Teardown : HP 8645A Agile Signal Generator - Page 1
Forum section: electronics / testgear

author: free_electron
author_rank: Super Contributor
timestamp: July 29, 2013, 03:48:52 am
content: It's been a busy weekend. This thing is a beast ! Picked up cheap. Dead. locks up on power up...Before we dig in : what the hell is an Agile Signal generator ?In short :its a standard signal generator sporting AM FM pulse and phase modulation of a carrier between 260 Kilohertz and 1.03 GHz. The machine can sweep its carrier or 'hop' its carrier. In other words you can feed it a list ( up to 8000 ) preset frequencies and signal strengths and 'hop' from one preset to another.So what is special about this beastie ? Well it can do all modulation form's at the same time ! So you could make an FM signal and then amplitude modulate that very slowly over time to simulate the fading effect and study how well your receiver copes. It has multiple modulation sources that are each individually controllable in amplitude , time and deviation . it also sports a programmable audio tone to be your 'test signal' and be modulated using the drift parameters.So far so good , pretty impressive. But there are plenty of other machines that can get close to this. So what makes this thing 'agile'. Well the 'hop list' Ok ... other generators can have presets and you can recall these. Some even allow automatic stepping through the list. But... not at the speed of this thing. This machine can change ALL its signal parameters with guaranteed lock-in in 15 microseconds for a full-span hop (going from 260 kHz carrier to 1 GHz carrier) or less... small Hop's are sub microsecond ! In fast-hop mode ( with limited modulation settings ) this machine switches its carrier around , with lock-in, up to 10 million times per second.This machine is used to generate signals that are spread-spectrum. Typical applications are military radio communications, Avionics , guiding systems for planes, surveillance receivers, GPS and other batshit crazy systems. Every aspect of the machine is programmable in the hop list and the sequencer has programmable dwell time between hops.so you could do things like this:Step 1 :105MHz carrier with an FM modulated signal : 500KHz modulation depth carrying a 1Khz audio tone at 50% amplitude. Fade the carrier an amplitude over 1 millisecond from -90dB to -50dB.Step 2 : 106.8 MHz carrier FM modulated 300 Khz modulation depth carrying a 2Khz audio tone at 33% modulation depth (amplitude). fade this (am modulate) over 3milliceonds from -70 to -30dB.and so on..program the time between each step ,the start and stop points and let it rip ...The machine has multiple marker outputs so you can trigger external equipment ( when it hits a specific step it will activate one of three trigger outputs. )This machine costed an insane amount of money when it was new (1988).It also employs completely insane techniques to do this kind of crazyness.But, without much further ado here is the eye-candy:.Stuck.... it would not go beyond this point. Time to take out the screwdriver and pop the lid.Duuuuuuust !. dust everywhere. My -insert deity here- this thing was dusty. Vacuuming and compressed air couldn;t handle it. It had to come completely apart. Besides being a fire hazard i had an idea the dust could be the problem or part of it ....oi vey... hardcore RF engineering with a truckload of SMC connectors sporting flexible coax and SMA connectors sporting hardline. this aint gonna be easy ... it took me 6 hours... from first screw out to being back in powerup state.Top to bottom : The large cartridge is a delay line. Not just any delay line. it is a spool of hardline coax mounted around a heating element with temperature controller built in. What otherworldly technology needs heated delay lines ? Totally bonkers this machine.Empty slot for a second phase modulator ( but then you need the dual delay line in the first slot ... )Next up is the Phase modulator.The two empty slots are for two optional modules( a frequency counter and some other insane thing i can't remember)Next another modulator. this cartridge holds two boards each doing one function. one is AM the other FMThen the fractional-n divider. this is basically a DDS engine (without the sinewave generator )it creates the carrier wave based off two numbers (which form a fraction of the reference)The fractional divider is two cartridges.Then the reference oscillator and fast lock-in VCO. The DCU (digital control unit) sets up the divider and fractional divider and programs the VO into one of a range of frequencies. the VCO is controlled by the main divider this forms a PLL system.The master VCO: the output frequency of the first VCO is fed into the Frac-N system whihc controls the master VCO as a fraction of the first VCO. Don;t ask me more details .. i need to study it. they basically have two VCO's. they program one to a certain frequency using a first PLL system. the second VCO is then programmed using another pll system (the frac-n) to be a fraction of the first vco. That is how they can tune so fast.the big metal cover holds the DCU (Digital control unit ) and the output attenuators..The heated hardline-coax delay line. You need a PHD in complete madness to come up with this one... Even grey-beards fear to thread in this domain....The phase modulator. don;t ask me how it works. i have no