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Author Topic: Icom 746 Pro/Antenna Tuner  (Read 2204 times)
KB3OMJ
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Posts: 7




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« on: March 03, 2007, 01:44:45 AM »

First of all let me say I am a new ham in need of a radio.  I have been looking at the Icom 746 Pro.  Being retired I am a careful buyer - I don't want to make costly mistakes.  I know that Icom has had problems with earlier models, so I sent an email to Icom to make sure these issues have been addressed.  This is their reply:

From a Technical Support standpoint, we do not take very many calls
about this radio, and that speaks well of the design. Early on in the
life of the radio, we experienced some "teething pains" and since then,
the radio has been very solid. All radios require good installation
practices as well as good operational practices, but when done properly,
the radio is very solid and will provide excellent service. The internal
tuner is somewhat misunderstood in that it will tune your antenna nicely
provided that the initial mismatch falls within 3:1. Beyond that, the
tuner is not able to bring down an impedance mismatch over 3:1 and it is
not able to tune a long wire antenna. For that, we recommend either a
manual tuner or a long-wire tuner, such as our AH-4. I hope that this
will be helpful.

Because I plan to use a G5RV it looks like the internal tuner would be useless, as well it would be useless for a mismatch over 3:1.  If that is the case, why is this radio so popular?  I can buy the AH-4 external tuner, but would this cause a problem with the internal tuner?

I am asking for some good advice from those more knowledgeable than I.  If anyone can help me make a decision I sure would appreciate it.

Thanks,

Dick Williams KB3OMJ
Edinboro, PA
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N3OX
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« Reply #1 on: March 03, 2007, 09:20:56 AM »

On some bands, the G5RV is quite useable with just the internal tuner on the rig... you might want to look at:

http://www.vk1od.net/G5RV/

But, you're right that you won't be able to use it on all bands.

A wire fed in the middle with the AH-4 would be a good idea to get more bands... you'd want to put the AH-4 out as close to the antenna as possible for best results, and only use open wire line between the tuner and the antenna.

A good rule of thumb is that you want the antenna to be not much shorter than a halfwave at the lowest frequency of operation... around 3/8ths wavelength long is really the lower limit for good results... which is about 100-105 feet across 75/80m...

If you get the AH-4, you can disable the IC-746's internal tuner and just use the AH-4... you certainly wouldn't want to use them both at the same time.

The internal tuner is popular because sometimes it's very useful to be able to work into a 3:1 SWR... on 75/80m, for example, it takes a lot of work to build an antenna that stays below 2:1 SWR across the whole band.   The rig's internal tuner lets you operate a regular 80m dipole cut for the middle of the band across the whole thing and still keep the rig from folding back output power.  Internal rig tuners aren't designed for multiband antennas; they're designed to make matching your antenna a little less critical.

- - - - - -

Anyway, a good approach might be to get the AH-4 and put it at the end of the G5RV's matching section like VK1OD recommends above.  That should work reasonably well on *all* HF bands from 80m and up.

By the way, I grew up in Erie and my dad teaches at General McLane...

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K7UNZ
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Posts: 691




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« Reply #2 on: March 03, 2007, 01:12:59 PM »

If you are going to use a G5RV antenna, then you will need an external tuner.....period.  The antenna was designed for 20 meters, and has become a "multi-bander" because it will radiate on other bands through the use of a wide range tuner.  Bear in mind that a "tuner" does nothing to improve your antenna, it simply allows you to pump more power into the antenna.  Also, that twin-lead is not just a feed line, it is part of the radiating system and needs to be treated that way.  It radiates....

It has nothing to do with how good the '746PRO is....which by the way, is a very good radio.  I have one (hi).

A 3:1 SWR range is pretty much standard for any internal tuner, and will satisfy requirements for most multiband antennas.  But not something like the G5RV, which can exhibit 10:1, or higher, SWR on some bands.

I think you kinda have the cart before the horse, if you're trying to find a radio to match an antenna, especially one like the G5RV.

Keep in mind that the antenna connector on the radio was designed to work with a 50 ohn, unbalanced antenna system.

