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Author Topic: 33 Ft. 40m Vertical  (Read 19323 times)
AD5MD
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« on: July 28, 2011, 07:54:49 PM »

I have installed a 33ft 40m mono band vertical and with the mediocre radial/counterpoise installation that I have I know that even if its swr is 1:1 - 1.3 across the band, its performance is marginal. 

Now my question is this...will a vertical current feedline choke help improve its overall performance like what a manufacturer/store website claims?  If so, is there another model/brand which is not too expensive? I was thinking of giving it a try but the cost of the choke is almost the same as the antenna...so I have to research more before pulling the trigger. Any inputs from experienced vertical users in the forum?  Thank you

73,
de Ernie, AD5MD
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N3OX
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« Reply #1 on: July 28, 2011, 09:23:33 PM »

Now my question is this...will a vertical current feedline choke help improve its overall performance like what a manufacturer/store website claims?  

That depends on how much current is actually flowing on your feedline Grin You could have a lot or a little just based on the exact details of the installation... and if you have only a little the choke won't do anything.  (if you want to measure, current meters are pretty simple:  http://www.w8ji.com/building_a_current_meter.htm)

For transmitting performance it really depends on what your radial system is.  If it's on-ground radials it probably won't do anything much for transmitting, but might still help on reception.  If you have a bad common mode current problem with elevated radials a choke could help a fair bit on both transmit and receive.

Chokes CAN be cheap if you are willing to roll your own.  They're just coax wound on a ferrite core, installed in a box.  Some choke ideas are here:

http://www.karinya.net/g3txq/chokes/

The "17 turns RG-58 on a FT-240-43" (about nine bucks plus shipping) would be a good choice for 40m.  For high power, you can substitute teflon coax types for RG-58 and still get the same common mode performance but not have to worry about the power limit of the coax.  

That said, radials are important but sometimes people go overboard and make you think you will get BAD performance unless you plate your backyard with copper (or install the mythical 113 radials 0.5 wavelength long).  Really 60 radials 1/4 wavelength long is a small fraction of a dB from "perfect"  and things like 8 or 16 radials 20 feet long on 40m are probably a dB or two down at worst and plenty to prevent the coax from being an "important radial"

So what do you actually have?  Does it actually seem deficient?

« Last Edit: July 28, 2011, 09:26:11 PM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K9IUQ
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« Reply #2 on: July 29, 2011, 05:33:30 AM »

I have installed a 33ft 40m mono band vertical and with the mediocre radial/counterpoise installation that I have I know that even if its swr is 1:1 - 1.3 across the band, its performance is marginal. 

Now my question is this...will a vertical current feedline choke help improve its overall performance like what a manufacturer/store website claims? 
73,
de Ernie, AD5MD

Here is my experience. 3 years ago I built a 40 mtr 1/4 wave vertical. A friend gave me 33ft of large (2 1/2 inch) tapering fiberglass rod. I ran a 10 ga wire up the middle. I feed it with RG-213 and use a DX Engineering feedline choke at the base of the antenna. There are 60 radials of 16ga 33' wire spaced evenly under the vertical. This setup provides excellent DX and domestic coverage. It outperforms my 40mtr horizontal wire antennas 95% of the time.

The SWR on this antenna is 1.5:1 or less across the whole band.

When I first put up the antenna I only had 8 radials under it. The SWR was around 1:1 almost like my dummy load. As I put more radials on the antenna the SWR went up until it stabilized around 36 radials at 1.5:1

The more radials I put on it, the better the antenna performed.

Does the feedline choke help? I really do not know as I have always fed the antenna with it.

Stan K9IUQ
 
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AD4U
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« Reply #3 on: July 29, 2011, 05:52:59 AM »

When you use a ground mounted 1/4 wave vertical (33 ft is a 1/4 wave on 40M) and you have a GREAT SWR over the entire band, that just about guarantees that your antenna system is very lossy and inefficient - dummy load.  A 1/4 wavelength vertical on 40M with a good ground plane (lots of radials properly installed) will not exhibit a low SWR over the entire band.

