The difference an antenna makes on HF

[HomerBB]

Is it not reasonable to say that an isotropic antenna has no/zero gain because it radiates equally in all directions?

And if so, is it not reasonable to say any antenna that radiates more in any direction unequally exhibits at least directional gain over an isotropic antenna that may be expressed in dbi?

And, are all antennas in the real world somewhat directional as opposed to an isotropic antenna given the influences of the environment upon them?

So wouldn't all antennas in the real world exhibit both negative (-dbi) gain, and positive (dbi) gain based on what you were referencing regarding the antennas being discussed.

I make mine from Fred Sanford's junkyard, so I am exempt from being beat up on for weird questions. I enjoy the hobby, and don't take too many things too seriously.

 

[w8fax]

This is true....the dBi reference is many times misunderstood and has been purposely left out I think. There is also NO WAY that antenna can have gain in ANY direction without loss of gain in another. Antennas do not generate power. That's the whole idea of a yagi, or any other directional antenna. These terms, dBi and dBd, have resulted in much misunderstanding in ham circles, and has also been used to construe unfounded or incorrect claims of antenna gain by manufacturers for their own "gain". A yagi that claims to have 10 dB forward gain in space, will certainly be a different animal when everything else is taken into consideration. Height above ground, type of ground, matching network, material, etc all will have a definite effect on an antenna's TRUE gain, and is usually found to be much less than the manufacturer claims. This was part of the reason why ARRL stopped commercial antenna makers from publishing gain numbers in their ads. Now you notice that gain factors are not given, but you are referenced to the manufacturers web site for the "numbers". A lot of the "gain" stuff over the years has been pure B.S., relying on the fact that the manufactures KNOW that it will be misconstrued. Kinda like the myth that an SWR of 1:1 means you have a good antenna and it is also working great. But that is for another discussion.

 

[Captain Kilowatt]

Is it not reasonable to say that an isotropic antenna has no/zero gain because it radiates equally in all directions?

It is perfectly reasonable to say that.

And if so, is it not reasonable to say any antenna that radiates more in any direction unequally exhibits at least directional gain over an isotropic antenna that may be expressed in dbi?

Again, perfectly reasonable and true.

And, are all antennas in the real world somewhat directional as opposed to an isotropic antenna given the influences of the environment upon them?

You're on a roll. One thing however,antennas tend to be rated as if they were in free space because the environment they are operated in is variable and the manufacturer has no control over where they are mounted and what objects may be around them to influence the performance whether it be a positive or a negative effect.

So wouldn't all antennas in the real world exhibit both negative (-dbi) gain, and positive (dbi) gain based on what you were referencing regarding the antennas being discussed.

If you want to get right down to it then yes. Any antenna that radiates more in one direction that another has positive gain in some areas and negative gain in others such as the nulls of a directional yagi or the over head null exhibited by a vertical antenna.

I make mine from Fred Sanford's junkyard, so I am exempt from being beat up on for weird questions. I enjoy the hobby, and don't take too many things too seriously.

If that is the case the only weird questions you may be asked is how did you get that kitchen sink to match up with the rear axle of a '67 Chev and get it all to resonate on 27.185 MHz.

 

[Captain Kilowatt]

This is true....the dBi reference is many times misunderstood and has been purposely left out I think. There is also NO WAY that antenna can have gain in ANY direction without loss of gain in another. Antennas do not generate power. That's the whole idea of a yagi, or any other directional antenna. These terms, dBi and dBd, have resulted in much misunderstanding in ham circles, and has also been used to construe unfounded or incorrect claims of antenna gain by manufacturers for their own "gain". A yagi that claims to have 10 dB forward gain in space, will certainly be a different animal when everything else is taken into consideration. Height above ground, type of ground, matching network, material, etc all will have a definite effect on an antenna's TRUE gain, and is usually found to be much less than the manufacturer claims. This was part of the reason why ARRL stopped commercial antenna makers from publishing gain numbers in their ads. Now you notice that gain factors are not given, but you are referenced to the manufacturers web site for the "numbers". A lot of the "gain" stuff over the years has been pure B.S., relying on the fact that the manufactures KNOW that it will be misconstrued. Kinda like the myth that an SWR of 1:1 means you have a good antenna and it is also working great. But that is for another discussion.

The really big reason certain publications like QST and CQ disallow gain figures to be posted is because most manufacturers were starting to include "ground gain" in their figures. Ground gain can add another 5 to 8 dB over and above the true free space gain. This was causing a huge misunderstanding of antenna performance as well as pitting "honest" manufacturers against "shady gain inflators" in a war of dB's. Two basically identical antennas could have gain figures that differed by as much as 6 dB or more when in fact they had the exact same gain the difference being that one manufacturer was including ground reflection gain and the other not.

 

[W1MSG]

Geez I feel inadequate looking at those big towers and beams. I'm looking at the new Mosley Mini Mono Beam for 20m. My main antenna right now is a 75m loop about 25 ft up.. It works pretty well on 20 and 40 with the tuner ..

 

[HomerBB]

If that is the case the only weird questions you may be asked is how did you get that kitchen sink to match up with the rear axle of a '67 Chev and get it all to resonate on 27.185 MHz.

:laugh: