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srs gimme model numbers to look at or something, i am not averse to going up to $200 shipped but would like to find a slightly better deal
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Sep 12, 2016 03:32
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Jonny 290 posted:2225 worth a hundred? or do i want a cheap used storage scope how important is accurate frequency response and accurate frequency measurement, and at what frequencies
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Sep 12, 2016 03:44
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i'd likely pick up some old $50 bench counter to do frequency measurement itself. counting grids is ok but i know its not that accurate steps like "peak the RF voltage at TP2 by adjusting L1", thats what i want to do as far as radio repair goes. for homebrew, uh as long as i can line up LO's and mixers for lovely superhets and broken direct conversion receivers, im happy
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Sep 12, 2016 03:58
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iirc the recommendation was get a scope with a bandwidth 5x your maximum frequency to eliminate sampling artifacts?
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Sep 12, 2016 07:13
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atomicthumbs posted:iirc the recommendation was get a scope with a bandwidth 5x your maximum frequency to eliminate sampling artifacts? that's assuming you're getting a digital sampling oscilloscope you can't go wrong with any tek from the 70s-80s, if all you need is 2 channels then 100$ for a 2225 sounds great jonny with analog the specified bandwidth means you're getting -3 dB at that frequency so if you dont care about measurement accuracy and all you want to know is "what's this wave shape" or "is there something there" you can go over the specified freq Olivil fucked around with this message at 02:16 on Sep 13, 2016 |
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Sep 13, 2016 02:13
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yeah at best i'll be looking at the input/output of an amp board or filter or something, i cannot imagine that for the first year of scope ownership i'd need more than 2 traces i recognize the dopeness of digital storage scopes but also dont think its critical for my needs rn
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Sep 13, 2016 02:14
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Olivil posted:that's assuming you're getting a digital sampling oscilloscope keep in mind that a square wave at the rated maximum frequency of the scope looks nothing like a square wave though if you're comfortable with the fact that your scope will lie to you at higher IFs it's fine though
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Sep 13, 2016 06:34
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I was really kinda looking closely for a 2236 b/c integrated voltmeter and freq counter, but they run close to 225-250 shipped off eBay. Got a line on a tek 2235 locally overnight, 130 bucks, tested, good, not calibrated tho. What do we think? representative sample 
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Sep 13, 2016 15:17
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see if you can get a HP 5334/5335 universal counter or a decent philips/fluke one instead of some integrated crap. also once you start measuring frequency it's just a matter of time before you're building multiply redundant timebase distribution networks, be warned. the 5335A had an RF prescaler option that went to 1.3 GHz, but if you get one i designed a board last year that will do 3 GHz (though that layout may only work with certain FW revisions since they allegedly changed the divide ratio from 20 to 32 or 64 later, not too hard to respin my design for that ratio though) i've also made a replacement board for the input comparators that works reasonably well i've never liked tek skopes (sue me) so i don't know if that's any good unfortunately
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Sep 13, 2016 19:51
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longview posted:also once you start measuring frequency it's just a matter of time before you're building multiply redundant timebase distribution networks, be warned. high stability oscillators are cool
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Sep 13, 2016 21:09
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earlier today i replaced the GPS module in my primary Z3810AS RFTG set, the old motorola oncore receiver had decided it was december 1996. this confused the clocks i built that run off the timecode output somewhat since their epoch starts in 2000. the raspi NTP server just ignored it and the 10 MHz output was fine since it still counted seconds properly. fortunately "new" modules can be had for around $10 a piece so i bought two to have a spare just in case so now the system's working on getting a 3D position fix before it will even think about putting out time or frequency, and since i did a factory reset on both receivers they have to re-learn the oscillator characteristic etc etc. will probably be a week or two before they're back to normal. it's a good job i had a nearly identical cold backup set sitting on the shelf to put in service while waiting for the parts! 
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Sep 13, 2016 21:32
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my watkins-johnson has a frequency reference module which has four extra outputs for attaching other equipment but I can't attach any other equipment since it spits out 50mhz
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Sep 13, 2016 22:08
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My tek 2247A is very needs suiting.
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Sep 13, 2016 23:29
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Yeah i slept on the integrated counter gimmick and decided it was stupid to spend $100 extra on a lovely old 80s frequency counter that would also break if my scope ever did. Guy with the 2235 is holding it for me till Friday (it's been up for a month and no takers, slow craigslist market and he refuses to ship it again) -- and then after I get that, i'm gonna order a stack of QRP crystals and some SA612's and i am going to build a radio.