As so many have posted in the past you need to add more radials.  How many you "need" depends on lots of factors such as (but not limited to) soil conductivity in your area.  There is no magic number of radials needed  and there is no magic length.  

Old broadcast handbooks suggest installing 120 radials each 1/4 wavelength long.  In practical situations you often have to get by with fewer radials that are not 1/4 wavelength long.

In most cases having just a few radials under a ground mounted vertical makes a very poor antenna.  I am not aware of any "add on" devices that will compensate for the lack of radials.

Dick  AD4U

« Last Edit: July 29, 2011, 05:54:57 AM by AD4U » Logged
N3OX
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« Reply #4 on: July 29, 2011, 07:25:49 AM »

When you use a ground mounted 1/4 wave vertical (33 ft is a 1/4 wave on 40M) and you have a GREAT SWR over the entire band, that just about guarantees that your antenna system is very lossy and inefficient - dummy load.  A 1/4 wavelength vertical on 40M with a good ground plane (lots of radials properly installed) will not exhibit a low SWR over the entire band.

That really depends on what you mean by "low SWR."    I think it's important to be specific because a 33.5 foot #12 wire fed against a PERFECT copper ground plane will show less than 1.7:1 50 ohm VSWR across the entire 40m band with a minimum SWR in the center of the band of 1.4:1.

That's certainly usable with almost all solid state transmitters  "low" in some measure. Not as low as the OP's 1.1-1.3 which may indicate substantial losses.

However, I do think it's worth remembering that just inserting 15 to 30 ohms of loss resistance at the feedpoint of a vertical doesn't make a "dummy load."  It's more like something between 1 and 5dB  of loss.  So if you have  a nice 50 ohm VSWR, it's still going to radiate pretty okay.

I think we do a bit of a disservice calling quarter wave verticals with sad radial systems "dummy loads," because really, even if you mount the thing on a single ground rod, probably not more than half or two thirds of your power goes into the dirt.  This is a lot better than some other types of terrible antennas, especially "no radials" verticals, which massively concentrate the fields around the antenna in a way that can cause even more loss than having a sparse or terrible radial field.

I'm not saying that a quarter wave on a ground rod or a few short radials is a GOOD antenna, nor is it one to be recommended as a matter of course, but I think hyperbole about how much there is to gain by adding radials makes verticals very unattractive to some people. If a certain installation is within 1dB of perfect on 40m with 16 radials 17 feet long, even thinking or talking about 60 or 120 radials 33 feet long or longer is not worthwhile.

You're not "getting by" if you're 1.2dB or 0.7dB away from perfection.  Rather, you're in the range where you wouldn't even notice if the copper fairies came and made your backyard a clean shiny disc of high conductivity copper.  In fact, if you're running a radial field that's within 1dB of perfect and the copper fairies come, you should probably rip it back out, sell it for scrap, and buy some ham radio stuff that actually makes you substantially louder like a beam and tower.

The problem is always about knowing if you're 6dB away from perfect (worth working on, kind of a lot of improvement to be had) or 1dB away from perfect (probably not worth working on unless you're a good measurer and 1dB keeps you up at night)  The problem is knowing when to stop and really the best tool there is field strength measurements.

And reading all of N6LF's articles is pretty illuminating:

http://www.antennasbyn6lf.com/design_of_radial_ground_systems/
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AD4U
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« Reply #5 on: July 29, 2011, 10:32:09 AM »

When you use a ground mounted 1/4 wave vertical (33 ft is a 1/4 wave on 40M) and you have a GREAT SWR over the entire band, that just about guarantees that your antenna system is very lossy and inefficient - dummy load.  A 1/4 wavelength vertical on 40M with a good ground plane (lots of radials properly installed) will not exhibit a low SWR over the entire band.

That really depends on what you mean by "low SWR."    I think it's important to be specific because a 33.5 foot #12 wire fed against a PERFECT copper ground plane will show less than 1.7:1 50 ohm VSWR across the entire 40m band with a minimum SWR in the center of the band of 1.4:1.