73, GL....Jim/k7unz
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KB3OMJ
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Posts: 7




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« Reply #3 on: March 03, 2007, 01:39:08 PM »

I may have given the impression that the G5RV was what was most important.  Allow me to clarify.  I really like the 746 Pro.  I was advised by a few friends that it was a good radio especially with the power supply thrown in. I brought up the G5RV because I have considered that antenna, and a few folks I know swear by them.  I am not locked in to one.  I should probably had more questions about the actual radio than the antenna due to problems with older 746's.  From what I have read in the product review section it is a very good radio.  

What antenna would be your choice if you were to buy this radio?

Regards,

Dick Williams
Edinboro, PA

General McClane is about 2 miles from me.
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K7UNZ
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Posts: 691




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« Reply #4 on: March 04, 2007, 05:57:37 AM »

Yep, the '746pro did have some "teething problems", not unusual in today's radio market, but a current model will have had all of them corrected.  Actually, that's one reason most guys don't rush out to get a "new" radio when it's introduced (hi).

As for the '746pro, after looking long and hard, I am very happy with mine.  Bought it about a year ago. I consider it to be a '756 without all the glitz and glamor of color display and chromed knobs.  If my FT-990 (which I've had for 16 years now) ever dies, then the '746 will take over as the main rig (hi)!

G5RV's do work well for a lot of people Dick, but as I said, you have to expect to use an external tuner.  But as with ANY antenna, one size does not fit all.  If that were possible, we would all be using the same antenna.  The fact is that what works great in one location may be a total dud in another.  I wish I could answer with something more difinitive, but it depends so much on YOUR local situation that I really can't.

73, Jim/k7unz
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N3OX
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« Reply #5 on: March 04, 2007, 08:34:47 AM »

The IC-746 is a fine radio, and I think they have worked out the bugs.  

As it turns out, the antenna is often more important than the radio, as long as the radio isn't limiting what you want to do.  And, if you don't have a good antenna, all radios, no matter how nice, are useless.  

That means the question below doesn't have a simple answer:

"What antenna would be your choice if you were to buy this radio? "

A G5RV is a *fine* start.  Get one and get on the air. It won't tune on all bands. On some of the bands that it will tune, it won't work very well.  On some HF bands it will both tune to a 1:1 SWR using your internal tuner and work extremely well.

As K7UNZ points out, though, there is no one antenna that is the *best* antenna.

You just need to *start somewhere* and add antennas as you need them (or maybe you'll just be satisfied with the G5RV)

When I started at my parents' house in Erie, I started with a single 150 foot end-fed wire that went over the top of a tree.  I could tune it on all bands and make contacts.  I started to notice that 20m was the band I was on most, so I decided to try a dedicated antenna for that band, and I put up an inverted vee.  It was much better than the end-fed wire on 20m, so I kept it.

I continued this process for different bands over the next few years of high school and summers between college semesters.  By the time I moved out at the end of college, I had a tribander on a 30' tower for 10-15-20, a 2 element yagi for 12m, a rotatable quad loop for 17, a sloping dipole for 30m, a full-size groundplane vertical for 40m and an inverted vee for 80m.  The original 150 foot wire had retired when I put up the beam.

Then I moved to Maryland and was living in an apartment, and gave up ham radio for a little while.  I wanted to get back on, so I started with an end-fed wire about 40 feet long ;-)  I went through a couple of cycles of improvement at the apartment, too, but what I ended up with was a simple hundred-foot dipole fed in the center with a remote tuner.  I had to keep my antennas invisible because I wasn't allowed to have them, but I still spent time improving my antenna system until I thought it was good enough.

The point is, you have to do what your operating habits dictate and space, budget, and restrictions allow with your antennas.

You might put up a G5RV and find that you have tons of fun with it and you need nothing more.  You might find, like I did, that you want to work lots of DX and you'll end up constantly improving your antenna system.  

