Big vertical on 75!

[k4kyv]

After 25 years, I finally tuned the 127' vertical to 75!  Ever since I first put it on the air in 1982, I have used it only on 160, as a quarter wave.  Up in the AM Ghetto, the half-wave high dipole seemed to be all I needed, since DX wasn't really much of a possibility.  I never had any problem working into Europe with the dipole on CW.

With the expanded phone band and the possibility of working DX on AM, I decided to see if I could make the vertical work on 75.  I threw together a simple parallel tuned matching network with a 400 pf bread slicer and an EF Johnson edgewound coil I found in the junkbox.  To my surprise and  delight, I was able to get the SWR down to 1:1 on the third try, of moving the point where the feedline taps on to the coil.  When I ran the transmitter up to full power on AM, nothing arced over on voice peaks.

My first 75m contact with the vertical was today at mid-afternoon, with Howard, W3HM.  Can't wait till  tonight to see what kind of signal reports I get at various locations over the country.

[w3jn]

I'll be on the lookout for ya, Don!

[Steve - WB3HUZ]

Very cool. Can't wait to hear it.

[KA7WOC]

Don,
Heard Larry check in with you from LaGrande,  you were FB into Whidbey Island, Wash.  Congrats on ant and 75m. 
bob

[W1RKW]

Don,
I woke up in the middle of evening last night about midnight and flipped on the bedside radio and you were coming in nearly full strength into CT.  Nice signal and audio.

[k4kyv]

I worked several stations with it.  Couldn't tell if it really was any better or worse than the half wavelength high dipole.  The comparisons with receiving the 3810 kc/s time beacon in Ecuador wasn't a lot different from normal.  Broadcast signals from Europe, and the French AM group on 3550 still came in much better on the beverage, with about the same difference as I have observed with the dipole.

I need to set it up so I am capable of running A - B comparisons to tell if it really is worthwhile.  At least I know how easy it is to load the tower up on 80m.  The dipole + feedline total length per leg is about 3/4 wavelength, so it is an anti-resonant length and the dipole seems to have zero effect on resonant frequency, unlike when using it as a quarter-wave on 160m.  Also, when I loaded it up, the tower was hot with rf as indicated by a neon lamp, but the dipole feedline didn't have enough rf on it to light the bulb.

My General Radio antenna impedance bridge covers 160, but its range doesn't go high enough to measure anything on 80m.

Thanks for all the reports and to those who made a special effort to call me on  the air.

[Steve - K4HX]

Here's what the modeling shows. The red line is the dipole at 120 feet above ground. The dashed line is the 120 tall vertical with 120 radials that are 120 feet long.

You can see the dipole beats the vertical, even at the lower angles.

[flintstone mop]

Here's what the modeling shows. The red line is the dipole at 120 feet above ground. The dashed line is the 120 tall vertical with 120 radials that are 120 feet long.

You can see the dipole beats the vertical, even at the lower angles.

GEESH someone always spoils the dream. Can't we fantasize a little?? This wonderful world of RF.
Fred

[Steve - K4HX]

What's the fantasy in a single vertical? They will never compare favorably to a dipole that is 0.5 WL high (except when the vertical is at the seaside).

[k4kyv]

That pretty well jibes with reports from Jean, F6AQK.  Although at times the vertical gave a good comparison with the dipole, he consistently tells me the signal tends to be better with the dipole.  Also, one report from the west coast, near Seattle, was that both antennas peaked about the same signal strength, but the vertical had deeper fades.

The dipole is close, but not exactly a half wavelength high.  The  mid-point supported by the tower, where the feedline is attached, is at 119 ft, but it droops down to a little over 100' on each end. I consider it more like a true horizontal dipole than an "inverted vee", but actually it is a semi-inverted vee configuration.  Wonder if the modelling program would calculate how the droop changes the radiation pattern from that of a perfectly horizontal wire.

At Timtron's suggestion, I may try loading the vertical on 40m as a full-wave.  It might be ideal for 40m daytime operation, with no cloud-burning radiation straight up vertically or extreme low angles, but with strong omni-directional lobes at about a 45° angle.

[Steve - K4HX]

40m:

Unless you wan't a null at the higher angles, the fw vert will give you little over a 60' high dipole. The fw vert might actually be a better antenna for night time stateside coverage.

[W2VW]

Maybe the unused antenna has some effect on the one in use.

[KA2DZT]

Maybe the unused antenna has some effect on the one in use.

Maybe Don will let me run a line from my station to his unused antenna, this way both antennas will be in use at all times.

Fred

[flintstone mop]

What's the fantasy in a single vertical? They will never compare favorably to a dipole that is 0.5 WL high (except when the vertical is at the seaside).

I comprende...........160M would be a different story.
From 80M to 15M the management of RF gets a little easier. Then you have to worry about multiple lobes and canceling lobes as you go higher.
Fred

[K5UJ]

In medium wave broadcasting a half wave base fed monopole (actually it is more like 190 degrees usually) is used per FCC authorization to get a higher field strength in the groundwave at some distance (usually 1 km or mile, forget which) from the tx antenna compared to what would be achieved with a 1/4 w. monopole.   This is all with the standard good ground system.   I am not completely sure this carries over to 80 m. because the groundwave (in the medium wave sense) is almost nonexistent, but I think the property of interest here is more of a lower "take-off" angle on 80 with the half-wave monopole.   It is being compared to a dipole however but the modeled plot steve put up seemed to indicate the 180 degree monopole had a slightly lower angle than the dipole. 

