Antenna trap

Hello, don't really know a thing about antenna traps except they isolate parts of an antenna and there a parallel resonant circuit that uses an inductor and a capacitor. I will read up more on them.

I'm wondering if I could use a receiving/transmitting 11 meters antenna along with a antenna trap to reduce the length of the antenna by cutting off about a foot of the end of the antenna, that way I could use the same antenna on 10 meters as well?

It would be a mobile dipole antenna 1/4 of a wavelength.

If that's how traps work then couldn't a person use say some type of slider trap on say a full wavelength 1MHz antenna and get it resonant on every band above it?

In theory a 10m trap would end a 10m antenna at a 1/4 wavelength and allow another short section to resonate on 11m but in the real world the two bands are too close together for that to work.

The two closest bands I've combined with a trap are 17m and 20m where I have a resonant 1/2 wavelength wire for 18.13MHz then a 17m trap then about two feet of wire to resonate the entire length around 14.25Mhz. Since my antenna is using half wavelengths, the wire after the trap is twice as long as if the antenna was 1/4 wavelength, so there would only be about 1ft of wire after the trap if I started with 1/4 wavelength.

In the case above that 1ft of wire is to add an additional 3Mhz or so to an 18Mhz antenna but for a 10m/CB antenna you would only be adding a little over 1Mhz, so the additional wire length might just get lost.

There are ways to broad band an antenna but I'm not sure what the best method would be for CB/10m. Maybe a 4-6" wide metal bar at the feed point that would accept two 1/4 wave whips each tuned to the different bands? Or you could just get the Laird CW27 base loaded NMO antenna that does cover both bands with no tuning and it works very well. They are usually expensive but I just bought another one used off Ebay for about $9.

Driverj30t9 said:

Hello, don't really know a thing about antenna traps except they isolate parts of an antenna and there a parallel resonant circuit that uses an inductor and a capacitor. I will read up more on them.

I'm wondering if I could use a receiving/transmitting 11 meters antenna along with a antenna trap to reduce the length of the antenna by cutting off about a foot of the end of the antenna, that way I could use the same antenna on 10 meters as well?

It would be a mobile dipole antenna 1/4 of a wavelength.

If that's how traps work then couldn't a person use say some type of slider trap on say a full wavelength 1MHz antenna and get it resonant on every band above it?

Click to expand...

prcguy said:

In theory a 10m trap would end a 10m antenna at a 1/4 wavelength and allow another short section to resonate on 11m but in the real world the two bands are too close together for that to work.

How come the 11m and 10m bands are to close to work with a trap?

I would want to use 26.965 to 27.405 and 28.000 to 29.700 .

The two closest bands I've combined with a trap are 17m and 20m where I have a resonant 1/2 wavelength wire for 18.13MHz then a 17m trap then about two feet of wire to resonate the entire length around 14.25Mhz. Since my antenna is using half wavelengths, the wire after the trap is twice as long as if the antenna was 1/4 wavelength, so there would only be about 1ft of wire after the trap if I started with 1/4 wavelength.

That would be a nice antenna to have.

There are ways to broad band an antenna but I'm not sure what the best method would be for CB/10m. Maybe a 4-6" wide metal bar at the feed point that would accept two 1/4 wave whips each tuned to the different bands? Or you could just get the Laird CW27 base loaded NMO antenna that does cover both bands with no tuning and it works very well. They are usually expensive but I just bought another one used off Ebay for about $9.

Click to expand...

Sounds like the metal bar and the whips in such close proximity to each other would detune the antennas.

Can't use a NMO mount because I don't want to put any holes in my company truck. Maybe Laird has a mag mount antenna or mirror mount antenna with that frequency range.

Can mirror mount antennas be base loaded or are mirror mounts only center and top loaded?

Also have you heard of anyone using dipole antennas with coils in them to cut down on the space an antenna takes up? Figure I might as well ask well I'm at it here.

Gonna have to look up ways of broadbanding an antenna then if I can't use that trap or find the right commercial antenna.

antenna trap

An antenna tuner is all you need for an 10-11meter antenna.

The easiest, cheapest way to go would be with the Hustler system.

You install a mast, that has threads on the top. There are resonators (or coils) for all the bands from 80 to 6 meters. You screw on a resonator for the band you want to use on top of the mast.

https://www.dxengineering.com/searc...toview=SKU&sortby=Default&sortorder=Ascending

Pick up a mast and an RM-10 and RM-11 resonator. Swap them out for 10 and 11 meters. If your license class permits, you can buy more resonators and work down to 80 meters.

