Linked Repeater Networks
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Many National Weather Service offices in the U.S. include Amateur Radio as a part of their operations plan, and most of those utilize a linked repeater network of some sort. We’re going to cover the general concept of a linked repeater network as well as how they work, and why local weather nets are often held on non-network repeaters.
A linked repeater network is a coordinated group of repeaters that rebroadcast radio transmissions picked up by other repeaters on the network, allowing ham radio operators hundreds of miles apart to communicate using a simple handheld, mobile, or fixed base radio. As a result, the NWS can keep up with weather conditions over a broad area, and operators can be forewarned of incoming weather conditions that may require local monitoring.
So, how do linked repeaters actually link? Linked repeaters have a 2nd radio interfaced with the repeater’s main radio, often called a “remote base”. This allows a signal coming in from the Remote Base to be transmitted by the repeater’s main radio and a signal coming in on the repeater’s main radio to be rebroadcast on the Remote Base.
Best Power Practices III
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In Best Power Practices I and II we discussed a variety of issues related to properly powering your gear. We covered the need for dedicated power wiring as well as the desirability of using standard connectors.
Power Wire Gauge
We previously discussed the need to utilize wire of the proper gauge for feeding power to our radios, and also the fact that conventional vehicles do not have wiring from the factory capable of carrying the current required for a typical mobile amateur radio. Utilizing that wiring will likely result in damage to the wiring over time.
So, you've decided to properly power your rig with dedicated wiring for your gear. But what kind? Certainly you want to use stranded wire in a mobile rig, as solid wire eventually suffers from the vibration of the vehicle and will become damaged over time. Stranded wire is also more flexible and tolerate of being routed through the vehicle. The insulation type is important, particularly in automotive applications, where temperatures (even in the cabin) can be quite high. Cross-Linked polyethylene (XLP), and Polyvinyl Chloride (PVC) will do the job, but plain polyethylene will break down at temperatures in the cabin, much less in the engine compartment.
Best Power Practices I
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Operating a mobile rig in a motor vehicle or as a base can create some interesting challenges, and while many installations may work, they may be optimal, and could potentially damage your radio or automobile. We’ll break things down into a few different topics.
Connecting Vehicle Power
Most motor vehicles are not really wired for an accessory that draws the current a typical mobile amateur radio will. Still, many of us have (or do) run our radio using the “Accessory” or “Cigarette Lighter” jack. That jack is typically rated for 10 amps, and for intermittent usage. A conventional amateur radio with 50 Watts AM or FM output power will approach that limit and could, especially with older radios, max out the power draw, and at worst exceed capacity. Additionally, the adapter connection does not provide a solid ground or hot connection, often increasing current draw. There is little other wiring in the car that can handle that load either.
So, if you’re at or above capacity, why doesn’t the fuse blow? Because fuses require an excess of current for some sustained period of time. Even though the fuse isn’t blowing, the wiring is getting hot, and the insulation will eventually begin to break down.
Running power specifically for your radio is the best practice.
Cross-Band Repeating
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Cross-Band repeating has great potential for use in EMCOMM, extending our ability to utilize handhelds as well as providing gateways to more distant repeaters.
Before we get too deep into cross-band repeating, lets review how a typical repeater works. A repeater, generally, receives a signal on one frequency and re-transmits what it receives on another nearby frequency. The difference between the receive and transmit frequency is what we call an "offset". On a 2-meter repeater that offset is usually less (negative) or more (positive) by 600 kilohertz. Repeaters also often have a "sub-audible" tone (often referred to as PL tone, a proprietary name used by Motorola). A sub-audible tone is a very low frequency tone that we can't hear, but the repeater can detect; If the sub-audible tone is not present then the repeater will usually just ignore the incoming signal, allowing the repeater to ignore a distant station that might be transmitting an unusual distance due to atmospheric conditions or filter out random noise on the frequency.
A radio operating cross-band will function much like a regular repeater; but unlike typical repeaters, which have the input and output frequencies on the same band, the input and output frequencies will be on entirely different bands, usually 2M and 70cm. The reason for this is the significant difference in frequencies allows the simultaneous transmit and receive with simple circuits built into the radio, rather than needing large and bulky duplexers required for same-band repeating.
Many in our group who can't directly reach the repeater with an HT utilize cross-band repeat capability. To cross-band to a 2 Meter repeater using a 440mhz HT, merely run an HT in simplex on an appropriate 440Mhz frequency and then on your mobile or base station set one VFO to the same simplex frequency as your HT and operate the other VFO as normally for the repeater. Once the VFOs are set you'll need to put the radio in cross-band mode - how to do this varies by radio, so check your user's guide or search the internet. When the radio is in cross-band mode it will transmit everything that comes in on the repeater output to the 440Mhz frequency, and repeat everything from the 440Mhz frequency to the repeater. Your HT now has the same range as your base or mobile rig!
