What's with not tuning Ham radio antennas?

SSTJ

SSTJ

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So, why is it that we don't have to tune our Ham radio antennas? Or our GMRS antennas? I assume it has to do with the higher frequency, in comparison to CB. But if so, how does the difference in frequency take away the need to tune?

I assume that one would have to tune a 10-meter antenna, since that's roughly the same frequency as CB?
 
CB guys need something to do. There is a good article about SWR that AARL published awhile back that explains why it isn't too important but the people that use CB don't really read much. If you have good cables there is almost zero drop in radiated power with poor SWR. At the extreme ends you can get odd echos but for short cable runs most people find close enough good enough. If you have really long cable runs or are building your own antennas and using high power it starts to matter but most mobile stuff is low power and short runs so it doesn't make much difference.
 
pagrey said:
CB guys need something to do. There is a good article about SWR that AARL published awhile back that explains why it isn't too important but the people that use CB don't really read much. If you have good cables there is almost zero drop in radiated power with poor SWR. At the extreme ends you can get odd echos but for short cable runs most people find close enough good enough. If you have really long cable runs or are building your own antennas and using high power it starts to matter but most mobile stuff is low power and short runs so it doesn't make much difference.
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Interesting. So, it's not that the difference in frequency makes tuning less necessary for VHF or UHF frequencies ... it's that tuning is never really necessary for most mobile rigs? I wish I had known that about a month ago when I scoured this forum for tips on how to improve my CB SWR ...

I'm going to hunt down that article.
 
I like and am a member of the ARRL but I don't always agree with some of the tech some people post there. I always tune for a good low SWR. For those who claim a high SWR on a CB (or ham) won't affect much, I disagree there too.

In fact, tell the CB manufacturers there's no problem with a high SWR and they'll disagree. Like Uniden, Cobra, etc. who had a spike in burned out CB radios returned under warranty during the CB craze in the 70's and 80's. The problem was that hardly anyone jumping on the craze knew anything about CB antenna installations or the need to tune them/check them with an SWR meter to make sure the antenna wasn't shorted dead to ground. Most of them had damaged final amplifiers (the transmitter portion) burned out from excessive SWR. That's when they decided to redesign the transmitters to add an automatic circuit to turn the transmitter power way down when it encountered a high SWR.

So if you don't think it's important to tune an antenna, that's your decision. It's not mine however, especially after learning how important it was during my 1966-1970 days in the Air Force working on/repairing ground and aircraft HF, VHF, and UHF radio systems. I had ample demonstrations of what a high SWR can do to a transmitter and heaven help you if you damaged a USAF transmitter from a high SWR after all the training on that subject. If there was one thing Air Force inspectors checked during pop inspections, it was the SWR levels on all of our antennas. And we had a lot of them since we had a separate antenna for each frequency in use, and there was a lot of them especially in air traffic control systems.
 
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@Jerry Bransford

Thanks for this. May I ask, then, what you think about my original question? Why do I see so much more emphasis on tuning a CB antenna than I do for a Ham antenna? For instance, I don't think I've come across a single "tunable" Ham antenna in my (brief) shopping experience so far, nor have I found any tuning recommendations in the manuals of my Yaesu dual-bander or my Comet antenna. Is it that the higher frequency makes it less of an issue? I haven't read the article linked above yet, but maybe it refers primarily to these higher frequencies?
 
You can tune any antenna. I just tuned a firestik 5/8 2m, basically the same as a cb. They come "long" by design, because it's easier to cut away than it is to add. I ended up cutting about 1.25" off.
 
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DEValken said:
You can tune any antenna. I just tuned a firestik 5/8 2m, basically the same as a cb. They come "long" by design, because it's easier to cut away than it is to add. I ended up cutting about 1.25" off.
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Thanks, and yep, that makes sense, especially for a Firestik antenna that's designed for frequencies so close to the CB range.

But what about these, for instance? There is no mention of tuning on the page, and they don't look 'tunable' by design, and I for one would be hesitant to start cutting them up.

Again, I'm not doubting that it's possible, nor even doubting that it's important (though I need to read Pagrey's article). I'm just confused by how much talk there is about tuning CB antennas, and yet I haven't come across anything similar in my shopping and setup of my Ham dual-bander. What am I missing?
 
SSTJ said:
@Jerry Bransford

Thanks for this. May I ask, then, what you think about my original question? Why do I see so much more emphasis on tuning a CB antenna than I do for a Ham antenna? For instance, I don't think I've come across a single "tunable" Ham antenna in my (brief) shopping experience so far, nor have I found any tuning recommendations in the manuals of my Yaesu dual-bander or my Comet antenna. Is it that the higher frequency makes it less of an issue? I haven't read the article linked above yet, but maybe it refers primarily to these higher frequencies?
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If you buy a VHF, UHF, or a dual-band antenna just note whether it was designed to be tuned or not. Some are, some aren't.

The same type of antenna when used for HF ham and CB in the HF frequency band need to be tuned in the same way.

Antennas on handheld VHF/UHF radios are tuned for the mid-points of the bands they're designed to be operated on so they don't need tuning.