I run the Hustler system on my Jeep Wrangler. I have a 54 inch mast and resonators for all the amateur bands from 80 to 10 meters. The system works well.

When designing a dipole with traps, the traps become a 'loading coil' bellow their resonant frequency. I would guess any trap for 10 meters would add too much inductance for an antenna to be resonant on 11 meters. Traps are a better solution when you have more 'room' (as a percentage) between the bands in use. As an example, the five (non WARC) ham bands are at least about 50% of the lower frequency to the next band and often double. That makes for a lot more wiggle room.

Quarter wave verticals with a trap almost at the top would tend to be top heavy and wind loading would also be an issue.

Keep asking questions, they help learning and are free.

10 and 11 meter antenna

Some ant has loading coils with adjustable taps . Just slide the tap for the band you like.

Hi Driver
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I am not quite sure if I am reading your question correctly...you want to use a 10/11 metre Dipole as a mobile antenna?. That's quite an animal- I think you meant a quarter wave, electrically shorten'd vertical.
However far as a true dipole antenna goes, as PRC pointed out, the frequency difference between 27 and 28 Mhz is so close that, while in theory traped elements can be inserted, it probably won't make any real life difference in how the antenna preforms. Also home made traps have to be proofed against the elements and tuning them is not always as easy as the books make it seem.
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I would suggest a compromise- if its a full half wave dipole you're after, cut it for resonance somewhere between the two bands - say 27. 8 Mhz., and see what the SWR is. Remembering this is a compromise, so don't expect a 1:1 SWR- but if its less than 2:1 it should be fine. Even at 2:1 you're looking at only an approximated 10% reflected loss- no one will hear that. Play around with that resonance number.
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You might try a "fan' design; place a 10 meter dipole, insulated, a few inches below one on 11 metres-- tying them in at the same point on the dipole's centre insulator. This will broadband the design, but makes for a more awkward antenna mechanically. There are exotic variations on this theme, keeping in mind that as you increase the diameter of the radiator, you shorten its over-all length and broaden its bandwidth.
Have you a section of six inch irrigation pipe?... I'm not being Entirely facetious, but I hope you can see what I'm getting at.
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Shortening a mobile vertical and making it dual band is more of a challenge. Challenging electrically and, to me- mechanically. Again, before I'd get too involved in redesigning my antennas, I'd try that compromised centre resonance frequency.
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I like JWT's suggestion- if you want dead-on 1:1 SWR's, get a Hustler mobile antenna and two resonators-- I personally love Hustlers- I have a modest 10 foot vertical back n New Mexico that I use on 60 metre's (mostly) with a Hustler resonator- Changing bands takes less than 5 minutes- I just change the resonators.
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Hope this give you some alternative ideas...
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Lauri
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Ahhh that's right, an antenna tuner. Read about them a while ago but apparently that knowledge didn't stick. So traps are out of the question. I don't want to use the laird antenna because it's not the right type of mount. Sounds interesting using those resonators or an antenna with loading coils and taps but then I'd have to fiddle with the hardware, that would be fun when it's -30 below, or when I'm driving and don't have time to stop. So sounds like an antenna tuner would be the best option. I could write down the right dial settings on the tuner so I could turn a few knobs to the right settings and adjust while I'm driving. Or like what Lauri was saying maybe make a compromise between the two bands, I'm okay with a 2:1 ratio.

As an example, the five (non WARC) ham bands are at least about 50% of the lower frequency to the next band and often double. That makes for a lot more wiggle room.------- What did you mean by 50% of the lower frequency to the next band and often double? Can you give an example?

I am not quite sure if I am reading your question correctly...you want to use a 10/11 metre Dipole as a mobile antenna?. That's quite an animal- I think you meant a quarter wave, electrically shorten'd vertical.

UGHH, I gotta make sure to use quotes on here.

Yeah that's what I should of said, I want to install a quarter wave antenna, actually dual antennas on my truck, and then also have an element pointing downward under the 1/4 wave antennas to act as a ground plane and radiator. Won't be able to make the downward pointing antennas to long, maybe three or four feet. So not really a dipole but sorta similar physically. Not my idea, prcguy said it works well for him though so I"ll give it a try. Didn't know increasing the diameter decreased the electrical length. Hmm.

The antennas I'm thinking of installing ARE dipoles too though, they have two poles or elements going in opposite direction from each other. Although it would be a vertical dipole, not the more typical horizontal, at least I'm pretty sure horizontals are more common. I don't know if they"ll be exactly in line though with each other with the mount, and there not going to be totally symmetrical or a 90 degree wavelength on each side.

