I recently had a reader email regarding his low power (QRP) field antenna utilizing the NVIS mode. He commented on his systems lack of performance.

He is using a dipole with 65’4″ legs for both the 40 and the 80 meter band. He is using a bnc-to-binding-post adapter as his “cobra head” with WD-1 field phone wire for antenna wire. His radio system consists of a Yaesu 857 and an AT-100 Pro Auto Tuner. He is trying to use NVIS to fill in the skip zone gaps in his AO.

Here are the problems that I see:

1. Trying to use one home made dipole for 2 bands.

Using the formula 234/f Mhz (for quarter wave length) and assuming the middle of the 80 meter band is 3.75 Mhz, that gives us a length of 62.5′ for each element.  So the antenna is now a half-wave dipole and is good-to-go for 80 meters.

For 40 meters that same formula results in a quarter wave length of 32.7 or 33′. He is now trying to use what amounts to a full-wave antenna for the 40 meter band. A full wave antenna is a bear to work with due to the very high impedance at the center feed point which makes them very difficult to match.  Nearly impossible to use with any coax.

2. Lack of a matching device at the antenna feed point.  Here is a picture of his feed device or “Cobra Head”. (Don’t worry dude, I removed all geo-location data from the pic). By the way, I definitely would not have any loops tied in insulated antenna wire for strain relief. You’ve built in RF chokes. Non-insulated wire – no problem.


When you are working with NVIS, the input impedance changes with the height of the antenna above ground. From as low as 15 ohms near the ground to as high as 120 ohms when the antenna is raised. Depending on the coax such as RG-58 (5O ohms) or RG-8 (75 ohms), you will have mismatches. If you are using this system with regular long-haul comms and the antenna suspended at least 1/4 wave above the ground, it will work just fine.

The tranceiver tuner will take up a lot of the slack, but it will not reduce the losses, it just hides them from the transceiver. When working QRP you need every watt to radiate from the antenna.

Here’s how I would fix the problem.

1. Order solid or braided, non-insulated wire from thewireman.com, measure out the required maximum length for 2, 1/4 wave sections on the longest band you will use and spool each up. Hint:  There are very, very, very few resources available for 160 meter DF. Remember, you can always go shorter, but it’s hard to go longer if you don’t have enough wire in your ruck and you’re 100 miles from no-where. Cut (not a physical cut but a measure to length of wire rolled out, the rest still secured on the spool) your antenna length for the freq you will be on, using the above formula. Then spool it back up when you are done.

2. If running in NVIS mode, install a 1:1 current balun like this:


You can find it here: http://www.balundesigns.com/qrp-model-1110-1-1-isolation-choke-balun-1-54-mhz/

While it won’t fix all your problems, but it will clean up your signal.

3.  Add a 30′ max length of RG-58.

4.  2 – 50′ sections of 550 paracord with a large bullet type bank fishing sinker tied to one end of each.

5.  Measure out the antenna wire from the spools and secure the remainder. Attach each free running end of the wire, as well as the coax, to the balun. Attach a section of 550 cord to the end of each spool, throw the sinkers over a tree limb and host each end up to the height desired and tie the weighted ends off. Move the antenna up and down until you hit the sweet spot with the guy on the other end.

Bottom line: If your going to drop a grand on a high end QRP rig and tuner, you really need to spend some time on the most important part of your comms system, the antenna.


About as good an article re: NVIS as I’ve seen. Great pics.

Originally posted on brushbeater:

I’ve brought this up enough times already; let’s de-mystify this beast. Communications fall into one of two categories: Line of Sight(LOS) and Beyond Line of Sight.


If you can see it, in theory at least, you should be able to communicate with it. Low-band VHF(10M/11M/CB) and above(UHF, Microwave) works in this manner. VHF can have some characteristics of HF; but that’s beyond the scope of this article. Squad level communications work in this manner. This would be your mobile rigs and HTs. Keeping it simple, if there’s something big in between you and the person your talking to(like a mountain or a bunch of buildings) or long distance, you need a repeater to compensate. Line of Sight(plus repeater) looks like this:


Beyond Line of Sight

So what if you’re outside the range of repeaters? Eventually the energy from your radio or repeater will fizzle out. At some point…

View original 732 more words

HF Transmission Lines

Posted: 10/07/2015 in Uncategorized

Several good mentions have been made in the comments section by readers regarding the transmission line (T/L). Since this is the next logical item in the system to discuss, what follows is my take. Most of the information provided is pretty basic for low power (less than 100 watt) stations. You could spend a lifetime studying T/L and antenna theory, but I have better things to do, as I’m sure you do. So well keep it simple. If most of this information is old hat and you are curious about my setup, go to the bottom of the article.

