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   Home   Help Search  
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Author Topic: Need Antenna Tuner Help  (Read 4211 times)
K1JWJ
Member

Posts: 14




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« on: September 12, 2017, 11:32:50 AM »

If this post is in the wrong category, please advise.

I am setting up my new shack and starting with an IC-735 which will run into an "Optimized G5RV/ZS6BKW" antenna in an inverted V at 42' (no balun).

I presume I will need an antenna tuner, but do not know where to start. Some say I need a minimum of a 1500 W unit, others say I may need nothing. The antenna mfg. says no tuner necessary on 10, 12, 17, 20 and 40 meter bands. Other bands it is needed.

Somewhere in there there must be something that will do the job with this set up.

Advice will be gratefully accepted.

73

Jeff (K1JWJ)
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VE3FMC
Member

Posts: 33




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« Reply #1 on: September 12, 2017, 12:20:45 PM »

If this post is in the wrong category, please advise.

I am setting up my new shack and starting with an IC-735 which will run into an "Optimized G5RV/ZS6BKW" antenna in an inverted V at 42' (no balun).

I presume I will need an antenna tuner, but do not know where to start. Some say I need a minimum of a 1500 W unit, others say I may need nothing. The antenna mfg. says no tuner necessary on 10, 12, 17, 20 and 40 meter bands. Other bands it is needed.

Somewhere in there there must be something that will do the job with this set up.

Advice will be gratefully accepted.

73

Jeff (K1JWJ)

Hello Jeff

What you could do is try the antenna without a tuner (which you do not have) and see what the SWR readings are like on each band.

I doubt you will get away without a tuner as I had one of those antennas and I needed a tuner on some bands.

Now here is the big thing about buying tuners. If you plan on running an amp down the road by all means buy a tuner rated at 1500 watts. You do not need a new one, there are plenty of good used 1500 watt tuners for sale.

If you do not plan on running an amp then buy a decent tuner that handles 200 watts. But my thoughts are buy the 1500 watt tuner now and you are set for future use.

Look for old Dentron, Nye Viking, Drake etc tuners and you will have a good unit. I bought a used Palstar AT1500 for $300 Canadian about 5-6 years ago and it has served me well.
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K1JWJ
Member

Posts: 14




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« Reply #2 on: September 12, 2017, 12:30:57 PM »

Thank you kindly for the advice.

73

Jeff (K1JWJ)
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KE6EE
Member

Posts: 1844




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« Reply #3 on: September 12, 2017, 12:33:25 PM »

Since used tuners of good quality are widely available on various ham classified sites as well as on ebay, you should invest $200-$300 in a high-capacity unit which will serve you for a long time as you, probably inevitably, fiddle with different antenna designs.

A most useful kind of fiddling. I bought a new Palstar differential 1.5 kW tuner when I started out. It has worked well and the differential tuning (ganged variable caps) makes tuning quick and easy.

I have since obtained used MFJ and Ameritron tuners, one a true balanced tuner and the other one an especially well-designed, efficient and wide-range one. Both these tuners needed mechanical reworking (variable inductor gear required adjustment and realignment) which was not a great challenge for this fiddler.

Keep in mind that a low-power-rated tuner (e.g. 200W) is more likely to arc or otherwise fail even at relatively low power if the tuner has to deal with a high SWR.

Better to get a big one to begin with.
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KC4ZGP
Member

Posts: 1637




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« Reply #4 on: September 12, 2017, 12:35:51 PM »

Hey Jeff,

Do you like building. Then build one. Wind your own coil. Use copper tubing to make your capacitors. Just like the real, real old days.

Kraus
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WB6BYU
Member

Posts: 17047




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« Reply #5 on: September 12, 2017, 12:52:01 PM »

The ZS6BKW version of the G5RV is supposed to work parts of 40 / 20 / 17 / 12 / 10m without a tuner.
The exact resonant frequency and SWR at that point will depend on the height above ground, wire
diameter, and the exact configuration.  In some cases the SWR will be very close to 2 : 1, and it
will depend on your specific radio how much power it will put out into such a load without a tuner.

