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The component values will vary depending on the frequency.As supplied the RF-CHK part is designed for the RCS 27 Mhz range. It will also work with the 27 Mhz Trackside TE.
It may work with other frequencies, I do not know.
Locolinc and the TE on board are 75 Mhz. AirWire is 900 Mhz.
GOOD point that I didn’t realize; if Airwire is 900 MHz, I doubt that the chokes shown in the photo would be effective there… in fact, as far as I know, NO choke is effective at UHF frequencies. To get RF choking action at UHF frequencies there are other tricks that are commonly used… tho I seriously doubt they’d be needed.
I don’t know anything about the Airwire control system, but I DO know about the normally used RF signal protocols and practices found on the 902 - 928 MHz ISM (Industrial, Scientific, Medical) “license free” radio band where Airwire is undoubtably operating.
There are several ISM bands scattered throughout the radio spectrum; they’re essentially the junkyards and garbage dumps of the radio allocations tables. They serve as home to signals that are so NASTY that nobody else wants them nearby!
The band is inhabited by such desirable radio neighbors as large, restaurant style microwave ovens (home microwaves are on 2450 MHz; they have a much smaller oven cavity and can operate efficiently at that much shorter wavelength), some forms of medical diathermy machines (used for heating therapy of deep layers of tissue without overheating or burning the skin), industrial dielectric heating of plastics, high pressure laminating of wood products, and similar noise generating, noncommunications uses of RF energy.
Since ISM radio bands don’t require a license, several technologies have taken a chance on using the 902 - 928 MHz band. Among them are cordless telephones, garage door openers and consumer telemetry devices; the remote reading weather station in my back yard uses that hunk of spectrum. A lot of low power video systems, like wireless home surveillence cameras, use this band too.
As the final straw… the FCC has thrown open the 902 - 928 MHz band to high power transmitters by declaring it to be an Amateur band! Try powers of up to 1500 watts PEP, not counting antenna power gain, using most any flavor of modulation you can think of, including stuff like pulse and full bandwidth TELEVISION!!!
Apparently, Airwire model railroad control systems have chosen to inhabit this scrap heap radio band too.
First off… Airwire is undoubtedly an FM signal; VERY good! As long as you can provide a control signal that’s strong enough to drive the receiver into saturation, any electrical noise motors and such make is totally unimportant. That should make the need for motor filtering with Airwire unnecessary unless you’re REALLY trying to stretch range, or trying to eliminate receiving antennas to keep them from spoiling the scale look of your rolling stock.
Second… Airwire is PROBABLY a narrow band signal (relatively speaking). Again, VERY good, if the receiver has filters that adequately take advantage of the NBFM characteristics. I assume that the Airwire folks are following Best Practices for that band; it’s cheaper that way, because it allows them to use cheap, off the shelf RF modules for the radio protions of the system, so the receiver is probably pretty good.
So far anyway… Airwire should be OK. There isn’t much of an interference problem yet, unless you happen to live down the street from a Kentucky Fried Chicken or something like that! Amateur interest in the band (the most likely source of high power interference) has so far been minimal at best… with REALLY sensitive receivers, the crud and noise level on this band STINKS!
Mr. T.