That's certainly usable with almost all solid state transmitters  "low" in some measure. Not as low as the OP's 1.1-1.3 which may indicate substantial losses.

However, I do think it's worth remembering that just inserting 15 to 30 ohms of loss resistance at the feedpoint of a vertical doesn't make a "dummy load."  It's more like something between 1 and 5dB  of loss.  So if you have  a nice 50 ohm VSWR, it's still going to radiate pretty okay.

I think we do a bit of a disservice calling quarter wave verticals with sad radial systems "dummy loads," because really, even if you mount the thing on a single ground rod, probably not more than half or two thirds of your power goes into the dirt.  This is a lot better than some other types of terrible antennas, especially "no radials" verticals, which massively concentrate the fields around the antenna in a way that can cause even more loss than having a sparse or terrible radial field.

I'm not saying that a quarter wave on a ground rod or a few short radials is a GOOD antenna, nor is it one to be recommended as a matter of course, but I think hyperbole about how much there is to gain by adding radials makes verticals very unattractive to some people. If a certain installation is within 1dB of perfect on 40m with 16 radials 17 feet long, even thinking or talking about 60 or 120 radials 33 feet long or longer is not worthwhile.

You're not "getting by" if you're 1.2dB or 0.7dB away from perfection.  Rather, you're in the range where you wouldn't even notice if the copper fairies came and made your backyard a clean shiny disc of high conductivity copper.  In fact, if you're running a radial field that's within 1dB of perfect and the copper fairies come, you should probably rip it back out, sell it for scrap, and buy some ham radio stuff that actually makes you substantially louder like a beam and tower.

The problem is always about knowing if you're 6dB away from perfect (worth working on, kind of a lot of improvement to be had) or 1dB away from perfect (probably not worth working on unless you're a good measurer and 1dB keeps you up at night)  The problem is knowing when to stop and really the best tool there is field strength measurements.

And reading all of N6LF's articles is pretty illuminating:

http://www.antennasbyn6lf.com/design_of_radial_ground_systems/


Read the original post.  He said the SWR on his antenna was 1:1.3 ACROSS THE ENTIRE 40M BAND.  Not much but a dummy load is that good.

Dick  AD4U
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N3OX
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« Reply #6 on: July 29, 2011, 02:47:23 PM »

Quote
Not much but a dummy load is that good.

That's not really true.  Let me give you an example with modest loss but less than 1.3:1 VSWR across the 40m band.  If I add 10 ohms of ground loss to a quarter wave #12 wire fed against a perfect solid copper ground and then feed that with 100 feet of RG58 coax, that adds an extra 2.25dB (1dB warms worms, 1.25 dB warms coax) of loss in total but makes the VSWR across the 40m band less than 1.3 to 1.  If you're a careful measurer you could measure 2dB maybe, and you could improve it a bit with more radials and better coax, but most people wouldn't notice it on the air and it's hardly "dummy load" level.

This example shows lower SWR with broader bandwidth because of loss, but it's just not that much loss.  You don't NEED a dummy load disaster to get under 1.3:1 across forty meters.  It's not a bad thing to remind people that dummy loads show good flat VSWR without radiating anything.  I agree with the spirit of that.  But turning an antenna with 20-30 ohm radiation resistance into a 50 ohm dummy load is not straightforward.  You can't just add loss resistance to dial up an arbitrarily large amount of loss while lowering the 50 ohm VSWR.  Eventually the SWR will start to go up again when you cross over 50 ohms.

This is in contrast with something like an 80m hamstick dipole or a 40m mobile antenna.  The radiation resistance a few ohms or even a fraction of an ohm.  You can EASILY get 20dB of loss and a 50 ohm impedance by adding series resistance to a short mobile antenna.  One ohm of radiation resistance and 49 ohms of loss resistance is nearly 17dB of loss.  But for a quarter wave vertical, the loss of "series resistance matching" probably tops out at 3-4dB in the absolute worst case.  That's nothing to sneeze at but it's also not really a "dummy load."