The transmission line is the link from the output/input connections of the transceiver to the antenna. Actually, everything from the output of the power amplifier (PA) section of the radio, and the input to the RF amplifier section, to include a tuner if one is used, to the feed point of the antenna is part of the T/L. So, no, the T/L is not just a piece of cable. To complicate things a bit further, the antenna and it’s associated T/L are known collectively as the antenna system.

The perfect T/L would move all of the power transmitted from your radio to the antenna as efficiently as possible, which means no loss of power. If I am sending a radio message to one of my folks and my radio is set at 25 watts, I want all of that 25 watts to radiate from the antenna.

That same TL needs to move received signals from the antenna system back to the radio with no distortion or loss of signal strength. If my antenna picks up a transmission at 100 milliwatts, I want all 100 milliwatts to be present at my receiver section.

The ultimate T/L would be inexpensive, durable, easy to install and remove, and require very little maintenance. An added bonus would make it nearly invisible to prying eyes.

An important item to remember: most transceivers require a 50 ohm impedance at the output in order to be perfectly “matched” to an antenna. Any deviation in either direction, more or less impedance, causes loss of efficiency and in extreme cases can damage your radio, T/L and antenna.

There are several different transmission line setups available but the two most common are:  ladder line and coaxial cable.

Ladder line (also called twin lead or open-wire) consists of two parallel  conductors separated by an insulator.  ( http://www.universal-radio.com/catalog/cable/3028.html ). The insulator is usually plastic or air. “Twin lead” was once commonly used with TV antennas and is identified easily as it has a continuous plastic strip separating the two conductors.  “Window ladder” is used with amateur radio and is identified by the rectangular air gaps spaced at regular intervals in the plastic that separates the conductors. The characteristic impedance of twin lead is 300 ohms and window ladder is 450 ohms. Ladder line uses the air between the two parallel conductors as it’s dielectric and if installed correctly has very little loss.

The primary advantages of ladder line with respect to coax are:

1.  Lower loss.

2.  Can drive a balanced antenna (eg: dipole) without a balun.

3.  Cost.


1. Usually requires periodic mounting standoffs

2. Must be kept away from metal objects.

3. Can lose its low loss features when wet or icy.

4. Requires a tuner when used with unbalanced antennas.

Coaxial cable or “coax” also has two conductors, however one in located in the center of the cable while the other surrounds the center conductor for the full length of the cable. The conductors are separated, in most cases, by a plastic or foam insulating material and the outer conductor is protected by an insulating cover. The center conductor is normally a single copper wire while the outer conductor is a braided wire which is usually, but not always, made from copper. Depending on the coax, it’s characteristic impedance is 50 or 75 ohms. Much closer to the radio output requirements. Use a good quality 50 Ohm coaxial cable with appropriate power rating such as: RG58, RG8X, RG8, RG213, Belden 9913F7, Davis RF Bury-Flex. A coax with a dense (or double) braid is worth the money. Simple installation; ideally the coax will go directly from the antenna feed point to your transceiver.

The primary advantages of coax with respect to ladder line are:

1. Most transceivers are equipped with coax connectors. If using ladder line, a balun or tuner is required.

2.  Coax is not effected by nearby metal objects.

3.  The impedance of coax doesn’t change when it rains or snows.

4.  Ease of setup and tear down.


My setup:

I’m a coax guy. Just keep-it-simple-stupid. Rolls up tight and unrolls right, every time.

The transmission line (T/L) for my semi-permanent base station consists of a 30′ section of RG-8 coax with soldered Amphenol 83-1SP silver plated PL-259 connectors. The tuner is an ICOM AT-100. (LDG AT-100 Pro as a backup). The antenna is the Buckmaster 300 watt 7 band (offset center fed) OCF dipole. My backup antenna is a Carolina Windom 300 watt 8 band OCF dipole.

Why 30′ of coax? That’s the distance from my transceiver to the antenna feed point with a few extra feet of coax for slack. Don’t make it any longer than necessary. Why use coax instead of ladder line? I have found that coax is far more durable in the environment that I operate in. In addition, I can attach it directly under the metal roof of the building my radio room is in and make “fairly” sharp twists and turns that I can’t make with ladder line. The entire system can be pulled down, coax rolled up and thrown into a Pelican case and be ready for transport in about 5 minutes. If you don’t move your station on a regular basis, then something like ladder line might work better for you. Last but not least, the area I live in has an environment that is nearly considered rain-forest. Ladder line does not behave well in wet and icy conditions.

