This is the second installment of JohnnyMac’s Inverted L antenna project for 160m. Catch the first here. Check out the original on his forum. The ability to build your own gear and get it working is not only a rewarding skill, but both economical and can never be taken away. True preparedness comes from knowledge.
Article Two – The Execution
The items ordered and purchased locally for the proposed 160-meter, 3/8 wave, inverted ‘L’ was stockpiled in my work shed. I received the afore mentioned pneumatic potato gun i at my local ham clubs Christmas party on December 9th, so I had run out of excuses to not get “cracken” and hoist that bad boy.
I started shooting the mortar shell the next day over the selected trees. It wasn’t as easy as it might sound as temperatures were in the teens and the wind was a steady 10 mph with some 20 mph gusts to consider. Not unlike a sniper working up a dope sheet it took me awhile to get the right angel and windage to make it over the correct spot on the tree. Then also consider the temperature which as mentioned earlier, was in the teens. Apparently, the PVC ball valve leaked when outside too long due to the temperature. So, I would get one to two launches before I had to take the gun back into the cabin to warm up.
Started with 60 psi which got me up to around 70 feet, which was too low for my needs. Finally ended up having to use 120 psi to get the mortar shell and monofilament line over the 120-foot-high pine trees located in the desired locations.
Once I was successful launching the mortar at the right angle, taking windage into account, and warming the launcher to the appropriate temperature it was time to send up the first messenger line. The messenger line was Paracord, which I like to use as it is light and smooth so easier to send up first over a limb of a tree. The Paracord would eventually be pulled back with the heavier and rougher ¼”, 3-strand polyester line with a sailboat block spliced to the end. By the time I had accomplished setting the line for both trees I tied off the bitter ends of the anchor line, went inside to warm up, and start our Sunday roast.
Being close to Christmas with lots of errands to run and some poor snowy weather I didn’t get back to hoisting the wire until the beginning of the following week. I solicited my 14-year-old neighbor Gannon, who holds a General Ticket for help. We first started building the end for the antenna. Below is the finished product.
As you can see in this picture we had a piece of 1 ½” x 1-foot length of PVC pipe which we drilled two 5/16” holes about 1 ½” in on both ends which we passed a 5/16”, 3” carriage bolt through. We used lock nuts to secure the bolts against the PVC walls.
As illustrated below, we slipped a piece of heat shrink on the wire end to be used later. Bent about 1 foot of wire around a 1/16” galvanized eye and wound the bitter end three times to secure the bitter end wire to the thimble. Once done about three inches from the thimble-throat down the wire we took 2” of the cover off the main wire and 3” of coating off the bitter end and wrapped the two bare wires together then soldered. Once this was done we scooted up the shrink wrap over the soldered point and 3-wire wrap to the thimble throat and applied heat to shrink it down. Last, we warped the thimble with amalgamated tape and then over the shrink wrap. I am sure this step was not necessary but being a recovering boater and having crossed several oceans in small sailboats, I tend to go a bit overboard on connections.
Once that was accomplished we moved to the ¼” 3-strand line which would pass through the block that will be hoisted as the anchoring point for the end of the antenna. Again, we used a ¼” galvanized thimble and spliced the bitter end into the line. Now we could have just used a bowline knot instead of splicing the block and anchor point for the antenna however, a knot only gives you 50% of breaking strength of the line while a splice iii gives you 90%.
Last, we ran the bolts for both ends through their respective eyes on the PVC end piece using lock nuts to secure the bolts to the PVC. Care must be taken NOT TO OVER TORK the buts or the PVC pipe will crack.
Now let me digress just a bit to review the securing system for the antenna. As written in Part One we were using an anchoring line with a sailboat block attached to one end. The anchoring line would provide the desired height of the antenna. The adjusting line would pass through the block while the other end was attached to the antenna. This line would be used to adjust the horizontal/vertical/length and position of the antenna.
As we also discussed in Part One, the antenna wire was set up as 3/8 length of a 160-meter wave which equated out to 200 feet. We measured/determined the middle of the wire and affixed red surveyors tape at that point. Once accomplished we took a ¾” 90-degree PVC pipe and did a clinch knot around the middle of the PVC pipe and spliced the bitter end into the line. Passed the bitter end of the wire through the PVC pipe to the red surveyors tape in preparation for hoisting.
