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KD4E
05-16-2011, 06:38 PM
I have a used ZeroFive 43' vertical on the way.

I'd like to try loading it with a remote-switched tapped coil for 160-10m use.

I understand that I may end up having to add caps to the taps and switch L/C combos, or a remote-turned air variable combined with the tapped coil, but I'd like to keep it simple and begin with only the coil.

I don't have the modeling apps, and would probably confuse myself with them if I did, am I correct in guessing that a 20-turn 5" diameter air-wound coil using copper refrigeration tubing would be sufficient?

Thanks! & 73, KD4E

W8JI
05-16-2011, 08:59 PM
I have a used ZeroFive 43' vertical on the way.

I'd like to try loading it with a remote-switched tapped coil for 160-10m use.

I understand that I may end up having to add caps to the taps and switch L/C combos, or a remote-turned air variable combined with the tapped coil, but I'd like to keep it simple and begin with only the coil.

I don't have the modeling apps, and would probably confuse myself with them if I did, am I correct in guessing that a 20-turn 5" diameter air-wound coil using copper refrigeration tubing would be sufficient?

Thanks! & 73, KD4E

Doc,

On 160 meters the VAR power at the base of a 43 foot vertical is about 150 kilowatts with 500 watts of applied power. The feedpoint has 14,000 peak volts (10,000 V RMS) at 15 amperes RMS current if the ground system is perfect.

At 1500 watts VAR power is 450 kW. Base voltage is 24.5 kV peak (17,300 V RMS) and base current is 26 amperes. This assumes a lossless ground system.

On 80 meters things are about 4 times better. 80 meter base voltage at 500 watts is 2700 V peak (1900V RMS) and base current is only 7.2A RMS on 80 meters at 500 watts. At 1500 watts current and voltage is 1.73 times more than at 500 watts.

The ONLY reason your 43-foot vertical would not catch on fire is if the system has significant power losses. If the system lost 10 dB of power in a crummy ground, voltages and currents would be about 1/3 of the values above.

So here are the questions you should ask......

What can be used to switch the loading components in and out to change bands?

What will the base insulator stand before arcing?

In dry weather clean Teflon has a carbon track length of about an inch at 10 kV. This assumes a normal deburred edge of tubing, no exceptionally sharp points. So with new Teflon, to base load the antenna over a reasonable ground system in wet weather, you should have about 2 inches of surface path length or more. A direct arc in dry weather would be about a half inch or so on 160 meters with small points at opposite sides of the gap.

Does it look like the base will handle that, and if the base insulator will handle it what about the switch or relay?

As a general rule if you can use a 43 foot vertical on 160 you either have totally reworked the base insulator and built a custom switch or you are radiating less than 25 watts of effective power. There is no free lunch.

:-)

On 160 you need an inductor around 700 ohms reactance. On 80 meters 265 ohms reactance.

That would be about 80-100 turns 5 inches diameter on 160. This ignores base capacitance.

On 80 it would be about 40 turns.

73 Tom

KD4E
05-16-2011, 09:09 PM
Does this explain why it comes with an UNUN and that they specify 100-150 feet of coax?

This is the specific model:
http://www.zerofive-antennas.com/content/multiband-foldover-43-foot-10-160-meter-freestanding-vertical-5kw-4-1-unun

I will be mounting this on a 40' long, 8' wide 9.6' tall steel shipping container - that will be the initial "counterpoise".

I have a thought to increase the length from 43' to 57' down the road as I understand that really helps on 160 and 80M.

WDYT?

W8JI
05-16-2011, 09:40 PM
Initially that antenna shipped with a 4:1 VOLTAGE balun, which excited the shield of the coax with significant voltage. That was later changed to an unun to stop the feedline from radiating RF to the earthworms.

To make the antenna reasonably efficient on 160 at any kind of power level at all, it would take either top loading with a large capacitance hat, converting it to an inverted L antenna or T antenna, or doing something very special with a loading coil. IMO the only 160 solution I would use is a top hat, T, or inverted L. Increasing height to 57 feet might help 80, but it won't solve 160.

73 Tom

KD4E
05-16-2011, 10:02 PM
What gauge wire at what length might I attach to the top to facilitate 160m, please?

How high above grade must I keep the far end to avoid detuning or a vertical-value defeating angle?

What impact might it have on 80-10M?

OTOH, I do have a 260' 450 slotted-line fed NVIS doublet at 5' above grade (soil is generally dry clay/sand here) - perhaps that is all I need for regional 160m? I am not a contester, though I am occasionally amused by DX, and I do wish to have reliable 160m comms to assist in disaster/emergency events.