Why RG-8? My loses are pretty negligible with only 30′ of coax, especially since I keep my power out well below 100 watts, and only operate this system on the lower ham bands. It is a cost vs. performance issue. I chose to forego the extra expense needed to mitigate the small losses that I would probably encounter by not using a more expensive coax.

Why not use crimp together fittings instead of soldered? Less power lost due to heating and potential arcing in a loose fitting. If you don’t know how to properly solder and seal your fittings, then you could buy cable made to length with fittings installed. Best answer, stash another arrow in your quiver and learn how to solder and build your own cables (as well as other stuff). Go here and learn how to do it correctly: http://www.k3lr.com/engineering/pl259/ . The Amphenol silver plated fittings are just about bullet proof.

Why do I use a tuner when this antenna works without one? Since the Buckmaster is a OCF and is almost an exact copy of the Fritzel antenna, it’s characteristic impedance of 300 ohms is matched by the balun (6:1) at the antenna feedpoint to that of the coax (50 ohms). Buckmaster has tested and recommends running the center of the antenna at 30′ and the ends at 10′ to avoid high SWR. However, I run my antenna about 15′ above the ground in the NVIS mode, and this will lower the input impedance of the antenna to somewhere in the 100 to 75 ohm area. So, being the cautious guy I am with my equipment, I run a tuner to protect the transceiver. And even though my SWR is good at the output of the tuner, I should probably perform an antenna analysis and change out the balun. Something for the future.

With my field radio system everything needs to fit into a small molle bag attached to my ruck.

I use RG-8X in the field because of it’s small diameter and weight. It also handles the frequencies up to and including 10 meters, loss wise, much better than regular RG-58. Since the KX-3 runs only about 12 watts max, that’s important. I keep two 25′ sections with a connector to join the two together if I need 50′ of coax.

The tuner is integral to my Elecraft KX-3.

I use “FLEXWEAVE” 14 AWG 168 bare copper wire or “Hot Rope” 0.133″ on a spool, purchased from TheWireMan.com. I determine what frequency I am going to use and “cut” each 1/4 wave dipole antenna to length. Using un-insulated antenna wire rolled up on small spools allows me to unroll it to the length needed without actually cutting the wire. Any wire left unused and rolled up on the spool is electrically shorted together and only adds the width of the spool to the antenna length. If one were to use insulated wire on a spool it would act as a balun. Care must be taken not to short out the wire against objects including yourself.

No balun is used, I just connect a bnc-to-binderpost adapter ( http://www.amazon.com/Parts-Express-Binding-Posts-Adapter/dp/B000LFWQH4 )  to the antenna wire and to the coax. A dipole at 10′ usually has a characteristic impedance of between 75 and 50 ohms, just what the radio is looking for. The tuner does the rest.

Provided by Jeff Alan, a reader and frequent comment provider. I am blessed to have many that have a vast knowledge of  radio experience and don’t mind sharing it.


The article is lengthy, but has a ton of good basic information.

In light of the recent discussions over at Western Rifles regarding, “Get your ham license so you can get some experience under your belt” versus “Who does the government think they are telling us we need a license”, the introduction to the article pretty much explains why the bands are regulated.


Posted: 09/25/2015 in Uncategorized


HF versus VHF/UHF

Posted: 09/23/2015 in Communications

Guys, lots of questions coming in regarding HF vs. UHF/VHF radios and antennas. Let’s flog that deceased equine a little longer; If you get your Amateur license at the Technician level, you won’t have to ask these questions any longer.

VHF/UHF radios work on the frequency bands that inherently use short/very short antennas, plus, they are usually very small, light weight, easy to operate, and run off of batteries. What’s not to like! I think this is why most folks initially purchase these radios as inter-squad level comms.

And while they do have those advantages, one of their major disadvantages is that they usually only work when they are in unobstructed view (line-of-sight) of one another. Put most any obstruction between the two (an area known as the First Fresnel Zone) and you have no or very poor comms. The obstruction could be just about anything; a hill/mountain, forest, large buildings, moving vehicles, or any combination of these things. In addition, factors such as power output and receiver sensitivity are also in play.

So, how do we get around (or over) those obstructions? Use a repeater mounted above the obstruction. Then you are relying on someone Else’s infrastructure. And if you do get comms over the mountain to your buddy in the next valley, how do you get to the valley beyond him? Another repeater.