Those fan designs are neat, something to look into. I have some old plumbing pipe laying in the garage that the people that use to live here left, I've been wondering if I could find some use for for radio. I think I get you, just experiment around with stuff.

Probably challenging for most people dual banding an antenna by trimming it. Outdoor setup would be interesting. I basically have a fear cage around my place though with telephone wires.

Hey Driver.....
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You have the right idea- experiment !
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While some sort of counterpoise on the other side of a mobile's vertical antenna is a possibility, I have never seen a real life example. The body of your vehicle provides about as good of one as you can expect. Even if its not optimum, as in a mirror mounted vertical, it will still work pretty well.... all things consider'd
Anything mobile for 10/11 metre's, excepting maybe a 108" roof mount'd whip, is going to be a big compromise anyhow- But put the losses into perspective- its going to take over 12 dbs of loss before anyone will hear it, real world. I think the important things are mechanical stability, then esthetics, then performance... buts that's me. I would rather have an antenna that is not going to fail due to some Mickey-Mouse construction- and I certainly don't want it to draw attention like I'm trying to be some sort of Ghost Buster's tactical vehicle.
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Also be careful of using antenna tuners. I'm not saying they don't have their place, but keep in mind if you put one between your transceiver and the coax running to your non-resonant antenna, you are just kidding yourself with that supposed 1:1 perfect match. That coax and antenna are not working as a resonate unit. The tuner makes the transmitter THINK it is, but you dissipating power in heating up it, and the coax - not in radiating a signal.
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Unless you are placing that tuner at the very base of your vertical, and making it part of the the antenna-the total coax fed assemble, -- then strive to have the antenna resonate on its own merits-- no short cuts....
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Lauri
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Most multi band antennas for the ham bands in the 'old' days were five band (think 80m-40m-20m,15m,10m). The ham bands above are harmonically related (40 is the 2nd harmonic of 80 3.5Mhz*2=7Mhz ect). -That makes tolerance for antennas and traps quite a bit easier as the trap does not have to be tuned as 'tight'. When working with 11 meters (27 Mhz) and 10 meters (28 Mhz) you are talking about frequencies that are only separated by about 4%-much more difficult than 50% (or more).

It would actually be easier to make a 'trap' that passed both 11 and 10 meter signals than one which would
completely 'stop' 10 M and completely "pass' 11 M.

You have the right idea- experiment !

Exactly. Part of the fun of the hobby.

While some sort of counterpoise on the other side of a mobile's vertical antenna is a possibility, I have never seen a real life example. The body of your vehicle provides about as good of one as you can expect. Even if its not optimum, as in a mirror mounted vertical, it will still work pretty well.... all things consider'd.

Neither have I seen one, neither have I. Perhaps there won't be any discernable difference, but I'm going to try 1/4 whips with and without a counterpoise because prcguy said he noticed the quarter whips with the counterpoise improved the signal strength noticeably.

Anything mobile for 10/11 metre's, excepting maybe a 108" roof mount'd whip, is going to be a big compromise anyhow- But put the losses into perspective- its going to take over 12 dbs of loss before anyone will hear it, real world. I think the important things are mechanical stability, then esthetics, then performance... buts that's me. I would rather have an antenna that is not going to fail due to some Mickey-Mouse construction- and I certainly don't want it to draw attention like I'm trying to be some sort of Ghost Buster's tactical vehicle.

I think the important things in a setup for me would be probably in the same order, maybe performance coming before asethetics though. I don't know, I think 1/4 whips with a radial might look cool, guess I don't really care if people would be checking them out.
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Also be careful of using antenna tuners. I'm not saying they don't have their place, but keep in mind if you put one between your transceiver and the coax running to your non-resonant antenna, you are just kidding yourself with that supposed 1:1 perfect match. That coax and antenna are not working as a resonate unit. The tuner makes the transmitter THINK it is, but you dissipating power in heating up it, and the coax - not in radiating a signal.

You are correct on the placement of the antenna tuner. Thanks for reminding me about that. I may have forgotten and been thinking my SWR was all roses. I think I"ll use automatic antenna tuners at the base of the antennas. Guessing I need two of them since it will be a dual antenna mobile installation. I've heard of issues with blown front ends using those auto tuners and I'm not sure how close to an antennas resonance frequency they can work at. I will use a SWR bridge as a precaution.

wyShack said:

Most multi band antennas for the ham bands in the 'old' days were five band (think 80m-40m-20m,15m,10m). The ham bands above are harmonically related (40 is the 2nd harmonic of 80 3.5Mhz*2=7Mhz ect). -That makes tolerance for antennas and traps quite a bit easier as the trap does not have to be tuned as 'tight'. When working with 11 meters (27 Mhz) and 10 meters (28 Mhz) you are talking about frequencies that are only separated by about 4%-much more difficult than 50% (or more).