clue. its all RF black magic. I see striplines , pin filters and other otherworldly stuff in there... Notice the shine of the metal inside. this ain't your run of the mill aluminum casing... this here be mu-metal domain... also notice the spiral EMC gaskets everywhere. A lot of these boards have warning stickers on em that say : no solvent cleaning... probably some whacky board material or components that can't handle that. I didn't dare touch anything. i used clean, dry air to blast the things dust-free ( i actually used a scuba cylinder filled with breathing air as that is ultra purified , dry and guaranteed oil free. ) I made a kind of a hood out of cardboard hooked up to a vacuum cleaner. put hood over open cartridge and blast clean air through the ventilation holes. worked like a charm. one or two blasts and all dust was gone. the vacuum cleaner sucked it all in.The modulator can. A very weird mix of surface mounted parts (oldest SMD part i found was dated 1987) , thru hole parts, hermetically sealed parts , leadless packages and old To-100 style ic's... very weird stuff indeed. If it had a vacuum tube somewhere it would have technology from all era's ( actually the front VFD's count as vacuum tubes , so in a sense it does ).below you clearly see the madness at work:.Sourface mounted resistors and caps, ceramic ic's like the PMI part, hermetically sealed ic's like the siliconix part (DG145) TO-100 power regulators( with black heatsink : LM305) and craze TO-unknown power opamps ( the big round cans , they had heatsinks on em Harris 2541. no idea what this is. these are dated 1986 so some of these chips were bought before and stocked by HP before this machine was built. its manufacturing date is 1988 ... with parts from 1986 ...the frac-n machine:.another can of otherworldly technology. the big asic in the center ( white lid) is an HP ic that holds the divider core. the 74377 on top hold the program word. the two intel eproms are 27256 ( those must have cost a fortune in 1986... ) holding some lookup table. they drive the analog devices DAC. a hardline carries the vco output signal from the left to the detector at the right.The black heatsink top right holds another ASIC from HP (number was written on the heatsink. i didn't dare remove it.two closeups of the insanity :..If you have not been driven mad by now ... stay tuned. we'll get there ...The other divider. More sheer black magic...all i see is what looks like a bunch of pin diodes and filter stages... but it is a divider ... your guess is as good as mine how it worksThe second VCO (under control of the frac-n system).The power stage at the right. Driven by a philips power transistor..The master VCO system:...Now we leave the RF madness behind and take a peek under the metal cover that holds the DCU (Digital control unit)First board : a mystery device form analog devcies... i suspect this is an early DSP ... very early ....Next we hit the hopping controller. a bunch of 42256 rams which form a -very- wide databus..the next boar din line is the output attenuator. it uses two relay driven attenuators built by Agilent. small detail : there is a xicor eeprom ( oodles of cash for that one on 1986... ) holding the attenuator constants.....I did not take a picture of the last board which is the central processor. it's a simpe board holding a motorola 68000 (68K) in PGA package (pin grid) 4 27c1024 eproms ( there's a ton of code in this thing... ) and a tms9914 GPIB controller. nothing else.The frontpanel has two VFD's driven by high voltage drivers from TI and under control of a 8031 with its own eprom.I also did not take pictures of the massive power supply in the back ( all linear with big Philips electrolytics screwed into the board )Right. So now we have a clean machine let's see what is going on. a quick check of all the voltage ( easy since they provided testpoints for each and every one ) finds nothing wrong. The DCU main processor status indicator shows 'HOLD' (there are 4 led's that show a diagnostics code).time to pull that one out and take a closer look.. hmm. there is a nicad battery on this board. voltmeter ... 0 volts ... well that's a dead one... 3.6 volts 50 maH. i take the battery pack from a disused dect handset (which happens ot have nicds in it and be 3.6 volts) , solder two wires and McGyver it in.Powerup ...and i am greeted by this screen :.this takes a while... an indicator on the left VFD is playing knight-rider ( or battle star galactica cylon. by scanning back an forth over the text).Well this takes a sweet long time.. tension builds....after a good 10 minutes (this thing also has a crystal oven installed. a real one.... the highest cost option) it briefly flashes 'Complete'and then shows me this :.A quick test with a frequency counter confirms it. the beast is working , passed all self tests, calibrated itself (due to battery loss all calibration was lost. this machine has a built in self calibration system. it has a precision Rf detector and voltmeter and goes through a test multiplexer to trim each and every point in the system digitally.And this is what it can do :.It works. 6 hours of ripping it apart, vacuuming it ,replacing its nicad battery and it is fully functional.Somewhere, someone, that tossed this thing out, today felt a temporary chill crawling up his spine and doesn't know why... ah well. Too bad for him.

