Do you want to learn about Ham Radio? Have questions?
Having issues with your ham radio?
We have the answers!
Bring your radio and the manual for it and we will have the people there to help you!
Lake County Amateur Radio Society Operations Day May 3, 2014 10:00 am to 3:00 Location: Lucerne Community Church in the Fellowship Hall 5870 East Highway 20 in Lucerne, CA 95458
All levels of Ham Radio Operators are welcome! Licensed or not!
For further information, contact Kristine (KI6YYW) via e-mail � firstname.lastname@example.org
VHF/UHF radio propagation in mountainous terrain can be difficult and sometimes may seem impossible. As you know, higher frequencies travel primarily line-of-sight. Unlike HF, they do not reflect off the ionosphere, so their range can be rather limited (although knowledgeable DXer’s know special tricks, like meteor scatter.)
However, all is not lost. It is possible to make sense out of using higher frequencies in mountain communities, and at the November WARS (Willits Amateur Radio Society) seminar Tim Hanna, WB9NJS, described some of his experimentation and research on this topic.
Tim got interested in mountain VHF propagation after being surprised that he could communicate over 2M FM from his home QTH in Willits to Wayne, W6WMV, in Finely (south of Clear Lake.) The signal path is a good distance and there are two significant mountains in the way; regardless, Tim was still able to communicate quite well.
In his presentation Tim reviewed the ways radio signals change direction:
- Reflection: wave changes direction by bouncing off other objects (a metal fence post for example).
- Refraction: wave changes direction due to variations in the air (or other medium). Examples are cold and hot spots where the density of the air differs.
- Diffraction: wave changes direction by passing over sharply defined edges — often called the “knife edge effect”.
Next, Tim introduced a handy mapping tool for analyzing signal paths. The software is from DeLorme and makes it fairly easy to go from a flat map of the path to an elevation profile view that helps you see the obstacles that are in the way.
Once that was done, an elevation profile could be generated:
Looking at this profile, you might begin to wonder how Tim’s signal was able to reach Wayne in Finely. There are a two peaks that should block the signal. Tim speculated that perhaps knife edge diffraction was helping his signal bend over one or more peaks.
Tim also noticed another possibility. It could be that signals were being reflected off Mount Konocti behind Wayne. If so, the signal map becomes:
To plot such an elevation profile, the profile is “unfolded” to show it by distance. It becomes:
To understand this profile, note that that tall peak on the right isn’t blocking the signal, it’s reflecting the signal. That’s how reflection is shown on a profile plot.
So, this signal path seems more likely. Although there may be a knife edge effect at the peak closer to Tim, the reflection of the signal from Mount Konocti behind Wayne makes sense. The middle peak becomes less of a factor because it’s no longer in the way.
Tim went on to show several other signal paths for unusual radio contacts he’s made from his QTH on the west side of Willits. Some are not such direct paths as the one to Wayne in Finely, but looking at the elevation profiles helps you understand how such paths are even possible. For example, he’s able to communicate with K6FTY who lives a considerable distance to the north. The trick again is to use a directional antenna to reflect the signal off various high-elevation peaks.
Thanks again to Tim Hanna for his educational WARS presentation. It’s good information for those of us who live in the mountainous terrain of Mendocino and Lake Counties. If you find you can’t make a VHF/UHF QSO directly, you now know that you can try reflecting or diffracting your signal off various peaks to increase the likelihood of your success.
Earlier I mentioned the McARCS coastal meeting where we built cheap Yagi-Uda antennas (many thanks to Steve, KJ6EIF.) The design was based on WA5VJB’s cheap yagi, and by “cheap” I mean about $5. The antennas were made from lengths of ordinary house wiring attached to wooden garden stakes. The feed method was a simple half-folded dipole (no gamma match or balun needed.)
Even though we closely followed the instructions, the antennas didn’t tune as well as we expected. They resonated lower than we wanted, and the SWR wasn’t the best. After some experiments we suspected the problem to be the insulation left on the directors (to make the elements stronger in the wind.) That insulation affects the velocity factor, making those elements electrically longer than they should be, and on a Yagi, that creates major problems.
Last weekend I decided it was time to see if the antenna could be fixed, or whether the boom should return to the tomato garden. I discovered that it only took a few clips here and there to make the antenna just about perfect. Here’s what I did:
- Mounted the antenna on a mast with the elements vertical (and mounted it from the end, not the balance point.)
- Connected Steve’s antenna analyzer to the feedpoint. The SWR was about 1.5:1 and resonated at 143.5 MHz.
- Wanting to fix the SWR problem first, I snipped 1 cm from one side of the 1st director. The SWR fell to 1.3!
