OWL is the Winner!

[K5UJ]

OWL, old fashioned tanks, and tuners are overated 

I wouldn't go that far--maybe if you have room for a bunch of antennas to cover HF and 160 you can do the coax feed thing for all of them.   I use it for the unbalanced ones, but if I didn't have ladder line and the Matchboxes I'd have a tough time covering 10 to 80 m. with two dipoles. 

[WD5JKO]

Something I find baffling is that one particular size of solid copper wire is extremely hard to find.  It is easy to find #'s 18, 16, 14, 12, 10, 6 and 4, but for some reason nobody wants to stock #8, which I find useful for coil stock, as well as for constructing OWL.

  I am not sure how this applies to OWL specifically, but combining two equal gauge wires in parallel drops the effective wire gauge 3 units. The circular mils double, and the ohms are cut in two.

  So two # 16's is equal to #13,

  and two # 12's is equal to #9

  This comes in handy with insulated DC wiring, and for using bare magnet wire twisted tightly with a drill, and used to make a balun. I tend to use what I have, and this technique works well.

Jim
WD5JKO

[k4kyv]

In the 50's at my parents the Viking 1 loaded fine on 160 into a 80M dipole fed with 72 Ohm twin lead. Worked the commuter mobiles several days a week with no tuner plus loaded on 80 and 40 where I worked plenty of DX on 40 CW.

The 15M folded dipole was made the HB way with hollow phenolic dowels spaced 6" apart and fed with TV ribbon also loaded fine and I worked the world including WAC as a Novice with a HB 6AG7, 807 and later with the V I. Thats the last time I came close to anything resembling OWL.

OWL, old fashioned tanks, and tuners are overated    Different strokes for different folks.......what works works to paraphrase Yogi Berra.

The thermocouple rf ammeter I inserted in the feed line didn't lie, at least not for comparative readings.  

--maybe if you have room for a bunch of antennas to cover HF and 160 you can do the coax feed thing for all of them.   I use it for the unbalanced ones, but if I didn't have ladder line and the Matchboxes I'd have a tough time covering 10 to 80 m. with two dipoles.  

Plus, it's hard to suspend a half-dozen separate dipoles off the top of a 120' tower.  I never did like the idea of cluttering the space over my house or shack with a jungle of dipoles, one for each band.  Not only does it look like crap, it's more stuff in the air to need maintenance, plus they all interact with one another when confined to the space available at most ham installations.

 I am not sure how this applies to OWL specifically, but combining two equal gauge wires in parallel drops the effective wire gauge 3 units. The circular mils double, and the ohms are cut in two.

  So two # 16's is equal to #13,

  and two # 12's is equal to #9

  This comes in handy with insulated DC wiring, and for using bare magnet wire twisted tightly with a drill, and used to make a balun. I tend to use what I have, and this technique works well.

Jim, the #8 was for a coupling coil.  I wouldn't use two paralleled wires for that - a little too JS even for my liking .  I managed to acquire some #8 by dismantling an old air core inductor in which all the plastic support strips had disintegrated (a good example of why I never throw anything away).  It was already in the form of a coil, so all I had to do was enlarge it a little using a fabricated temporary form to re-form the spiral to the correct size.  I used bakelite strips and glued them to the wire with epoxy for the permanent retainers, and mounted the coupling coil over the main coil, suspended in place with the plastic goop squirted out of a hot glue gun.

For OWL, it would be better to  keep the wires separated and make up a 4-wire line in a rectangular configuration.  That would  give you lower Zo than with two wires each with twice the circular mills. Lower resistive loss due to the skin effect too, since 4 separate wires would expose more surface area for a given number of circular mills.

[KM1H]

I wouldn't go that far--maybe if you have room for a bunch of antennas to cover HF and 160 you can do the coax feed thing for all of them.   I use it for the unbalanced ones, but if I didn't have ladder line and the Matchboxes I'd have a tough time covering 10 to 80 m. with two dipoles.

 

One decent trap antenna covers the same bands unless youre into the odd ones such as WARC and 60M. Use a pair at right sngles to compensate for directivity.
No tuner needed at or close to resonance. Much past 1 wavelength and all the lobes create nulls using OWL.

Plus, it's hard to suspend a half-dozen separate dipoles off the top of a 120' tower.  I never did like the idea of cluttering the space over my house or shack with a jungle of dipoles, one for each band.  Not only does it look like crap, it's more stuff in the air to need maintenance, plus they all interact with one another when confined to the space available at most ham installations.

With a 120' tower Id have some rotating aluminum on top for at least 20 and up but Ive never heard you above 40M either. A couple or 3 trapped slopers covers 160-40 with switchable directivity and even gain and F/B if done right. Or just 2 trapped inverted vees at right angles to compensate for nulls on 80/40. If you dont move around much a tuner isnt even needed. A shorty 40M rotary dipole at 120' would be a killer or a shorty 2el even is very manageable.

