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Author Topic: Talk to me about tuners  (Read 3839 times)
KJ6TCO
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Posts: 4




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« on: January 23, 2012, 11:47:59 AM »

I'm a new ham, just got my tech license and intend to get general in a week or two (and try for extra). I know I need an antenna tuner, most likely an external automatic tuner like the Icom AH-4. This is because for the next year (or more) the space available for my antenna is very limited to our back patio (about 30 feet wide and 15 feet deep), I need to do make more stealthy antenna here.

The rest of my equipment is an Icom 7000, power supply, and an HT. I really want to get involved with my local ARES group and have actually joined. They hold meetings on 75 meters. I believe an NVIS antenna would be fine for joining in on the local ARES net. 

Basically my goals are:
Get on 75M for local ARES stuff.
Function on 10-20m for dx.

Do you all think this would work? Will the tuner make it easier to get a working antenna up with my restrictions? And if so, is the Icom AH4 the best for me?
Thanks
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KQ6Q
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Posts: 991




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« Reply #1 on: January 23, 2012, 02:04:00 PM »

For now, consider a Buddipole setup with the tripod base - you can set it up for any of the bands, and take it with you if you need to. you may need a tuner to help out, but just a coax to coax model will do - in the $100 range. You could spring for an external auto-tuner for a few hundred more. personally, I'm delighted with the automatic internal tuners on my Icom 746Pro and Icom 703. There are some external models designed to work with the 7000.
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K3WEC
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Posts: 260




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« Reply #2 on: January 23, 2012, 08:38:24 PM »

I believe an NVIS antenna would be fine for joining in on the local ARES net.  

The so-called NVIS antennas are underrated, in my opinion.   I've talked all over the country on both 40m and 75m, pretty darn reliably, with a fan dipole stapled to my backyard fence.

You will be just fine with local ARES, and well beyond, with a very low dipole on 75m.
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KJ6TCO
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Posts: 4




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« Reply #3 on: January 24, 2012, 08:02:20 AM »

For now, consider a Buddipole setup with the tripod base - you can set it up for any of the bands, and take it with you if you need to. you may need a tuner to help out, but just a coax to coax model will do - in the $100 range. You could spring for an external auto-tuner for a few hundred more. personally, I'm delighted with the automatic internal tuners on my Icom 746Pro and Icom 703. There are some external models designed to work with the 7000.

I've considered the Buddipole and see there are mixed reviews, it seems like there are lots of fans and lots of critics, I haven't concluded whether it's a good idea or not. One negative is that you set it up for one band at a time, vs tuner + wire can work many bands at once.

The tuner (Icom AH4 is designed for long wire/random wire) would leave open a lot of room for experimentation and expansion if we move somewhere with more yard (unknown).

Thanks for the input, it helps with my own thought process. It seems like I'm favoring the tuner + random wire for now, although I see the Buddipole or similar setup as interesting.
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WB6BYU
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Posts: 13486




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« Reply #4 on: January 24, 2012, 10:13:34 AM »

In that case you may want two different antennas.

A lot will depend on how high you can get the antenna.  At 20' or so a horizontal
dipole or inverted vee becomes a reasonable alternative for the higher bands.
That will fit in the available space.  You can put multiple dipoles on a common
feedpoint and have direct coax feed on 20 / 15 / 10m without needing a tuner.

If you are more limited in height, a vertical may be a better option, though you
do have to give some consideration to radials in many cases.  The HyGain
12AVQ is a trap vertical that covers 20 / 15 / 10m with direct coax feed and
is something like 12' tall IIRC. 

Both of those would give you operating on at least 3 bands without needing
a tuner.

If you are going to use a tuner I'd suggest a single dipole (roughly sized for 20m)
fed with twinlead to a tuner for the first case, or a vertical wire about 8 - 14' long
fed against a radial system for the second.  You maybe able to use an "inverted L"
that goes up as high as you can get it then runs horizontally.  The AH-4 is designed
to feed wires but not coax (though it can do so if needed.)  It probably isn't the
best choice if you are going to use a balanced antenna, but should handle the
vertical or inverted L options.

I would NOT recommend a loaded dipole antenna (such as the Buddipole) for the
higher bands in your situation because you have space to put up a half wave
wire, which will be more efficient and convenient (not to mention much cheaper.)


Getting on 75m will be more difficult - you're trying to squeeze a 120' antenna into
a 30' space.  Your limitations are efficiency and operating bandwidth due to using
a shortened antenna.  Clearly the antenna needs to be horizontally polarized for
optimum NVIS propagation.  Height above ground is still important for best
efficiency - the ground losses increase at lower heights - but I've made contacts
with a dipole draped over some waist-high bushes.