I also plan to get a multi-band dipole up that could be tuned for 160m. It will be a good deal higher above grade! :-)

Thanks!

W8JI
05-17-2011, 01:46 AM
When I had an 80 meter vertical and wanted to work 160, I ran a single insulated wire connected to the top out about 75 feet. When I wanted to work 80 and 40, I dropped the wire against the vertical and shorted it to the vertical at the bottom (and top).

I don't know why you have a NVIS antenna at 5 feet. All that does is increase losses. It does not make it a better NVIS antenna at all. Anything below 35 feet high on 40, or 70 feet on 80, or 140 feet high on 160 is a very good very efficient NVIS antenna.

73 Tom

KL7AJ
05-17-2011, 02:07 AM
With an ideal ground system, the 43' vertical has a radiation resistance of around 2.3 ohms, and the required loading coil would be about 960 ohms. This would give you a circuit Q of well over 300, whicih means the voltage at the top of the coil will be about 300 times what the feed voltage is! Fortunately, ou can tame things down drastically with fairly moderate capacitive loading at the top end....even a single wiire broought away for a distance from the top of the pole.

Eric

KD4E
05-17-2011, 02:21 AM
Please define "distance" ... 10', 20', 100'?

Should it be at a right-angle to the vertical or is it OK if it slopes down a little?

KL7AJ
05-17-2011, 02:24 AM
If you can arrange it so that the total length including the pole is around 1/4 wave, that would be great...you'd have an inverted L. The more horizontal you can get it, the better, but if it slopes down a bit it won't hurt too bad.

KD4E
05-17-2011, 02:30 AM
Hmmm, so with a 43' vertical I would need about 80' of wire off the top for a 1/4 wave on 160m?

What impact might that have on 80-10m?

KK3Q
05-17-2011, 07:21 PM
Does this explain why it comes with an UNUN and that they specify 100-150 feet of coax?

This is the specific model:
http://www.zerofive-antennas.com/content/multiband-foldover-43-foot-10-160-meter-freestanding-vertical-5kw-4-1-unun

I will be mounting this on a 40' long, 8' wide 9.6' tall steel shipping container - that will be the initial "counterpoise".

I have a thought to increase the length from 43' to 57' down the road as I understand that really helps on 160 and 80M.

WDYT?

I wouldn't run the Zero Five off of the ground.

You likely will need a better counterpoise than the shipping container will provide. Others may tell you that you don't need radials under the 05 but I use one and have good luck with it mounted on the ground with 75 radials under it. When I installed the antenna I started with 25 radials and kept increasing them in groups of 25. I did not see a tremendous difference between 50 and 75 but there was some. I used 3500 feet of 12 gauge wire and the Zero Five works on all bands, including 160 meters.

I do not own an amp and do not do SSB on 160, just PSK and CW running 50 to 90 watts. It is not gangbusters on 160 but then I am not a top band contester either. I have a couple of pictures on my site if you are interested: http://www.kk3q.net/Zero-Five/

W8JI
05-17-2011, 07:43 PM
Hmmm, so with a 43' vertical I would need about 80' of wire off the top for a 1/4 wave on 160m?

What impact might that have on 80-10m?

Doc,

Keep in mind ANYTHING that makes contacts will often be OK for people, even if only 1% of power is radiated. For example I have worked Europe, Australia, Japan and other DX on 160 from my mobile (Europe on SSB) but antenna efficiency is less than 1%. If I compare that mobile antenna to a simple Inverted L, there is about 15-20 dB difference. That difference is about like changing power from 10 watts to 1,000 watts.

What you need to do with the antenna is get the current at the top higher and have much less feedpoint reactance. Then matching problems and feedline losses will decrease astronomically.

As I said, when I did this with an 80 meter 1/4 wave vertical I just pulled the wire out as far as I could. When I wanted to work higher bands, I laid it against the vertical and connected it to the vertical bottom. It was a little inconvenient, but worth a free 10-20 dB in signal. That's like someone giving you a free big amplifier. :-)

You might just want to use the antenna on all bands with the top wire pulled out. With a 43 foot vertical you might need a 100 foot long top wire.

What you do really depends on how you operate and how much room you have. I think if you got your NVIS antenna at a height that is reasonable, instead of low and lossy, you would be a whole lot for satisfied with it. That "slot antenna" stuff and very low height is not a good plan at all.

