Building a Wireless Remote Speaker, MP3-based Caller
by Ivan J. Eberle AKA LionHo

While building your own e-caller with a wireless remote may seem like a lot of work--compared to purchasing one of the dazzling new commercial units which start at a few hundred bucks--consider the following. When I'm out calling on a stand nowadays, I'll be palming a credit-card-sized remote (i.e. MP3 device) with an LCD display that scrolls the titles of 65+ downloaded and recorded tracks. These tracks vary in length from 6 second clips of actual mountain lion screams downloaded for free, to several minutes-long mouthblown call fawn and rabbit loops--including silent pauses--that I've recorded myself and stitched together on the PC (any or all of which I may have just effortlessly uploaded to the device mere moments before heading out the door). In addition to custom track titles, I can see at a glance whether the track is presently in single play or continously looping mode. The MP3 display also gives me a quick visual on volume level, and battery life remaining. Argueably, such an MP3 based wireless caller offers a degree of precision and control that is--as yet--unmatched by any commercial e-caller's hand-held remote offerings.

First, why is a remote speaker necessary? To me, it's more than just a question of not being the point source of the fawn bleats, not getting stalked and eaten by a mountain lion, or becoming the object of a 200 lb tom's affections when he comes to investigate the female-lion-in-heat shrieks. Instead I can be comfortably off to the side for better photographic composition of my wildife subjects. Another plus is that as long as I'm sitting some distance away from the speaker, my ears don't ring of rabbit din like they have in recent years, whenever I've just let loose with a long sequence on my Crit'R call. With a remote speaker, I can better hear the subtle signals of the quail pweets and the woodpeckers getting nervous, or the hushed crunch of leaves, as a predator stalks closer through the woods. I'd been using remote cabled speakers, with cassette tape and CD players, for 17 seasons of calling before building a remote wireless speaker, MP3-based caller.

Some callers, not yet having pored through the Predator Masters archives for threads pertaining to the use of the Azden or Nady wireless microphones, may ask how in the heck a wireless microphone is going to be used as the heart of a wireless remote speaker. Not to worry; for our purposes, the "wireless microphone" simply means using the transmitter and receiver radio pair that makes up the wireless part of the boxed wireless lavalier microphone kit. This transmitter/receiver set (and most importantly, the radio link between them) simply replaces an unruly length of speaker cable. That's all there is to it. The "microphone" transmitter side gets plugged into the line out/speaker/headphone jack of whatever player device you're using, and the amp or speaker gets plugged into the receiver side for a wireless link.

(Note that the description below of  the rig I built also mentions that I'm using the wireless microphone as a microphone. But this use is secondary, because I have a digitally-recording MP3 device and also do field recordings with it. Most fellows using either the Azdens or the Nadys, however, won't be concerned with this at all. They'll simply set the little lapel microphone off to the side, never to give it another thought.)

There is a difference to be recognized here with the commercial players that come with remotes: Johnny Stewart, Foxpros, Loudmouths, Predation, and Wildlife Technologies callers don't transmit the sound over their radio link, just a signal that switches their unit on or off, switches tracks and volume up or down etc. While this, theoretically, is the better method (since the radio link cannot degrade the quality of the sound), in actual field practice, there may not be any significant loss in the signal quality using a wireless microphone regime. Wireless microphones have surprisingly high fidelity. While the popular Azdens and Nadys are inexpensive consumer camcorder-grade gadgets priced between $40-150, they're excellent when used within their limitations.

What limitations? Bear in mind, all wireless microphones--regardless of brand and cost--are very low-power transmitters having a decidedly short radio range. The Nady 151VR-LT unit operates within line of sight out to approximately 100 yards, depending on terrain, conditions and antenna position. But for my predator calling purposes, since I'm into photography and rarely set the remote speaker more than a hundred feet away, this is not much of an issue. Others who need to set the speaker at a greater distance may run up against the radio range limits of the these units and find the signal quality unworkable. Commercial e-caller's advertising aside, however, it's hard to imagine many scenarios where calling a predator to within 200 or 300 yards, rather than 100 yards, would be an actual advantage (grizzlies and Alaskan Brown bears being two noteworthy exceptions).

Azden versus Nady: Azden units are purported to have a range advantage over the Nady units. The Azden units have a selector switch for a second frequency. Yet the Azden specification for dynamic range on the upper end is only 15,000 Hz whereas the Nady is 20,000 Hz. The Nady also has adjustments for the output levels while the Azden unit does not. This may be a important consideration when using a player device with a particularly loud or pre-amplified output, JS Preymaster users in particular. Preymaster users attempting to mate their amplified-output device to an Azden unit will need to reduce the volume of the input to the transmitter with a separately-purchased inline volume control.  (Radio Shack P/N ???). Either the Azden units or the Nady 151/351 take 9V transister-radio type batteries, and offer modestly amplified output jacks adequate to drive a small horn. That is to say, they eliminate the need for a separate amp when used with a speaker like the Speco SP-5. (Though a lightweight compact package, 9V battery life will be restricted to approximately 45 minutes of continuous calling, however). The inexpensive Nady DKW-1 transmitter uses a transistor-radio battery, but has a 12 volt receiver that will require a separate amplifier for our predator calling purposes.