One of the problems, of course, is that the installation will depend heavily on your
specific circumstances, but here is a suggestion that might work on all bands.
Start with a vertical support - the peak of the roof, perhaps, or a telescoping push-up
mast, or whatever.  Let's say you can get it to 20'.  Install an inverted vee fed
with twinlead with the feedpoint at the top.  Run the wires down to supports at the
corners of your available space - about 15' horizontally either side, so as long as the
ends of the wires are over 5' off the ground the wires will be flatter than 45 degrees.
(Getting these points up 8' to 10' or more will be better.)  From there run the wires
to the adjacent corners for another 15'.  (This would actually give you a pretty good
40m antenna.)  To improve performance on 80m, install loading coils somewhere near
the corners of the antenna.  These likely will be some number of turns of wire on a
piece of PVC pipe, and will need to be calculated (which several of us can do for you.)
Those will also act like RF chokes on the higher bands, so the center sections do most
of the radiating on 10 through 20m and the coils + end wires bring it close to resonance
on 80m.  Once you get the coils close enough you can fine-tune the 80m performance
by adjusting the lengths of the wire ends.  It will probably work on 40 also, but not
as well as it would without the coils.  (So you can short out the coils to operate
that band.)

If you can put the wire antenna (and possibly the antenna tuner) on the roof then
you may be able to make it bigger.

This isn't the greatest antenna, but should meet your needs with reasonable performance
in a small space at low cost.  You'll need a tuner that can handle the balanced line,
which might be an autotuner or a manual tuner in the shack.   A tuner with a coax
output could be used with an external balun.

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KG6IRW
Member

Posts: 40




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« Reply #5 on: January 24, 2012, 10:04:55 PM »

I have a similar problem in that my house is on a 40' by 80' lot.  All the houses around me are 2 story houses while mine is a single story.  That means that anything I string above the house is, basically, broadcasting into my neighbors' kitchens.  When I got my General, I rewarded myself with an HF rig, an Icom 706MkIIG and purchased an AH-4 remote tuner.  This tuner fed a long wire positioned just above the house to minimize the neighbors' noticing and getting alarmed.  The long wire was, at that time, about 40' total and up about 20'.  This worked well!  I worked up and down the west coast of the US and, sometimes, into Asia with it from the QTH in the Pacific coast.

Later, I sold the '706 and the AH-4, tried all sorts of dipoles along with a number of different rigs.  The thing that _really_ changed things for me was improving the grounding system for the antennas.  Today, some 10 years later, I have returned to a remote antenna tuner, now the SGC 230.  The difference now is that I've got 2 ground rods driven where I have the tuner mounted to the fence connected with a set of #4 gauge wires _and_ added a series of raised radials that are stapled to the fence on both sides of the house.  These are random lengths.  I can tell you that my ability to get out on _all_ the bands has greatly improved with the addition of the grounding system.

Given you are planning to use an Icom, the AH-4 does, indeed, integrate seamlessly with the rig and will allow you to just push a button and get it to tune - easy!  I'd suggest you plan on paying attention to the grounding of the remote tuner to get the best out of the installation.  It has worked for me.

Cheers,

David
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KJ6TCO
Member

Posts: 4




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« Reply #6 on: January 25, 2012, 08:48:47 AM »

Thanks for all of the great advice. I've decided to go with the AH-4 autotuner and experiment with some wire configurations. I'll start with something very basic, take notes, and move up to something like an inverted L (I think one would fit here pretty well). I'm currently doing research on the ground system I need.

I have read that if I make the antenna out of a wire loop and attach both ends to the tuner then I don't need a ground system?
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W6RMK
Member

Posts: 662




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« Reply #7 on: January 25, 2012, 02:50:43 PM »


I have read that if I make the antenna out of a wire loop and attach both ends to the tuner then I don't need a ground system?

That's sort of true.  The loop needs to be big enough.  And if it's outside, you need to bond things (coax shield) to your house's electrical safety ground.  But you don't need an "RF ground"

But then, you wouldn't need one for any sort of dipole looking thing, either.  You only need an RF ground if you're building a vertical (or something that looks like a vertical, such as a L or flattop)
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N2MVV
Member

Posts: 16




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« Reply #8 on: March 01, 2012, 10:14:47 AM »

As far as an automatic antenna tuner, check out the LDG IT-100.

It works great on my Icom 718 and works on the Icom 7000.

Read the reviews.

Eric (N2MVV)
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