- Then, trimmed the other side of the 1st director another 1 cm, and the SWR dropped to 1.1:1. Even better!
- Clipped 1 cm from both sides of the 2nd director. No effect (on the analyzer that is, but maybe in the gain and pattern.)
- Thinking I was on a roll, I snipped 1 cm from both sides of the reflector. Whoops… the SWR climbed just a hair.
- Now the big decision was how to deal with the driven element. It’s not easy to cut because half of it is a loop. Throwing caution to the wind, I just snipped 1 cm from the non-loop side and bingo! The resonant frequency jumped to 146.23 with an SWR around 1.1:1.
- Finally, I clipped 0.5 cm from each side of the 1st director. The SWR landed at 1:1!
Hurray! The antenna was right where I wanted it.
I measured the SWR as 1.32 at 145, 1.02 at 146, and 1.3 at 147. That’s just about right for the FM part of the 2M band.
Now, I just need to figure out where to bolt it outside, and then… do I want to point it toward the Mendocino coast, toward the Bay Area, Eureka, or Clear Lake? Decisions, decisions. Hey Steve, could next year’s workshop be about building our own rotators for $5?
There are strange things done in the midnight sun
By the men who moil for gold;
The Arctic trails have their secret tales
That would make your blood run cold;
The Northern Lights have seen queer sights,
But the queerest that’s ever been said,
Was that night on the marge of Lake Lebarge
My HT battery went dead.
(My apologies to Robert W. Service and his Cremation of Sam McGee; a favorite of mine, and somehow fitting here.)
I think we all have rechargeable battery tales, don’t we? For nearly four decades now, ever since my father bought a military surplus ni-cad battery array, I’ve been in a constant battle with batteries. There is perhaps some irony in the root of those two words, battle and battery, which are French in origin.
There are many myths, not-so-sound advisories, and nutty ideas about rechargeables. These days, I ignore them all and go with what works well for me.
Here are a few of my conclusions:
- Keep your batteries “topped off”. In other words, recharge often and recharge fully. How often? Every day, if possible, but for sure never go longer than a month. Have you noticed that those solar lights in your yard will run for two or more years, often 700-1000 cycles, because they diligently follow this rule (of course, they have no choice.)
- Use a good quality charger. If it’s not providing a complete charge, or if it charges with too much current (battery gets really hot, causing internal evaporation), you need to find a better charger.
- Avoid complete discharge, if possible. Sure, you will get all kinds of advice on this point. Just keep in mind that you’re using a reversible chemical reaction that emits heat and deteriorates “at the edges” of the curve: full discharge and over-charge.
- Use a good battery tester to confirm that your battery has reached the end of its life. I don’t know of any good battery testers, so I made my own. It’s a shunted milliamp-meter that pulls nearly full current for a very brief period. This technique makes the condition of the internal resistance quite obvious.
The second point is worth expanding on. Some battery chargers are devious. The worst ones, like on my cheap Ryobi cordless drill, never stop charging, eventually drying out the electrolyte. I lost three drill batteries until I noticed their sly trick (selling more batteries.)
Most average battery chargers will allow a battery to go dead even while it’s in the charger. They may do a good job charging, but once done, the battery will begin discharging on its own. It’s aggravating to take a battery out of the charger, only to find it’s dead. (Note this will happen on many laptop computers too.)
A good charger will top off the battery with regularly timed cycles, or provide a trickle charge. However, obtaining the correct trickle charge is non-trivial, and most chargers won’t do it properly. Actually, I don’t know of any, so if you own one (or built one) let me know.
Also, keep in mind that a dead battery pack does not mean all of its cells have gone bad. I often break open dead battery packs and test the cells separately. It’s usually just a single cell that died (1 in 6 or more) but most people replace the entire pack, costing $60-90. Another sly trick?
Anyway, I’ve written about this topic a few times in the past, and I could go on forever. You probably have your own special tales to tell. I invite you to post them in the comment section.
While not a truly scientific test, I did a short test yesterday with two different ten meter antennas. I have a 10/15/20 meter trapped antenna horizontally polarized that was originally used as the driven element of a three element antenna. Now just a dipole. The other antenna is a homebrew dipole that is hanging vertical from my tower. The bottom is just a few feet off the ground. I am on top of the hill so this will make some difference but not much.
Monday afternoon after repositioning the horizontal antenna so it now favors the northeast–Ukiah is off the end of it–and hanging the vertical, I got on the air.
Listening on ten meters with the horizontal antenna I could hear some southern Mexico stations, Centeral American, and some Brazilian stations on it. Mind you, they were off the end of it so that was the LEAST favorable direction of the antenna. Switching to the vertical made no or very little difference in signal strength. Thus the received signal had to be coming in from a higher angle of radiation so that it got both antennas about the same. A bit later while on the vertical I heard a weak but readable signal from San Francisco. A contact was made and when I switched to the horizontal antenna, all was lost.