Okay I get what your saying now. How come most multi-band antennas were 5 band in the days of old?

Click to expand...

Antennas have the ability to resonate on multiple frequencies. But just because they can, does not mean their radiation patterns will be the same. That in itself is another highly involved topic
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But as a safe rule of thumb, an antenna will resonate on odd multiples of its primary frequency. For instance, a 7Mhz. vertical will work on 21Mhz, but not work on its even multiples; 14Mhz, or 28Mhz.
I don't know how, based only on harmonic relationships, you could 5 bands out of one antenna with out traps- but I hope this gives you some ideas.
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One thing that does happen operating on higher harmonics is he bandwidth expands. Thus it MAY be possible to use a 40 metre antenna on both 15 and 12 with acceptable SWR's.
I have a 60 metre (5.4 Mhz) vertical that has a perfect SWR of 1.0:1...but it also works well on 17 metre's (18.1Mhz) with an SWR of 1.5:1. All this, despite the fact its not exactly the 3rd harmonic.
You'll find there's more to these beasts than meets the eye....
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I'll leave you with this other way of thinking about antennas-- this is my favorite perspective, anyhow.
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Think of them in degrees of a Sine Wave. A full wavelength is 360 degrees... a quarter wave vertical is 90 degree's, a half wave is 180, etc. Now think the current's path along the antenna... to have a perfect transfer - ie: "radiation," that flow must complete a 360 degree journey- from base to antenna tip back to the base. If it doesn't come out 360, then you don't have resonance.
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An example: A quartewave vertical is 90 degrees (a "90 degree antenna")- forward flow is 90, there is a reversal at the end which for all practical purposes can be assumed as 180 degrees, and the reverse flow back to the base, another 90 degrees.
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90+180+90 = 360 degrees ------------->> Resonance
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As long as the numbers add up to multiples of 360, your fine... but try out those figures for a half wave vertical......
180+180+180 = 540 degrees -------- >> This is not resonant- and why half wave vertical are a mess.
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Please bear in mind this is a ***Very ! *** over simple explanation - and it does not take into consideration various matching schemes to make things come out 360's, nor the antenna's radiation patterns (for how else would a 5/8th wave antenna work ?)
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But I hope this sheds some light on multi-band'd antennas.
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Lauri
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Lauri-Coyote said:

180+180+180 = 540 degrees -------- >> This is not resonant- and why half wave vertical are a mess.

Click to expand...

Unless you add half-wavelength radials at the lowest freq, which become the other half of the antenna, and then you start to approach resonance - right?

I am a afraid I should have prefaced that I was referring to verticals, and re-assert that this is a general guide.

Lauri-Coyote said:

Antennas have the ability to resonate on multiple frequencies. But just because they can, does not mean their radiation patterns will be the same. That in itself is another highly involved topic.

Click to expand...

Was not aware of that. That will take some looking into. What's the jist of it?
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Lauri-Coyote said:

But as a safe rule of thumb, an antenna will resonate on odd multiples of its primary frequency. For instance, a 7Mhz. vertical will work on 21Mhz, but not work on its even multiples; 14Mhz, or 28Mhz.I don't know how, based only on harmonic relationships, you could 5 bands out of one antenna with out traps- but I hope this gives you some ideas.

Click to expand...

I always thought it was all the harmonics of a frequency that were resonant. Guess not. So how come it's odd multiples and not all multiples? They must have used traps for the five banders. That or a really long antenna?? I don't know much but I'm sure they had all the stuff they have now days, tapped coils, tuners and traps, hustler resonators, jk, but resonators, and perseverance plus ingenuity. Just wondering why most antennas were five band back in the day though when now they have lots of antennas for specific bands or dual or tri- band respectively.
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Lauri-Coyote said:

One thing that does happen operating on higher harmonics is he bandwidth expands. Thus it MAY be possible to use a 40 metre antenna on both 15 and 12 with acceptable SWR's. I have a 60 metre (5.4 Mhz) vertical that has a perfect SWR of 1.0:1...but it also works well on 17 metre's (18.1Mhz) with an SWR of 1.5:1. All this, despite the fact its not exactly the 3rd harmonic. You'll find there's more to these beasts than meets the eye....

Click to expand...

