|
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
|
|
RE: 43ft multiband vertical
|
Reply
|
|
by N3OX on November 17, 2008
|
Mail this to a friend!
|
"did advertising hype finally overcome all reason? "
It's a combination of advertising hype and a not-insane-impedance on any band radiator.
The 43 foot magic number basically does produce modest losses on 80m and up especially if you spend $180 on a fancy balun with 10AWG silver plated teflon and massive cores, and big money on expensive coax.
ES1TU's setup may have 3.6dB feedline loss on 80m, and probably quite a bit less on the higher bands.
With longer runs of lesser coax on the lower bands, 80m and 160m performance can drop like a rock. -10dB or more. But the same can be said for some of the radialless verticals that cover the low bands.
43 feet into a 4:1 balun into low loss coax is not really my idea of good system design, but it works OK enough that people think "hey, this antenna is working," and when they work VP6DX and TX5C with it they feel like they have a world class DX setup.
I worked VP6DX by shining a laser out the window, but that's not the point ;-)
73
Dan
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by NO9E on November 17, 2008
|
Mail this to a friend!
|
Looks to me that using the 43 vertical as a support for dipole or inverted V could be the best choice.
I have 4 antennas for 40m. One is DX77 no radial vertical close to home and on a 5 ft pole. The second is full size vertical in a yard far away from the house with 8 ground radials. The third one is a W9INN dipole about 40ft up and the last one is a 80m ladderline fed dipole at about 70ft.
Both verticals receive similarly although DX77 is much noisier especially at night when all electronics is on. The 40ft dipole is much quieter and usually about 5-10db stronger. In most directions the 70ft dipole seems like a beam compared to the rest, and often a signal perfectly clear on that dipole is buried in noise on the verticals (some 20db difference). This is for both local and DX. The verticals are slightly better in some directions where the dipoles have a nulls.
Feeding nonresonant antennas through long coax and a balun seems fishy to me. I would erect a dipole for comparison, if possible. Than I would do matching at the vertical for 40m and see whether it is just the vertical that does poorly or is it a loss in matching.
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by N0CGF on November 17, 2008
|
Mail this to a friend!
|
|
ES1TU, In my 30 years as a Ham, and my experience with Vertical and Dipole antennas make me to second the recommendations NO9E have given you.... 73's N0CGF
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by AD4U on November 17, 2008
|
Mail this to a friend!
|
Just for the record, I was not making "light" of ET1SU's antenna, when I posted. But I definitely was questioning the reasoning and the physics behind the 43 foot high vertical that so many seem to be using.
Based on over 40 years hamming, I still feel a dipole up as high as possible fed with either coax (single band) or open wire and tuner (multi-band) offers (by far) the best bang for the buck.
Dick AD4U
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by K0OD on November 17, 2008
|
Mail this to a friend!
|
NO9E: "Looks to me that using the 43 vertical as a support for dipole or inverted V could be the best choice."
I presume you're mostly joking but I've actually considered beefing up my DX Engineering vertical, maybe taking it up higher and using fiberglass for a top section and then using it (with the nice tilt base) to support an inverted V.
--
NO9E: "The verticals are slightly better in some directions where the dipoles have a nulls."
Yep, high dipoles are very effective but they have nulls: Bad on transmit but can be useful on receive. Best to be able two select between two dipoles in different directions.
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by N2EY on November 17, 2008
|
Mail this to a friend!
|
ad4u WRITES: "What is the basis of the Love Affair some HAMs have with 43 foot verticals? Is 43 feet the magic length for verticals, or did the laws of physics change, or did advertising hype finally overcome all reason?"
43 feet is about 5/8 wave on 20 meters. That's the longest you can make a vertical before the pattern breaks up into lots of high-angle lobes.
---
I see several problems with the installation described.
First, on the bands above 20 meters (17, 15, 12, 10) the 43 footer is radiating a considerable amount of RF at high angles, where it is pretty much wasted.
Second, on the bands below 20 meters, its base impedance is low and reactive, and made even worse by the 4:1 "balun" (which should really be an unun).