You can find an extensive analysis of the antenna in part 3 of this article.
Note however that it models the antenna as a straight element rather than an inverted vee.


First, I'd recommend that you use a 1 : 1 current balun (or "feedline choke", which is the same thing)
at the junction between the parallel line and your coax.  That reduces the RF that flows on the outside
of your coax, and can introduce added losses when the coax is laying on the ground.  No, you don't
"need" the balun:  you can connect the coax directly the parallel line and make it work, but the choke
is good practice.

A tuner may still come in handy, since the low SWR on the antenna does depend on the specific installation,
height above ground, etc.  And just because the SWR is low at some point on a band doesn't mean it will
be low enough where you want to operate:  on 10m, for example, the minimum SWR is around 28.8 MHz or
so, and you may need a tuner to operate below 28.5 MHz.  And the resonances may shift when the antenna
is installed as an inverted vee.

If you think you are going to get a kW amp in the near future, then buying a full power tuner might not be
a bad idea.  On the other hand, I've picked up used tuners at swapfests for reasonable prices, and they
hold their value pretty well unless you misuse it, so you won't lose much on the investment if you start off
with a lower power tuner.  I always have a manual tuner available in case I'm experimenting with antennas or
something doesn't work as expected.  You wouldn't necessarily need it to get on the air, but they
sure can come in handy.  (Sometimes I use the antenna switch and SWR/power meter function, even when
I don't need the tuner part.)
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W5DXP
Member

Posts: 4191


WWW

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« Reply #6 on: September 12, 2017, 02:56:46 PM »

The antenna mfg. says no tuner necessary on 10, 12, 17, 20 and 40 meter bands. Other bands it is needed.

I believe the IC-735 reduces its output power when the SWR reaches 2:1. So without a tuner, don't expect to cover all of any band except maybe 12m. With a tuner one can cover all 5 bands plus some of 80m. That antenna just does not work well on 30m and 15m even with a tuner. A 500pf series capacitor on the input of the choke makes 80m easier to handle. I definitely would put a 1:1 choke at the ladder-line/coax junction. Here's some of my ideas about my ZS6BKW on which I do not use a tuner.

http://www.w5dxp.com/ZS6BKW80/ZS6BKW80.HTM
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G3RZP
Member

Posts: 8123




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« Reply #7 on: September 13, 2017, 03:59:54 AM »

Kraus,

Why should one use copper tube for the capacitors? And how do you build suitable high value capacitors from copper tube? For the coils, yes. Probably 3/16 diameter tube will do with maybe 12 AWG wire for 80 and 160, since you want a high unloaded Q and a low (10 - 20) working Q.
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KC4ZGP
Member

Posts: 1637




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« Reply #8 on: September 13, 2017, 05:08:03 AM »

Kraus,

Why should one use copper tube for the capacitors? And how do you build suitable high value capacitors from copper tube? For the coils, yes. Probably 3/16 diameter tube will do with maybe 12 AWG wire for 80 and 160, since you want a high unloaded Q and a low (10 - 20) working Q.

Simple. A length of copper tubing perhaps 25cm diameter inserted into a length of copper tubing of 50 CM diameter.

Look at magnetic loops with trombone capacitors. My loop employs such.

There you go.

Kraus
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VK6HP
Member

Posts: 151




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« Reply #9 on: September 13, 2017, 05:52:09 AM »

I use a ZS6BKU as an inverted-V, with the apex at about 45'.  As W6BYU says, do yourself a favor and use a good current balun at the coax to ladder line interface: with my 1:1 "tuner grade" choke balun, I found a useful reduction in common mode current and a corresponding drop in received noise.

I don't need to use an external tuner on 40, 20, 17, 12 and most of 10m.  The SWR is generally very good and any band-edge tuning is easily accomplished either with the internal tuner in my TS-590S, or the pi networks in my boat anchor radios.  My RG-213 coax feedline is about 60' in length, so there's no significant loss on bands where the doublet is meant to work well.