Once that was done it was time to hoist the anchor line at the north tree (Antenna horizontal end) and at the south tree (90 degree PVC elbow). Once both locations looked horizontal we hoisted the PVC Pipe end and 90-degree end using the adjusting lines in unison.
At about this time my helpers father and the clubs President whose antenna I was copying showed up. What a blessing indeed as we needed the extra hands and eyes to get the wire positioning correct and get past some tree branches in the middle of the antenna.
Using the two adjusting lines at both anchoring points, we let out or took in the wire to position it just right. One person stood away from the antenna and instructed folks to raise/lower the support or anchor line to position it just right. Once done there was hot chocolate and coffee served for all.
The next part was simple enough. I took a 2 x 6 x 48” piece of scrap board, screwed it to a log on the ground under the vertical drop of the antenna. Fastened the aforementioned 4:1 Unun Balun v to the board and ran the antenna wire to the antenna side of the balun.
Once I accomplished that task I pounded into the ground a 4’ copper ground rod under the balun/antenna wire. Ran a 4’ piece of 12 gauge wire from the grounding rod to the ground part of the balun. Measured out three pieces of wire to use as radials for the ground at: 70’, 45’,30’ and were attached to the grounding rod and ran out in a ‘Y’ pattern from the rod set at about 120 degrees apart.
Gratefully went inside to warm up and solder on the PL-259 connectors to both ends of the 100’ hank of RG-213U marine grade coax. Hooked up the coax to the balun and the other end to my Yaesu 817nd QRP radio. Waited till dark to try it out after that night’s dinner.
After dinner and with the sun set the moment of truth came. I tuned the coax using my LDG Z-817 tuner and unfortunately the tuner would not tune the antenna. However, I listened to a lot of chatter while I spun the dial.
To my surprise I heard an amazing amount of traffic on 160-meters. Finally, I threw caution to the wind, said my call during a pause of a rage chew, and was promptly invited to join the friendly QSO. The stations were hearing me and of course I could hear them. It was reported that I was coming in just above the noise but 100% readable. One of the stations asked what I was running. When I told him, I was promptly lectured on my use of a 5-watt QRP radio on the 160-meter band. I let him lambaste me and may have egged him on a bit for fun and to check out my antennas TX and RX-ing qualities. After we said our 73, I moved on up the dial to call CQ on an open frequency. I was immediately picked up by a ham about 300 miles away who gave me a signal report. Although he was hearing me like the earlier contact reported, I was just above the noise level. Regardless he was amazed that I was hitting him with the 5-watt radio on my new antenna. He strongly suggested I take an analyzer to tweak my antenna length to obtain a better resonance. I moved over to 75/80 meters and again I got several contacts tuning with the Z-817 tuner which tuned up nicely. The next day, I was able to make contacts on 20 and 40 meters too, using the Z-817 tuner.
In my next and final installment of my Home Brew, 160-meter, 3/8th wave inverted ‘L’ I will discuss the process of tuning the antenna to 160-meters.
i Potato Gun
ii ARRL Antenna Book, 23rd Edition 25.4
iii 3-Strand Splice with Thimble
iv Radio Works
v Balun Designs
17 thoughts on “Top Band Magic: The Inverted L on 160M, Part II”
The wavelength is long which can make antennas cumbersome, but I’ve noticed a few ops doing real well on 160 when higher frequency bands are dead.
In our current solar minimum it’s behaving similar to 80.
As we move closer to the Solar Minimum, which is forecast to be in 2019 or 2020, the frequencies at which the ionosphere will support NVIS communications will continue to go down. Over the past 90 days the average F0f2 (Critical Frequency) has been in the 5Mhz to 7Mhz range during daylight hours, and in the 2Mhz to 4Mhz range during night time periods. When the Critical Frequency goes below the desired operating frequency, NVIS communications become degraded. It is important to note that NVIS communications are lost well before “DX” capabilities, because the Angle of Incidence for NVIS communications is near perpendicular to the ionospheric layer(s) which reflect the signal back to earth.
The formula which describes this relationship is MUF=CF/cosθ
Where MUF is the Maximum Usable Frequency for a given communications path, CF is the Critical Frequency (F0f2), and cosθ is the cosine of the angle of incidence (the angle at which the radio wave encounters the ionospheric layer).
