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Hands down best 2 meter base vertical antenna

Discussion in 'General Technical Questions and Answers' started by KI4RVY, Jan 10, 2007.

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  1. KI4RVY

    KI4RVY Ham Member QRZ Page

    Hopefully this is a good place to ask instead of starting a new post.

    What is the difference between Diamond's db rating and Comet's dbi? Both have simmular numbers but they are rated different.
     
  2. N0NCO

    N0NCO Ham Member QRZ Page

    WB2WIK,

    Yes, of course. When I sweep my antennas, I compensate for feedline losses. Good info - as many do not truly understand the physics behind antenna performance.

    Back when I taught RF engineering in college, I used to tell my students that a great match has little to do with antenna performance, and also that a matched condition has little to do with resonance. After all - dummy loads have a great match but don't resonate, and they make very poor antennas. An antenna can be perfectly tuned for resonance, but if it's a 300-ohm antenna, the match into a 50-ohm system will be 6:1.

    As far as the performance goes - the only antenna I was talking about is my broadband 2m/70cm mobile antenna, which is not lossy, but is quite broad-banded. I've made a number of controlled comparisons with it vs. my "high-gain" 2m/70cm whip. In-band, the "high-gain" whip easily outperforms it - however - when receiving, say, 10 MHz out-of-band or further, the broadband whip usually wins.

    73...

    Joel - N0NCO
     
  3. KG6YTZ

    KG6YTZ Ham Member QRZ Page

    In that case, personally, I'd be more inclined to trust Comet's number, given in dBi, or decibels over an isotropic radiator [a purely theoretical radiator, BTW, which emits a perfectly spherical pattern and thus has zero gain]. Diamond doesn't say whether its rating is dBi or dBd, or gain over a 1/2 [?] wavelength dipole, and that omission makes their number generally meaningless without a reference point for comparison. Gain over what?

    Zero gain dBd is, I believe, 2.2 dBi. In the real world, I'd say that dBd is probably more relevant and more useful than dBi.
     
  4. N0NCO

    N0NCO Ham Member QRZ Page

    KI4RVY,

    Some companies use dBi which is gain as compared to an isotropic radiator (spherical pattern), while others use dBd, which is supposed to be gain as compared to a dipole in free space. Others don't specify which reference they use. I don't know what standard of comparison Diamond actually uses - however, if they claim gain figures close to Comet's figures for antenna designs of the same wavelength - it's most likely dBi.

    I usually assume dBi, unless stated otherwise. Rating antennas in dBi isn't really cheating. In the engineering world, dBi is commonly used, since it is a well-defined standard of comparison. Satellite antennas are often rated in dBi, as well. To convert dBi to dBd, subtract 2.14 dB from the dBi rating.

    Various antenna manufacturers have had a long history of inflating Amateur antenna gain figures, although I think things are better now than they were in the past. Not all companies have inflated their numbers, but a number of them have done so over the years.

    Of course, there is no magic in antenna design. One manufacturer's 5/8-wave whip will have pretty much the same gain in a given installation as any other 5/8-wave whip would have - providing the construction materials used for both whips are similar. The same goes for any antenna design. If the materials & designs are similar, the gain will be similar, as well.

    Once you have a feel for what is realistic and what defies physics, it's not too difficult to separate the truth from the hype - when it comes to antenna gain figures. A very good resource for this knowledge is the ARRL Antenna Handbook, however there are other great sources, as well.

    If you're interested, here is a link to a group that has done many unbiased antenna comparisons - in real-world conditions: The Northern Lights Radio Society

    We are an organization of Upper Midwest amateur radio operators who are active in weak signal (SSB/CW) work on the VHF, UHF, and Microwave bands. Check out our website, and you will find lots of useful technical information relating to VHF, UHF, and SHF weak-signal communications techniques.

    Scroll down about a third of the way, and you will find a section on Microwave Contests, Gatherings, Picnics, and Antenna Measurement Parties. You will find some links to antenna measurement results. These are not mobile vertical whip comparisons, however you can get an idea as to what real-world antenna performance is like. Some are commercially available, and some are home-brew.

    You can check the manufacturer's websites & compare the advertised gain to the measured gain for some of the factory-built antennas. Unfortunately, some model numbers are not listed. Keep in mind that the absolute numbers are only valid for the measurement conditions, however the delta between the test antennas and the reference antenna should be reasonably accurate for most situations. As the saying goes - your mileage may vary!

    73...

    Joel - N0NCO
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Interesting, Joel.

    What, exactly, is the mechanism that makes it more broad banded?

    I can think of ways to make antennas, including VHF mobile antennas, more broad-banded, but most of those ways introduce some loss. One way that doesn't, which is to use parallel multi-resonant radiating elements, works well and isn't lossy but also isn't practical for a mobile whip antenna.

    Interesting that you notice a difference on "receiving" signals outside the VHF ham bands, based on antenna bandwidth. That probably varies with receiver design, but my mobile VHF-UHF transceivers are noise matched inside the ham bands and thus degrade in sensitivity outside the ham bands, all by themselves! I also don't care, since the public service (WX, police, etc) signals are very strong and if I lost 2/3 of my sensitivity it wouldn't matter.

    But if you can explain the mechanism the designer used to broadband your particular mobile antenna, that would be interesting to know.

    WB2WIK/6
     
  6. KC0NBW

    KC0NBW Ham Member QRZ Page

    the 10 meter ringo antenna has a decoupling cone mounted x distance below the feedpoint/tuning ring that supposedly makes the antenna more ''broadband''than the 11 meter version without it

    i don't have one of the 10 meter versions so i have no idea how or if it works or affects the performance of the antenna.
     
