Mobile tri-band antenna

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ur20v

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I'm having a hard time finding a nice tri-band (2m/1.25m/70cm) antenna that fits my needs - primarily, one that *ISN'T* a fold-over type. But that seems to be all I am finding, and I'd rather not have to switch from a 2m/70cm antenna to a separate 1.25m antenna every time I change bands.
 

Kb2Jpd

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I'm having a hard time finding a nice tri-band (2m/1.25m/70cm) antenna that fits my needs - primarily, one that *ISN'T* a fold-over type. But that seems to be all I am finding, and I'd rather not have to switch from a 2m/70cm antenna to a separate 1.25m antenna every time I change bands.


There are a few on Amazon. Most are fold over because a household garage isn't that tall. But if you can afford the effort and the cost, get a diplexor and get with three antennas.

Why?

The mono band antenna can be purchased with a collinear design. More rf Sent to the horizon than with a standard 1/4 wave.

Adam Kb2Jpd


Sent from my iPhone using Tapatalk
 

ur20v

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That seems to be the direction I'll be heading. I did come across the "COMPACtenna" -
COMPACtenna 2m/220/440 Antenna - but there seems to be a lot of contentious debate (mostly by people who haven't used it) as to whether it actually works, and I don't know if I want to be the guinea pig.
 

Ed_Seedhouse

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That seems to be the direction I'll be heading. I did come across the "COMPACtenna" -
COMPACtenna 2m/220/440 Antenna - but there seems to be a lot of contentious debate (mostly by people who haven't used it) as to whether it actually works, and I don't know if I want to be the guinea pig.
Reading the blurb at that site is not encouraging. Sure looks like pseudo scientific mumbo jumbo to me. The laws of physics just aren't going to let a 7" high antenna radiate well on 70 cm let alone 2 meters.
 

N8IAA

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That seems to be the direction I'll be heading. I did come across the "COMPACtenna" -
COMPACtenna 2m/220/440 Antenna - but there seems to be a lot of contentious debate (mostly by people who haven't used it) as to whether it actually works, and I don't know if I want to be the guinea pig.
Since Dr. Jack built it, it will work. I had Jack in a ham radio class in the mid to late 80"s. Got his novice and upgraded within a year. He is a medical doctor who became obsessed with the poor performance of the mass produced antennas. He was and is a math wiz. His antennas work.

Just a note, most of the Japanese antennas were/are made to be resonate on different frequencies than used in the US. Now I know I will get all kinds of responses to this last statement, but, take it with a grain of salt, and don't flame me:)
Larry
 

prcguy

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There was an encouraging review on RR on the original larger COMPACtenna but it seems the design was changed and its replacement is a dog. Too bad, I was going to purchase one until I read about the degraded replacement.
prcguy

That seems to be the direction I'll be heading. I did come across the "COMPACtenna" -
COMPACtenna 2m/220/440 Antenna - but there seems to be a lot of contentious debate (mostly by people who haven't used it) as to whether it actually works, and I don't know if I want to be the guinea pig.
 

N4GIX

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I note that the claimed Nominal gain +3 dBi is effectively not much more that Unity gain after subtracting the 2.8 dB to normalize it to the real world...
 

ka3jjz

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I've always been taught that any claims of db gain without a reference point are nothing more than marketing baloney. If you said 3 dbi or 3 dbd now we have a point to compare. dbi is a reference against an isotropic source (something that radiates in all directions equally) and dbd is against a dipole (2.14 dbi
gain).

I'd take those 'gain' measurements with a pound of salt...Mike
 

N4GIX

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I've always been taught that any claims of db gain without a reference point are nothing more than marketing baloney. If you said 3 dbi or 3 dbd now we have a point to compare. dbi is a reference against an isotropic source (something that radiates in all directions equally) and dbd is against a dipole (2.14 dbi
gain).
I quoted "Nominal gain +3 dBi" Notice the little "i" for isotropic? :roll:

So, making the allowance for the conversion, it remains less than "unity gain" against a dipole...

...which is only to be expected being so short.
 

prcguy

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+3dBi gain would be more gain than a dipole. "Unity" is another fuzzy term and without a reference its just another sales word.

Sorry if it seems we're ganging up on you but when you use certain industry standard terms, the numbers should make sense, but they don't appear to here.
prcguy

I quoted "Nominal gain +3 dBi" Notice the little "i" for isotropic? :roll:

So, making the allowance for the conversion, it remains less than "unity gain" against a dipole...

...which is only to be expected being so short.
 

N4GIX

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+3dBi gain would be more gain than a dipole. "Unity" is another fuzzy term and without a reference its just another sales word.

Sorry if it seems we're ganging up on you but when you use certain industry standard terms, the numbers should make sense, but they don't appear to here.
prcguy
It's just basic math. I spent close to 30 years in the LMR field, after serving in the U.S. Army as a 31E40 (Field Radio Repair Supervisor).

Not to simply be contrary, "Unity gain" is very well and simply defined...

dBi = dBd + 2.15
dBd = dBi – 2.15

+3dBi - 2.15 = 0.75 dBd

Unity gain* is defined as 1.0 dBd, therefore this short antenna is -0.25 dBd below "Unity."

*Nota bene: "Unity gain when referring to an antenna means that the output equals the input. Effective radiated power for a unity gain antenna is found by taking the power input into the antenna and multiplying it by 1. So if you are providing 25 watts to the base of the antenna, the ERP is 25 watts."
 
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northzone

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QUOTE "Unity gain* is defined as 1.0 dBd, therefore this short antenna is -0.25 dBd below "Unity." END QUOTE

This is incorrect . It is well known that unity gain is equal to 0.0dBd, G=1 not db=1
 

jonwienke

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0dB is the same as multiplying by 1--no change. 1dB is the same as multiplying by ~1.2589.
 

northzone

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Yes, that is my point. Is does not mater if you are talking dBd, dBi, or dBm. A gain of 1 db is equal to a power increase of x 1.26. No gain (unity) is a gain of 0 db.
 

jonwienke

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No, unity gain is 0dB, AKA multiplying by 1.
 

prcguy

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There is no standard for the term "unity gain" without reference to something known. Many different and well known antenna mfrs compare unity gain to a dipole, or a 1/4 wave ground plane, an isotropic radiator and other things depending on what direction the wind is blowing. There is no consistency in the industry to unity gain.

Sometimes an antenna mfr will tell you what they call unity and even when referencing a 1/4 ground plane, some mfrs only state 1/4 wave ground plane where others state a 1/4 wave monopole over an industry standard 32ft dia ground plane made to very specific dimensions, which is very different than what we would think of as a 1/4 ground plane.

ERP calculations that go to the FCC or other meaningful recipients do not relate to any "unity" gain antnena. Its either dBd or dBi, with the vast majority using dBi and the info you send to the FCC is labeled EIRP in this case. dBi is universal and can be referenced to linear or circular polarized antennas where dBd does not relate to odd polarizations very well. If there were an antenna industry standard size taco that radiated, and it was repeatable, then "dBtaco" would be an actual standard where "unity" is still fuzzy because its different depending on who you ask.
prcguy


QUOTE "Unity gain* is defined as 1.0 dBd, therefore this short antenna is -0.25 dBd below "Unity." END QUOTE

This is incorrect . It is well known that unity gain is equal to 0.0dBd, G=1 not db=1
 
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