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Post by part15engineer on Nov 30, 2019 16:57:02 GMT
going to ship them off to station 8 he has more experience with them and he said he will fix them for me.
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Post by thelegacy on Dec 1, 2019 4:24:28 GMT
He does really good work with those rangemasters as well as many other types of transmitters.
Once you get it done I'm sure there won't be any more harmonics or Spurs causing problems.
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Post by sparepart on Dec 1, 2019 13:33:31 GMT
they were attempting multiple things, increased audio frequency response, increased power, and interface a GPS standard. Re adding a GPS standard - How is that accomplished? My attempts to divide down our lab's 10MHz source ( GPS disciplined NTP master) have been useless from a spur and noise perspective.
SP
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Post by part15engineer on Dec 1, 2019 16:46:03 GMT
i believe it was a failed experiment which is why they were sold to me. i'm going to have station 8 restore them for the most part only adding his proven mods to them that improves carrier stability and audio quality.
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Post by Boomer on Dec 1, 2019 23:58:55 GMT
Thanks for the update Part 15 Engineer, and I hope you can get a system together using those! Keep us updated.
CDL, the idea is that in some way the GPS signal phase locks the master oscillator in the transmitter to the GPS signal. It's one of the steps that was being suggested in AM Revitalization a few years back, to lock everyone's carriers to GPS so they'd be zero beat to lower audible interference between stations, getting rid of the 'thump thump thump' of carriers that are off frequency slightly and beating off with each other.
The 10 mhz output would be divided by 1000 to get 10 khz for a broadcast band PLL reference frequency. A 10 mhz crystal oscillator could feed 3 divide-by-ten ICs, 7490 TTL or 3 4017 decade counters. The resulting 10 khz reference would be used for the for the channel spacing on the AM band. That's simplified, I've studied it, but haven't experimented with it yet, though it's easy and inexpensive to do these days, with the small GPS receivers, like used with the Arduino.
Nowadays hip cats would want to use a GPS reference to tune a DDS module, using an Arduino Nano microcontroller, which can also drive an LCD readout of your frequency and support a knob to tune it as a VFO. Sorry analog man if that's gibberish! I'm not worried about stability as much, just after my last crazy crystal driven oscillator, I want to try something all different and new.
From my studies a GPS reference can mean microhertz stability on the broadcast band, like .001 hz! The aim? For advanced hobbyists who want to run several transmitters on a frequency, to cover a long boulevard in a town for example with a solid signal. Audio also has to be time aligned as well.
Boomer
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Post by sparepart on Dec 2, 2019 1:02:12 GMT
Boomer,
Played with using 74HC390 as a divider, did not get very far. From a logic perspective, it worked fine, however from an EMC/RF viewpoint, not very good at all.
SP
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Rich
Full Member
RF Systems Engr (retired)
Posts: 112
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Post by Rich on Dec 3, 2019 9:53:16 GMT
RE: From my studies a GPS reference can mean microhertz stability on the broadcast band, like .001 hz! The aim? For advanced hobbyists who want to run several transmitters on a frequency, to cover a long boulevard in a town for example with a solid signal. Audio also has to be time aligned as well. At first this conclusion seems obvious, but unfortunately the radiated fields from each system add and subtract according to their path lengths and compass bearings to receive locations.
For two Part15 AM tx systems separated by 2 km (1.24 miles), and driven with absolutely equal r-f power and r-f phase, the net radiation pattern looks like this:
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Post by part15engineer on Dec 3, 2019 14:24:35 GMT
I have given up on a GPS locked Single Frequency P15AM Network. in theory it sounds nice in practicality it comes up goose eggs unless you are a really good engineer with top notch test gear including a Potomac FIM-41 and the knowledge to properly use it.
i believe to date everyone who has attempted an SFN on P15AM has given up on it and just gone with staggering frequencies.
there was one guy in PR who was granted a long term STA to test an on channel booster for a commercial AM and he did get it to work properly but the FCC has since revoked the STA and that experiment is no more.
but to my knowledge he is the only one who got anything near a SFN to work properly.
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Post by part15engineer on Dec 3, 2019 14:26:44 GMT
i have repurposed the GPS units as a external reference for my test gear on my bench that is capable of accepting a 10mhz external reference.
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Post by Boomer on Dec 8, 2019 0:25:23 GMT
Transmitters moving on for the new decadeFor those who have been studying synthesizers, or using direct digital synthesis or DDS, there's a newer chip out that makes an even smaller, simpler oscillator for transmitters, using the newer Si5351 IC. I found this page through the 'ProgRock' crystal replacement, using the same IC, and I believe it can be GPS controlled as well. I feel that tight frequency control, even GPS can be beneficial, finding that the lower my beat frequency with other stations is, the better the signal holds up in the distance and with moderate interference. www.zl2pd.com/sugarcube_plus.htmlAs a long time Analog Dog I'm trying to break into this field, thinking that custom crystals are so gone, and this is future. As always, it's for those who are more advanced, you don't need this to enjoy the Part-15 hobby, the old circuits can work just fine, even coil and capacitor VFO or the $12 frequency synthesizer. Boomer
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Post by End80 on Dec 9, 2019 17:35:50 GMT
Transmitters moving on for the new decadeAs a long time Analog Dog I'm trying to break into this field, thinking that custom crystals are so gone, and this is future. As always, it's for those who are more advanced, you don't need this to enjoy the Part-15 hobby, the old circuits can work just fine, even coil and capacitor VFO or the $12 frequency synthesizer. Boomer I don't understand why crystals for out hobby have disappeared from the market.. I mean I realize there's not much of a market for them anymore, but from what I understand they are very inexpensive to manufacture and they have a strong profit percentage, and there still appears to be a strong market for the hobby car and other craft crystals, so if they're making them anyway why wouldn't they go ahead and cut a few hundred for the MW frequencies as well and sell them too?
