Antenna Choice

The antenna that has become the choice for the upgrade is an inverted vee on the high bands and a tee top vertical on the lower.  It is based on the modelling described in the March 27, 2016 post  “Antennas For the Remote Base”.  It is best described as a bunch of compromises. No compromise would be 64 feet.  Ours will be 40 feet.   No compromise would be a dipole.  Ours will be an inverted vee. Instead of two supports the inverted vee will only need one. Fiberglass camo poles will be used for the support and will look something like this.

camo pole in sky

At the 20 foot middle level are guys ropes.  At the top is what looks like more guys but will actually be the inverted vee antenna.  Inside the fiberglass camo poles will be ladder transmission line. At the base will be an autotuner. The inverted vee will be resonant on 20 meters.  With the tuner at the base the inverted vee can also be made to cover 17 and 15 meters. It might not cover 12 and 10 because of the high impedance at the second harmonic.  We might need to construct a second antenna for 10 using a PAR EF-10 on a fiberglass Jackite pole.  Back to the main antenna, a relay will be used to switch around the configuration for the low bands.   The second configuration will use the transmission line as a vertical radiator.  The inverted vee at the top will become a top hat tee.  In this configuration when the relay is activated there will be four radials on the ground connected to the tuner. These radials are each four feet wide and 50 feet long welded wire fencing laid flat.  This configuration will be used for 30, 40, 60, 80, and 160 meters.

One area that did not get compromised is the ability to work all bands.  Not every band models as the best DX antenna ever but every band will have the ability to operate.  We are currently assembling the necessary parts and hope to begin construction within a week from today.

A Look At The Comet CHA250B Antenna

Comet Antenna, of Japan,  developed a 24 foot vertical antenna for HF that requires no radials, is multi band, and I picked up one at a recent hamfest.   How good is it?  Reviews on the Internet are mixed which means even though some people hate it others love it.  Why?

CHA-250B1

It is extremely clean looking with no top hat radials or spines or traps to break up the visual lines.  It has a mysterious matching device at the base.  Not mentioned in the sales brochure and almost buried in the instructions is an important note that might be a clue as to it’s love-hate reviews.  This antenna must be mounted a minimum of 35 feet above ground.  How many reviewers had their antennas mounted correctly at 35 feet or more? From the Comet instructions:

Comet instruction

Aha.  The secret to this antenna is to put it ridiculously high, use the coax and mast for a counterpoise, and let the coax or the mast do the radiating.  It is marketed as a small yard solution awkwardly worded this way on the Comet web site:

if you live in an antenna restricted area and must manage with antenna or space restrictions or you simply wish to operate incognito you will be forced to make significant antenna compromises. The CHA-250B will make the most of these circumstances!”

A 35 foot mast with a 24 antenna adds up to 59 feet tall.  Does a 59 foot vertical equal incognito?

Enough of the negativism.  One must get past the surprise of the height requirement and just think of this is as a 59 foot vertical antenna.  The Comet CHA250B is a 59 foot vertical.  How does it model in EZNEC?   Will it work some DX?  Our reference antenna is a full size quarter wave ground mounted vertical with lots of radials over average soil.  We care most about the gain at a take off angle of 15 degrees and secondly how “full” the pattern is.  That is, does it have serious nulls that would compromise operation. Here is a view of the antenna with rf current modeled at 14.1 MHz.

Screenshot 2016-03-28 20.06.47

Let’s run through the bands and I’ll make comments starting with the toughest of all, 160 meters.  A gain of 0.77 dBi on 160 is quite respectable.  And there are no nulls.  Nice.  This should work some DX on top band.  This is roughly equivalent to a full size quarter wave vertical. HOWEVER, I’d be skeptical of a model showing a 24 foot antenna having a .77 dBi gain on 160.

Screenshot 2016-03-28 20.02.23

Next band up is 80 meters which often proves to be the hardest band when it comes to 5BDXCC.  The pattern here looks good, too, with -0.21 dBi.  Again, I am skeptical of the model.

