Mo's Cool PPG Pics and Stories

Observations on Communications Equipmnt for PPG Use


Compiled by Mo from messages by Nick Scholtes (Nick.Scholtes@tellabs.com) taken mostly from message #23299 in the PPG Pilots Club forum at http://groups.yahoo.com/group/pilotsppgclub/.


The FRS Option
Realistically, FRS (Family Radio Service) radios are not very good choices for PPGing because of their extremely limited range. But, the reason that I think they've become accepted is because they don't cost very much, and because in a large percentage of our flying we are not very far from who we want to talk to, so they're OK. PPC guys chose an even worse radio, and that is the CB! I'm REALLY glad the PPG community didn't follow that lead!

Cobra FRS-310WX Details

14 Channel FRS Radio with Weather

The High Performance "Walkie-Talkie" Up to 2 Mile Range. The microTALK FRS 310WX is the best choice for outdoor enthusiasts: 10 Channel NOAA Weather reception provides information on the latest conditions, VibrAlert TM works like a silent vibrating pager - perfect for quiet environments you don't want to disturb or noisy environments where you can't hear a ring alert, and water resistant construction allows the microTALK FRS 310WX to go where others cannot.

Features:
  • 10 Memories
  • Auto Scan
  • Private Call
  • Voice scrambling
  • 38 CTCSS sub-tones
  • Backlit LCD screen
  • Incoming call alert
  • Charging pads
  • Water Resistant
  • 10 Channel Weather Reception
  • VibrAlert Silent Alarm
  • Private Call Voice Scrambling
  • 14 Easy Access Channels
  • Front panel push buttons
  • 38 sub-channels per channel
  • Backlit LCD screen
  • Ultra Compact/RetractableAntenna
  • 500mW Output Power
  • Auto Scan
  • Auto Squelch
  • Talk Confirmation Tone
  • Speaker/Mic Jack
  • No License or Service Fees
  • 10 Memories
  • Memory Scan
  • Dual Channel Watch
  • 4-AAA Alkaline or NiMH Batteries
    • The FRS radio I like is the Cobra MicroTalk FRS310WX. It's kinda' hard to find, and the only way I've found it is through the web. One place you can find it is www.savesucash.com. If you go there, it sells for $55, plus $10 for S&H, less a $20 mail-in rebate, so it's a total of $45.

    Actually, there are three radios in the "300WX series", the FRS305WX, the FRS310WX, and the FRS315WX. All three of these radios are excellent, and the only difference between them is some really obscure features that you'd never use for PPG (like various call-tones and stuff like that). Get whichever of the three are available and cheap. I like the 310 best because it has a knob for adjusting the volume, the others have buttons.

    I don't recommend ANY other FRS radio, because none of the others that I have found meet all six of the criteria below, and none of them are as high-quality as the Cobra FRS310WX.

    The worst offenders are the Motorola Talkabouts. It's a shame those radios are so popular, they really suck! I could go on-and-on about their deficiencies for PPG use, but I won't bore you.

    The reasons I like the Cobra FRS310WX is because:

    1) it has the "standard" FRS interface with one big plug and one little plug,

    2) the plugs enter from the top of the radio where they're easily accessible and they aren't vulnerable to breakage (like they are on the Motorolas where they enter from the side),

    3) it has 14 channels and 38 privacy codes,

    4) it can disable that damn "Roger Beep" tone,

    5) the batteries last a LONG time, probably at least 5 times as long as in the Talkabout 250,

    6) and most importantly, it has the best microphone interface of any FRS radio that I've tried. They won't overdrive, and the sound quality from the mic is just absolutely excellent. You'll be heard and understood by everybody, even if you're under full power.

    This last one is really important. This weekend we had a fly-in at my house. Several pilots were there that had switched to this radio. The quality of their microphone transmissions was unbelievably good, and it was interesting to see how much better they were compared to what they used to be with the other radios. It's a night-and-day difference.

    For anybody that wants to use an FRS radio for PPGing, I say spend the $45 and get this radio. I know alot of folks that use the ParaTour helmet and Motorola Talkabouts. This combination just doesn't perform very well at all. The Motorola Talkabouts have a very poor mic interface that is overdriven with about 1/4 throttle from our motors. Add to that the fact that the ParaTour helmet has some "funky" stuff in it (inside it has two capacitors that are supposed to filter the mic to make it sound better, but they don't really work in practice. I instantly remove them from everybody's helmet that I see and it performs much better. Also the ParaTour helmet has this potentiometer in there that also causes problems. Lastly, it doesn't use a "noise cancelling" mic like it should). At full throttle there's no prayer of being understood. Use the Cobra FRS310WX and you can be heard at full throttle, no problem, even with the ParaTour helmet.