For DX contacts, the MUF must be calculated at the mid-point of the great-circle path between the two stations attempting to communicate, because that is the area where the reflection/refraction of the radio signal occurs. For a path from NC to Germany, for example, the point at which we calculate the MUF is over the North Atlantic ocean.
For NVIS communications, the reflection point is always very nearly overhead, so working out the great-circle path is not necessary – just use the F0f2 specified for your location.
As a rule of thumb for MF&HF (1 to 10Mhz) when the F0f2 is 2Mhz below the operating frequency, then an increase of 10dB in signal levels is required to maintain communications (vs. the F0f2 being equal to the operating frequency). To compensate for such a “path loss” we must either increase antenna gain by 10dB, or increase transmitter power by a factor of 10X, or some combination of those two.
Generally, you can assume that the MUF for NVIS comms will be 1Mhz above the Critical Frequency at best, and equal to the Critical Frequency at worst; so if the F0f2 is 7Mhz, then there’s not much chance of achieving NVIS comms above 40 Meters. If the F0f2 drops to 5Mhz, then while NVIS may still be possible on 40 Meters, it will require 10X the power to achieve the same communications as when F0f2 = 7Mhz, and you should be using 80 Meters instead.
When the F0f2 drops below 3Mhz — which is happening about 60% of nights lately — then your final alternative is to go to 160 Meters for NVIS comms.
As we move towards Solar Minimum, the F0f2 will be dropping below 3Mhz on more than 90% of nights, and for the winters of 2019 and 2020 the F0f2 will very likely fall to 1Mhz to 2Mhz every night, particularly in the months of November through March. During this coming ~2 year period, the F0f2 may well not go above 4Mhz or 5Mhz, even during daylight hours, so 80M will be your *daylight* NVIS band, and 160M will be the only option from ~1/2 hour after sundown until about 1 hour after sunrise.
This is why NC Scout, Johnny Mac, myself, and many other ‘radio guys’ are spending so many words talking about 160 Meters lately – we want you to take the opportunity to be prepared for what’s coming.
LodeRunner, if you don’t mind a lowly General shadowing you for a couple of days, Sign Me Up.
You wrote/explained it far better than I could ever do so.
If you think that was good, stay tuned.
Loderunner is spot on WRT NVIS operation during solar minimums. 40 will be the daylight and nighttime medium to long haul band, as 20 used to be, and 80 and 160 will be daylight NVIS. 160 will be the only option on many nights, especially in winter.
One thing to keep in mind, though, WRT night-time NVIS- In the context of amateur DX operations, the fact that you can (sometimes!) be heard for very long distances on 80 and 160 at night is not a drawback, but a plus and a pleasure for DX hounds. I enjoy working lowband DX, because most of the time it is a challenge.
This may not be the case during emergency situations; you want to be VERY careful about who can hear you, because at least on 80 and up, if you can be clearly heard, you can be reliably DFed. One of the other reasons I suggest 160 is precisely because it is such a long wavelength and because it has odd propagation characteristics making it technically more difficult to DF skywave 160 signals. Many satellites, especially geosynchronous ones, orbit much higher than the elevation of the night-time F layer, making it harder to eavesdrop on or to DF any MF or HF communications that are BELOW the FoF2.
Sideband is nice for hobby use, but there are many other modes much more efficient, starting with CW. There is a reason that much long haul communication is still done in Morse Code, but Morse is not the only solution by any means. If you are not exploring the use of digital modes for NVIS, you are missing a potential force multiplier on your comms. FSQ, Olivia and Contestia are modes which are robust enough to handle the band fade inherent in NVIS communication, and will allow reliable high volume message traffic.
My modest inverted Vee is reliable within 300 miles during the day, and I can cover longer hops out to 1500 miles at night. Using CW I’ve worked SA and EU at night.
And yes, it is a bit like 80, except that a lot of DX on 160 is high angle.
Inverted Vee antennas have a substantial Vertically polarized component to their radiation pattern, which can make them very effective “DX getters”, particularly off their ends (where the Vertical component dominates).
So if I had to guess, I’d say that the ends of your Inverted Vee are pointed NNE and SSW. Correct?
Reblogged this on FOR GOD AND COUNTRY.
First I would like to thank NCScout for posting my amateurish attempt at passing along my experiences building, tuning, and using my home brew 160-meter antenna. IMO, ham radio is all about sharing successes and failures with fellow hams.
