When discussing efficient low power communications, it is impossible to deny the effectiveness of narrow bandwidth data, even at low power levels. But wait, there’s more to it than that!
The Holy Grail of man-portable field communications is efficiency! A more efficient field station is often lighter, and more manageable, than the alternative.
Efficient field stations require:
- An efficient antenna
- An energy efficient radio & power supply
- An efficient and effective mode.
An efficient antenna allows us to use less output power to complete a connection. An efficient antenna also translates in to greater range, without necessarily increasing output power. In many cases, an efficient antenna also improves reception.
An energy efficient station using low current on RX, and an efficient PA for TX, benefits from reduced power supply requirements. In the field this translates to longer operating time with smaller power supply. If you’re the operator carrying the power supply, this is a big deal!
Choosing the correct operating mode for our connection is just as important as choosing the best radio, an efficient antenna, and reducing current consumption. In some ways, choosing the best operating mode is even more critical, when our objective is using the least amount of output power possible, to make the connection.
Over March and April 2023, I have used no more than 3-watts from a (TR)uSDX for the local and regional Winlink connections made daily. The antenna is an off center fed dipole for 80/40/20, configured for NVIS. I am using a low current consumption radio called (TR)uSDX (~80ma RX & 500ma TX @13.8v). The session connection has been VaraHF at 500hz, but Robust Packet is also incoming for testing.
In the above image, there is a connection being made between my own station in KP25 and LA7F about ~500km away at 300°. This is a typical NVIS connection from my home station. Station distance can range from ~30km out to 600km from my location. At closer range or with a good path to target, an efficient antenna, and narrow bandwidth eg 500hz Vara HF or Robust Packet, results in reasonable connections using 0.5 to 1 watt.
The enablers here are:
- Efficient antenna
- Effective antenna configuration
- Narrow bandwidth
- Error correction
- Speed throttling
As mentioned earlier in this article, an efficient antenna is the best way to get the performance out of a low power radio. Where a broadband antenna can be effective across a wide swath of spectrum, rarely if ever can it be efficient. The common cure is using more TX power to make up for the losses. If you start with an efficient antenna, more of your power will go out the antenna in the first place, rather than being dissipated as heat inside the balun.
Effective antenna configuration
By effective antenna configuration, I mean that we should be using the best antenna configuration for the station we are trying to make a connection with. In the example of local or regional communication using NVIS, the best case scenario has both stations set up using NVIS antenna configurations for the band, and range the connection is taking place on. This can best be described as “targeted-range configuration”. If the station you are targeting is 100km away, but our antenna is configured for DX, our signal will shoot right over that station, as if it didn’t exist. Use the best configuration for the targeted range!
We all know CW if ever effective. It is extremely narrow (like a laser beam), making it very effective at low power, long range communications, in less than ideal conditions. This is also true for narrow bandwidth data modes like FT8, and JS8. When we start discussing SSB, I like to use the analogy of a shot gun vs a long rifle. Like a shotgun, SSB can put lots of information out over the air, but requires quite a bit of TX power to do it effectively. This is especially true over greater range. SSB can be compared to a shotgun blast with bird or deer shot, without a choke. It is very effective at hitting everything within a short range! The same shot becomes less effective, the further out we go. In contrast, CW along with FT8, JS8, and other narrow bandwidth modes are like a long rifle, with a very long barrel. The longer barrel increases muzzle velocity, without any increase in the initial energy expenditure (aka powder). The longer barrel is our “efficient antenna”, the powder is the amount of current required to complete the connection. Is this making sense?
When we get into more advance data mode like PACTOR, Vara, Robust Packet, … We get into the helping hands. One such helping hand is error correction. I like to use the analogy of a “spotter” ensuring the quality, speed and bandwidth of our connection remains effective, and on target.
In practice, our station sends out a small part of the total payload (aka message) at a time. If the payload is made of 100 parts (just an example), our station sends out one small part of the total payload at a time. Our station also assigns a numerical value to the partial payload. When the partial payload is received, the receiving station will calculate the numerical value of the partial payload, then ask the sending station if that numerical value is correct. The original sender says yes or no. If yes (fire for effect), it responds yes, then sends the next partial package. If no (adjustment), it resends the partial package. This “Error Correction” is much more efficient than two humans trying to send and transcribe a complex topic from within a room full of people, with lots of background noise. The error connection adds overhead, but also adds reliability to our connection sessions.
Speed throttling is another way data modes like PACTOR, Vara, Robust Packet, add reliability to a connection session. If there are poor band conditions, QRM, QSB, or strange atmospheric conditions making a solid connection difficult to achieve, we can use throttling to help. Throttling is built-in to some advanced data modes. Remember the negotiation between stations in the error correction section mentioned above? Well some data modes will also send signal reports along with acknowledgement of partial payloads. This signal report is used by the TNC or modem to throttle up, or throttle back its speed and or bandwidth. If the signal quality is not good enough, throttling will slow down the connection to make it more readable, for the receiving station. In some instances, throttling will also decrease bandwidth, eg switching from 2300hz down to 500hz, making it easier for the receiving station to copy the data.
Energy efficiency – Addendum
Ultimately the goal of this article is helping readers understand how to deploy the most efficient station, with the least amount of gear possible. To this end, current consumption cannot be ignored. Green radios are notorious for having incredibly low current on both Transmit and Receive. This is why they can run on a couple of lead acid batteries for days or weeks at a time. If we try to put an FT991A or IC-7300 in the field, we end up with rigs burning through 1-2 amps just sitting there doing nothing. In contrast, (TR)uSDX, TX-500, KX2/3, IC-705 use between 80-250ma on receive. They also have an efficient PA for low power TX as well. These points are important because they allow us to field smaller radios, using less power, taking less space, and ultimately being easier to carry!
Current consumption also affects the size of the battery. More current consumption means higher battery storage requirement. Higher battery storage capacity adds size and weight to our stations. More efficient comms gear affords us an opportunity to achieve our comms goals, while carrying far less weight.
Just some additional Food for thought.
Ultimately, the station used in this article consisted of few easy to carry component.
- (TR)uSDX A QRP Radio
- N9SAB Antennas An extremely efficient antenna
- Microsoft Surface for Ham Radio Tablet computer
- DigiRig Mobile Digirig audio interface
- DIY Pocket Sized Solar Gen. Pocket portable solar gen
Any of the other radios mentioned in this article can also be used. What is important is we understand how efficiency and the correct data mode can improve our off-grid communications successes. If we just do some research and planning during the planning stages of our communications systems, we can achive much better results overall.
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