Screenshot 2016-03-28 20.02.44

Now for the esoteric band, 60 meters.  Pretty good again. Very usable.

Screenshot 2016-03-28 20.04.04

How does it do on one of the most popular bands, 40 meters?  Can a person work some DX here?  Yes, as long as the band has gone long, very long.  This band has one of those dreaded serious nulls above 30 degrees and stateside signals will be missing.  No NVIS either.  A person will need a separate 40 meter antenna to work domestic stations.  On the other hand interference from strong U.S. stations should not be a problem when working DX.  This is the first band where the pattern is not ideal.

Screenshot 2016-03-28 20.03.15

Moving on up through the bands, next is 30 meters, the first WARC band so far.  The pattern looks good here.  Good gain at 15 degrees and a nice plump pattern the rest of the way.

Screenshot 2016-03-28 20.03.44

The big one, in fact the biggest one for working DX, the 20 meter band.  How does it look?  It’s not equivalent to a beam but it holds it’s own against a quarter wave vertical. It also has plenty of plumpness for higher angles, too.

Screenshot 2016-03-28 20.04.28

Now for the upper bands beginning with the WARC band, 17 meters.  Wow, even a dB of gain here.  A little disappointing above 45 degrees but otherwise a usable band. Critical frequency never goes this high to allow NVIS contacts on this band, anyway.

Screenshot 2016-03-28 20.04.48

Now we’re getting into what our grandparents called Ultra High Frequency, 21 MHz. How does it do?  Fine.  Like the 17 m band, we don’t have much high angle radiation but in the low angles used for DX it looks good.  And it has 2 dBi gain even.

Screenshot 2016-03-28 20.05.05

Skipping 12 meters because we assume it will behave the same as 10 meters, here is a look at the “light” band (from the phrase, “DC to light”).   Ten meters is a very usable band on this antenna on the rare occasions the band is open.  Rooster tails are almost ready to appear but they haven’t yet.  Therefore no serious nulls. In addition we have almost 2 dBi of gain.

Screenshot 2016-03-28 20.05.29

Overall it would be reasonable to assume this is a good multi band antenna usable for both DX and domestic contacts on almost all bands.  How in the world we can erect this at 35 feet is questionable.  The author’s or translator’s grasp of English is not strong as indicated by the use of the word “erectric” instead of “electric”.  Could it be that the author does not have a grasp of the measurement system and he (or she) actually means 35 centimeters or something else?  An attempt to find a copy of the instructions written in Japanese failed.  The thought was maybe there had been a failure in the translation if we could find the original instructions.  We will attempt to put this antenna up at 35 feet and see how it plays.  At that height it’s hard not to play well.

 

 

 

 

 

West Mountain Radio RR4005i Remote Power Monitor

When one dials into the Remote Power Monitor this is the greeting screen.  It shows voltage and current draw from each device.  It also provides the ability to turn on or off any device over the Internet.   Very dangerous because the Internet equipment can be turned off remotely leaving us disconnected with no way to turn it back on.  If that happens it would require a site visit to restore.

Screenshot 2016-03-25 19.12.57

 

Happy Sunday

Finally the stars have aligned and we are having a happy Sunday afternoon watching the DX come in on 20 meters and seeing our signals posted over a large part of the world. This is only on 20 meters because we are still using only the PAR/LNR EF-20 end fed half wave vertical while we ponder antenna improvements.

Screenshot 2016-03-27 15.03.49

Antennas For the Remote Base

The equipment is behaving and it’s time to turn our eye toward antenna improvement and more gain for DX.  Our original intention was to start with the PAR/LNR EF-20 on a 39′ fiberglass Spiderbeam pole to get on the air fast.  This is the antenna that has proven itself in multiple locations over the years and it has worked well here so far. Now all we want is more.

