***Disclaimer: I am not a guru when it comes to this stuff. I am definitely a student, and this is just a record of what I have been using thus far. I don’t want to give the impression that this is the way. All of this is likely to change if I learn a better way.*** […]
Archive for the ‘Communications’ Category
A reader recently requested I elaborate on the comms equipment battery charging system I carry in my Ruck.
First let me say that the setup I use is not what I would prefer but it works. I would prefer an ultra light weight system that I could attach directly to my Elecraft KX3 and charge the batteries using its built-in battery charger. The radios built in charger requires 13.8 volts dc but I haven’t found a pack-able panel that supplies that voltage. Most backpack/camping panels supply 5 vdc. That would require 3 sets of panels connected in series to get the necessary voltage. So, what I’ve had to resort to is removing the batteries from whatever radio I’m using, and charging the batteries in a charger that’s connected to the solar panels.
My current setup consists of the XTAR VC4 Charger and the Renogy Solar 14 watt E-Flex Solar Power Panel with dual USB ports.
I chose the XTAR based on its light weight and size, its ability to recognize and charge 4 different batteries at once and charge a wide range of Li-ion, Ni-MH and Ni-Cd batteries, plus pretty good Amazon reviews. So far its performance has been good. On the downside, it’s not waterproof, but then I haven’t found one in its class that is. And while it’s not fragile, it’s not private-proof and should be packed in your ruck accordingly. Last but not least, you have to use the XTAR provided USB to charger cable. Why they didn’t design it to accept a common double sided USB cable or micro to USB cable is beyond me. So until I can find a spare or make my own, I have 1 cable and no spare. That makes it a critical failure point. The old “2 is 1 and 1 is none….”.
I chose the Renogy 14 watt E-Flex solar panel due to the fact that the solar panels I installed with my home system were also purchased from Renogy and I have been pleased with them. They offered the E-Flex as a camping solar system and I thought for the low price, I’d give it a try.
The E-Flex weighs in at 1.3 lbs, folds up small, has dual USB charging ports and a pretty nifty charge indicator that glows brighter as the suns intensity increases. One downside is the flimsy attaching loops arranged around the perimeter of the assembly. Other manufactures offer heavy duty grommets that can be used for attaching points. Another is the small storage pocket does not seal completely, so be cautious what you store in it.
Charging time for 4 – Panasonic 2500 mAh Eneloop Pros runs about 6 hours depending on the available sunlight and angle. Charging time for 4 – 2000 mAh Eneloop standards is about 4 hours.
Now you have to ask yourself, which is lighter and takes up less room in the ruck? Lots of spare batteries or a few spares and the recharging system? I would say that’s METT-TC dependent.
What is the Mission? Is it short enough that I can just take some extra batteries? Or is it a long term affair where the weight of the recharge gear will be less than the weight of the batteries. Will we be using vehicles instead of walking? Then we just use our cigarette lighter plug-in inverter and charger.
Terrain: If it is a long term affair, what will the weather be like? Cloudy weather would preclude using the solar panel. Will I have the opportunity to lay out a panel for a few hours during the day or will we be constantly on the move? Is the terrain heavily forested?
Troops: Am I or someone on my team in good enough physical shape to hump the extra weight over rough terrain? Do I have the space in my ruck?
Civilians: Are they on our side? Will we be operating in a non-permissive environment where laying out a panel might draw the interest of a civilian who then compromise our location?
I know, I left out Enemy and Time. You get the gist.
A reader recently asked if I would recommend the Yeasu 817 as an alternate for the Elecraft KX3, in the tactical HF radio role. In my opinion, if the KX3 wasn’t available, the 817 would be my rucksack radio of choice. After all, the original 817 (now the 817ND) is a time tested radio that has been around for nearly 20 years and is just about bullet proof.
The price point for the 817 is seductive, averaging about half the price for a maxed out KX3. That being said, there are a few differences. The KX3 is an SDR (Software Designed Radio) that has a ton of options available and so many functions that it can be overwhelming to a new radio operator, while the 817 is pretty straight forward.
My list of requirements for a rucksack HF radio primarily focuses on a few items.
First is weight; my motto being ounces is pounds. The KX3 comes in at 1.5 lbs while the 817 comes in at 2.6 lb.
My second requirement involves power issues. Power out: KX3 – 10 watts, 817 – 5 watts. Not a big deal if you are fairly experienced with QRP. If you are new to ham radio, you might be a little frustrated initially with the limitations of either of these low power radios.
Power consumption is major concern when in the field with no resupply. I don’t want to charge batteries after every contact and I don’t want to pack around large batteries. I charge the 8 Eneloop AA batteries for my KX-3 using a small Renogy solar panel and XTAR battery charger while in the field. The normal rx power consumption for the KX3 is 150 ma versus 300 ma with the 817. The 817 is well known as a power hog but the problem can be partially mitigated if you get rid of the 1400 mah nicad battery pack that comes with the radio and go with the W4RT 2700 mah battery pack built especially for the 817. Look here: http://www.w4rt.com/FT-817-Accessories/One-Plug-Power-FT-817.htm How you would charge the battery in the field would take some thought. I would probably change out the crappy stock battery access door with the W4RT door at the same time. Here is a pretty good link regarding the power issues with the 817: http://www.ka7oei.com/ft817_pwr.html
Third issue: using CW and digital vice voice comms. Voice comms is pretty much out, this is a QRP rig after all. Both radios have internal keyers for CW and will support digital modes.
Fourth, is the radio rugged and waterproof. Neither is water proof or even remotely water resistant. Keep your radio in a dry bag. I would say the 817 is a little more rugged than the KX3 but you can rugged-ize the KX3 somewhat if you drop the extra bucks and buy the gemsproducts SIDE KX cover and side panels.
My fifth requirement is an internal antenna tuner. In a tactical situation, you shouldn’t use the same freq. twice. Unless you want to cut the antenna to proper length for each different freq. used, you need a tuner. You have that option with the KX3, but not with the 817. That problem can be solved by purchasing the Emtech ZM-2 ATU (Antenna Tuning Unit). Find it here: http://emtech.steadynet.com/zm2.shtml
The 817 has more band coverage than the KX3, which tops out at the optional 2 meter band. The 817 also includes the 6, 2 and 70 cm bands. In certain situations, I would caution the use of a radio in those VHF/UHF bands.
Just my thoughts. Whatever radio you go with, get out there and get on the air.
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.
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…
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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.
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.
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.