As this signal was coming on the horizon, and was vertical polarized, it shows that for local ground wave the polarizations should be the same for maximum signal transfer. The cross polarization from horizontal to vertical will lose allot–typically 20 to 30 db–over the short distrance while not losing so much over the long skip distance.
Just a note, nothing scientific or so. It does show that the need for some of us to have both polarizations is indeed a fact. My problem is that my vertical antenna is causing me audio rectification in the computer speakers. Need some chokes.
Just an observation. Ten has been pretty good about noon on here as has fifteen meters.
From the 10M Mendocino/Lake/Northern Cal net last night I got a better idea of how a 10M vertical performed for nearly-local traffic (see prior blog.) Generally, it confirmed that the more direct (line of sight) the signal, the more important the polarization. In other words, there are fewer obstacles to skew the polarization.
For example, experimenting with polarization in QSO’s with Steve, KJ6EIF, who was also running vertical and line-of-sight (6 mi), the difference in signal strength for vertical vs. horizontal was 12-15 db. So, that’s closer to the 20 db cross-polarization figures I mentioned in the prior blog.
For more distant signals, like Wayne, W6WMV, who was over the ridge and down in the valley just south of Clear Lake (23 mi), and also on a vertical, the polarization difference was only 3-5 db. That’s still significant because it brought his signal up to being readable.
Oddly, I noticed no difference in signal strength of polarization with Dave, N0EDS, who is on the north side of Clear Lake (20 mi) and puts out a great signal here. One possible reason is that my antenna field was being distorted in that direction due to the metal roof of my house. (As mentioned earlier, the test antenna was not that far off the ground.)
One other thing to mention from last night’s net, Lee, N6MIV, over on the coast in Gualala had a terrific signal (40 mi and multiple ridges). He was using a 200 ft horizontal wire (G5RV), and he could hear my horizontal signal, but not so much the vertical. We didn’t get a chance to determine the signal difference. Maybe next time we can experiment more with that.
Well, hopefully sometime in the next month we can repeat the experiment with the test antenna a little higher off the ground. Where it is now is quite likely causing a distorted field, which will throw off the results.
I’d like to invite all Mendocino and Lake county hams (and anyone else who can hear us) to participate in our 10M HF net on 28.405 MHz at about 20:15 PT Wednesday nights.
Someone in Lake County dropped off an old CB StarDuster antenna at Dave’s (N0EDS) shop last week, and he was so kind as to give it to me for a special antenna project.
The project was to determine if using a vertical antenna on 10M for nearly-local QSO’s would improve signal strength to other hams also on verticals. In theory, matched polarization, e.g. vertical to vertical, buys you 20db of signal. Or, perhaps better stated, cross polarization loses you 20db.
For VHF and UHF, antenna polarization is important. This was used to an advantage when the convention for ham radio used horizontal polarization for SSB (and other modes) but vertical polarization for FM. Horizontal is somewhat better for DX work and residential setups, and vertical is easier to implement on vehicles or handheld devices.
Ok, so I dusted off the StarDuster, shortened its elements to fall around 28.405MHz (a favorite local freq) connected up some old RG-8… and gave it a try.
The results were not as I expected: The antenna provided roughly the same signal strength for nearly-local contacts as a 10M trapped horizontal dipole at 25 feet. Of course, it does have the benefit of being omnidirectional, where the dipole does not.
As I thought deeper about why I wasn’t seeing 20db difference… I think it’s the nearly-local factor that’s the problem. To get to Lake County, the 10M signals are passing over a 3000 ft ridge on Cow Mountain, refracting over the top (and perhaps some ground wave in there too — it’s hard to know how far that travels around here.)
It occurred to me that refraction (and even reflection) is going to have an effect on HF polarization, just as it does with visible light. You know… why polarized RayBan’s became popular years ago… many substances polarize light, the sky, lakes, windows, and more. Glancing at the ARRL Antenna Book, it confirmed this premise.
So, the 10M signals where losing most of their polarization as they bent sharply over the top of the mountain. Perhaps even the fact that the ridge is mostly horizontal was a factor (as I remember from spatial filtering laser lab experiments back in school.)
Well, that’s why I enjoy ham radio: new lessons to learn everyday. The next parts of the project are:
- Determine what effect antenna height has in this result. The StarDuster is very low to the ground which perhaps could be part of the problem (it’s basically a half-wave dipole.)
- Determine if a different type of vertical antenna might perform better. I’ve got a lead to follow on this.
- Figure out if my old RG-8 coax is any good. Not sure yet how to do this… but would be good to know.