Anything will radiate, and how poorly something radiates doesn't usually bother the person with the bad antenna so much. It just mostly bothers the poor souls who have to listen to him. :-)

73 Tom

KD4E
05-17-2011, 10:04 PM
I located it at 5' above grade based on reading a variety of recommendations about NVIS antennas - I even built a fence of wood posts and plastic deer fence to create a structure on which to hang it.

Is there new NVIS design and performance data which says that they no longer should be located low?

BTW: It has actually performed very well so far, even though the feed system is - temporarily - lossy.

I intend to add a dipole much higher in the air - but it will still be somewhat NVIS on 80 & 160m since it is likely to be under 45' at the highest point.

K4SAV
05-18-2011, 02:46 AM
Is there new NVIS design and performance data which says that they no longer should be located low?

No, the answer is the same as it always has been, although many people get it wrong. Maximum NVIS gain for a 160 meter dipole over average ground occurs close to 100 ft height. Maximum NVIS gain for an 80 meter dipole occurs close to 50 ft height.

Jerry, K4SAV

KD4E
05-18-2011, 03:54 AM
I have no competence to challenge anyone about antenna theory and know Tom, Jerry, and Dean Straw to have excellent credentials ... my problem is that 50-100 feet is impossible here anytime soon, even 30' for a 260' dipole/doublet is not an option, so I looked at alternatives.

I just found this (see below) on another thread - but am not sure why rich wet soil would be better for performance (with a very-low doublet/NVIS wire antenna) - rich wet soil has high-conductivity and therefore would seem to absorb more signal. The soil here is well-drained sand with some clay - it would seem to be largely invisible to RF - is the thought that a rich wet soil would reflect received signals into the NVIS wire antenna?

Does the receive impact of various soil types at various proximities to the NVIS dipole/doublet have to be compared and contrasted with the transmit impact?

Since I am stuck with a very low antenna I have conceptualized it more in terms of a Beverage than a traditional dipole. Perhaps incorrect but that was part of my thinking. (BTW: I used to have a book about wire antennas that included tests with buried dipoles!)

Within a few weeks I will be doing a series a A-B tests of the vertical and the low-doublet/NVIS and hopefully some time soon add an elevated dipole to the mix. I will share my results.


http://www.w8ji.com/nvis_n_v_i_s_antenna.htm

It includes actual measurements.

At .005 wavelength (1 foot high 5MHz) the field strength was -17dBi, down 25dB from 0.12 wavelength height.

At .02 wavelength (4 feet high at 5MHz) the field strength was -5dBi, down 13dB from 0.12 wavelength height.

At .04 wavelength (8 feet high at 5MHz) the field strength was 3dBi, down 5dB from 0.12 wavelength height.

At .06 wavelengths high (12 feet at 5MHz) field strength is down 3dB from 0.12 wavelength high.

To convert these points to other frequencies multiply the height in wavelength by the wavelength in feet. Use F / 984 = wavelength in feet.

For example 3.8MHz would be 984 divided by 3.8 = 259 feet. This means a .02 wave high antenna (13 dB of power loss) would be 259 times .02 = 5.2 feet high.

We can reasonably expect, over very good soil, a 5.2 foot high antenna would be down 13dB from an antenna 31 feet high. This would be true at any distance.

73 Tom

K4SAV
05-18-2011, 04:42 AM
Ground quality does change the maximum gain height for NVIS, but not by a lot. The more conductive the ground that lower the antenna can be. However we are splitting hairs here. Lower heights may be perfectly acceptable for NVIS even though the gain may be a little lower. For example, an 80 meter half wave dipole over average ground, at an elevation angle of 90 degrees, has less than 1 dB difference between heights of 33 and 75 ft and anywhere in that range. So the point of maximum NVIS gain is a pretty broad curve. However if you make the height 5 ft, you loose about 11.3 dB gain compared to what you could get at the best height.

You realize that a vertical has a null overhead, so if you are trying to shoot a signal straight up, it isn't going to work very well.

Jerry, K4SAV

W8JI
05-18-2011, 12:25 PM
I located it at 5' above grade based on reading a variety of recommendations about NVIS antennas - I even built a fence of wood posts and plastic deer fence to create a structure on which to hang it.

Is there new NVIS design and performance data which says that they no longer should be located low?

BTW: It has actually performed very well so far, even though the feed system is - temporarily - lossy.

I intend to add a dipole much higher in the air - but it will still be somewhat NVIS on 80 & 160m since it is likely to be under 45' at the highest point.

Someplace between 30 feet and 70 feet will be ***optimum*** NVIS height for 80 meters. Someplace between maybe 50 feet and 150 feet will be optimum for 160.