[K5UJ]

One decent trap antenna covers the same bands unless youre into the odd ones such as WARC and 60M. Use a pair at right sngles to compensate for directivity.
No tuner needed at or close to resonance. Much past 1 wavelength and all the lobes create nulls using OWL.

That's a useful suggestion but my lot size doesn't allow for two low band dipoles at a right angle to each other--I have to admit only using traps a long time ago when I had a 4BTV for a brief time.   Traps violate an antenna rule of mine (which is certainly debatable) that prohibits anything outside that can dissipate power or crap out (always at night up in the air in January).  With ladder line what's outside is wire only which is about as basic as you can get--the matching device stays in the shack where I can get to it not up in the air.

Everything's got pros and cons--I'm not under the belief that open wire line has no downsides--Pin 1 Brown says noise pickup with coax is dramatically less than with open wire line for example (with dipoles, not verticals). 

[flintstone mop]

I agree with KM1H that "upper band" use would be better with a Yagi.
My Cushcraft A3S is very unpredictable for reliability. Sometimes all bands work perfectly and another time only 40M works. I do not have $400 to find out what is going on up there.
I have been very happy with my new OWL re-design and the main dipole stretched out flat for 160M, 60 feet high. The 3KA Dentron tuner does a nice job.
I have about 160 feet of ladder line now.
I have walked the antenna with a sort-of field strength meter before and after the re-design and there is significant increase of RF out there now. Checking 160 and 80 M.

[KM1H]

Im not against anybody using whatever they want whether it works good or not. What I dont like is when someone claims their wire is superior to anybody elses when its purely subjective.

My 75M inverted vee at 180' lays down a dynamite signal....usually.... but having both a low angle and NVIS lobe generally helps especially for DX at grayline when the band is changing and the EU and JA/VK can be high or low. Ive busted many a pileup against some serious big guns with it and other times Im left playing with myself I have a sloper starting at 100' on another tower to compare with.

[k4kyv]

I'm not under the belief that open wire line has no downsides--Pin 1 Brown says noise pickup with coax is dramatically less than with open wire line for example (with dipoles, not verticals). 

If that's the case, something is wrong.  Sounds like common mode is leaking through somewhere.  OWL and coax should reject noise equally well if everything is properly balanced and any opportunity for common-mode antenna current along the feed line is suppressed.  The receiver should hear only the signal that appears right at the feed-point of the antenna; the type or length of feed line running from the antenna to the receiver should make no difference.

[K5UJ]

Mine measure about 10% difference in current on each side i.e if 100 ma. is on one side, 90 ma. is on the other.  That's probably the result of one end of the dipole being held up by a tree and the other end held by an aluminum mast, albeit one that's insulated and floating off ground.

[KM1H]

I would suspect that very few could have a perfectly balanced OWL 24/7.

[k4kyv]

Just having it appear balanced because an rf ammeter in each leg of the OWL reads the same at one point of measurement, doesn't necessarily mean that the line is perfectly balanced.  Sometimes the standing waves on the two wires may be shifted apart just in the right manner that the currents are identical at one point, but different everywhere else.  For example, the point of measurement could be just prior to a current loop in one wire, and just past the current loop on the other, each reading slightly less than the current right at the loop.  Everywhere else before and beyond that point, the currents would be different up to the next spot where the pattern repeats itself. In such a case, the common mode current would be slightly shifted in phase relative to the differential current, creating a different interference pattern on each of the two wires.

[k4kyv]

Here's the latest results of the tests.

This time, feeding the 160m series-fed 1/4λ vertical monopole through a matching network with 440Ω OWL vs. 50Ω coax.

Measured impedance of the antenna feed point at the output terminal of the matching network at the Dawg House:

1800 kc/s  140Ω + j269
1900         225Ω + j363
2000         420Ω + j475

Feeding with 50Ω coax, using a simple L-network.  With fixed inductance and variable capacitor, perfect match SWR=1:1 zero reflected power achieved at each frequency by adjusting the variable  capacitor.  RF ammeter at the antenna feed point reads with TX output power adjusted to 75 watts:

1800 kc/s  0.683 A
1900         0.535 A
2000         0.40 A

Feeding with 440Ω OWL, using parallel tuned circuit with antenna tapped down on main coil.  OWL fed directly to 14-turn coupling coil. No resonating capacitor. Closely coupled to 26-turn antenna coil parallel tuned with variable capaicitor, antenna tapped on at 17 turns up from grounded end of coil.

1800 kc/s  "reflected" reading (0-1 scale): 0.015     Antenna current @ feed point: 0.741 A
1900           (perfect match)                   0                                                     0.57 A
2000                                                    0.035                                               0.39 A

Apparently the OWL feed system is more efficient at lower end of the band, but at the top end the coax feed system is equal to or slightly better than the OWL feed system.