- - - - - -

The IC-746 plus a G5RV is a good starter station, either way.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
HAMMERTIME
Member

Posts: 176




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« Reply #6 on: March 05, 2007, 07:02:29 PM »

Let me say that the 746 Pro is a fine rig, at least so far. I have had mine for a year now.
 With that said, unless you have antenna restrictions at your property, I would take the $1500.00 and spend it differently than just using it all on the 746 Pro.
  I would buy a few sticks of Rohn tower sections and the necessary foundation items, a used tribander of some type,( These can be had for a couple of hundred bucks normally) a used/inexpensive rotor,and some new feedline and rotor cable.
  I would save about $300 for a used older rig and get on the air that way. You will enjoy making alot more contacts that way.
  But, if you can't do that for whatever reason, get you a Hustler 6BTV from DX Engineering and put a great radial field under it and skip the G5RV all together.
  The more radials you lay out, the narrower the bandwidth will be on the Hustler but I think you will find the 746's tuner will tune the band edges just fine except for 75/80 meters. I had a G5RV and it does not compare to the Hustler verticle in A/B comparisons at my location.
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BOOKERGLOVERN5ARA
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Posts: 4




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« Reply #7 on: March 11, 2007, 07:35:35 PM »

Hi
The others have addressed the antenna(s) issues and such. I too have the 746pro. I use it with an  LDG-z100 external tuner. I use the external tuner first, then turn on the internal tuner, and finish the job that way. The manual describes this I believe. Anyhow, I have a 43' vertical and had a mystery wire/coax antenna up (until recently for 160m) and I tune well to almost all bands and areas I desire.

Limited space here for antenna's so a tuner is a must. As for the 746, it's a winner in my book.

Best wishes and welcome.
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N1QKH
Member

Posts: 27




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« Reply #8 on: March 12, 2007, 07:15:17 AM »

I bought a 746Pro in 2001 and used it with a G5RV. The 746Pro has given good service and I would buy another if I had it to do over again.

Later on, I took the coax out of the G5RV (at 65 feet elevation) and fed it with ladder line via a 4:1 balun, using the internal tuner in the 746Pro. This worked on (all bands) 75m and above. This simple upgrade made the G5RV work a lot better on 17m and on 75m. When doing this upgrade, you need to take care not to let the ladder line be a 1/4 wave length at some frequency you want to use (adding a bit of ladder line or taking some away will fix the problem if one particular frequency is hard to tune. Many hams, I have talked to, have started out with the G5RV and then gone to the 75M dipole, fed with ladder line. This setup is easier for the internal tuner in the 746Pro to drive.

Either way, this will get you on the air and you will have no problem working all over the US and overseas, even with the not-so-good sunspot conditions we have, right now.

73 de Don N1QKH
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K4SC
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Posts: 26




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« Reply #9 on: May 09, 2007, 10:12:38 AM »

You have probably already made your decision by now, but I thought I would address your question anyway since my experience directly relates to yours.

I purchased a 746PRO in March of 2006 along with a G5RV.  The G5RV is installed at an elevation of 55' on the ends and the ladder line hangs straight down, perpendicular to the earth.

I have had absolutely fantastic results using just the internal tuner on all of the 80/75, 40 and 20 meter bands.  By that I mean it not only tunes but results have been great.  I have heard others say it won't tune on 30 meters, but I am able to get a match and have made some contacts there as well, although I have no basis for comparing my results with any previous experience on 30 meters.  As far as 15 & 10 meters goes, I have not seriously attempted anything up there, yet.  I have even loaded it on 6 meters successfuly, but recently put up a 4 element yagi and can see that even though I get a match, the antenna is not performing well there.  Much of the ability to match though is a result of coax losses.  In my case I am running 100' of RG-8X.  I previously ran approximately 70' and did have some matching issues.  Therefore even though the antenna loads on all bands,it is not really effective.  This is why I state the results on 80/75/40/20 are very good, but won't extend that claim to the others.

As for the radio itself, I am very pleased with it's performance.  I wouldn't consider buying any radio for serious use that didn't have IF DSP.  Many have Audio only DSP and they are not in the same league.  I use mine for digital modes a lot, and it is very handy to be able to overcome the AGC action caused by strong sitnals by customizing the pass-band with the twist of the dual-passband knobs.

I do not have as high a praise for the PS-125 supply they are giving away with the radio.  Mine died within a month and had to be replaced.  In the interim I bought a standard 30 amp (non-switching) power supply and am still using it.  The PS-125 is a backup now.

Hope you are enjoying whatever you ended up with.
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