A Sensitive Issue

ARDF rules can have a large impact on the cost of equipment. There are many examples of this that can be cited. But there is one notable example where current rules are unnecessarily increasing the cost-of-entry to the sport. And this issue can be readily addressed with a simple clarification of the rules.

High-end ARDF receivers costing US$250 or more, typically provide excellent performance specifications: selectivity, stability, weight, ergonomics, and sensitivity. Inexpensive alternatives generally underperform the expensive units in all respects. But the most significant parameter that prevents under-$50 units from being usable is sensitivity. If you can’t hear a signal, you can’t hunt it. Period.

Not to get too geeky, but sensitivity on the 3.5 MHz band is noise limited. That means that the background noise level is well above the sensitivity threshold of most receivers. The receiver might be plenty sensitive to receive a weak signal, but the received noise is louder than the signal, making it unreadable.

Noise performance is improved by increasing selectivity (narrowing the receive bandwidth) to allow less noise through while still allowing the desired signal to pass through. But high selectivity requires high stability, otherwise a receiver would drift outside the narrow passband and lose the desired signal. So high-sensitivity 80m receivers must also have high selectivity, and high stability. That means that the requirement for high sensitivity affects many aspects of the receiver design. The bottom line is that greater receiver sensitivity means greater overall receiver complexity and cost.

The bottom line is that greater receiver sensitivity is achieved by increasing the complexity and cost of the receiver.

A question we have to ask ourselves: is high receiver sensitivity an essential part of ARDF? Is it really necessary to promote the use of high-sensitivity, and therefore high-cost, receiver designs in all ARDF events?

Is it really necessary to promote the use of high-sensitivity, and therefore high-cost, receiver designs?

I submit that it is fitting and proper that some ARDF events be conducted in a manner that allows low-cost receiver designs to be used. I believe that competitors can still exhibit their quick feet, quicker thinking, and signal interpretation abilities even if the signals they are hunting are relatively strong. Furthermore, we need to have events that accommodate inexpensive receivers in order to lower the cost-of-entry to the sport. And this could be done simply by requiring sufficiently-high radiated power levels from the fox transmitters and beacons.

We need to have events that accommodate receivers that pose a lower cost-of-entry to the sport.

The obvious candidate for a low-cost-of-entry event is sprint. The small field of play means that quite low radiated power levels from the foxes could be used while still allowing receivers with poor sensitivity to detect them all from every location on the competition map.

In fact, the Region 1 rules appear to require sufficient radiated power levels already. See Region 1 ARDF Rules Part B paragraph S6.1. The minimum sprint transmitter power is 300 mW. So why can’t a low-cost R3500D receiver hear all the sprint transmitters on a regulation course?

So why can’t a low-cost R3500D receiver hear all the sprint transmitters on a regulation course?

The answer: the rules do not specify the foxes’ radiated transmit power. The rules specify only the transmitter output power. The rules say nothing about the antenna match, or the antenna’s efficiency. And according to my observations, little of the minimum 300 mW of output power is actually being radiated by sprint fox antennas. At least, not on the sprint courses I have experienced in the USA.

The rules say nothing about the antenna match, or the antenna’s overall efficiency. So little of the minimum 300 mW of output power is actually being radiated by sprint fox antennas.

One solution to the apparent rules deficiency would be to specify a specific antenna design and placement. Another solution: have the rules specify the actual amount of power radiated from the sprint fox antennas. But those rules could prove difficult for organizers to implement or measure. Instead, I would suggest that the rules simply describe a reference transmitter output power and matched-feedpoint antenna system to be used for comparison.

With a standard output power and antenna design, organizers would only need to compare their fox transmitters’ signal strength to that of the reference. If the fox signals were as strong, or stronger, than the reference then all is good. If not, then the fox transmitter’s output power might be increased, or some modification to the foxes’ antennas or the antenna matching system could be made. In most cases, the comparison exercise would only need to be performed once for a given fox (transmitter plus antenna) system design.

With a standard output power and antenna design, organizers would only need to compare their fox transmitters’ signal strength to that of the reference.

Such a radiated-power reference system could be specified for each of the four event types used in ARDF. This would eliminate the need for the vague and non-existent “receiver of average sensitivity” called for in current Region 1 rules (see Part B, paragraph 27.3).

The reference-based approach could allow low-cost receivers to work just fine for sprint, and perhaps some other events as well. Allowing newcomers to fully participate in at least one ARDF event format for an initial investment under US$50 could prove to be a big deal.