Here is the link for a well put together article on comms for the beginner from INFORMOPS. Take a look toward the end of the article for some visual descriptions of the challenges regarding VHF/UHF comms. I should have had his blog listed as one of my favorites a while back, my mistake. HT to PSYOP Soldier for reminding me.


Antenna Systems

Posted: 09/21/2015 in Communications

I am going to attempt to answer several readers comms questions over the next few weeks by giving an explanation of my current HF setup for local to mid distance comms.

I use a digital software, RMS Express (part of the WINMOR package) in conjunction with a certain antenna system, HF transceiver, 12 volt power supply, a PC, tuner and a modem. This setup allows for reliable HF communications from 0 out to about 300 miles, across the wildly varied terrain of the Southern Appalachian mountains and adjoining foothills. This system will pretty much give me coverage in all of the valleys and ridges in my area. Try that with a VHF/UHF system even if you have repeaters. My current setup requires no external infrastructure outside of a 12 volt car battery and a way to keep it charged. I can use my car charging system, home solar system or a man-portable solar system depending on which rig I use; my base station or my tiny man-portable system.

First, you have to have your General or higher Amateur Radio License to access the frequencies you will need to make this work. If you are thinking that you and your buddies will put this system together after SHTF and start talking, then you are delusional. The group I routinely make comms with all hold General and Extra Amateur licenses and it still took about 3 months for us to work the bugs out. If you think that you can pirate the frequencies to test and maintain your system you are even more delusional. The “Ham Nazis” will catch you and turn you over to the FCC. They will look up your bogus call sign on the internet and DF your location just for sport (look up “foxhound”). And rightly so. They took the time and expense to study and pass the test. It’s not that hard. Now that we have again beaten the proverbial dead horse regarding licenses (much like Mosby and PT) lets get on to the equipment.

The antenna I currently use, and have a lot of success with is the Buckmaster 300 watt, 7 band OCF antenna.


I chose this antenna for several reasons.

Being a offset center fed (OCF) antenna (45′ on one side, 90 on the other, total of 135′) allowed me to physically locate the feed point of the antenna closer to my radio room with a shorter lead in RG-8 coax, about 30′ long. I had less room to fit the antenna along one side of the building than the other.

The antenna is resonant on nearly every band I use, it always tunes up quickly, doesn’t require a tuner (I still use one) and, if properly installed, has very little VSWR. Some radio guy will me write to say “My such-and-such antenna works better and costs less. Great, send the info. on it. The Buckmaster has worked great for me for years now. Dodge, Chevy, Ford, whatever…..

If you are interested in working down in the 160 meter band (which I am for reasons I won’t go into here) then go for the Buckmaster 8 band antenna. Just remember you will need approximately 270′ of space, or nearly a football field. And, you will most likely need a tuner for 160 meters.

On their website, Buckmaster shows the antenna slung up higher at the mid-point than at the ends. That is correct if you intend to make HF comms like most Ham operators, as long-haul as possible. I, however, want to make comms that will fill in the area between the ground wave and the sky wave. The dreaded “Skip Zone”. If I want to make long-haul comms, I will raise the center rope.

Here is a link that describes the skip zone:   https://en.wikipedia.org/wiki/Skip_zone     Pay particular interest in the words “vertical incident”.

Since most of the folks I want to talk to are in my region (Meat Space Folks) I need a technique that overcomes the skip zone. That technique is Near Vertical Incident Skywave or NVIS.  Yet another link if you have the time:


Bottom line for me and most of the folks I talk with: we have our antennas generally about 12′ off of the ground for the entire length of the antenna. Once you are on the air, you can adjust it up or down and see what happens.

Some folks will say it is a more efficient use of RF power to build an antenna for the center freq you are using in each band and use a tuner. That is true, however, if you work off of a Signal Operating Instruction (SOI) that says to change your frequency twice a day, every day (60 total for each band per month), then the multi-freq antenna becomes more desirable.

My antenna is attached to trees using Dacron UV resistant ropes that I found at The Wireman. His link:  http://www.thewireman.com/   I attached marine pulleys (also bought at Wireman), to trees at the 2 ends and center points, attached the rope to the end insulators and center balun connector, connect one end of the RG-8 coax to the balun and hosted away. Then I tied the free running ends of the ropes to fence staples at the base of the trees. You can attach strain relief to the ends of the coax for extra security.

In good SF comms tradition, I drilled a hole into the exterior wall of my radio room and fed the coax though it. I still have not foamed the hole shut. I have a friend who would be mortified if he saw my radio room. His looks like the helm of the Star Ship Enterprise. Too each his own, mine is functional, and can be torn down quickly and thrown into a couple of Pelican cases.