Hey Keith, Scott and the gang; Around here (New Mexico) we (at least 5 of us, last count) are using these. We are very pleased (so far) with them. We have been using them for about 5 years-ish. They sure seem to fill in the nulls nicely and the loss over a perfect situation seems to be less than 20% or so... (Filling in the nulls when using high gain yagi antennas for reception is much more important than the small losses at the transmitter. <- You *ARE* using yagis for the receivers right ????)
http://www.digikey.com/product-search/en?lang=en&site=us&KeyWords=ant-433-cw-rh-sma-nd Part number at DigiKey is: ANT-433-CW-RH-SMA-ND Hope this helps ! es vy 73 om de Bob w9ya On Thu, Apr 13, 2017 at 9:23 AM, Keith Packard <[email protected]> wrote: > Scott Myers <[email protected]> writes: > >> My first question is on the uplink/downlink frequencies. It simply states >> 433 MHz. I assume this to be an approximate frequency in the 70 cm band and >> not the actual exact frequencies. Rarely is something right at >> 433.000 MHz. > > Right, the radios are designed to operate in the neighborhood of 435MHz, > but you can configure whatever frequency you like around that. > >> Are there separate uplink and downlink frequencies (full duplex) or does it >> switch on/off transmit/receive at each transceiver (Telmetrum and >> Teledongle) using the same exact frequency. > > During flight, it's a unidirectional transmission from flight computer > to the ground. This lets you have multiple ground stations tracking the > same flight, and makes the communication work better over long > distances. > > For bi-directional communication in 'idle' mode, it's a half-duplex > channel on a single frequency. Doing full-duplex communication would be > very difficult in a single band, and would require separate transmit and > receive radios which we don't have. > >> How wide is the data bandwidth in KHz? > > We're using 38.4kbps and 20.5kHz deviation GFSK, yielding a bandwidth of > about 100kHz. > >> (I think they are all coded and using "telegraph" messaging >> handshaking to avoid conflict with another Telemetrum, but I could be >> wrong.) > > No, telemetry is uni-directional, so any receiver tuned to the right > frequency will see the data. > >> I see there is a starter "kit" that uses the Teledongle. But there is also >> the TeleBT, which seems to do everything the Teledongle does, PLUS adds >> bluetooth for use with the Android App. It seems that starting with the >> TeleBT would the better choice and don't even buy the Teledongle, but I >> wanted to make sure I wasn't missing something on this. > > Agreed. The TeleDongle is a bit cheaper and smaller, but that's about it. > >> I saw the history on older versions with the problems with pyro events and >> battery rail sag and that it is supposed to be solved now. (An age-old >> problem on many avionics packages.) > > We have added a comparator to the pyro circuit which monitors the > voltage coming in to the electronics power supply. This cuts off the > pyro firing circuit when the voltage sags below that necessary to keep > the flight computer processor running. There's a ballast capacitor at > that point in the circuit, so the circuit ends up pulsing current into > the pyro device. With a short across the pyro terminals, we end up > hitting about a 90% duty cycle. > > This requires using a lipo without a current limiting circuit, which is > what we provide in our store. > >> I think I'd rather put a second LiPo on the Telemetrum and give the >> pyro events their own rail and simply avoid any potential rail sag >> issue. > > I'd encourage you to check out what we've done and see if you still > think this is necessary. You increase the complexity of the system as > you now rely on both batteries working correctly for the pyro circuits > to fire. > >> Just a small LiPo should do the job. I'm guessing others have done >> this and I read where that is an option on the board. I'd like >> feedback on that. > > I have seen lots of people using two batteries, and in fact, you can use > a higher voltage if you like -- the pyro circuits are designed to > support up to 15V or so. > >> Of course downside is mass of the connector soldered to the board and >> having to support the feed line to account for high-G conditions so the >> connector isn't broken from the board. > > Our new boards have metal on both sides of the board so that the > edge-launch SMA is at least better supported, but yes, we've seen > multiple boards snapped at the SMA connector due to high G loads. > >> I'd like some feedback and discussion on the use of the SMA connector. >> I can't figure out how to order the Telemetrum with that option >> anyway. Perhaps it is a field mod? > > We used to have it on the price list; I'm not sure how Bdale manages it > these days. But, the boards are designed to work well with a simple wire > whip, so unless you're going to mount it in an airframe that requires an > external antenna, it really is nice to just use it as designed. I've run > the wire through the ebay bulkhead and up alongside recovery systems in > several airframes with good results. > > -- > -keith > > _______________________________________________ > altusmetrum mailing list > [email protected] > http://lists.gag.com/mailman/listinfo/altusmetrum > _______________________________________________ altusmetrum mailing list [email protected] http://lists.gag.com/mailman/listinfo/altusmetrum