Why is it that bandwidth expands on higher harmonics? Sounds like a win, just more noise to deal with though. Nope it's a little more then the third harmonic. What would the SWR be normally if it's a 1.9MHz difference from the resonant frequency? I don't doubt you. .
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Lauri-Coyote said:

I'll leave you with this other way of thinking about antennas-- this is my favorite perspective, anyhow.
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Think of them in degrees of a Sine Wave. A full wavelength is 360 degrees... a quarter wave vertical is 90 degree's, a half wave is 180, etc. Now think the current's path along the antenna... to have a perfect transfer - ie: "radiation," that flow must complete a 360 degree journey- from base to antenna tip back to the base. If it doesn't come out 360, then you don't have resonance.
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An example: A quartewave vertical is 90 degrees (a "90 degree antenna")- forward flow is 90, there is a reversal at the end which for all practical purposes can be assumed as 180 degrees, and the reverse flow back to the base, another 90 degrees.
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90+180+90 = 360 degrees ------------->> Resonance
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As long as the numbers add up to multiples of 360, your fine... but try out those figures for a half wave vertical......
180+180+180 = 540 degrees -------- >> This is not resonant- and why half wave vertical are a mess.
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Please bear in mind this is a ***Very ! *** over simple explanation - and it does not take into consideration various matching schemes to make things come out 360's, nor the antenna's radiation patterns (for how else would a 5/8th wave antenna work ?)
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But I hope this sheds some light on multi-band'd antennas
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Lauri
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Click to expand...

It is improving my understanding of antennas. Thanks.

I might add that antennas will "resonate" on both odd and even multiples of its fundamental frequency but the impedance will be more usable when fed with low impedance coax on the odd harmonics rather than the even. If your discussing an offset center fed or end fed with matching transformer you can generally use the antenna on most odd and even multiples with a usable low VSWR.

As mentioned, the radiation patterns from the various combinations gets busy and deserves its own thread.

Thank you PRC....
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I needed someone to bring me back to earth--- I was drifting off into far too much...
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What I wanted was to present a simple way at looking at a quarter ground mounted vertical ('ground' as in the other quarter wavelength being "mirror'd" below the base) since this represents the majority of mobile antennas.
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A half wave vertical *can* certainly be resonant, but as said, it is not an easy antenna to match, especially with coax cables. The current at the feed point will be minimal, and voltage maximum and the input impedence off the charts. Its the odd multiples of a quarter wave that present these antenna's optimum base impedances for coax .... and that was my desired -- to present something useful real world without going overboard into antenna theory.
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The '5 Band Antenna' is a very popular concept. However, I think Driver, you are talking of wire dipoles here (though there are many multi- band verticals using similar designs.) Irregardless, you'll need to place 'traps' in them. I'll give you a "Coyote's" brief design description of one-- as if we were were building it together....
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Start with a half wave dipole approximating the physical length at 80 metres' (~3.6Mhz).... then place L/C 'traps' at the the half wave length of 40 (7.2Mhz.) Theses 'traps' will pass 80 metre's, blocking and resonating the shorter section to 40; On 20 thru 10, the antenna will be working on a capacitive reactance principle that I won't go into here (Heaven knows I done enuff damage).... - but it will work, and the SWR will be reasonable.......
.........................I'll let you explore that one.....

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Lauri
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Most of the time an antenna's SWR 'curve' is low for a few percent of the operating frequency-so the higher the frequency band the 'wider' in frequency(MHZ) terms. Many antenna designs (like multi band dipoles) used today have not changed for many years. The five band antenna likely is one from before hams got the 'WARC' bands in the early 80's. Physics don't change with time and while technology may change, the basic principles of electric and magnetic fields are the same as they always were.

Guess I am getting old-I remember the excitement of getting the 'new' bands and also the scary feeling knowing that a new 'rig' (a big chuck of cash back then) would be needed.

I have delite'd for years in re-discovering all things historical.
I think we too often sell ourselves short when we feel we must embrace the newest and latest. So true- the physics don't change- we just get better at understand her ( ) and develope the better toys to go along.
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I've mention'd in these forums before how my great aunt was a Marconi Girl... the very fact she could communicate to ships at sea with rotary spark and coherer receivers absolutely astounds me... yet I really wish she could see how far her great niece has come.... for I am sure we'd have so much radio to talk about in common.
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("So that is what a Valve is !.... we've been hearing about Mr. Fleming....... ")
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In the end, we are/were approaching the same science, just a little differently; .... our different eras....... What will my great nieces say of me?....lol
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You are hardly old, Wy.... with that heart you will always be a youth among the stars.
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Lauri