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Post by thelegacy on Dec 11, 2019 4:47:04 GMT
I am sure there is some type of scheme going on where it would be at the best interest of certain entities to keep hobby broadcasters from having these crystals. I don't know why though sense DDS and digital synthesized transmitters are readily available.
In this case it's probably the lack of demand. The law of supply and demand prevails here just like certain types of receivers that are no longer being manufactured even though they could be.
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Post by End80 on Dec 11, 2019 23:33:55 GMT
I am sure there is some type of scheme going on where it would be at the best interest of certain entities to keep hobby broadcasters from having these crystals. I don't know why though sense DDS and digital synthesized transmitters are readily available. In this case it's probably the lack of demand. The law of supply and demand prevails here just like certain types of receivers that are no longer being manufactured even though they could be.
While I like a good conspiracy theory, it's a laughable notion. There's no doubt it's anything more than lack of demand. The crystal caper creepily confiscates crystals..
Say that 3 times fast.
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Post by Boomer on Dec 12, 2019 9:22:49 GMT
The Crystal Monster
It would be the lack of demand for low frequency and custom crystals these days, and there just aren't the factories and equipment to make them any longer. Quartz tech has been changing since it started, going from natural mined quartz to grown crystal, and higher oscillation frequencies.
From the beginning of crystal oscillators, AM broadcasters used fundamental crystals, so if you were on 1480 AM, that's where your crystal was oscillating too. By the 1980s, most transmitters had adopted PLL or divider schemes.
PLL used a single crystal to synthesize any broadcast frequency, and dividers used a higher frequency crystal and divided it using a digital IC, divide by 2, /4, /6 for example, like the solid state LPB transmitters use. If your assigned frequency was 1000 khz, the crystal could be 4000, and the circuit made to divide by 4, and that way use lower cost high frequency crystals.
Now we're in a different era, one of clock oscillators for digital equipment, where many frequencies are synthesized from one crystal or resonator. Now it's cheaper and easier to make many small crystals on one frequency and digitally create any frequency from that, than to custom grind a crystal to something specific.
The latest oscillators don't even use quartz, they're called MEMS and use tiny slabs of silicon that resonate in a very exacting, small and controlled environment, and at high stability and resistance to age-related frequency drift.
Boomer
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Post by End80 on Dec 12, 2019 12:00:49 GMT
The Crystal MonsterFrom the beginning of crystal oscillators, AM broadcasters used fundamental crystals, so if you were on 1480 AM, that's where your crystal was oscillating too. By the 1980s, most transmitters had adopted PLL or divider schemes. PLL used a single crystal to synthesize any broadcast frequency, and dividers used a higher frequency crystal and divided it using a digital IC, divide by 2, /4, /6 for example, like the solid state LPB transmitters use. If your assigned frequency was 1000 khz, the crystal could be 4000, and the circuit made to divide by 4, and that way use lower cost high frequency crystals. Now we're in a different era... I'm not even sure which revision my Rangemasters are, the first one I bought from Keith about 20 years ago, which after a few years someone had stolen, along with several processors and other equipment (long story). It took me some time before I could afford another and a couple years later I asked if per chance he had any "used ones", which he did, so I bought it, which he discounted by a few hundred.
Anyway, both times he supplied two crystals of my choice (I selected 1700 and 1620, the quietest in my area).. Well, now after listening to your explanations of crystals; I'm kind of confused, because you seem to indicate that neither of my crystals are actually a "1620" nor a "1700", but rather something dividable by 2 of higher frequencies??.. LOL, I am so perplexed now!
I suppose eventually I'll buy one of his new crystal adapters should the need for a different frequency arise. I have no idea how much they are though, I meant to buy one this summer to have on hand but never got around to it -I get one next year.
Lastly, about 5 years ago I bought yet another Rangemaster on eBay for about $400.. It didn't come with any crystals so I pit my spare 1620 in it.. upon powering on the damn thing will transmit for about 4 seconds then shut off.. I turn it off and on again and it does the same thing every time. Keith told me it sounded like something wasn't seated right, I fiddled on the board to see if something was loose but didn't find anything. So presently I have one working Rangemaster and one not, but one is all I ever needed, although my intention has always been to use multiple installs spread around the area... never got around to doing that either, mainly because it became a lot more complicated than it seemed it would be to accomplish... or maybe because I've just gotten a little lazy with age.
Eventually I get the second one fixed.. eventually I'll do a lot of things.. eventually... But truth be told, for the last twenty years all I've really done is broadcast blindly.. with no idea if anyone in the area ever actually tuned in, nor have I ever promoted it. I've basically just broadcast to myself and have fun with it.
Who knows, if stations go all digital maybe it will result in a boom for part 15 broadcasters, people will be able to use their old AM radios instead of throwing them all away..
What the hell am I talking about? What's my point?.. I have no idea, just woke up, rubbed my eyes, and checked the forums.. Think I'll just go back to bed for another hour or two.. I feel like I'm just talking gibberish..
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