  7. KA0GKT

    KA0GKT Ham Member QRZ Page

    Now I know that I'm getting old...I was going to say the Stationmaster by Phelps Dodge...:eek:

    As far as antenna gain figures go, unless the company has a good antenna test range along the order of what HyGain at one time had at their Lincoln, NE plant, just about any figure could be called into question.

    Now, if you want a really high gain radiator, I think I could supply you with a 273 dBwn omnidirectional antenna if you are willing to pay the price, however I won't specify over which particular type of wet noodle the gain happens to be...I think I had linguinni in the fridge when I built it, then again, it could have been fettucini...I don't really remember.

    73 DE KAØGKT/7

    --Steve
     
  8. N0NCO

    N0NCO Ham Member QRZ Page

    Stephen,

    I've seen the stagger-tuned, parallel driven element idea used, too. KLM (now M2) uses that approach to broad-banding on many of their high-gain 2-meter Yagi designs. I know a Ham that tried it on 75/80 meters, using stagger-tuned dipoles. It seemed to work quite well for him.

    The wide-band whip I'm talking about is a relatively low-gain antenna, and it has a very favorable L/D ratio. Both contribute to the wider bandwidth. Other than that - I don't know what else they did to increase its bandwidth. I suppose I could cut one open & find out.......

    Here's the link to the manufacturer's page, if you're interested: Comet CA-2x4SR

    Performance-wise, I was talking about comparing the out-of-band receive performance of my high-gain 2m/70cm collinear vs. the wide-bandwidth 2m/70cm whip - using the same mount, same vehicle, same radio, same test setup:

    Using an IFR Com 120B and a Sinadder distortion meter, I performed a number of OTA SINAD tests at an elevation angle of ~0 degrees, from a distance of ~20 wavelengths. Given that I was comparing the two antennas on the same system, and at the same frequencies, I doubt that receiver design played a significant role in the outcome. Granted - I didn't do this on an antenna range, but it was a relatively low-noise environment.

    I expect that the collinear is so far out of resonance @ 20 MHz above its design frequency that it has little, if any gain up there. Therefore, any losses that the wide-band whip may have were more than offset by the collinear whip's drop in efficiency at those frequencies. Seems like a reasonable conclusion to me....

    I usually wouldn't be quite this anal about a mobile FM setup, but in this case, I'm either trying to pick up boats on Lake of the Woods, up on the Minnesota/Canada border, or listen to the ice fishing traffic in the winter. The lake is 80 miles long, and 60 miles wide. My hometown is on the southwest corner of the lake, just 5 miles south of Canada - and there's 80 x 60 miles of lake to the north. So, it's kind of a weak-signal affair.

    In lieu of a dedicated Marine Band antenna, this seems to be a workable compromise. A bonus is that it's ground-plane independent, so I can easily put it on any boat temporarily & work some 2 meter FM while I'm out on the lake.

    I sure do miss working VHF weak-signal from up there. When I lived there, I used to really enjoy working ground-scatter, deep-fringe direct-wave, aurora, and tropo. The noise floor is so low that a hot receiver is actually an asset......

    Hope to work you on the bands someday!

    73...

    Joel - N0NCO
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    >I've seen the stagger-tuned, parallel driven element idea used, too. KLM (now M2) uses that approach to broad-banding on many of their high-gain 2-meter Yagi designs.<

    ::I used many of those antennas back in the 1970s. The KLM 144-16 which used 16 elements on a 21' boom and had four driven elements actually had a log cell driven element system, same as any LPDA. It worked fine but turned out to be a waste of time since absolutely nobody needed that beam to work at both ends of the two meter ham band! All FM work is vertical, all weak signal work is horizontal, and nobody uses the same antenna for both. So, they discontinued it.

    >The wide-band whip I'm talking about is a relatively low-gain antenna, and it has a very favorable L/D ratio. Both contribute to the wider bandwidth. Other than that - I don't know what else they did to increase its bandwidth. I suppose I could cut one open & find out.......<

    ::That might break it. Might be possible to X-ray the networks though and see what's inside. I've done this lots of times with small electronic stuff, thanks to my dentist!

    >Using an IFR Com 120B and a Sinadder distortion meter, I performed a number of OTA SINAD tests at an elevation angle of ~0 degrees, from a distance of ~20 wavelengths. Given that I was comparing the two antennas on the same system, and at the same frequencies, I doubt that receiver design played a significant role in the outcome. Granted - I didn't do this on an antenna range, but it was a relatively low-noise environment.<

    ::What I was getting at is that all my 2m FM/mobile rigs are noise matched at 146 MHz, and fall off in sensitivity outside the 2m ham band, so this is very different from using an IFR Com 120B or any piece of test gear which holds flat sensitivity no matter where you dial it up.

    -WB2WIK/6
     
  10. N0NCO

    N0NCO Ham Member QRZ Page

    Yeah, I thought I'd seen one of those before. If it would have been RH & LH circular selectable - like some of the current M2 cross-polarity offerings, the wide-band design would have made more sense, I think.

    Is your dentist also a Ham operator?

    Hmmm..... (Note to self: look for new dentist....)

    Yes - that's why I used it. The old 120B is a pretty good box. The 120A was not. I had one the first of 'em. It was so slow, I could go get coffee while it finished drawing the screen! [​IMG] My favorite service monitor is still the old IFR 1500, though. You could actually sweep a front-end with that one. Not with the 120 series, though.

    I like playing with antennas. I've been building them since I was a kid - quads, inverted-Vs, half & quarter-slopers, long-wires, and such. It's one of the best ways to learn about RF, I think. It was for me, at least....

    By the way - in the ARRL January VHF Sweepstakes thread, Glen mentioned something about you being in QST. Which issue? Will you be participating in the contest this weekend?

    If so - good luck! 73...

    Joel - N0NCO
     
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