Next, a series variable capacitor was inserted in the antenna line to cancel out the +j reactance. This was compared to a 215Ω non-reactive dummy load at 1900 kc/s, and the results were consistent. Coil taps had to be moved to achieve match.

With the antenna and series capacitor, adjusted to resonance at 1800, the antenna current read 0.742 amps.  Reflected on 0-1 scale read 0.

Changing frequency to 1900, reflected indication brought to zero by adjusting the series capacitor. Parallel tuning capacitor in resonant circuit re-adjusted.   Antenna current 0.55 amps

At 2000 kc/s, the lowest the series tuning cap would bring the reflected reading was 0.3.  Antenna current reading, 0.3 amps.

The series capacitor had to be re-adjusted with frequency, along with the main tuning capacitor.  Efficiency was about the same at low-frequency end of the band as without the series capacitor, after coil taps were re-adjusted. At 1900 the efficiency was  slightly  lower after both capacitors were re-adjusted for maxumum antenna current and minimum reflected power.

At the high end of the band, efficiency was much lower regardless of capacitor settings or tap locations.

The tuning network works best tapping the antenna directly onto the coil, without a series resonating capacitor. Reflected power can be reduced to zero or near zero all the way across the band by adjusting only the main tuning capacitor.  But efficiency drops off at the high end of the band to about the  same as with coax/L-network feed, whereas efficiency is substantially better at the low end of the band.

Will probably use this in the final circuit, since it seems to be the best compromise.

[K5UJ]

Don,

Thanks for  providing all the data and results.  I'm surprised by two things:  1.  the high reactance.  some would not surprise me at all but hundreds of ohms--I guess the dipole and feedline to it inside the tower makes for a wild Z on the tower.   2.  it is paradoxical to me that the current would drop off at the high end of the band (although I don't know why I think that), but since the Z goes way up I guess for a fixed power level to the load, that will happen.  I'll bet even with less current the antenna is more efficient up there near 2000 kc. 

It would be interesting to perform field strength measurements between the low and high ends of the band with a small amount of power, maybe 10 or 20 watts and a measuring instrument with a small vertical antenna a mile or two from your antenna.  Any receiver with a d'arsonval S meter and detailed scale on it would be good enough.  that would tell if the tower is more efficient at the high end of the band.

[KM1H]

 

But efficiency drops off at the high end of the band to about the  same as with coax/L-network feed, whereas efficiency is substantially better at the low end of the band.

A 1% difference is substantial?

[k4kyv]

The DC input to the final is 100 watts.

Calculating power to the antenna, using the resistive component of the impedance and the formula IČR, yields:

76.8 watts at 1800

73.1 watts at 1900

63.8 watts at 2000

If those measurements were anywhere near close, it appears the system is very efficient at the low end of the band, but drops off steadily as the frequency is raised towards the high end.


With the coax feeding the L-network, current readings were:

1800  .683 amps   65.3 watts

1900  .535 amps   64.4 watts

2000  .4 amps      67.2 watts

Looks like the efficiency with the  coax/L-network is consistently in the mid 60s across the band, with a slight rise at the top end.


With this tuning configuration, the highly reactive load is fed to a tap on the antenna coil.  The variable capacitor that parallel-resonates the antenna coil is across the entire coil.  The coupling coil, which is bridged directly to the OWL is tightly coupled to the antenna  coil.  The resonating capacitor is adjusted until the reflected power meter between the OWL and the coupling coil reads minimum.  In this case, the tuning capacitor almost completely nulls out the reflected power at any frequency across the band, with no other adjustments.

This was surprising, since the tapped coil is being forced to transform reactance as well as resistance.  Placing a capacitor in series with the antenna to tune out the  reactance (which required entirely different coil tap settings) would work only across a small portion of the band.  At the top end, I was able to get the reflected power to zero, but the  current reading was only about 0.3 amps. That calculated to only about 38 watts!  The tapped-coil matching network functions more efficiently with the complex impedance than with a purely resistive load.  Using the series capacitor, to QSY across the band required adjustment of the resonating capacitor, series capacitor and moving coil taps.

Interestingly, the OWL beat out the coax in every test on every band, except with the 160m vertical at the top end of the band.

The weirdness doesn't surprise me a whole lot, since with the 80m dipole attached near the top of the tower, the antenna actually functions more like a vertical tee.  With the quarter-wave vertical, plus 1/8 wave legs of the dipole acting as a flat-top, that gives a total antenna length of 3/8λ... one of those odd eighth-wavelength situations midway between a voltage loop and a  current loop, which turn out highly reactive and usually difficult to match.

Also interesting is that the resistive component of the antenna impedance takes a big jump between 1900 and 2000, but the reactive component increases at each step at 1.8, 1.9 and 2.0 roughly 100 ohms.