author: Vgkid
author_rank: Super Contributor
timestamp: July 29, 2013, 04:25:16 am
content: This will be a really interesting teardown, I await more pictures.

author: c4757p
author_rank: Super Contributor
timestamp: July 29, 2013, 04:53:35 am
content: Holy shit! Dare I ask what the list price was? Dare I ask what it costsused?Absolutely beautiful though, the construction is fascinating. I love the heated delay line...And with all the stuff I've repaired, I have come to the conclusion that if it's more than 10 years old and contains a battery, the chance that the battery is the fault is about 200%.

author: free_electron
author_rank: Super Contributor
timestamp: July 29, 2013, 05:12:56 am
content: They go for about 1800$ on ebay. which is a very high price for such an old thing. But those machines are optionless.Mine has option 01 03 and G03.The new price was over 35K$ ... which, in 1989, was a LOT of money ! ( a quick look at an inflation calculator estimates it to be over 65K$ now... )another cool thing: it has a prominent yellow sticker on the top ( factory installed label from HP)it says : Warning : heavy equipment. Two-man lift.no kidding. this sucker weighs 76 pounds !

author: daqq
author_rank: Super Contributor
timestamp: July 29, 2013, 05:53:06 am
content: Very nice! And interesting technology - the heated delay line is bizzare...Look at U10 in:http://www.siliconvalleygarage.com/eevblog/8645a/8645avco3.jpgAnd the test points... or poles/stakes?

author: c4757p
author_rank: Super Contributor
timestamp: July 29, 2013, 05:56:55 am
content: Hehe... I saw that too. I'm a bit surprised they didn't consider that possibility when designing the board - those TO packages will pretty easily fit into a DIP footprint, but the other way around....I like the test points. I've got a couple things that have them. What would be awesome is a probe tip attachment that can grab them, or if they had a notch near the top so that a minigrabber could stay on.

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 29, 2013, 11:57:55 am
content: ADSP-1012A: 12x12 bit CMOS multiplier, see attachment.

author: free_electron
author_rank: Super Contributor
timestamp: July 29, 2013, 01:19:39 pm
content: Wow.. A hardware 12 bit multiplier... What a strange device... Must be a reason to have that, but what ? I studied the schematics of the machine ( i bought the CLIP : component level schematics and service manual. Agilent doesn't have it but artekmedia has a high resolution scan ) and it is part of the frequency synthesizer. This is probably part of the system that calculates the tuning word. Compined with the divider they can create the fraction they need... Hmm. Even though they have a 68000 cpu runnin at 16 MHz they need a hardware multiplier ... Then again. If you can do 10 million changes a second.. The 68000 would pop out of its socket, scurry away to a dark corner of the machine , curl up its tiny little pins and simply croak... Recalculating 10 million times with an 16MHz clock cant be done...-edit- looking at the datasheet this thing does the multyply guaranteed faster than 90nS .. Which is over 10MHz. So that is the reason.. It fits. No way a cpu could cope with that breakneck speed (not in 1986... , not with a 1MHz clock... Add on top of that the loading of data from an io port and sending it back.. And that cpu is multistep.. 16Mhz means it can do about 2 million instructions. No chance.Plus it needs to be guaranteed latency..So they crammed in a 64 pin , ceramic , side brazed , gold pin , hardware multiplier ( from analog devices ? Why are these guys dabbling in pure digital chips ? )... That chip probably cost a nice wad of cash at that time. This machine get weirder and weirder the longer i pick at it to figure out how it works..Also: notice there is not a single trimpot, trimcap or tunable coil in this thing ? For such a complex thing , so old ? If you compare with other machines from this era like the 8116 or 8112 signal generators : they are full of trimpots and adjustment points. Same for the 3124 and 3125 synthesizers. This thing ? Not one ... All driven by the DCU. The firmware sits in four 271024 eproms (those are 40 pin eproms with 16 bit wide datapath ! So no interleaving bytes. We are feeding a 16 bit processor. No bottlenecks there. ) so this thing has 256kilowords of code. That is a very large program for 1986...Crazy machine