With this antenna project, the building and launching was the easy part. The challenge has been resonance on the 160-meter band.10-80 meters wasn’t an issue however 160 has been a challenge. Some of you folks who know a lot more than me are probably saying to yourself, “No crap Sherlock!” In Part 3, I will go into all of the details.
Post my self induced forced education on an inverted ‘L’, I am making some incredible contacts with ease now. Of course not without some loss of hair and further graying of my beard, getting to this point.
In closing, if one does not get off their butt and try tough tasks they will not grow. An old mentor told me once, “If you are not uncomfortable in a new job or project you take on, you are not growing.” Amen to that!
JohnyMac, You’re correct, “resonating” the system is often the trickiest part of optimizing an antenna. Part of getting that last 1 or 2 dB of efficiency out of an antenna system often comes from broadening your thinking as to **HOW** you do the resonating. Given the same wire, installed in the exact same manner and location, and considering two different “matching networks” which present the same 1:1VSWR to the feedline, one network may be 20%, or even 50% more efficient than another.
Now, I’m not picking on commercially made “antenna tuners” here, but I will point out that many manufacturers design theirs such that they can claim the widest possible matching conditions – many will even “tune up” their own chassis and components with no antenna attached at all. This very fact tells you that such ‘tuners are not of the greatest efficiency – particularly if the antenna presents a “challenging” (read, “highly reactive”) impedance to the tuner at its terminals.
With very few exceptions, the efficiency of commercially made tuners goes down drastically when the reactance at the antenna port goes above about 100~150 ohms.
So, for instance, a typical entry-level tuner from Piece’o’Fine Junk Inc. might be 90% efficient when matching an antenna that presents a 210-j07 ohm load (that’s 210 ohms Rr and 7 ohms of capacitive reactance) but the same tuner may only be 50-60% efficient when you present it with a 40+j300 ohm load (50 ohms Rr and a moderate 300 ohms of inductive reactance) – a scenario very likely when feeding a “random antenna” on 80M or 160M.
I chose this second example, 40+j300 ohms, because it is very close to what a 3/8 wavelength Inverted-L antenna presents at the feedpoint. So if we just use the antenna tuner, the efficiency of the system might only be 50~60%…because of the tuner. But if we were to add 300 ohms of capacitive reactance in series between the antenna and the tuner – that is to say, we “resonate” the antenna *before* attaching it to the tuner, then the tuner is left with the much easier job of transforming 40+j0 to 50+j0 ohms, and the efficiency of the tuner would then be well above 90%. That’s roughly a 2.5dB to 3dB improvement in signal strength, just because we added a capacitor to the system.
Now put that in the context I discussed above, where you’re trying to work NVIS above the Critical Frequency – I stated that, as a rule of thumb, 2Mhz above F0f2 you will need 10dB more signal… well there is a substantial portion of your needed increase, right there. Or, conversely that 2.5-3.0dB could be the difference between being heard with 5 watts versus needing 8 or 10 watts to be heard by a particular station (all other factors being held equal).
Antenna System Efficiency is one of the least considered factors by most hams. They learn about VSWR, and stop growing their understanding at that point. Now, a dummy load presents a 1:1VSWR to the transmitter, but it definitely is not a good antenna.
As NC Scout said, there’s a full article coming on exactly this type of antenna modeling and optimization. I hope you’ll enjoy reading it as much as I did writing it.
JohnnyMac: I have never tried an Inverted L myself for a variety of reasons, but I think I will whittle myself up one and give it a try on 160 this winter. Thanks!
@Keypounder – Stay tuned – there’s more coming on the Inverted-L and NVIS comms, and also a look at a free online tool for calculating optimum NVIS comms frequencies.
Cool beans! Looking forward to what you are bringing to the discussion LodeRunner.
Please share your project with the groupleypounder74. I am sure there is a bunch of stuff we all can learn.
Looking forward to the next installment! I feel JohnyMac’s pain with respect to getting a home built antenna resonant. I too have had issues with that same problem. Creativity and ingenuity are key, and I’m sure they will come to play with this antenna. You guys have been harping on 160 being the place for NVIS for a long time, and I fully agree. I’ve got a 160m 1/2 wave dipole rolled up and sitting next to my portable comms bag. This time of year is the time to get out and explore 160m, when the band is quiet. Once you get comfortable with the band and how it operates, you will be able to use its advantages and disadvantages to suit your needs year round.
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