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Old 07-08-2008, 07:10   #1
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SSB: auto vs manual antenna tuner

Most Marine SSB stations use automatic antenna tuners. However, some members of my local radio ham club claim they would never use one on their HF rigs.

Obviously, in an emergency, you may not have the time for manual tuning (although it apparently is mostly done in under 30 seconds).

But, setting aside the advantage of saving tuning time, is there any other advantage an automatic tuner has over a manual tuner (if both were of the same price/sophistication)?

A related but not identical question, is the following: if your use is purely long range communication on the amateur bands, would you prefer the versatility of a good manual antenna tuner over an equivalently priced automatic?

Martin
(My situation: I've acquired an Icom M802 and have to choose between an Icom At-140 auto tuner versus a good quality manual Yaesu tuner)
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Old 07-08-2008, 07:43   #2
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One argument in favor of the auto-tuner is space; not always readily available at the nav station. So, if space isn't an issue for you, I'd recommend a manual tuner for the following reasons:
1. more reliable (the amount of money I made while out cruising derived primarily from fixing auto-tuners, primarily the SGC stuff),
2. for primarily amateur band use as you said, you aren't qsy'ing that much/ that frequently,
3. more precise tuning capability,
4. generally more rugged components
5. just as quick to tune if you have presets written down.
6. makes one feel less like the proverbial "appliance operator".
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Old 07-08-2008, 08:05   #3
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I agree with S/V Illusion and add:
1. The tuner should be mounted close to the antenna (in most instances) so a manual tuner may not be practical in some setups.
2. If one really is an "appliance operator" then a auto-tuner is more appropriate.

Also some (many?) marine operator only know (knew?) enough about RF principles to get the radio operators certificate and as such, the auto-tuner is the best solution.
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Old 07-08-2008, 08:45   #4
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While I agree, in principle, with several of the above comments, I would have to say that for most sailors an autotuner is the way to go.

1. As was mentioned, the tuner for an end-fed long wire antenna (i.e., an insulated backstay) belongs at the base of the antenna...as close as you can get it. On many cruising boats -- excepting those with their radios located in aft cabins -- this just isn't practical with a manual tuner.

2. Related point: the antenna begins AT THE TUNER, so all of the wire leading from the antenna lug on the tuner to the backstay or other antenna is an integral part of the antenna. In other words, it is a radiating part of the antenna system, and having it anywhere except above decks in the clear is gonna result in some loss of radiated signal.

3. Autotuners do, indeed, break down for many reasons. However, with a good installation and proper care, they can be quite long-lived (my SG-230 on the boat is almost 20 years old and still works perfectly). I have another SG-230 at my home QTH and it works perfectly, too.

4. IF you're a ham or anyone more than an "appliance operator", it's not a bad idea to carry a manual tuner aboard. I have a manual tuner, in addition to the wonderful SG-230 auto tuner, for backup and for use with antennas other than the backstay if I so choose.

5. No manual tuner you're likely to carry on a boat is going to return to the same low SWR just by "noting the numbers". Even the cheaper roller-inductor tuners with counters won't do this. They'll come close, and building a table of approximate settings for each desired band is a very good idea, but you very likely will have to tweak the tuner each time you use it to ensure low SWR.

Final note: The Icom M802 is notoriously intolerant of even a slight mismatch. I certainly wouldn't want to be fooling with a manual tuner hooked to an M802 in an emergency situation.

Bottom line, IMHO nothing beats the convenience of an auto tuner, nor can you equal it's efficiency using a manual tuner located far from the base of a backstay antenna. Nevertheless, if you're an active ham or an interested techie, by all means carry a good manual tuner aboard. If you're cash strapped, start with the manual tuner and, when funds permit, graduate to a good auto tuner later on.

Bill
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Old 07-08-2008, 09:04   #5
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Sildene - Thanks for asking this question. I had been wondering thi also but I am not close enough to HF installation to ask yet.
Great information here and confirmed my basic idea.
Thanks
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Old 07-08-2008, 10:45   #6
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Our Icom 710 with the AT130 autotuner has worked flawlessly for many years without any attention from us.
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Old 07-08-2008, 10:59   #7
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I don't know about boats and their changing locations, but my manual tuner at home, I simply took about 10 minutes one day, went through all the ham bands, and wrote down tuner settings for all of my most used frequencies. Now, when I want to talk, I simply sit down, tune to the frequency, set the tuner according to my little chart(or by memory if it's one I use ALOT) and go, it takes about 5 seconds. tuning without the chart still would take less than a minute. probably 30 seconds like you said, if you know what you're doing.

As long as my antenna doesn't change, the chart seems like it has held true over a year's time.