What is unknown is the efficiency of each antenna.  The dipole may simply be transferring more RF energy to space.   Fortunately this is pretty easy to test.   You only need to employ some sort of acceptably accurate measuring apparatus and control all the variables except the different antennas.   We know the monopole being vertical is basically omnidirectional.   So what you do is get some sort of receiver that is reliable with an easy to read signal strength meter and place it a mile or two away from the tx antennas broadside to the dipole.  Use a standard antenna that does not vary such as a vertical metal rod 3 feet long.   In the daytime so as to avoid skywave QRM  find a dead frequency, probably one just below 3600 will do, and feed some power into the antennas.  It doesn't take much--probably only 20 watts will do, you just have to be sure to use the same amount of power on each antenna, and note the meter reading on the receiver.  Obviously an assistant will be needed and you'll have to coordinate with HTs or cell phones. 

I suspect the findings will be that the monopole for some reason is not as efficient as the dipole, and that is where the problem is.  It is in theory a better dx antenna, but the dipole gets more RF into the air because it is high and horizontal and that makes up for its slightly higher angle.   I would measure tx power at the 50 ohm input to the tuning house--that of course introduces matching network losses as a variable but I guess the only way around that is to measure current on the other side of the tuning house and know the antenna Z on your chosen frequency.   It's curious because the tower has a pretty good ground system at Don's QTH but perhaps over the past 30 or so years it has gradually deteriorated?   Another thing I wonder is if the guy cables are not broken up in the right places for 80 m.  More likely the dipole is somehow causing a problem for the monopole on 80.

[Steve - K4HX]

Verticals have ground/reflection loss. Dipoles essentially do not. This means a vertical is already 3-6 dB behind a dipole before you even begin to look at the pattern (unless the vertical is next to or over sea water). Yes, a vertical can have a lower take-off angle, but look the gain of the dipole at the same angle. It is greater, so there is no advantage for the vertical.

[k4kyv]

No evidence to suggest that the ground system has deteriorated.  It is made with #12 bare solid soft-drawn copper wire.  I have checked the condition of radials from time to time, and the wire has not corroded beyond a brownish patina and slight etching of the copper on the surface.  The silver brazed connections are intact after 30 years, and the tuning at the L-network hasn't changed. No change in performance has been detected over the years.

The main advantage of the vertical on 160 for amateur use is the difficulty in getting a horizontal dipole up 180' or more.  A quarter-wave high dipole is somewhat of a cloud burner, but it would be fine for a 1000 mile radius or so.  I sometimes load the 80m dipole up on 160, with some loss no doubt because it is a quarter-wave dipole instead of a full length half wave, and I get good reports within a 1000 mile radius, but beyond about 200 miles, the vertical usually does better.

Ground wave could be useful for 160, but there is no-one within ground wave distance (about 25 miles) from here to talk to. A high dipole would be more useful on the AM broadcast band for widespread sky-wave coverage at night, but the main concern for AM BC operation is ground wave, and concern is even less for sky-wave in to-day's market.  The BC industry wishes they could do away with it altogether.  I was once  told by an old time engineer who did some of the work re-building XERF on the site of Dr. Brinkley's old border blaster across the river from Del Rio TX, that some time after WW2 they changed over from a horizontal V-shaped antenna to a tall vertical, and their coverage never was as good, plus they lost the 3 dB of gain directed towards the states that they had with the vee.

Timtron once told me about an interesting experiment he did with a vertical on 160.  Not sure if it was a vertical tee or a simple straight vertical, but he had a horizontal wire strung between two towers with the vertical wire dropping down to the ground from the  mid point of the horizontal.  He laid out some radials on the surface of the earth, and using a switching system tried feeding the vertical with and without the radials connected (he must have still had a ground  rod or something to feed the antenna against when using no radials).  He was surprised to see that the radials made absolutely no discernible difference in antenna performance, whether connected to the system or not.

[K5UJ]

Verticals have ground/reflection loss. Dipoles essentially do not. This means a vertical is already 3-6 dB behind a dipole before you even begin to look at the pattern (unless the vertical is next to or over sea water). Yes, a vertical can have a lower take-off angle, but look the gain of the dipole at the same angle. It is greater, so there is no advantage for the vertical.

Okay it looks to me on 75 meters that the vertical has the most gain at 20 degrees; the dipole at 30 degrees.  Yet, at 20 degrees while not in the lobe maxima, the dipole produces a stronger field by what looks like 2.5 to 3 dB if I read the graduations correctly.  So Don, you can use the tower on 75 to shoot a signal, ya just gotta run about 2 times more power   

[K1JJ]

They say we can never be too thin or too rich - and we can never have too low a take-off angle.

But alas, on 75M, the optimum take-off angle from east coast to Europe is something like 35-40 degrees and sometimes much higher depending on the solar cycle and season. The optimum takeoff angle for east coast to cover most of the USA is probably > 45 degrees.  I have proven to myself that my 75M loops take-off angle  at 1/2 wavelength high  (28 degree take-off) is too low most of the time.  It starts to really work in W5 / W7/ W6.  It just STARTS working in W4-land to some extent. The angle is too low.

So, a vertical (or 4-square with gain) on 75M can work well for DX > 2000 miles in general.  A dipole at 90-100' is the best compromise for general, closer-in USA work. Better yet, a pair of phased dipoles at 90' is a KILLER antenna for the overall job.

That said, on 160M, a vertically polarized antenna is the best DXing bet due to Earth attenuation properties. (Can't remember the techno name)  The optimum USA angles on 160M can be rather high too, thus a high dipole is a good bet for local work.  

Two antennas, one for local and the other for semi-DX, is always a great choice for the 160-40M bands.

For 10-20M, a simple stack that can be switched 0 or 180 degrees out will do the same thing. A system as simple as two stacked dipoles will do this.


T