662




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« Reply #12 on: September 16, 2012, 10:43:30 PM »

Oh, you said auto tuners. Beats me. I never cared much for auto tuners.

Manual tuners take a few seconds longer, achieve as good or a better match, don't make a bunch of noise. Also, once you learn where the knobs go for a given frequency, you can make a note of it (a chart so to speak) and return to that configuration in seconds. I seldom tune more than a few seconds.

Why would I pay good money to stop doing what only takes a couple of seconds?

Get off auto pilot. Become one with your antennas.

Or put up a resonant fan dipole with coax and skip the tuner altogether. Works the same either way except that even the finest tuners introduce loss. There's a reason that people like resonant multiband antennas...
« Last Edit: September 16, 2012, 10:46:51 PM by N4CR » Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W8JI
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« Reply #13 on: September 17, 2012, 03:12:20 AM »

300 watt solid state amp based on BLF175 fets in AB.  According to the spec sheet the FET can withstand VSWR of 50:1. 

SWR listed on the data sheet has almost nothing to do with how much SWR the FET can take in real life. A data sheet 50:1 SWR rated device can blow up at 2:1 SWR, or work fine at 100:1 in other applications.

Devices have maximum current ratings, maximum voltage ratings, and internal temperature ratings. If none of those are exceeded  the SWR can be a billion to one and it will work for years. If maximum voltage is exceeded from even a modest SWR, it can fail in microseconds. A somewhat modest SWR can also cause non-linearity and splatter. It is no different than mistuning a tube type amplifier.

My advice to you would be to ignore spec sheet SWR ratings, and try for a 1:1 SWR, and include an SWR shutdown system for protection.


Quote
Possibly going with the recommended 102ft all band doublet with a 45ft mast, with the ends at 25ft.  Id need right at 100 feet of ladderline to feed down the 45ft mast and then to the corner of the house the equipment is in.

Wire antennas and feedlines are easy to change. A G5RV with short coaxial feedline would work great on 80, 40, 20, and 12 meters, and have some untility on other bands. A ladder line fed doublet would be great on most bands also.

There are probably a half dozen antennas that would work for you, with most problems really being how they fit your space.

Quote
Hopefully this wont require a regular meter doubled up with baluns on each side.

Why do you want to measure SWR on the antenna side of the tuner? That is a monumetal task, and generally serves no real purpose to most amateurs. After all, a ladder line feeder is often operated with a terrible SWR yet losses are reasonably low.

From reading what you say and ask, it seems like you may (like many or most Hams) misunderstand SWR and what it does.

73 Tom
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W5DXP
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« Reply #14 on: September 17, 2012, 05:31:48 AM »

Will an external tuner be able to solve 80:1 - 90:1 that the ZS6BKW sees on 15m?  How about the 51:1 - 59.6: it sees on a G5RV at 10m?

Neither the G5RV nor the ZS6BKW can be considered to be an "all-HF band" antenna - consider them to be multi-band antennas that don't work well on some bands where the high SWR on the coax eats up a lot of power.

As Tom says, the G5RV works well on 80m, 40m, 20m, and 12m (with a broad-range antenna tuner).

The ZS6BKW works well on 40m, 20m, 17m, 12m, and 10m (with a broad-range tuner required on some bands).

Neither antenna works well on 15m. If you want the ZS6BKW to work well on 15m figure out how to switch out ~10 feet of ladder-line to make the series section transformer section ~30 feet instead of 40 feet. For the G5RV, figure out how to switch out ~4 feet of 300 ohm line.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
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