Also, my tuner is located at my radio, a good 100 feet from the antenna in a tree outside. I've yet, to see anything over 1.5:1 swr if I'm tuned according to the chart. 1.1-1.2:1 is much more common. Granted, I only run 100 watts, and if you ran more, you might need more precision, but my little 80 dollar MFJ tuner works just fine for me.
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Old 07-08-2008, 12:21   #8
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All good points. No auto tuner can tune as precisely as a manual one and given that good design practice dictates the feed wire be as short as practicable, locating the tuner isn't really a significant issue. It's far more crucial given today's poor propagation conditions and low output power to achieve the best match to the antenna possible with the minimum of loss. When choosing any tuner, one should pay more attention to it's design and inherent loss characteristics than any other criteria and therein lies the biggest mistake many people make - most auto tuners insert loss compared with a good roller inductor manual tuner which has much less.
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Old 07-08-2008, 13:59   #9
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Quote:
Originally Posted by sluissa View Post
Also, my tuner is located at my radio, a good 100 feet from the antenna in a tree outside. I've yet, to see anything over 1.5:1 swr if I'm tuned according to the chart. 1.1-1.2:1 is much more common.
Yes, but that swr is between the radio and the tuner. You can still have very high swr on the transmission line between the tuner and antenna. And on a boat with backstay and ground plane inadequacies, there can be very high votage nodes on that transmission line. Not saying it won't work, but there will be losses and possible damage to the coax feeding the antenna. Many home stations use ladder line to feed their antenna's to minimize these problems when using a single antenna on multiple bands, but that's not very do-able on a boat.

Eric
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Old 07-08-2008, 18:54   #10
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SWR

Talking about SWR, I note (SG-230 Smartuner) that the automatic tuner SG-230 mentioned in some posts, has the spec " SWR Typical: less than 2:1".

From what I've seen, the Auto-tuners do not appear to have an SWR display, so how would you know your communication problem is due to a poor impedance match (e.g. it may be higher than 2:1, but you wouldn't know). Do you ever use a separate SWR meter with auto-tuners, or is there no point?

Re. manual tuners, assume you have an SWR meter situated at your transmitter, followed by a manual tuner and coax feeder from the nav station to the backstay base (say 4-5m).

If you now achieve an acceptable SWR (say 1.5 to 1), is this not what the transmitter sees? Does the fact that the antenna tuner treats the 5m feeder line as part of the antenna, mean that the SWR on the dial near your transmitter is not valid?

Martin





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Yes, but that swr is between the radio and the tuner. You can still have very high swr on the transmission line between the tuner and antenna. And on a boat with backstay and ground plane inadequacies, there can be very high votage nodes on that transmission line. Not saying it won't work, but there will be losses and possible damage to the coax feeding the antenna. Many home stations use ladder line to feed their antenna's to minimize these problems when using a single antenna on multiple bands, but that's not very do-able on a boat.

Eric
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Old 07-08-2008, 19:05   #11
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Martin
That usually means the tuner can not deal with mismatches which present an SWR greater than 2:1 (nor can the transmitter). An SWR meter is essential to determine if and how well the tuner is managing the load, regardless of whether it is manual or auto but obviously necessary in order to use a manual tuner. You struck upon an important point in that the SWR meter indicates reflected power at the point at which it is inserted, not at the antenna feed point. In theory, the meter should be inserted at the feed point but the impracticability of doing so results in the next best (read - convenient) place. With a single wire feed (not coax), the SWR is critical only in that the transmitter "sees" an acceptable load. If it does, all the power will be transmitted to the feed wire and antenna regardless of the SWR there.
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Old 07-08-2008, 19:43   #12
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There is a great solution for the remote SWR measurement - the Wavenode WN-2. It can accept four remote sensors and display basic info for each on its own LCD... and is less power hungry by far than the other digital ones on the market (though more so than the cross-needle type that does not do remote measurement). It also has a USB interface and corresponding PC program for serious graphical antenna analysis, but I have not tried that yet.

One is going into my comms console, with three probes in use.

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Old 07-08-2008, 20:18   #13
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The subject of SWR as it relates to transmission lines (which carry power from the transmitter to the antenna) is extremely complex.....way beyond what could be presented here.

There are electronics and radio engineers who make their whole careers out of designing, testing, and re-designing transmission lines.

A good non-technical primer can be seen amongst the articles on the ARRL website:ARRLWeb: Transmission Lines/SWR
The next-to-last article entitled, "Let's Talk Transmission Lines" is a good place to start.

Here's one attempt to reduce an extremely complex subject to the simplest terms for a sailor:

1. Modern HF transceivers expect to see an antenna impedance of 50 ohms. Anything more or less than that -- a mismatch -- will cause them to reduce power or otherwise misbehave.

2. Every antenna has a characteristic impedence, composed of complex resistances, capacitances, and inductance. Almost NEVER is that impedence exactly 50 ohms. Depending on the antenna design, and on the frequency and other factors, it can be almost anything...from very low to very high.