Adding to the problem here is that radial systems are more complicated than adding a simple series resistor because standing waves aren't actually completely damped out on the radials (the current variation on radials has been confirmed in measurements on real systems, not just theorized).   W8JI reports that he can get 50 ohm feed impedance with the exact same field strength as an elevated radial antenna that shows 30 ohm feed impedance.  The complicated nature of real wire ground screens might mean if you shoot for low feed impedance and narrow VSWR bandwidth as a GOAL, that might be all you get.  And a decent broad bandwidth with low SWR doesn't always mean a disaster.  I'm not trying to say adding radials is bad advice, just that the right tool to check if they're helping is a measurement of signal levels, not the feed resistance at resonance or the VSWR bandwidth.

I also think that exaggerating the maximum losses of bad radials is going to put people off of using verticals even if they're the best choice.  Radials are important and they're a cheap way to improve your signal.  Ultimately, 3dB or 4dB of amplifier is big big bux and 3dB or 4dB of radials is just some wire.  But when I look at the lossy monstrosities that some people pick because the manufacturer says "no radials," eventually I just want to tell people to start with a fifteen dollar fishing pole with a quarter wave wire up the side fed against an 8ft ground rod.  It might work better than the other thing they're looking at.  Radials are unquestionably important from a dollars to dB perspective, and communicating that well is important, but inadvertently exaggerating how important they are does not serve a useful purpose.
« Last Edit: July 29, 2011, 03:02:25 PM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AD5MD
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« Reply #7 on: July 29, 2011, 05:40:29 PM »

At present I only have 20 radial wires cut randomly because of space limitations.  I have just bought some more wires and will try to add at least 15-20 more which I will try to squeeze in to the available space.  Thanks for the input guys, I've used beams since the mid 80s so I'm familiar with it but not with verticals.  I appreciate all the info/help I've been reading. 

Ernie, AD5MD
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N3OX
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« Reply #8 on: July 29, 2011, 06:00:47 PM »

At present I only have 20 radial wires cut randomly because of space limitations.  I have just bought some more wires and will try to add at least 15-20 more which I will try to squeeze in to the available space.  

How big is the available space?
 
« Last Edit: July 29, 2011, 06:03:17 PM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AD5MD
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« Reply #9 on: July 29, 2011, 07:12:59 PM »

more or less 40ft x 20ft.  Here is how the antenna is mounted:

                                                    Fence
                                  -----------------------------------
                                  '                                            '         
                                  '                                            '
                                  '                                            '
                                  '                     X                     '
                                  -----------------------------------
                                              Side of the house
                                                 "X" - Antenna

Looking at the above you will notice that I don't have any space to lay the radials at the back of the antenna (mounted approx 5ft from the house wall) so I only have the radials towards the fence and diagonally to the sides.  At present I only have 20 radial wires.  Tnx
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W8JX
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« Reply #10 on: July 29, 2011, 08:17:30 PM »

Why did you place antenna so close to house. I would have placed it near or on fence
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AD5MD
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« Reply #11 on: July 29, 2011, 10:59:06 PM »

The upper right corner of the space is occuPied by a hex beam antenna
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K9IUQ
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« Reply #12 on: July 30, 2011, 04:19:49 AM »

Why did you place antenna so close to house. I would have placed it near or on fence

This is why verticals get a bad name. Hams stick them right next to the garage/house hook up a ground wire to the outside water faucet pipe and then tell everyone verticals suck.

A vertical is one of the hardest antennas to install properly. They need to be away from obstacles like houses and they need an extensive radial system. Properly installed, a vertical will perform beyond your dreams.

Stan K9IUQ

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W3LK
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« Reply #13 on: July 30, 2011, 07:11:40 AM »


This is why verticals get a bad name. Hams stick them right next to the garage/house hook up a ground wire to the outside water faucet pipe and then tell everyone verticals suck.

A vertical is one of the hardest antennas to install properly. They need to be away from obstacles like houses and they need an extensive radial system. Properly installed, a vertical will perform beyond your dreams.

Stan K9IUQ



AMEN!!!
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AD5MD
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« Reply #14 on: July 30, 2011, 07:50:09 AM »

I answered a question hoping to receive a remedy or solution. Thank you
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