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1-10 of 18 messages
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Off-the-shelf 33cm mobile
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by KE6WNH on July 12, 2009
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No, I'm not going to solicit recommendations for units, I just need a little feedback on what the rest of you guys think of this...
Ed, KE6VRK, approached me recently re his intention to build 2 or 3 prototype 33cm mobiles---essentially something like an Alinco monobander---and if it works, he wants to promote it and get it into production and sell them. Finally, he says, we'd have 900 mhz radios which would not be PC programmable... he'd do a basic stamp for V/M operation, and alphanumeric would be another basic stamp, etc etc.
He is worried that the production rigs might not get FCC approval, but I tried to reassure him that the FCC mostly would want to make sure the rigs don't leak RF or spurious signals... there don't seem to be enough 5kc deviation devices in that band for interference to be much of a problem in the first place.
I asked him how he proposes to build such a unit... he answered, you use a freq synth chip which gives the right deviation signal, then couple it with a controller and work from there. The problem is that practically all the 900 mhz freq synths I looked up are for SS, the narrowest I've found is 60kc. Personally, I think it's quite a pipe dream, but I'm going along with it anyway, and I promised to help him test the prototypes and develop good shielded cases for them.
So, my questions are this:
1. would it be a good idea to include a TNC port on the production 33cm units?
2. does a .5/4/12 watt transmit power split seem about right, or should it be a little lower?
3. if the unit cost less than $200 and needed no mods, would you buy it?
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RE: Off-the-shelf 33cm mobile
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by W3JKS on July 12, 2009
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TNC port -- absolutely! It's also very useful for phone patch/echolink/etc. The unit should have access for audio suitable for higher-speed digital operations; at least 9600 bps, but preferably something around 57.6 kbps would be ideal -- it could become extremely popular with the digital crowd. Poor man's D-Star. :-)
12 watts is plenty, a 4-5 watt setting is good for feeding amps if you need one.
I was really hoping to see someone get into the 900 mhz business. Best of luck!
73s,
john W3JKS/AAT3BF/AAM3EDE/AAA9SL
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RE: Off-the-shelf 33cm mobile
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by KE6WNH on July 16, 2009
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Well, I've been in contact with KE6VRK, and he said that the biggest hurdle so far is to find a 900 mhz device which is neither digital nor SS. He was talking about disassembling a 900 mhz baby monitor to find out what ICs they use... but then after some sleuthing, I found a module called the RF900DV whose spec sheet says it will work either for data or voice apps, also a very interesting IC, the SA58646. The latter seems to me like it's just waiting for one of us hams to come along and put it to work in the heart of a 33cm HT.
So... who knows, maybe it's not such a pipe dream after all and KE6VRK will actually get around to designing the things and hiring me to cast a couple of aluminum cases for them. There will be hurdles---he may need to order 10,000 of them---but he's pretty intent on building it. Here's hoping...
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RE: Off-the-shelf 33cm mobile
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by W3JKS on July 17, 2009
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Well, Digikey sells them for $4.26, quantity 1. They list them as "non-stock", but it looks as if they also have a roll of 1500 of them on the shelf.
A Mitsubishi M67769C (RF Parts) will boost your 1-2 milliwatts to around 10-15 watts for $47.95! RF Parts also carries a PCB for the RF amp module (DEM2318) for $15.
Add-in some decent filters, rf relay ... a GMSK modem would be nice. :-)
73,
john W3JKS/AAT3BF/AAM3EDE/AAA9SL
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RE: Off-the-shelf 33cm mobile
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by KE6WNH on July 17, 2009
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Thanks very much, the RF power boost info will be handy to know when we get around to designing the finals, as I'll probably be asked to design the heatsink.
But, like I said, the hardest part was to find an analog signal source IC which can be V/M controlled as opposed to PC programmable... I talked to KE6VRK this morning and he wanted to know more about the IC and the module.
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RE: Off-the-shelf 33cm mobile
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by W3JKS on July 17, 2009
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NXP and RF Parts' websites have very good data sheets and application notes.
If you are willing to do some more work (well, maybe a lot more work :-), CML Microcircuits makes some really interesting chips including modulators spanning 30 to 1000 MHz (in one chip!) and a couple of really interesting baseband modules. The "function loads" allow these chips to do things like APCO25.
I would love to have a FT736R-equivalent with P25 and 19.2 kbps data in a box the size of my Alinco DR-135! :-) CMLmicro.com requires (free) registration but the functionality is really fascinating.
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RE: Off-the-shelf 33cm mobile
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by KE6WNH on July 17, 2009
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I will definitely relay your info to KE6VRK. He says he got a chance to look up the specs on the SA58646, and says once he can find a controller chip for it, he'll have the toughest part of it licked.
I'm starting to have visions of a deluxe 33cm mobile with SSB and ports for ATV... but that will need to wait until Ed is sure he can get the FM unit to work. One small step for a ham, one giant leap for hamkind... sorry, I couldn't resist. ;-)
73, Marty
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RE: Off-the-shelf 33cm mobile
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by W3JKS on July 18, 2009
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Well, if you want to use a PIC chip, take a good look at the DSPICs. They have enough basic DSP functionality to implement "sound card" modes like packet.
Personally, I really like the ARM9; I recently purchased a very nice ARM9 development kit for another project (Nextel to radio patch application) which runs Linux and the gnu tool chain from MicroMint. Does both USB device AND host, SD disk socket, has a couple of serial ports, plenty of GPIOs, keypad and LCD display drivers - all in one little board.
73,
john W3JKS/AAT3BF/AAM3EDE/AAA9SL
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RE: Off-the-shelf 33cm mobile
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by W3JKS on July 28, 2009
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I've been doing a bit of meandering through the huge number of transceiver ICs available. Analog Devices' ADF7025 is pretty interesting -- they have a 900 MHz evaluation board available and it will do data rates up to 384 kbps! D*Star done right, anyone? With data rates that high, we could run multiple voice and data channels, maybe full-duplex.
I'm thinking about laying down a few $$ for a pair of evaluation boards.
73s,
john W3JKS/AAT3BF/AAM3EDE/AAA9SL
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RE: Off-the-shelf 33cm mobile
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by N0FPE on July 28, 2009
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If it was $200-$250 I know plenty of folks that would buy it. And anything added other than straight FM operations would be gravy on the taters!!!
Dan
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