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Sep 13, 2016 23:54
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welp 9/14/2016 i made something that generates radio signals (sorta) built this thing on some copper clad using the old S-meter out of a dead icom i gutted this week. It's a crystal tester!  imagine my fuckin' shock when i plugged a crystal in and the meter swung! and then imagine my shock when i had a 10.240 mhz crystal in and waved it in front of my radio while tuning around and it about fuckin' blew my ears off on 10.241.500ish. same with a 7.68 crystal (was about 7.679.3 carrier) oh god im so excited e: subbed a quad-2 of course as i still have too many, all other values same except 1k trimpot on the meter oh and i just pulled a random big glass diode out of that icom and it measured .245 drop so I was like, sure, thats germanium Jonny 290 fucked around with this message at 12:54 on Sep 14, 2016 |
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Sep 14, 2016 12:45
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 its hideous and beautiful
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Sep 14, 2016 15:05
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Sep 14, 2016 15:11
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oh lmao thats not a huge blob of solder on the terminal board there, perspective trick, its the big anchor point on the board
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Sep 14, 2016 15:17
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electronics and circuits are really cool but i don't really understand how anything happens
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Sep 14, 2016 15:19
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 GPSDO working its way to stability, when left alone and powered for a few weeks it eventually gets down to less than 1µs/day drift which is sufficient for most applications -- jonny you should add a trimcap to the test point to check the tuning range of the crystals and maybe an output for a frequency counter
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Sep 14, 2016 16:30
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Captain Foo posted:i don't really understand how anything happens me irl on all subjects forever and always
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Sep 14, 2016 16:32
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longview posted:
now phase-lock it with one of these 
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Sep 14, 2016 18:48
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atomicthumbs posted:now phase-lock it with one of these cesium standards are cool but the dumb thing with buying an old one is they work by actually transferring matter through a beam (or something similar to that) so the tubes actually have a very finite life i do have a rubidium on cold standby, but that won't do time of day unless i build my own clock source using the PPS output (which would be cool but then i'd need to build some more redundancy switching for the timecode distribution) also have a LW radio clock which would work pretty well, but it's designed for the UK LF transmitter that doesn't come through very strongly here  that clock uses carrier frequency sensing for the pulsed clock code to generate a frequency standard; in 1980 that was probably a revolutionary new step but it means it has no ability to maintain frequency over time if it loses the signal like the GPS clocks. it also jitters a lot since it can only track the carrier when it's keyed, which is at most half the time. and there's no way to get the time of day out of it since serial output was an option. i'm working on routing the last board to make a quad input automatic time base switch, made the first board earlier this year (4xPLLs receiving a timebase with automatic switching, 77.75 MHz output) second board will accept the redundant 77.75 MHz and phase lock a 14.4 MHz clock (chosen for availability) very carefully, which a CDCE913 PLL will convert to 10 MHz with pretty low jitter. if no source is available i've added a second free running TCXO which can be switched in as a last ditch timebase, there's a tristate switch to select either failover to TCXO, no failover at all, or forced TCXO (mainly for special circumstances). both TCXOs will be heated (but not ovenized) to hopefully improve long and short term stability four outputs, 1 is an AC coupled 3Vp-p into 50 ohm high level output meant to drive a splitter near the measuring gear, the other three are 1.6Vp-p into 50 ohm DC coupled, each one of those will go to a a sub board with a triple video amp, giving a total of 9x~10 dBm clipped sine and 1x+15 dBm clipped sine output.
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Sep 14, 2016 19:10
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Captain Foo posted:electronics and circuits are really cool but i don't really understand how anything happens pfm my friend.