There is all sorts of outright foolish nonsense about NVIS antennas. If you read any article telling you really low heights are better for NVIS, you should just stop reading the article at that point because the author is just saying crazy wrong things. Antennas (and GS31B amplifier) articles for some reason are some of the worse technical stuff to hit our hobby, and NVIS antennas in particular seem to be at the rotted core of bad science. If you see articles about slot antennas at lower HF, be especially careful.

If I wanted to build a really lossy antenna that ate up most power in earth losses, I would make the antenna very low and very long. The longer it is in wavelengths and lower it is, the more the earth below the antenna will suck up signal.

73 Tom

G3TXQ
05-18-2011, 01:06 PM
On 160 meters the VAR power at the base of a 43 foot vertical is about 150 kilowatts with 500 watts of applied power. The feedpoint has 14,000 peak volts (10,000 V RMS) at 15 amperes RMS current if the ground system is perfect.

At 1500 watts VAR power is 450 kW. Base voltage is 24.5 kV peak (17,300 V RMS) and base current is 26 amperes. This assumes a lossless ground system.

On 80 meters things are about 4 times better. 80 meter base voltage at 500 watts is 2700 V peak (1900V RMS) and base current is only 7.2A RMS on 80 meters at 500 watts. At 1500 watts current and voltage is 1.73 times more than at 500 watts.

The ONLY reason your 43-foot vertical would not catch on fire is if the system has significant power losses. If the system lost 10 dB of power in a crummy ground, voltages and currents would be about 1/3 of the values above.

If Tom's analysis is not scary enough already, take those voltages and work out the flux density and temperature rise in the UnUn; if the UnUn doesn't explode, it tells you something about how much power is actually getting into the vertical.

73,
Steve G3TXQ

W8JI
05-18-2011, 01:34 PM
If Tom's analysis is not scary enough already, take those voltages and work out the flux density and temperature rise in the UnUn; if the UnUn doesn't explode, it tells you something about how much power is actually getting into the vertical.

73,
Steve G3TXQ

Just yesterday I walked by a charred chunk of fiberglass that used to be the base insulator on a 45 foot vertical I was experimenting with years ago. With about 40 radials and 400 watts on 160, it arced across a one inch length and set the insulator on fire. :-)

That's what happens when system efficiency is over 1 or 2 percent.

KA7NIQ
05-18-2011, 02:47 PM
I recently joined this NVIS Antenna Group (http://groups.yahoo.com/group/NVIS/)
Some in this group advocate very low, military style dipoles. I have tried low (under 20 ft) dipoles for 80 meters w/o very good results.

AD4J
05-18-2011, 02:48 PM
... am not sure why rich wet soil would be better for performance (with a very-low doublet/NVIS wire antenna) - rich wet soil has high-conductivity and therefore would seem to absorb more signal.

I think the answer is that the higher conductivity soil absorbs less of the signal than lossy, low conductivity soil.

When you commented earlier that you felt your low antenna was doing fine for short distances, it reminded me of an 80 meter dipole I once had. The dipole was normally up about 45' and I used it to talk to my uncle in the next state every week. Signals were usually about S9 +15 dB. One week, a falling limb broke a support rope and part of the antenna was draped across my back porch up about 10' (.037 wavelengths on 3.6 MHz). I got on for the sked with my uncle anyway. Signals were still good - S9+. This fits with Tom's measurements showing a drop of 5 dB at .04 wavelengths.

So, it doesn't surprise me that your dipole up just 5' still works. It's just that you could gain about 4 S units if it were up around 35'.

Jim, AD4J

G3TXQ
05-18-2011, 03:05 PM
Just yesterday I walked by a charred chunk of fiberglass that used to be the base insulator on a 45 foot vertical I was experimenting with years ago. With about 40 radials and 400 watts on 160, it arced across a one inch length and set the insulator on fire. :-)

That's what happens when system efficiency is over 1 or 2 percent.

Tom,

I just checked the thermal calculations on a 4" T400A-2 core - the biggest core I have data for - guessing the manufacturer might have chosen iron powder to reduce core losses. If I assume the 9:1 UnUn is a total of 30 turns, the secondary voltage on 160m would need to stay below 1400v rms to stay within the recommended temperature rise.

If Eric's feedpoint impedance of 2.3-j960 is correct, that would equate to a limit of 5W into the antenna; even if we allow a duty-cyle of 10:1 because it's a heating effect, the limit is still a lowly 50W.

Some of these designs must rely on the user having significant inefficiences in the system!

73,
Steve G3TXQ

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