Roll-Up VHF/UHF Antennas
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Emergency Communications deployment has similarities to camping and backpacking trips, where you need to pack everything you need with you without overloading yourself. Striking the proper balance is challenging, because no matter how hard you try you will usually find something you should have packed and something you should have left behind, because we never know what the requirements of the deployed location will be.
It's safe to say that one item likely to be on any deployment list is some form of enhanced antenna to improve the ability to reach out to distant repeaters, or even function as an ad-hoc cross-band repeater.
Arrow makes a great dual band J-pole that breaks down to be pretty portable, but requires a pole to be mounted to, as is the case with most commercial antennas. It's possible to bring a tripod along, or some type of mount that can be attached to your vehicle, but that may require your deployment be restricted to a parking lot or your vehicle. Sometimes that will be the case by necessity, but it does isolate you from your served agency members.
Drone Carried Emergency Repeaters
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One of the challenges of EMCOMM is we are often deployed at locations where infrastructure may be damaged, and that could include any repeaters in the area. As our simplex efforts have shown, simplex communications is challenging to say the least. Portable repeaters are a potential solution, but in some situations there may not be a high spot to deploy it to, or there may not be power to that area, and it may not even be accessible by vehicle to power it off its alternator.
People have discussed the use of balloons, but in that case, in addition to the balloon, you need the helium or hydrogen and it presents challenges keeping it properly tethered, not to mention requiring a particularly large balloon to carry a repeater payload or tether an antenna coax from the ground, much less carrying enough power capability to operate the equipment.
Some are proposing that Drone Carried Emergency Repeaters are a possible solution.
Near Vertical Incidence Skywave (NVIS) Antennas
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Why NVIS?
We as amateur radio operators are typically focusing our efforts on HF towards long distance communication, "DXing". You would think the same would be true for emergency communications as well; however, in many instances what is needed is solid communications within the area of the emergency and the areas immediately surrounding it. During an incident we will often need to communicate to different parts of the state and, perhaps, adjacent states to exchange information to the "outside world" until normal communications resumes.
So, that fantastic all-band fan dipole antenna you have 80 feet in the air, while great for talking to China from West Georgia, will quite possibly make it very difficult, if not impossible, to reliably communicate with Macon. Why? because HF DX communication relies on atmospheric skip, and your fantastic antenna is liable to be throwing your signal at an angle up towards the horizon, right over the heads of the people around you, only to bounce off the atmosphere and land in Asia or Europe or California. What is ordinarily a fantastic thing is actually proving to be a hindrance for emergency communications.
Snow Spotter Program
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Most amateur radio operators are familiar with the SKYWARN program, and reporting of severe weather conditions. We usually associate the SKYWARN program with reporting heavy rain, hail, and even tornadoes. But, the National Weather Service also runs an associated Snow Spotter program, gathering data to assist them in their mission to protect life and property, as well as developing better storm models.
Snow spotting, like conventional storm spotting, has specific conditions and information requirements. The NWS wants reports of:
- Change in precipitation type (rain to snow, snow to freezing rain, etc)
- Snow Accumulation of 1 inch or more
- Heavy Snowfall Rate (example: snowing at 1 inch per hour)
- Significant Blowing or Drifting snow
- If the snow, ice, or blowing snow is having a major impact on travel
- If what is occurring is not what is in the forecast
- Anything significant that you think we should know about
SKYWARN / Storm Spotting
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Amateur radio and the National Weather Service have a unique and exciting relationship, where amateur radio operators with an interest in meteorology can combine those two interests and provide valuable public service.
The National Weather Service (NWS) sponsors a weather spotting program open to all interested citizens, but with special consideration for amateur radio operators. The NWS SKYWARN program is a multi-faceted program designed to train public safety personnel, amateur radio operators, and citizens at large in the basics of storm spotting and reporting.
Where things get really interesting for amateur radio operators is the NWS maintains amateur radio stations at their centers, usually working in conjunction with repeater owners who link repeaters together forming a wide-area linked repeater network for amateur radio operators to report real-time directly to the NWS!
In Georgia, the NWS Peachtree City office is the center of the action for amateur radio operators operate equipment that, in conjunction with the linked repeater network, can maintain contact with amateur radio operators / storm spotters all across the state.
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