Although I can tune a lot of 80m with just the internal TS-590S tuner, I do often use an external tuner to cover the whole 75-80m band.  Similarly, the antenna can be loaded on 30m and 15m if you have a good enough tuner, but be aware that the SWRs are very high and the coax losses correspondingly large.  Still, my tuner handles it OK and particularly for initial digital work on 30m, I was glad to be able to have usable wire in the air.   But these days I normally switch to the (harmonically resonant) 80m horizontal loop for 80, 30 and 15m operation, as well as for some 20m DX.

So, I would say a tuner is not really necessary to get on the air but even a modest 200-300W tuner (store bought or homebrew), with inbuilt metering and provision for dummy load switching, is a handy thing to have around.
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G3RZP
Member

Posts: 8123




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« Reply #10 on: September 13, 2017, 06:33:28 AM »

Kraus,

You need 60pf for 7 MHz in a simple tuner - let's say 80pF to allow for reactance compensation.  For the 25mm and 50mm tubes, that means a length of 1 metre and a parasitic inductance of around 500nH. For 80m, double that.....

Gets a bit impractical compared to conventional parallel plate capacitors
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KH6AQ
Member

Posts: 7718




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« Reply #11 on: September 13, 2017, 08:29:18 AM »

I've used various 200 watt antenna tuners at the 100 watt level and have never had one arc. The MFJ-901B is $99 and should be able to tune your antenna.
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WB6BYU
Member

Posts: 17047




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« Reply #12 on: September 13, 2017, 08:50:24 AM »

Quote from: KH6AQ

I've used various 200 watt antenna tuners at the 100 watt level and have never had one arc...



I agree that, in most cases, such tuners will work fine, and that is what I usually use with no problems. 

But the power rating of a tuner depends on the impedance it has to match and many other parameters.
With an extreme load (particularly low and/or reactive impedances) the tuner may have high losses,
or generate higher voltages than expected.  The standard "T" circuit can have several settings that all
give a low SWR, but some will be more lossy than others.

I have a very beefy homemade tuner that uses parts considerably larger than the common "300W" tuners.
I've managed to arc the capacitors at 10W output trying to match a radical load (an 18" clip lead on 80m).

A friend used a "300W" tuner at 100W to match a loop on 160m.  He got great signal reports, until the
plastic coil supports in his tuner melted from the heat and the turns shorted together.

That doesn't mean you need a bigger tuner, just don't expect miracles from it.  I try to find a match with
one of the capacitors fully meshed, as that usually will be the most efficient setting.  And if you are
worried about heating, check the coil wires with a "digital temperature sensor" (aka "finger") after a QSO
and see if they feel warm.  Heating is most likely to be a problem when the capacitor settings are
"touchy", and when both capacitors have to be set at less than maximum to achieve a match.

But for most reasonable antennas they should work fine.
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KC4ZGP
Member

Posts: 1637




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« Reply #13 on: September 13, 2017, 09:46:21 AM »


I too have a 'beefy' t-matcher of a giant roller inductor coil and two HV capacitors from RF Parts.
The chassis is a steel desk drawer I found when we purging the warehouse.

it's beefy I say, beefy.

Kraus
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KH6AQ
Member

Posts: 7718




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« Reply #14 on: September 13, 2017, 09:48:44 AM »

Is this the antenna?    https://www.amazon.com/ZS6BKW-G5RV-Optimized-Antenna-Flex-Weave/dp/B00L8JKLFG

The ladderline-to-coax "W2AU LL-TRANSULATOR" does not appear to be a balun and as WB2BYU said, the antenna will benefit from a balun at this location. The MFJ-915 Line Isolator might be effective.

The MFJ-901B antenna tuner should tune this antenna but it's always in the circuit and cannot be switched out. The MFJ-941E has a bypass switch.
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