That's true on most VHF/UHF mobile antennas too though many are made to be tunable. My 2m mobile antenna was made to be tunable so I tuned it. I have used other antennas with such a wide bandwidth like 6MHz (covers the entire 2 meter band) that they don't need to be tuned. They don't perform quite as well as one made to work into a narrower bandwidth so they're a bit of a compromise but they still work well enough for most needs.
 
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SSTJ said:
Thanks, and yep, that makes sense, especially for a Firestik antenna that's designed for frequencies so close to the CB range.
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144 MHz is not really close to 27 MHz. I guess they are both radio so that makes them close on some scale but one is HF and the other is VHF. The main reason antennas like 2M are tunable is because people trying to get maximum range out of an antenna on a particular frequency need to tune. For example if you are using 144 MHz vs 146 MHz and trying to hit a repeater hundreds of miles away small changes can make a difference. The whole point is for trail communications it doesn't make much difference. I know that article is pretty technical but that's why I'm trying to make it a little more down to earth. Reading the post from @Jerry Bransford it should be very clear where he is coming from and how that shapes his advice. The reality is most of us don't need MIL-SPEC and looking at what you see available now should help you understand why people using GMRS and FRS are less concerned with it. If the advice about blowing up a radio with poor SWR had any shred of truth to it there would be plenty of stories floating around about dead GMRS and CB radios. Fact is not may people even have SWR meters that work beyond 100 MHz so almost none of the 2M/70cm antennas get tuned. Again, there is nothing wrong with tuning, I'm just suggesting test it with a friend and if it works then forget about it and go wheel.
 
pagrey said:
If the advice about blowing up a radio with poor SWR had any shred of truth to it there would be plenty of stories floating around about dead GMRS and CB radios.
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Are you serious? If you knew transmitters, impedances, and how a mistuned antenna can cause excessive current flow through its final amplifier circuit you'd never claim that. A bad SWR can result in a range of impedances the transmitters is forced to work into. For example 5:1 on a 50 ohm coax can mean a range of widely varying impedance, and a range of complex impedances in between. Some of those impedances can damage the transmitter from pulling excessive current, others may not. But since the length of the feedline isn't known, it's safest to keep the SWR low.

The transmitter's final stage is made of reactive components, components that store and release energy (inductors and capacitors). Those reactive components are selected to absorb some of that stored energy. Without that load absorbing ability, the energy instead appears as a high voltage or high current to appear in a circuit that may not be equipped to handle it.

And yes it is true that there were a lot of CB transmitter failures. As I mentioned above, CB manufacturers during the 70's and 80's CB craze saw a huge rise in the number of CB radios that failed due to antenna/SWR issues. That is the reason modern CB radios now have automatic protective circuits built into them, manufactures designed them into the transmitters to avoid the huge numbers of warranty failures they experienced during the CB craze. Since you don't believe what I'm saying I'm not going to continue pushing this but it's true and it did happen. I was around before, during, and after all that happened.

Here's one of many antenna articles that discuss the potential for transmitter damage from an antenna issue including a bad SWR. http://radiohamtech.com/SWR myths and mysteries.pdf
 
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pagrey said:
144 MHz is not really close to 27 MHz. I guess they are both radio so that makes them close on some scale but one is HF and the other is VHF.
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🤦‍♂️ Thanks. I thought he said it was a 10m antenna.

And yes, I can see your point that, for trail communications, tuning may not be too important. Especially now that, as Jerry mentioned, the unit is designed to protect itself from damage.

But I do enjoy tinkering and maximizing range (at least for Ham), so I now wish I had bought a tunable antenna for Ham. I just didn’t happen to come across any, and thought they didn’t exist.
 
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Jerry Bransford said:
If you buy a VHF, UHF, or a dual-band antenna just note whether it was designed to be tuned or not. Some are, some aren't.

The same type of antenna when used for HF ham and CB in the HF frequency band need to be tuned in the same way.

Antennas on handheld VHF/UHF radios are tuned for the mid-points of the bands they're designed to be operated on so they don't need tuning.

That's true on most VHF/UHF mobile antennas too though many are made to be tunable. My 2m mobile antenna was made to be tunable so I tuned it. I have used other antennas with such a wide bandwidth like 6MHz (covers the entire 2 meter band) that they don't need to be tuned. They don't perform quite as well as one made to work into a narrower bandwidth so they're a bit of a compromise but they still work well enough for most needs.
Click to expand...

Thanks again. I guess that, so far, I’ve only been looking at dual-band antennas that just don’t happen to be designed to be tuned. And of course the same is true for my little hand-held.

I’m sure that as I explore more options (and more frequencies), I’ll come across more about tuning. Was just surprised and confused that I hadn’t come across anything yet.
 
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I have by no means seen every 2M antenna, but every mobile 2M or dual band antenna I have (quite a few for a project) has a set screw that holds the whip in the base.
That is where the tuning is accomplished.
Take the whip out and cut to the desired frequency and hope to not cut too much.

As fas as why you hear more about CB SWR than ham/amateur, my only guess would be that hams may have more exposure to tuning antennas and it is already something that they have done.
 
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