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Sep 14, 2016 19:32
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longview posted:
yeah step 2 is add a trimmer (i have some beautiful 4-15pf trimmers in the box) and a buffer transistor and a counter/scope out Last night i ordered a shitload of crystals to goof with. a 22 pack with just about every interesting qrp frequency on 80-15 meters for $15, and a 33 crystal lot of Random New HC49U Crystals Most Are Not In Ham Bands for 10 bucks
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Sep 15, 2016 00:03
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Mr. Nice! posted:pfm my friend. please gently caress me, my friend
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Sep 15, 2016 01:20
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Mr. Nice! posted:pfm my friend. I don't know what this means
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Sep 15, 2016 02:26
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i did a bit of looking into a MC3374 based FM receiver, particularly the quadrature discriminator tank component. the MC3374 is the "bad" type of receiver IC that requires an LC network that provides a 90 degree phase shift at the IF. the network also has to have a very sharp phase shift around the IF, 90 degrees at the center frequency and down to (as much as) 0 degrees at center - the largest deviation and 180 at center + largest deviation. usually these ICs were made either for higher stability ceramic discriminators or an LC network. the LC network is slightly more flexible since the Q factor can be de-tuned to reduce the sensitivity and allow larger deviations + reduce distortion. ceramics should be more stable but i'm not an expert on quad discriminators (and i don't really like the concept since it requires highly stable and precise tuned components to get good performance) attempts to make my own tank using bits i had laying around were not successful... these tanks were usually little metal cans with a trimmed inductor for centering and using a random LC network isn't going to work very well. these tanks also cost a fair bit if you can get them (at least a few dollars a piece) so my plan is to use the 3374 as a mixer and IF amplifier, and maybe i can use the audio buffers/FSK comparator. i'll put a FET buffer on the tank output pin, the signal there should be an amplified and limited version of the 2nd IF. i'll tack on a 74HC4046 VCO+phase detector IC and make build my preferred kind of frequency discriminator; the PLL discriminator! the 4046 has everything needed; a fairly linear VCO capable of operating over a wide frequency range with decent stability, internal high gain self buffering reference input port, a choice of a poo poo XOR detector or a nicer phase-frequency detector and a built in control-voltage buffer to get at the audio signal without loading the feedback loop. the tuning sensitivity of the VCO can also be tuned somewhat independently of the center frequency. i'll use the NXP 74HCT9046A, which is a slightly more modern version with better stability and a current source output on the phase-frequency detector to eliminate the traditional dead band. a 9046 costs around $0.6, but they're completely off the shelf and guaranteed to be available basically forever (if NXP drops the 9046 i could always use the 4046 with reduced performance and cost)
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Sep 15, 2016 21:29
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that seems like some real stupid bullshit requiring the right kind of fairy dust LC network for the phase shift. I'm following along though!
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Sep 16, 2016 01:33
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I'm thinking about writing my research paper for an english class on ham poo poo. How badly am I gonna regret this?
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Sep 16, 2016 02:16
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Captain Foo posted:I don't know what this means pure loving magic.
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Sep 16, 2016 02:17
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Couldn't you just stick an IQ demodulator IC in front of it
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Sep 16, 2016 03:29
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Mr. Nice! posted:pure loving magic. oh lmao
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Sep 16, 2016 15:14
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atomicthumbs posted:Couldn't you just stick an IQ demodulator IC in front of it i could do that but i don't think it's super trivial to turn that into FM without a DSP? i want to figure out if it's possible to electronically trim the 4046 VCO center frequency (without using a varactor, the delta C makes it impractical), if that's possible then i can inject a calibration signal and auto-center the VCO. when that's doable i'll be able to reduce the tuning range of the VCO, improving modulation sensitivity and potentially noise/distortion without having to worry about thermal VCO drift making it unusable at temperature extremes...
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Sep 16, 2016 15:29
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so a few weeks ago i bought this ting on ebay, took a while to get the customs paperwork sorted since it came from the Czech republic, but it just got here this evening it's a complete radio transceiver tester, this one has DTMF/all known forms of tone signalling and full duplex testing as well approx 1-1000 MHz, RF generators covers down to around -130 dBm has a lot of automated features to simplify radio alignment, basically you hook up the radio/repeater/cellphone antenna leads, the microphone port, the receiver AF port (preferably the discriminator), there's some TTL outputs on the back that can be used to key the radio i think this thing will then receive or transmit RF and check the signal quality using its own receiver and modulator, calculate things like frequency offset, deviation, distortion/SINAD. it can also work as a moderately good spectrum analyzer, with the right software it could be a cell-phone or a cell-phone base station, and there's a lot of stuff i still haven't learned how to use yet unfortunately it's "broken", that is, it fails its own self test, blaming the discriminator board. the service manual doesn't seem to list the failing self check test number as relating to that board (no OCR on the PDF so can't just search for that step). however the only thing i can find wrong is that when used with the bottom high level T/R port the signal switching seems to be going on and off, when used with the low level port it's fine but reports the wrong RF carrier level. the frequency of the on/off switching is slightly dependent on what the CPU is doing; i suspect a bad connection to the address decoder on that interface. the low level could be related or it could be a bad relay contact/contact resistance in the fuse holder inside those ports. the input reports higher levels at higher frequencies so there is some capacitive coupling through whatever switch is causing that problem. when i pull up the scope like in that picture the input is perfectly stable (it also reports the correct RF level there) other stuff: the screen is a 320x240 or so electroluminescent with a ~digital video interface~, this is a finlux and that type of display is still being made (i checked and there's a company still making pin/interface compatible displays over 25 years after they were introduced). it's more than bright enough, wouldn't want to use it in the sun but it's completely readable under normal lighting. CPU is the purest of all, the glorious MC680000 in the gigantic DIP package, 256 kB of high speed SRAM is available though with soldering work the service manual says it can be upgraded to 4x that. there's also dedicated display memory with a display controller from zilog. all the AF/digital boards are on something similar to a VMEBus but the boards are bigger; i have an extender for eurocard racks that should work but i might have to remove the board clips from it all the RF modules are on similarly sized boards but in a separately shielded enclosure with a ~2x40 or so ribbon cable running between the boards.