    Somebody mentioned that you can buy other Cobra FRS radios really cheap. 'Tis true, but you get what you pay for, and the Cobra models other than the 310WX perform not-so-well for the PPG application. The 310WX is the only FRS radio I know of that meets ALL of the criteria I list. I would say this to the bargain-hunters: I have seen more people in this sport that are disappointed in their radio communication equipment than with any other piece of gear. I've seen people throw their radio or their helmet in frustration. Of everybody that has purchased the 310WX I am unaware of anybody unhappy with their gear.


    The GMRS Option
    Another radio band to consider is the GMRS (Global Mobile Radio Service). These radios are allowed by the FCC to put out more power than the FRS, 2 watts compared to the legal limit of 0.5. So if you want a radio that will go a little farther than an FRS, the GMRS radio will do that. However, the GMRS radio requires a license to operate (not a big deal really and nobody actually gets a license to use them) and it only has a subset of channels that line up with the FRS band, which other PPG pilots will be operating on.

    The GMRS radios that are marketed by Audiovox and others including Cobra, share some similarities with FRS radios, and also share some frequencies. But they are VASTLY different radios, although you can't really tell by looking at them or their packaging. The GMRS radios have 15 frequencies, compared to the FRS's 14. Of these 15 frequencies, seven of them are common to the FRS radios, but the remainder aren't. Also, the GMRS radios have different subcodes.

    If your buddies are satisfied with using one of the first 7 FRS channels, then the GMRS radios will be OK and will be compatible with the FRS radios. But if someone isn't aware of the difference, they'll be surprised when the GMRS radio set to channel 12 and the FRS radio set to channel 12 won't talk to each other.

    To me however (and please note that this is just my opinion), the GMRS is not a great option. It doesn't have all of the FRS frequencies so if you want to talk to other PPG guys that are on FRS channels, chances are they'll be on a frequency you can't get to. Also, the increased distance of the GMRS isn't a huge improvement over the FRS. So while it's better, it's not that much better. Specifically, I have no personal experience at all with the Cobra PR1000, but I do have experience with other GMRS radios.


    The 2-Meter HAM Option
    An even better choice, in my opinion, would be to go with a 2-meter HAM radio. One that I really like is the Yaesu VX-1 or the VX-5 (I prefer the VX-5). The advantages of the VX-5 are that it will go a WHOLE LOT farther than either the FRS or the GMRS. Also, it will tune in ALL of the FRS and GMRS frequencies (you will have to perform a minor modification to allow it to do this.) The VX-5 requires a license (most people operate them without a license, but I didn't actually say that!). Also, as yet another benefit, the VX-5 will also tune in the USHGA frequencies, so if you are out PGing sometime you can talk with the folks that are PG/HG at the site. The Yaesu is not the only radio that will do this, of course. ICOM, Alinco, and others also put out excellent radios that are very similar, almost identical, to the VX-5.

    If I were to get a radio that "went farther" than an FRS but I also wanted to use it to talk to FRS radios, I'd get the VX-5 or similar. Of course, you'll notice I didn't mention $$$$$ in any of my discussion! The retail cost for the VX-5 is over $200. In the case of radios, like anything else, you tend to get what you pay for, and the 2-meter radios are more expensive, that's for sure.


    FRS Channels and Sub-Codes Explained
    It's important to understand how the different channels and 38 sub-codes work. They are NOT extra "channels", as the radio manufacturers would like you to believe. They are a "filter". What this means is that let's say you're on channel 5 and you get "alot of chatter". If you get a radio that allows subcodes, and you turn it to channel 5, subcode 3 for example, here's what it will do: It will "filter" all of the chatter that's NOT on subcode 3 from your receiver so you won't hear it. BUT, and this is a big BUT, that chatter is still there on channel 5. So let's say that the chatter is there, but you don't hear it because the subcode filter has removed it. Because you don't hear anything you think you have a clear channel and you go and transmit to your buddy on the ground. If somebody else was transmitting at the same time, your buddy won't hear your transmission because you just "stepped on" somebody else talking on channel 5 and the two transmissions interfered. Then you'll be left wondering why your buddy didn't respond to you, or why he didn't hear you. So it's important to understand how the subcodes work, they are NOT extra channels, they're just filters, and that's a big difference.


    Noise-Cancelling Mic Explained
    How do noise cancelling mics work? First a little background. Actually, mics come in different flavors. One flavor is "unidirectional", which means it "hears" sound in one direction. You need to point them at what you want to hear. Then there's "omnidirectional" mics, omni meaning that they hear everything in all directions. That's what the mic element is that you got from Radio Shack (and that's what makes it not-so-good for our PPG application because it hears the motor noise). Then there are "noise-cancelling" mics, which are designed to be used in noisy environments like PPG.

