Bob, Very interesting. I'll give that a test while I'm at it. Thanks,
Scotty AC8DE -----Original Message----- From: altusmetrum [mailto:[email protected]] On Behalf Of w9ya Sent: Thursday, April 13, 2017 6:23 PM To: Altus Metrum Subject: Re: [altusmetrum] New Member Well, my point was that the helical/helix wound antenna would seem to be a problem compared to the "more orthodox" 1/4 wave.....but actually it works better because as the rocket spins and dips and dives through the entire flight profile, the nulls fill in nicely with an antenna of this kind....THERE, I said it, instead of implying it !! (Much better , I am sure.) As for "detuning".... you can check this rather easily using the rssi feature in the ground station software. I think you will find that unless you are placing the antenna right on top of your hardware, that it really isn't much of a problem, and even less of a problem with the helix/helical style antennas. Or put another way, go make some measurements of your own using the ground station's rssi feature and an sma connector on the xmitter for easy changes for ab easy afternoon of measurements. I am sure it will be quite "illuminating" for ya.... (pun intended....hi hi..) <- That's what we did a few years back, and the antenna I linked in the earlier message is "the cat's meow". es vy 73 om de bob w9ya P.S... Oh yeah, we also mount our flight electronics using "plastic" hardware (screws, washers, nuts...etc.) so that not only is that less conductive stuff...but also so that they will break before the circuit board will during hard landing. AND, *if* the board can be suspended by the cabling over a fiber-glass or wood surface; you will have done yourself proud. On Thu, Apr 13, 2017 at 1:20 PM, Scott Myers <[email protected]> wrote: > Sure, I've got a 7 element Arrow 440 yagi I've owned for many years that I've > used for foxhunting and rocketry. > > I'll say that if your transmitter's antenna didn't get detuned too much in > the installation or end up with some weird sympathetic harmonic with some > metal in close proximity, I'll agree that the receiving antenna is the more > important piece of the puzzle. But if by chance you end up with your > transmitter badly detuned, you'll struggle. I've had such things happen over > the years with other ham radio projects. But as BDale pointed out to me, > this is usually the exception rather than the rule and based on my radio > experience, I'd have to concur. I'm just doing my homework to make sure I > don't end up in the "glitch" zone. > > With my track record... > > Scotty > > -----Original Message----- > From: altusmetrum [mailto:[email protected]] On Behalf > Of w9ya > Sent: Thursday, April 13, 2017 2:52 PM > To: Altus Metrum > Subject: Re: [altusmetrum] New Member > > 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 > _______________________________________________ altusmetrum mailing list [email protected] http://lists.gag.com/mailman/listinfo/altusmetrum _______________________________________________ altusmetrum mailing list [email protected] http://lists.gag.com/mailman/listinfo/altusmetrum