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Sep 16, 2016 19:16
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longview posted:so a few weeks ago i bought this ting on ebay, took a while to get the customs paperwork sorted since it came from the Czech republic, but it just got here this evening owns
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Sep 16, 2016 19:52
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Oh that thing's fuckin' dope. That's the fixit factory right there. get that rolling and it just shits out working rigs
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Sep 17, 2016 01:05
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longview posted:i could do that but i don't think it's super trivial to turn that into FM without a DSP? i mean, don't those spit out an I signal and a Q signal with a 90 degree phase shift? i'm probably misunderstanding multiple things here
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Sep 17, 2016 01:23
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longview posted:so a few weeks ago i bought this ting on ebay, took a while to get the customs paperwork sorted since it came from the Czech republic, but it just got here this evening 
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Sep 17, 2016 09:02
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had time to do more troubleshooting since the forums were down the receiver port not working was user error; it was set to auto-frequency which only works with more than 10mW input, when it's not receiving at least that it apparently switches in some other stuff or changes filters etc. low level reported on the low level port was a bad connection between the front panel BNC (which has a miniature fuse in it, and several tiny spring/sleeve contacts) and the input limiter, which is a small PCB inside a can hanging on the voax between the BNC and the panel mount SMB connector which mates with the RF unit SMB connectors when it's inserted. that's a lot of custom machining and systems design, this thing wasn't cheap. to get at that part i had to pop off the front panel, which took more work than it should:  all but one, per usual. this one must have been made of actual mao-grade steel since the drill ate right through it. replaced all of them with M4x12 torx head to avoid future problems. once that was sorted the entire front panel comes off as an assembly with two connectors, very nice. removing the BNC holder frame required even more drilling out screws, they seriously over-tightened these at the factory, replaced with countersunk M3 DIN912s no dice sorting out the BIT fault on the demod board; the service manual assumes you have a memory card with a special software program that allows single stepping of the tests to measure things. as is i've checked most of the functionality that board handles and nothing seems to not work, but it's hard to know for sure. here's the setup for measurement:  din41612 96 way extender is just too short to poke out since the boards are bigger than normal, support via a tiny machinists vice keeps it in place. i've replaced all the electrolytics on that board with high value ceramics, but this hasn't had any effect (AC coupling caps are exclusively ceramics on this board and most of the others). power supply can also be pulled with a few screws, there wasn't any sign of bulging and the supplies are stable so i don't think this requires a recapping really. some other things i discovered: decode and encode PL tones works well, it will tell you the actual frequency and deviation on receive as well as map to default frequencies, and it's possible to activate the PL encoder in all the modes i've tried so far. haven't tested digital PL codes yet though they should work. DTMF works the MC68k is actually a QFP, not a gigantic DIP. the AF boards are exclusively SMD single sided except connectors and other weird components unit was built in 1998 or so, all the boards have the same serial sticker so this isn't a parts bin instrument there was a (broken) battery inside, someone has modified it to use a 7.2Ah lead acid instead of the ni-cad pack it came with; the charging should still work reasonably well but the charge voltage should probably have been adjusted up a bit. it was being float charged to 12.3V. they also decided not to mount the thermistor to prevent overheating, which is a bit of an oversight IMO. i pulled the main RF can to check if the pin diodes in the front end were ok, they were but i did get pictures that are in the SLR. somewhat interesting board-on-board design.
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Sep 17, 2016 22:01
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