    There are also two types of mic, the "dynamic" mic and the "electret" or "condenser" mic. The dynamic mic works like an old-fashioned stereo needle. Basically there's a magnet that's attached to a diaphragm, and the magnet is surrounded by a coil of wire. When sound hits the diaphragm it causes the diaphragm to move, which moves the magnet up-and-down in the coil of wire. Faraday's law says that a magnet moving in a coil of wire generates an emf (a voltage) in the coil of wire....... this voltage then is sent to an amp and used by the radio. Dynamic mics are big, heavy, bulky, and relatively expensive. But they work really great as noise cancellers, and they are often used in military stuff like tanks and jets and stuff like that. They are also considered by musicians to be much "purer" and hence are often used by professional singers and musicians. As a general statement, they are very high quality mics and are used in applications where very high quality is paramount. As a side note, if anybody wants to use a dynamic for PPG use, let me know and I can get one for you. They're about $60 (my cost), but they are THE CAT'S MEOW!

    Electret mics are very different, and they're cheap, and they're what are used in every application other than those listed above. They're what are used inside all of the radios we use, answering machines, computers, tape-recorders, etc.. Electret mics (uni and omni directional ones) have a little metal disc located in very close proximity to, but not touching, a little sheet of mylar that's very similar to Saran-wrap. This "Saran-wrap" stuff has a very thin coating of conductive material on one side of it. When the very thin coating on the Saran-wrap is placed in very close proximity to the little metal disc, you basically have a capacitor. Now, when sound waves hit the Saran-wrap, the Saran-wrap moves in response to the sound waves. This movement causes a change in the capacitance of the device. This change in capacitance is VERY small, and cannot travel long distances over a wire (for two reasons, one is that traveling over a wire would attenuate the already-too-small signal, and the other is that noise present on the wire would swamp the signal out). So, they put a very small amplifier DIRECTLY behind the little metal disc. The change in capacitance is piped to this amp, which amplifies the signal and sends it out of the mic to be used by the radio. All of these parts, the little metal disc, the Saran-wrap, and the amplifier are all contained in the little mic capsule. Oh, and as a side note, the radio itself provides the power, or "bias", required to run the amp. So the radio sends power to the mic to bias it, and the mic sends the amplified sound signal back to the radio, all on the same pair of wires. Kinda' cool! Works good, real cheap!

    Ok, now to your question, how does a noise-cancelling electret mic work?

    It turns out that if a sound is generated far away (more than a few inches) from a microphone (or from anything for that matter), the "sound pressure" generated by this sound hits the mic evenly from all sides. But if a sound is generated close to the mic, the sound pressure is only felt on one side of the mic. This little bit of physics is the principle that noise-cancellers take advantage of.

    In the description of the electret mic above, a noise-cancelling electret differs as follows: Instead of one plate of the capacitor being a little metal disc, BOTH sides of the capacitor are little pieces of mylar with a conductive coating on them. Further, the mic capsule itself is not sealed, rather it is exposed to the sound on both sides. If you buy a noise-cancelling mic you'll see it has holes for the sound to get in from the back. If you use one of these, don't put it in a holder that blocks the sound coming to it from the back.

    Ok, so now how does this work. Well, if there is a sound source (like a loud, screaming PPG motor) that is farther away from the mic than a few inches, the sound pressure that hits the mic will be even on both sides. Hence, both sides of the capacitor (both little sheets of Saran-wrap) will vibrate evenly, and because they are both vibrating evenly there will be no change in the capacitor, and hence no electrical current will be generated. Hence, the mic will not "hear" the background noise. But, if you put your lips very close to the mic and talk, the sound pressure will only be felt on one side, by the piece of mylar that is on the side you are talking into. So, there will be a differential amount of movement on one side of the capacitor than on the other. This will cause a change in the capacitance, which will produce a signal proportional to your voice. This signal is then sent to the little amp, and viola', you've got a noise-cancelling mic!


    Ordering a Noise-Cancelling Mic
    A pretty decent noise-cancelling mic can be obtained from Digi-Key, part number P9897-ND for $3.42. It fits directly into the ParaTour helmet, but it requires you drill a small hole in the back of the plastic mic holder in order for it to function as a "noise cancelling" mic (a "noise cancelling" mic needs to hear sound from both sides, not just one side). You can order the part at: http://www.digikey.com/scripts/us/dksus.dll?PName?Name=P9897-ND

    These noise-cancelling mics can also be installed in the homemade setup that I wrote about in my "build your own headset" http://www.poweredparaglider.com/under_helmet_radio_headset.html article.


    Mo's Cool PPG Pics and Stories Home
    <-- Go Back   |    Top of Page   |    Go Forward ->