2016-03-02 14.32.27

How to improve?  First of all the EF-20 works only for 20 meters. Any antenna that gives us more bands will be a big improvement.   Next step is to find more gain at low angles for a better DX antenna. Horizontal dipoles at the proper height are always better DX antennas despite verticals’ claim to low angle of radiation. Verticals only win if they are over salt water. For a full size quarter wave vertical over average ground a gain of 0 dBi is typical and much less for a shortened vertical.  Horizontal antennas have the advantage of gain from ground reflections which verticals don’t have.  That gives dipoles about 8 dBi more gain above average soil.  Our goal is to aim that 8 dBi at the angle we want by putting the dipole at the correct height.

What is the correct dipole height to achieve DX?  First we have to determine the take off angle and that is a function of geometry — the distance to the DX station and the height of the ionosphere at that given moment.  The angle changes minute by minute and station by station making it impossible to select a perfect angle.  We can look at tables and computer programs to come up with a range.  Very distant stations require angles as low as 3 degrees and stations fairly nearby can be worked with 40 degrees.  Accumulated wisdom seems to say the best compromise to work the most stations is 15 degrees and we will call that our optimum take off angle.  This is also the angle we will use for our calculations.

What is the necessary height to attain a 15 degree take off angle for a 20 meter horizontal dipole over average ground?  We have modeled multiple dipoles using EZNEC 5.0 to find the right one. It’s strongest lobe at 15 degrees is when it’s height is 64 feet. EZNEC assumes flat ground which we don’t have. We also haven’t measured our soil conditions although we have referred to the M3 Map published by the FCC ( and reprinted in the ARRL Antenna Book ). Because of these two approximations our models will only be representative and not perfectly accurate.  We could make a soil conductivity test some day and improve our accuracy. A method without driving spikes is presented in the 23rd edition of the ARRL Antenna Book.

Figure 1 – “Ideal antenna”

Screenshot 2016-03-27 14.48.49

Here we show a gain of 7.22 dBi at 15 degrees, which is also the angle with the maximum gain.  Thus we know we are at the proper height for maximum gain at 15 degrees. In addition there is a healthy lobe at 50 degrees for those close-in stations. Notice the  nasty null at 35 degrees. We’ll call this the ideal antenna except for geographic areas where the 35 degree angle is needed. It’s really not an ideal antenna at all.  It just has a maximum at the 15 degree angle we want.

Now, let’s see…could I put up a 64 foot dipole….hmmm.  Not totally unheard of using a pair of Spiderbeam 18 meter fiberglass poles.  For now we will keep the “ideal antenna” in mind only as something to compare to.

For purposes of comparison let’s model the EF-20 vertical we are currently using.

Figure 2 – Existing vertical antenna

Screenshot 2016-03-27 15.49.37

Yes, it has a low angle of radiation peaking at only 17.6 degrees like verticals are suppose to.  Unfortunately the gain at that peak is only .71 dBi.  At 15 degrees, gain is only .5 dBi which is 6.72 dB worse than the dipole.  Pitiful.  It’s a wonder we’re working any DX at all.  We’re giving up over 6 dB from our ideal antenna.  We need four times the power just to break even.  Instead of 10 watts we need to run 40.  Ouch.  Again, on the other hand,  not unheard of.  That’s only down one S-unit.

Tom Rauch, W8JI, makes another point in an article titled “The Myth Of Take Off Angles”.  He suggests taking a more holistic approach and don’t ignore nulls and missing angles of radiation.  Look at the whole pattern. An antenna with deep nulls and missing angles is going to miss DX from a lot of geographies. The dipole is missing everything that requires a 35 degree take off angle. The vertical has no nulls but it is missing the entire higher angles from 30 degrees on up.  That will make it hard to work stations close in.


 

Are higher angles essential?  Power must be increased by it’s square to double the distance. That is, we need to quadruple the power to double how far we reach.  Another way to look at it is we only need a quarter of the power to work close in stations which is 6dB less power.  Or our antenna can have a 6 dB reduction in gain at the high angles when using the same power.  Perhaps a pattern like Figure 2 is not such a problem after all. 

 


What heights are within our means?  We might possibly use surplus fiberglass camo poles to reach up to a half wave on 20 meters, 32 feet. We would need two supports of 8 poles each. Here is what our gain would look like at 15 degrees.

