• Get involved.
    We want your input!
    Apply for Membership and join the conversations about everything related to broadcasting.

    After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
    If you use a disposable or false email address, your registration will be rejected.

    After your membership is approved, please take a minute to tell us a little bit about yourself.
    https://www.radiodiscussions.com/forums/introduce-yourself.1088/

    Thanks in advance and have fun!
    RadioDiscussions Administrators

Dominator vertical antenna

The text on the e-bay page, and at the website of the supplier need to be read with care. Examples are the statements about the gain of this antenna, and what that gain provides in the way of added range.

NEC analysis shows that this design has a gain very nearly the same as a linear 1/2-wave dipole -- which is 2.15 dBi, or 0 dBd. The descriptions on the web for the Dominator say it has 6 dB gain (4 X more radiated power than a 1/2-wave dipole), and that the range therefore is about twice as great as with that dipole.

But while a power increase of 4 X doubles the field strength at a given distance, it does not double the distance to a given field strength.

As an example, 100 watts at 100 MHz from an antenna radiation center of 30.5 meters above ground level will produce a 1 mV/m field at/near the ground about 5.7 km away from the radiator, according to the FCC F(50,50) propagation curves for FM broadcast. Changing the radiated power for this example to 400 watts moves the 1 mV/m contour to 8.1 km. This is a range increase of about 1.42 X -- quite a bit short of double. And of course, NEC says that this gain is not available from this antenna in the first place.

Caveat emptor...

//
 
i think the REAL GAIN is the profit they make on the sale, if you get my drift.i agree with R FRY and would be real skeptical of the claims made on Ebay.When you put the math to it, it just doesn't add up....
 
"THE TRUTH ABOUT CIRCULARLY POLARIZED ANTENNAS

...In our example when you compare the Dominator 3/4 wave at 6 db, there is a 9 db increase in gain over the CP antenna. This massive increase in gain greatly outweighs any slight advantage of wasting half your power to transmit in both planes."

That one just irks me. I once knew an "engineer" who convinced perfectly sane translator broadcasters to abandon their circularly polarized transmit antennas for his 'special' vertical model. A single polarization 'talks' so much louder, he told them. Hogwash.

As you might expect, circular was better, and the verticals ended up on eBay. After all, if you're a 100 Watt LPFM or translator, you still have to comply with the licensed power limit regardless of the antenna you use, and cutting out a polarization is still a net loss in signal.
 
Thanks for the heads-up everyone, I think I'll pass on it.

Tom Johnson
CAT-AM 580
 
What a load of carefully worded roadapples! In the weather here, the ring dingus at the bottom will be filled with ice on the first good sleet storm.
Also, has the FCC rescinded the Rule which allowed FM broadcasters to add a vertical component up to (but not over) the power of the horizontal component? It's frightening to realize that, with the dearth of technical expertise in many smaller stations, some manager may well buy into this crap, and purchase one of these things. I don't expect to see Silliman and Surette selling pencils on the corner to survive as a result of it.
And remember... 40% of employee absenteeism occurs adjacent to thew weeekend. 40% - nearly half! Is that awful, or what?
 
littlejohn said:
Also, has the FCC rescinded the Rule which allowed FM broadcasters to add a vertical component up to (but not over) the power of the horizontal component?
Click to expand...

I believe that licensed LPFM stations can use v-pol, only, if they want (or h-pol only, or c-pol).
//
 
Thanks for the clarification.... makes sense for them to save a nickle here and there. Perhaps we'll see the DB-100 next? Stack some dipoles and go for the gain.
 
I do some work for a translator that has one of these. What is the actual gain? I beleive theri license says it has a multiple of X4.

R. Frye, If I understand you correctly, you say it has a gain on 0 DBu? Which I believe is a multiplier of "1"?

Man is that right. These folks are way underpowered if so. (Although anecdotally it always seemed a little weak on the air considering...)
 
Hi, "clouseau" ...

Below is an email I sent to the provider of the Dominator® antenna. So far I have had no response, although I did receive a response to an earlier email to him/her.

So from this I guess we are free to draw our own conclusions.

R. Fry - http://rfry.org

---------------

Thanks for your latest reply.

I hope you'll send me whatever accurately produced engineering data you have or may receive from Sirio Antenne.

Actually, I can produce an accurate electrical model of your antenna patterns and gains myself using Numerical Electromagnetics Code, if you can send me the mechanical dimensions for it (I won't share the info you send or the NEC results with anyone else).

Radiation is generated when r-f current flows along an exposed conductor. The field strength radiated in a given direction is a function of the mechanical dimension, form, and orientation of the radiator and the amount of current flowing in it. These are laws of physics that apply to every antenna.

So every non-sectionalized, linear antenna of a given length will produce nearly identical radiation patterns and "gain" on a given frequency when the same r-f current is flowing in them. This is why I am having difficulty understanding the claim of 6 dB more peak gain for the Dominator than for a conventional j-pole of the same overall length.

It looks like you have a good antenna design, but probably everyone knowledgeable of professional antenna theory and practice is going to be suspicious of the gain claimed for it -- especially if the claim cannot be scientifically supported. I know your intended market probably doesn't include too many antenna engineers, so you may not see this as much of a problem.

But if you hope to sell these for use by licensed LPFM stations, I believe you will need to provide radiation pattern and gain data for it acceptable to the FCC. Your LPFM customers will need to know these, so that they can set their radiated power to the value in their station license, and to evaluate the radiation hazards for their installation site..

Regards,

Rich
 
Two words... PIRATE ANTENNA.

I think if a person holds a license, getting the maximum circularly polarized signal out there would be a MUCH better idea. If a person is pirating a signal and is just looking for maximum gain in an antenna for whatever exciter or transmitter he/she owns, a higher-gain vertical makes sense. I wouldn't even think of using one of these things for a real radio station, however, for folks that don't have license parameters to deal with, considering using the Dominator or other vertical-only antennas does make some sense.
 
"Perhaps we'll see the DB-100 next? Stack some dipoles and go for the gain."

I once had a supposedly 'very sharp' FM broadcast engineer ask me to stack a pair of dB-224's on his tower for high-band Marti pick-up

the 'reasoning' went like this: according to him (never mind what the book said !), a dB-222 has 3 dB of gain, so if you add two elements (dB-224) you are up to 12 dB (according to him you added 3 dB gain with each element) and a pair of stacked 224's would give him 24 dB over a dipole
 
Status
This thread has been closed due to inactivity. You can create a new thread to discuss this topic.


Back
Top Bottom