3. In order to make the transceiver happy, it is somehow necessary to transform the impedence of the antenna system to the 50 ohms the transceiver is looking for. On a boat, this is normally done by inserting an antenna tuner somewhere in the transmission line between the radio and the antenna.

4. With the characteristic insulated backstay antennas employed on sailboats, the best place to put such a tuner is very near the base of the backstay. Then, a short length of highly insulated wire (GTO-15) is used to connect the tuner to the backstay. That wire is also a part of the antenna.

5. A transmission line, usually a coax cable, is then used to connect the tuner to the transceiver. It's length is relatively immaterial, since if the tuner does it's job well, the impedence will be transformed to 50 ohms AT THE TUNER, and all along the coax between the tuner and the transceiver there will be a very low SWR.

6. Placing a tuner -- manual or automatic -- close to the transceiver, or even in the transceiver itself, will work OK in that it will -- within reason -- take whatever impedance it finds on the transmission line and convert it to the 50 ohms needed by the transceiver. HOWEVER, it will NOT change the SWR on the transmission line itself between the tuner and the antenna, and very high losses can occur. Partly, these losses are due to high SWR and partly (or mostly) they may be due to the fact that the line between the tuner and the antenna is a radiating part of the antenna system itself. If some or most of that line is buried deep in the bilge or the bowels of the ship, radiation losses can be great.

7. IMHO, EVERY SSB installation should employ a separate, high quality power/swr meter with cross needles. This will give the operator a continuous visual check on the transmitted signal. It will show whether or not the transmitter is transmitting, and how much power is being put out. Simultaneously it will show the SWR, which is a proxy for how well the antenna system, including the tuner, is functioning. You want to see that needle on the left bouncing up high when you speak into the microphone, and you want to see the needle on the right moving only slightly, indicating a good match to the antenna. Anything else will tell you instantly that something is wrong.

8. Many transceivers have built in LEDs or LCD "bars" for power out and SWR. IMO these are insufficient to the task. I never trust them and, as they're not calibrated, they're like so many "idiot lights" on passenger vehicles, i.e., only a very rough indicator.

Sorry for rambling on so long.

Bill
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Old 07-08-2008, 21:26   #14
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I'm sure we all welcome rambling of such quality any day.

Thanks Bill, and other posters, for taking time to explain.


Quote:
...and all along the coax between the tuner and the transceiver there will be a very low SWR.
Bill, please correct me if I'm wrong as I work through this (just re-phrasing):

a) If the antenna tuner is successful, the input impedance it presents to the transmitter, is approx pure 50ohm (good, no reflections). The coax link between antenna tuner and transmitter will not spoil this nice match since the coax itself is rated to be 50ohm.

b) If the antenna tuner is unsuccessful, the input impedance it presents to the transmitter is a mismatch with 50ohm, and thus power will be reflected back to the transmitter (bad).

c) An SWR meter situated at the transmitter side, will always tell me whether condition "a)" or "b)" is present. One would expect that it should do this reliably notwithstanding the presence of any coax length between transmitter and antenna tuner.

Thus, if 'bad' things are happening beyond the antenna tuner, the SWR meter at the transmitter will tell you. When 'good' things are happening beyond the antenna tuner, the SWR meter will tell you. But in this 'good' case, it won't alert you to the fact that part of your output power is being lost in the wiring between antenna tuner and actual antenna.

Martin


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Sorry for rambling on so long.

Bill
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Old 07-08-2008, 22:43   #15
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Martin,

Yes, that's pretty much it.

Power/SWR meters should always be installed as close to the radio as practicable. In that position, they will then closely approximate the SWR as seen by the radio.

Note that a good (low) SWR is not synonymous with an effective antenna system. After all, a dummy load presents a 50 ohm pure resistive impedance to the transmitter, but it doesn't radiate much at all! Just generates heat :-)

Similarly, a good tuner -- manual or automatic -- can provide a decent match to your bedsprings, but that won't be a very effective antenna!

Basically, what you're trying to do is to transfer the maximum amount of power your transmitter can put out thru the transmission line and into the radiation resistance component of the total impedance of the antenna system, with minimal losses into other components (like the tuner itself, the transmission line, or the frequency-dependent R/C/inductive components of the total impedance of the system). This is a neat trick, and how successful you will be at doing this depends on a whole host of factors. Some of these you have a measure of control over, and some you don't.

If this sounds like a lot of gobbledegook and makes you despair, don't! In practice, it's all quite simple. If you follow the basic steps in installing your radio, tuner, antenna, and ground systems things will work out pretty well, and you won't have to lie awake nights worrying about all those electrons bouncing back and forth on your transmission line :-)

OK, time to take out the trash and hit the sack. Gotta tackle a recalcitrant M802 in the morning.

Bill
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