Figure 3 – 20 Meter Dipole At 32 Feet

Screenshot 2016-03-27 15.24.52

Wow, 4.03 dBi vs. 7.22 dBi at 64 feet.  That is quite a hit.  More than 3 dB is given up. That’s half our power.  We could live with this by just turning up the power.  If we were going to run 10 watts we could crank it up to 20 watts and break even.  We might have to settle for this. Notice the maximum gain is 6.74 dBi at 31 degrees.  That angle is going to maximize signals to the U.S. East Coast where a concentration of hams live.  Trying to reach Europe competing with those strong East Coast signals could be a problem.  This is a real negative for this particular height.

Next let’s look at a little more height. If 32 feet uses 8 camo poles how about adding two more poles for each support to reach 40 feet?

Figure 4 – 20 Meter Dipole At 40 Feet

Screenshot 2016-03-27 15.35.24

Hmmm: 7.22 dBi – 6.15 dBi is down only about 1 dB. Still a loss but a 6 dBi gain at 15 degrees is nothing to sneeze at. That’s quadrupling our gain over the existing vertical plus there are no severe nulls. We have a peak at 24 degrees and that might be low enough to put the first hop beyond the East Coast, minimizing the strong competing signals.  This might be a compromise we can live with. Two supports of 10 camo poles each could be quite an undertaking.  Still nothing compared to the work involved of putting up a tower though.  A few years back we put up a loop at 28 feet using 7 camo poles for each end.  It looked like this.

image1[1]

These 7 section poles stayed up through winter and summer weather for a year and a half with no issues before I took them down.  But what if the supports were 10 sections high instead of 7?  Would it survive?

Would it be possible to eliminate one of the two support poles and put up an inverted vee on just one support?  Here’s a model.

Figure 5 – 20 Meter Inverted Vee At 40 Feet

Screenshot 2016-03-27 10.35.35

We’re back to that slightly disappointing 4 dBi range and we have that dreaded peak toward the East Coast again.  Compared to our ideal horizontal dipole at 64 feet with a gain of 7.22 dBi at 15 degrees we are giving up 3 db, half our power. We can overcome that by cranking the output but the real problem is those East Coast signals overpowering the European stations.  This is similar to the model of a dipole at 32 feet using two supports.  At that time we said we might have to live with doubling our output power to break even.

Conclusion

If you got this far, congratulations!  It’s a lot of boring graphs and reading.

Any of these horizontal antennas more than doubles the gain of the existing vertical but would they double the performance?  The existing vertical has one thing going for it. It’s low angle minimizes strong signals from the East Coast that can wipe out weak signals from Europe.   Table 1 summarizes the work.

Table 1

Antenna               Description                                           Gain @15 deg  Peak gain


Ideal antenna     horizontal dipole up 64′                    7.22 dBi           15*

EF-20                    end fed half wave dipole vertical    0.5 dBi             17.6

Dipole                   horizontal dipole up 32′                     4.03 dBi           31

Dipole                   horizontal dipole up 40′                    6.15 dBi            24

Inverted Vee       inverted vee up   40′                           4.78 dBi            27

*Peak gain is at 15 degrees but there is large lobe at 50 degrees that allows strong U.S. signals to over power the DX.

Multi Band

Multi-band operation hasn’t even been mentioned.  For other bands the plan is to use this antenna for all the high bands 20 thru 10 meters along with an SGC SG-230 auto tuner at the base.  The transmission line from the tuner up to the feed point would be ladder line.  For the lower bands we would use the transmission line as the antenna and the inverted vee would become a top hat.  For radials we would lay out welded wire fencing on the ground.  A relay would switch between the low bands and the high bands controllable over the Internet, of course.  The SG-230 would be used for both high bands and low bands.

A lot to digest and we’ll need some time to think about the best compromise. I have no decision for now.  Thank you for enduring this long post.