Third, the SWR on the coax and the operation of the "balun" into a reactive load increase the losses.
--
IMHO, a 43 foot vertical can be a good DX antenna for 20, 30, 40, and 80/75 meters. Maybe even 160. IF all of the following conditions are met:
1) Good ground system (lots of radials)
2) Not installed near RF-absorbers like buildings full of structural steel, plumbing, wiring, ductwork and metal siding.
3) A low-loss matching network is installed *at the base of the antenna (the feedpoint)* and adjusted for each band.
73 de Jim, N2EY
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by W5DXP on November 17, 2008
|
Mail this to a friend!
|
> ES1TU wrote: What am I doing wrong?
I'm confused about using a 4:1 BALUN (BALanced to UNbalanced) device between unbalanced coax and an unbalanced monopole with radials. If your radial system is tied to your coax braid, that will short out one of your 4:1 BALUN windings. Or did you mean to say "4:1 UNUN"?
Without the balun, the SWR on the coax would be about 10:1. You might try the antenna without the BALUN if your autotuner will achieve a match.
--
73, Cecil, w5dxp.com
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by W5DXP on November 17, 2008
|
Mail this to a friend!
|
> K0OD wrote: Yep, high dipoles are very effective but they have nulls: Bad on transmit but can be useful on receive. Best to be able two select between two dipoles in different directions.
My 20m rotatable dipole doesn't have any nulls. :-)
--
73, Cecil, w5dxp.com
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by WA1RNE on November 17, 2008
|
Mail this to a friend!
|
Taking 80 meters as an example, a 43 foot vertical presents a horrible feed impedance for a 4:1 balun and 50 ohm feedline - around 10 -j300 ohms, a predominantly reactive load.
It's been stated numerous times on this and other forums: baluns are designed to work with resistive loads that are a match for their design impedance.
Not to imply that you believe this, but baluns are not designed as "magic" impedance matching devices that somehow automatically compensate for reactive loads. Unfortunately, baluns are being misused this way in some applications which at the end of the day, amounts to a lot of frustration to the user who, like yourself is trying to figure out why they can't obtain a decent match to a transmission line and the antenna isn't working to expectations.
Assuming the radials are sufficiently long for 80 meters, I would chuck the 4:1 balun and feed this antenna at the base with either an autotuner or a manually tuned network.
...WA1RNE
|
| |
|
RE: 43ft multiband vertical
|
Reply
|
|
by WB6TMY on November 17, 2008
|
Mail this to a friend!
|
A 5/8 wave vertical will produce the lowest angles of radiation and strongest ground wave. This is why Class 1A clear channel AM Broadcast stations have specified 100 degrees of electrical length (height) for many years.
As a dipole goes higher, it produces more low angle radiation.
Sooooo.....
How high and how long can you build your dipole ?
On some band it will almost certainly be less than 1/2 wave high, and on that band going down to 160 meters a vertical is a valid consideration you may wish to apply.
That being said, there are verticals and ground planes. Even if you can only get your radials up 10' - high enough that people don't hit their heads when they walk under them, The ground plane will almost always outperform a ground mounted vertical. There are several reasons for this I won't go into here.
At my QTH I was able to get my dipole up 45' and so I have invested in a vertical for 160 80 & 40 meters. When I lived in Santa Rosa it was on my roof for an unobstructed view at the horizon and it was an absolutely dynamite antenna compared to my dipole on 40 80 and 160.
Of course, my dipole is not very high and I don't have a beam. So "dynamite" is an easy achievment.
Now then I just want to say one more thing that is slightly off topic. Your super duper 100dB beam that squirts that lovely RF out in a half power beamwidth the size of a pencil has a pattern shaped like a tear drop. That's because as the signal approaches the antipode all angles point to the target. Often for this reason a vertical with 0dB can outperform the finest beams in this one particular application. I have heard it argued that more than 10dB in a beam is getting close to all the gain that is useful. I won't go into this except to say, "look it up."
TR, WB6TMY
http://www.radions.net/spamfltr.htm
|
| |
|
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.
|
|
|