One final caveat: proper frequency selection may prove critical to your to e-caller remote happiness. Some of the frequencies Azdens and Nadys use are now shared by new digital TV broadcasts (wireless VHF microphones have traditionally used a non-utilized portion of the television channel radio spectrum for channels 7-13. But new HDTV broadcasts use ALL the available spectrum). If you consistently call and hunt within the TV broadcast area of a metropolitan region, it's recommended you scan the available wireless frequencies in those areas with a handheld scanner before ordering. Note that with digital TV interference, you won't hear any voices--only buzz and hash that won't go away with the scanner's squelch adjustment. This is because the signal is encoded differently than an analog (ie microphone/voice) broadcast. Barring access to a scanner, you may want to carefully check your retailer's return or exchange policy before ordering.

Here are some channel codes and corresponding FM frequencis for Nady units:

Channel A:  171.905 MHz
Channel B:  181.150 MHz
Channel D:  209.150 MHz
Channel E:  215.220 MHz
Channel F:  203.250 MHz
Channel G1: 172.450 MHz
Channel H:  191.300  MHz
Channel N:   197.150 MHz

(Note that not all models may be available in all these frequencies.)

The following link is a table of television frequencies:

Unfortunately, the interference problem on existing wireless mic frequencies will only worsen as more television stations switch to broadcasting in digital format. This process is scheduled for completion in 2008.

My Rig:

For my E-Squaller,  I used a PoGo! Ripflash Plus MP3 recorder/player with 128 MB RAM. It has a line-in and a USB cable both, and will convert the tracks from a CD to MP3s without a computer. In other words, you can just plug a CD player into it line-out to line-in to rip tracks. Or you can load MP3's the conventional way via the USB and a computer. Or best of all, field record directly to the device using an external microphone--for instance a Nady 151VR-LT wireless lavalier microphone hidden at a densite/bird's nest/bunny slaughterhouse, and upload the sounds via USB to a PC for editing. It also accepts has an SMC flash card slot for adding  an additional 128 MB RAM. Got mine from for $105 with shipping:

The MP3 device is mated to a Nady 151VR-LT wireless microphone Tx and Rx pair, Channel A (171.90 MHz). Special ordered the frequency from,  $82 with shipping.

Could've gotten other frequencies off-the-self without special ordering, but 171.90 MHz was the only clean channel I could find on my scanner locally.

Though it's possible to run a small horn directly off the Nady 151VR-LT receiver, I wanted more volume and less distortion using better speakers, so I added a Velleman-kit 7 W mono amp. (Runs off 8-18VDC, both the Nady Rx and amp are powered by the same 8 cell pack). The amp can be built from a kit for a fifteen dollars savings, but I opted to order it pre-built from Hobbytron for under $30. Note that while this unit is a built board, it does not  come  with  an enclosure, and will still need to have wire leads soldered  to it:

The speaker I settled on was one I already had, from an old car stereo. It's a 100 watt Pioneer Coaxial speaker, model TS-1625; it sounds magnitudes better than either of the two Speco horns I experimented with. The horns were spec'd at 15Khz on the high end, but I couldn't reproduce my lipsqueaks and live-recorded mouse squeaks with them. The best thing I can say about the horns is that the larger of the two is somewhat louder than the Pioneer.

I use a two AAA NiMH batteries in the PoGo! for two to three hours of play between charges, and a 9V NiMH in the Nady transmitter for a stand's worth (approximately 1.5 to 2 hours)  per charge. The 8 cell AA NiMH pack for the Rx/Amp side is good for 3 hours of continuous calling. For the Nady receiver I made a dummy plug with a pigtail out of a gutted 9V Radio Shack alkaline battery case, soldering the pigtail to the original terminal tab, and filled it with 5 minute epoxy. The Nady receiver is powered by the same 8 cell AA pack that powers the amp. (While all the rechargeble batteries used can be charged individually in my Panasonic NiCD charger, it was more convenient to solder up a switching harness with a charging plug for the receiver/amp side so that a small 9VDC wall adapter could be used charge the 8 cell pack.)

The remote speaker, amp, Nady receiver and battery pack all fit inside a McAllen Realthre fleece camo handwarmer muff. By sheer coincidence the round Pioneer speaker grille was a snug fit in one of the elastic ends. A drawstring was threaded through the other end, and MP3 and the Tx are carried in the zippered outside pocket. The muff has a strap for carry like a fanny pack and rides well.

With my rig, the Nady can also be "turned around" (from how we predator callers ordianarily use it to broadcast sound to the remote speaker), and the little lapel microphone put to use to actually field record sounds. Haven't used it extensively yet for this purpose, but I have gotten some California Quail noises that are useful. Also now record my hand calls more cleanly this way now than I was doing using the soundcard and a stand-alone wired microphone on my laptop. When the Nady/PoGo! is used as a recorder, the output jack of the Nady Rx does not have enough signal for the Line In of the PoGo! device, so the Nady Rx headphone jack is used instead. But I am quite pleased with the low noise recordings it makes. I just love a good two-fer like this. Also the MP3 player is an MP3 player, and holds a lot of music (at the risk of committing sacrilege, I use my MP3 for more than just predator calling--a three-fer!)

So what's the downside? A homebuilt e-caller requires more of an investment of time. Yes, it does have a few minor inconveniences and quirks. For example, there are three different types of batteries to charge after a session of calling: 2AAA NiMHs from the MP3, a 9V transistor-radio type NiMH from the wireless transmitter, and the 1.2 AH 8 cell AA pack that powers the receiver and amp. Another quirk is that when the  MP3 is first powered up, there is a small audible pop through the speaker (this can also happen when switching tracks). While inconvenient, this is easily remedied either by first muting the MP3 player volume, or by using the mute (Standby) switch on the Nady transmitter. To a grizzled old caller such as myself, such minor inconveniences pale in comparison to the many others experienced daily, while actually calling predators.