Post Note

At a hamfest yesterday I picked up a multiband vertical.  It’s a Comet CHA250BX.  It is 23.5 feet long with a very unique matching network at the bottom.  I think it is attempting to be an end fed half wave on each band. The coax provides a counterpoise. I plan to use a non metallic mast so it doesn’t interfere with the coax radiation.  Based on the model below I do not expect good things.  It’s advantage is it’s multi band  and it will be easy to put up considering it doesn’t need radials.  It might be a good interim antenna until I decide what to go with.

Figure 6 – Comet CHA250B Vertical Antenna – 20 meters

Screenshot 2016-03-27 19.58.00

 

March 28, 2016 Followup –  After sleeping on it and looking over yesterday’s work again I’m more confused than ever.  The existing EF-20 has the advantage of minimizing U.S. interference but the gain is very low.  Boosting power beyond 25 watts is not an option.  The 4 dBi antennas might not be a real improvement because they all have the U.S. interference issue.  Even the “ideal” antenna has that issue.  Should I be looking at something different instead that would give gain only at low angles?  Phased verticals or a four square? Loops?  Or a beam on a very tall tower (like 100′)?  Am I being overly concerned about East Coast interference?  Should I just put up a compromise 4 dBi antenna and see how it goes?  Time to take a break and ponder all this.

Ok, times up.  The compromise I am choosing is the inverted vee at 40′.

Hill Top Smill Top

I tried to operate from the top of a hill on the property temporarily but I could never get the test working.  Meanwhile I had been wanting to perform an HFTA as described in the ARRL Antenna Book.  HFTA stands for High Frequency Terrain Analysis.  That software program might tell me if I should move the setup to the hill top permanently.  After an evening of working with HFTA I concluded moving would not make a significant difference. In the directions of DX like Europe and Africa the terrain continues to slope down even though I’m not at the top of the hill.  In fact it slopes down toward Europe for more than a mile.  That sounds like a pretty good location.  Here are the two terrain plots toward Europe (45 degree azimuth).  Terrain drops off at a sharp angle.

Screenshot 2016-03-25 14.37.15

Figure 1 – Terrain toward Europe as seen from hill top ( red diamond is dipole at 39′ up).

Screenshot 2016-03-25 15.02.52

Figure 2 – Terrain toward Europe as seen from original location ( down the hill about 45′).

My conclusion: there is a downward slope toward Europe at both locations so it doesn’t matter.  HFTA is a fantastic tool. I must make note of the peak at 10,000 feet out.  It is much more of a concern when I am at the lower position.  This concern might be a reason to go up the hill later if performance isn’t what I hope for.

Square One Revisited

Today I feel like it’s back to square one.  It’s so frustrating when things don’t work. Got into the site today and restore the equipment.  Everything is back to the way it was March 3 when it all worked.  But it doesn’t work this time.  When I press the “ON” button on the control panel nothing happens.  The only clue is a “SIP Error” .  I’ve gone through all the simple stuff, checking each setting on both ends for differences, cables tight, rebooting, etc.   I was getting this yesterday when the equipment was at the temporary location on the hill top.  I was using a wifi-to-ethernet adapter and I thought that was possibly the problem because it was the only new piece introduced. Today I moved all the temporary stuff back down the hill to the original location and restored it.  Back home it still doesn’t work.  Tomorrow is a hamfest so I’ll be busy, plus there is supposed to be another snowstorm.  When I can get back to the site in a few days I plan to fetch the equipment back home and see if I can figure it out.   Back to square one.

Found it.  I had the port forwarding screwed up. I had the sip ports forwarded to the wrong i.p.(typo).  AHA!   The system comes up now.   Next is to test transmitting.

Yes!!!  It can transmit.  PSKreport is posting spots all over the U.S.  Just made a contact with AA7IX but unable to complete due to transmitter dropping. Levels?    Keep on it.  Oh, yes.  AA7IX is in Cheyenne which is in our black out zone, the donut hole. Hope is restored. Below is a screen snap of a K6TU analysis of my antenna, looking similar to a HAP Chart.

Screenshot 2016-03-24 16.12.48