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Author Topic: ICOM AH-4 versus LDG IT-100  (Read 4954 times)
AC0LX
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« on: April 03, 2010, 01:11:20 PM »

I'm struggling to understand the differences between the Icom AH-4 automatic antenna tuner and the LDG IT-100.  The LDG is about half the cost of the AH-4.

I have an Icom IC-706mkIIG that I will be interfacing with the tuner.

I'd like to operate on a sailboat this summer.  I will likely pull a wire antenna to near the top of the mast.  The length of the wire (antenna) will probably be around 30ft.

Both of the tuners will have problems tuning an antenna that is a lam/2 multiple of the frequency I'm trying to operate.  Right?

The LDG has a coax output, whereas the AH-4 has just a ground terminal and the antenna terminal.

I'd also like to buy something that's flexible for other stuff.  For example, if I have a slightly mis-tuned dipole, it would be nice to be able to use the tuner to get reasonable SWR.

Can I use them to feed a coax fed dipole?  Or does the tuner need to be right at the feed point of the dipole?

I know I'm asking a lot here.  Maybe there are some good references I could be pointed towards?

Thanks everyone!
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WG8Z
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Posts: 193




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« Reply #1 on: April 03, 2010, 02:17:36 PM »

I like the ah-4,run it with my 706 feeding a 135' doublet fed with ladderline...works great 6  thru 80m and 160m when fed as a marconi against a 1/4w counterpoise this setup works excellent on Field day and Jota and whenever I play portable....Pretty much idiot proof...
A friend has LDG and the ah-4 will tune stuff the LDG won't.....
On my pontoon boat I feed a 30' fiberglass pole hanging a wire works well there....
Just my nickels worth.
My experience convinced me coax is not your friend when dealing with multiband wire ant's,ladderline is your friend.
73 Greg
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N8EMR
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Posts: 235




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« Reply #2 on: April 03, 2010, 04:38:28 PM »

Two different types of tuners.  The AH-4 a wire/whip tuner and the LDG a unbalanced line tuner.   I would go with the AH-4 if your going to just use the backstay or run a wire. The AH-4 is very similar to the Icom Marine tuner and would work well on the sail boat.
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WX7G
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« Reply #3 on: April 03, 2010, 04:52:51 PM »

I have not used either of these tuners but I have tuned the port stay on a 32' sail boat using two different tuners. Working against the sail boat keel it tuned well and did the job at 5 watts on four field days.
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WG8Z
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Posts: 193




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« Reply #4 on: April 03, 2010, 07:35:54 PM »

"The AH-4 a wire/whip tuner"
Cool thing is Gary, it works well with ladderline fed doublets and loops as well...I know this for a fact...
Youv'e heard it. Called the "Net" a bunch of times /P/4.
Pretty much retired my "949 Mighty Fine" after I got the AH-4. Don't get me wrong I love my Kenwood Hybrids and my Swans and the Johnson Matchbox's....But sometimes Appliance operating has it's moments too.
Just Key the Mic and talk,,,QSY to another band,no worries, just key the Mic and talk. So easy any ARES member can do it. Hi
73
de Greg
"The Voice of Cincinnati"
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K0BG
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« Reply #5 on: April 04, 2010, 06:58:42 AM »

The two tuners were designed for different uses, albeit there are some things they both can do. Since your plan is to use a wire as the element, I'd pay the bucks, and go with an AH-4, or perhaps one of the SGC units. The AH-4 can match loads from about 8 ohms to about 3,500 ohms which is a little less than they advertise. Even then, at the edges they get rather lossy. The SG230 is a better choices in some respects, as it is sealed, and can be submerged for at least a few minutes. Not so with the AH-4.

The LDG requires a balun to match high impedance loads, which adds its own bit of loss. While they're good tuners, they don't handle saltwater climates very well.

I have a good friend who owns a 43 foot cat. I installed an IC-706 and AH-4 in it several years ago. The starboard stay was already insulated at the top, and the bulkhead attachment is in fiberglass. The AH-4 is mounted below deck, and drives the stay through about 12 inches of wire. The ground side runs down to the starboard keel grounding plate using a 3 inch wide chunk of monel. It is not the most efficient set up, but works well enough for the casual use it is put to.

One last comment about feeding ladder line with an AH-4. It is almost impossible to choke the common mode off the control line and coax feeds. While you can get by in some installations, it isn't a the best choice.
« Last Edit: April 04, 2010, 12:15:22 PM by Alan Applegate » Logged

WG8Z
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Posts: 193




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« Reply #6 on: April 04, 2010, 09:53:32 AM »

>One last comment about feeding ladder line with an AH-4. It is almost impossible to choke the common mode off the control line and coax feeds. While you can get by in some installations, it isn't a the best choice.
---------
Thats what I have been told. Even thought it might be a problem myself,especially with my 50'coax and control cable extension,(provided I maintain a somewhat perpendicular orientation)..... But hey, I tried it anyway at a JOTA event with the ARES clubs Equipment... It worked so well I couldn't wait to get one myself....There may be common mode current but never has caused any TX Audio  or RX noise problems.
A/B tests between an AH-4 and a Johnson Matchbox feeding a 135' doublet produced NO measurable differences TX or RX on any band 10m thru 80m with the exception that the AH-4 worked better on 17M
Oh well,I'm happy
73
Greg
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AC0LX
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« Reply #7 on: April 04, 2010, 05:29:29 PM »

Thanks for all the replies.  Still a tough one to understand.

So the fundamental difference is that the AH-4 is for a random wire and the LDG is for an "unbalanced coax fed antenna".  

Do I understand it correctly that if I were to use the LDG with a balun, I would have a setup very similar to the AH-4?  Although, I gather from the comments that this would introduce a lot of loss and maybe wouldn't be the best solution.  

Another question as I'm thinking about this.  If you were to use the LDG with a balun, does the section of coax wire betwen the LDG and the balun become part of the antenna? (If we assume a "random" wire.)
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K0BG
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« Reply #8 on: April 05, 2010, 06:09:08 AM »

The simple answer is no.

The circuitry in both is similar, but the component values are a lot different. The LDG does not have the matching range the AH-4 has. LDG uses a 1:4 balun to extend the matching range. I do not know if the balun is of a voltage or current design. If it is the former, that could be a problem in and of itself.

The thing you have to be careful with is the RF output voltage. Even with just 100 watts, the output side can exceed 10 kV! This occurs for several reasons (high impedance loads), and during tuning to a lessor degree. You can't use coax at the output side, unless the SWR is say less than 10:1 or so. All of this is promulgated on the AH-4's intended use. Take a look at the AH-2, the antenna meant to be fed with the AH-4. Pay attention to the base insulator.

If the intended installation is using a remotely-tuned antenna, then there is no reason to use any matching other than a simple L shunt. The only exception is with mobile antennas which cover 160 meters. By the basic design parameters, their input impedance is going to be close to 50 ohms. However, their 80 and 40 meter input will be closer to 25 ohms. In these cases, a switched UNUN of switched L is the way to go.

You might want to read my web site article on Antenna Matching, and the one on Auto-Couplers.
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