|
New to Ham Radio?
My Profile
Community
Articles
Forums
News
Reviews
Friends Remembered
Speak Out
Strays
Survey Question
Operating
Contesting
DX Cluster Spots
Propagation
Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers
Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net
|
|
1-7 of 7 messages
|
Page 1 of 1
|
|
Choosing an HF vertical antenna
|
Reply
|
|
by KC8SBV on October 3, 2001
|
Mail this to a friend!
|
Why is it, when you shop for an HF vertical ant, the concept of gain/loss gets abandoned? They all exhibit loss to some degree, yet no one will fess up and report it. Does anyone measure this for commercial antennas? Cushcraft, Gap, Butternut, Hy-gain, Hustler, MFJ?
Thanks,
Ed
|
| |
|
RE: Choosing an HF vertical antenna
|
Reply
|
|
by KC8SBV on October 3, 2001
|
Mail this to a friend!
|
I have found the ultimate antenna for my HF radio. It is 2 slinkies hung on a rope, with coax attached. Finally my search for an inefficient antenna is over. Can't wait to get on the air.
http://www.antennasmore.com/helitrix.htm
|
| |
|
RE: Choosing an HF vertical antenna
|
Reply
|
|
by AC5E on October 3, 2001
|
Mail this to a friend!
|
HI; Besides the fact that antenna gain figures in general have a tendency to get inflated far beyond physical possibility, (advertisers call that "puffery, and the lawyers call it "deceptive advertising) the main problem with gain figures for vertical antennas is that they are so utterly dependant on outside influences.
In theory - any half wave vertical SHOULD exhibit around 2.2 dBi of gain and a feedpoint impedance of 70-75 ohms. Just exactly the same as a horizontal dipole. Because the construction details don't much matter, a vertical half wave antenna is in every sense of the word a dipole standing on end.
But in practice the feedpoint impedance can be anything from 35 ohms or so up to over a hundred. "Gain" can be anything from zero to 2.2 dBi.
A quarter wave vertcal, common for 80 and 40, should have around 1.9-2.0 dBi of gain and a feedpoint impedance of 35 ohms or so.
But the actual gain depends on your ground system, ground resistance (or admittance, or conductance) and the efficency of the matching network. Two of those factors the antenna manufacturer has absolutely no control over.
Realistically: a half wave vertical far enough in the air to substantially eleminate ground losses is an excellent antenna. In fact, it is what a dipole should be - because that is what it is.
A quarter wave vertical with a really good ground system; one good enough to bring the feedpoint impedance close to the theoretical value; is also an excellent antenna. Good enough that a DX station will not be able to tell the difference between a really good dipole and an equally good vertical.
73 Pete Allen AC5E
|
| |
|
RE: Choosing an HF vertical antenna
|
Reply
|
|
by WB2WIK on October 3, 2001
|
Mail this to a friend!
|
The important thing with HF verticals is to maximize their efficiency; unless stacked or phased in arrays, they won't have any gain, but losses can be minimized with excellent installations that will place most HF vertical antennas on an extremely level playing field.
When I install a Gap Titan, Butternut HF6V, Hustler 6BTV, Hy-Gain 18AVQ, Cushcraft DX-88 or whatever, I can make them all "play" nearly identically, and make any one of them work extremely well. Unfortunately, it appears that many cannot, due to lack of experience and understanding of what makes an HF vertical work.
Willingness to elevate the vertical, install resonant radials, and make active use of an Antenna Analyzer during/post installation to effectively tune the entire installation goes a long way towards making any HF vertical system effective. "Gain" or "loss" doesn't enter into the formula. "Matched bandwidth" and "efficiency" do, and these can be optimized on a per-installation basis. Unfortunately, that optimization doesn't come out of the carton.
73 de Steve WB2WIK/6
|
| |
|
RE: Choosing an HF vertical antenna
|
Reply
|
|
by K4MZW on October 3, 2001
|
Mail this to a friend!
|
Your question about gain/loss and antenna manufacturers advertising brings up a good point. Having been personally involved with the sale and manufacture of HF antennas I have some insight.
Principally all antenna companies (Manufacturers) actually sell(manufacture) two products. "One" their antennas and "two" their specifications, in some cases the two are not even remotely connected to each other.
Much has been written on the published "gain" figures of antennas, most of which begin their comparison to either a dipole, in the case of a beam, or an isotropic antenna, in the case of a dipole, as their point of reference.
Let's take a commercial dipole antenna from company X who claims gain of say 3.5db(i) since the "isotropic antenna is a "theoretical" antenna one must assume the 3.5db(i) claim is also theoretical. Further one could say since most companies compare their beam(yagi) antennas to have gain over a dipole and the dipole is compared to a "theoretical" antenna then their claims of any gain must also be theoretical. Are you getting my "drift" here?
In order to establish any gain figure one must have some "benchmark" to start from. So....when we use a "fantom" antenna as our benchmark then all our calculations are to be taken with ever so many grains of salt.
Keep in mind that 6db is equal to 1 s-unit, and it takes a doubling of power to achieve the equivalent of 3db! Therefore if you have a "barefoot" rig running 100 watts and you get a signal report from a European station of 5-7, it would take 400 watts (100 x 2=200 x 2=400) to get a signal report of 5-8!
So if your dipole antenna is compared to a theoretical antenna who is to say what the original signal report, with the theoretical antenna would have been. If the dipole has a 2.2db gain the result (less than 1/2 an s-unit) would be unmeasureable at the receiving station anyway.
The next time you are listening to signals see if you can detect any appreciable difference between say a signal at 5-6 and a signal at 5-7. While there may be quite a difference between a signal of 5-6 and one at 5-8 it takes 1600 watts of power in our example to accomplish this.
What is my point? Spend your money on antennas and when you have done the very best you can, then, and only then, worry about power. Don't scrimp on antennas, feedline or connectors!
I never could understand the fellow who spends $3000 on a radio and connects it to $15 worth of wire from the hardware store then brags to his buddies about how cheap he was able to find connectors at the last hamfest! This is usually the guy who says the bands are in bad shape.
Don't be "fooled" by the unrealistic claims of some manufacturers "gain" figures. Send an e-mail to their technical department and ask for Smith charts of the tests they have conducted. Get the facts before you spring for the unrealistic claims of some manufacturers.
Good DX
Jack
|
| |
|
RE: Choosing an HF vertical antenna
|
Reply
|
|
by ANON5 on October 5, 2001
|
Mail this to a friend!
|
Is the gain difference of a linear loaded 1/4 wave vertical significant over a 1/4 wave trapped version similarily installed significant? For example, Hygain markets both types. As I am going to have to be putting it up at sunset and taking it down at sunrise (CC&R's), I am wondering if the trapped versions will be less likely to get detuned during handling and bumping around. They also look a little sleeker from the neighbors' perspectives.
Thanks much for your comments.
John, KD7OIU
|
| |
|
RE: Choosing an HF vertical antenna
|
Reply
|
|
by K4MZW on October 8, 2001
|
Mail this to a friend!
|
Buy a couple of cans of flat black spray paint and it will be much less noticable to the neighbors.
I have also seen umbrella stands used with good success, you could make an easily tilted hinge mechanism to simply lay the antenna down during the day.
With the current interest in patriotism, have you considered a flagpole?
Jack
|
| |
|
Email Subscription
You are not subscribed to this topic.
Subscribe!
My Subscriptions
Subscriptions Help
Check our help page for help using
Forum, or send questions, comments, or suggestions to the
Forum Manager.
|
|
|