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 29, 2013, 05:28:33 pm
content: Quote from: free_electron on July 29, 2013, 03:48:52 amWaitwaitwhat?! Nooo, that can't be!"These are not the PIN diodes you are looking for!" My bet is that those are varactors, not PIN diodes, and that ... just ... might ... be a passive, distributed parametric frequency divider. Built with discrete components. In 1988.

author: free_electron
author_rank: Super Contributor
timestamp: July 29, 2013, 06:31:11 pm
content: i never heard about such a divider , went and looked It up. The schematics sort of match the principle . One path is indeed a varactor with matching network in and out, the other path is a pin diode (that's how they pick off the frequency they want from the divider apparently...These dividers have extremely low phase noise (which fits the specs of this machine).The Motorola chips select one of the pin diodes.Damn that machine was lightyears ahead of anything out there.This machine is beyond anything I've ever seen in terms of crazy technologies. anyone know why you want to heat a delay line ?

author: KJDS
author_rank: Super Contributor
timestamp: July 29, 2013, 06:39:24 pm
content: It's an interesting beast designed at a time when RF engineers needed to be magicians specializing in the black arts, and bodybuilders too.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 29, 2013, 06:44:12 pm
content: Quote from: free_electron on July 29, 2013, 06:31:11 pmTo tune or stabilize the delay would be my guess. Some dielectrics have rather peculiar temperature dependencies of their dielectric constant, which influences the propagation delay. Teflon/PTFE happens to be one of those materials, IIRC....but this is not exactly a major effect, which is why you normally wouldn't bother compensating for it.

author: KJDS
author_rank: Super Contributor
timestamp: July 29, 2013, 07:06:01 pm
content: I'd be interested in seeing a block diagram to work out where all those parts fit together.

author: MetraCollector
author_rank: Regular Contributor
timestamp: July 29, 2013, 10:35:07 pm
content: Thank you free_electron, beautyfull.Now I know what is Tesla BM596 counterfeit of.However, Tesla fake weights the double and half-life of that evil machine is 3 days.http://www.radiomuseum.org/r/tesla_generator_bm_596.htmlhttp://elektrotanya.com/files/forum/2013/03/BM596.jpg

author: free_electron
author_rank: Super Contributor
timestamp: July 30, 2013, 04:03:04 am
content: i don't think that tesla comes even close ... it may generate a carrier and be able to modulate it but not to the extent of the 8645a ... and not with the specs of the 8645a

author: marshallh
author_rank: Unknown
timestamp: July 30, 2013, 04:14:28 am
content: Much of the pcbs area looks to be some early inhouse HP autorouter..(I assume) Any idea who was using what software around that time?

author: free_electron
author_rank: Super Contributor
timestamp: July 30, 2013, 04:18:23 am
content: HP had some cad software to do pcb layour. i know they used Valid a well as intergraph and Calma.it mayhave been something that ran on HPux. no idea. fact is their schematics are very nicely drawn on computer. everything is commented , cross referenced. very nicely done.

author: nukie
author_rank: Frequent Contributor
timestamp: July 30, 2013, 04:26:09 am
content: Right angle tracks !! Yay.Thanks for the teardown it was interesting glimpse into these equipment.

author: c4757p
author_rank: Super Contributor
timestamp: July 30, 2013, 04:27:43 am
content: Quote from: nukie on July 30, 2013, 04:26:09 amIt sure beats the aw-screw-it-angle tracks in the Keithley teardown....

author: KJDS
author_rank: Super Contributor
timestamp: July 30, 2013, 07:47:45 am
content: Quote from: c4757p on July 30, 2013, 04:27:43 amIt's RF, it is supposed to look like Slartibartfast has played a hand

author: MetraCollector
author_rank: Regular Contributor
timestamp: July 30, 2013, 01:29:46 pm
content: Quote from: free_electron on July 30, 2013, 04:03:04 amYes, definitely. I used to collect some tesla and metra stuff and explore how it works and then discover what it is fake of. EVERY of their instruments are counterfeit of some HP or any other. However, 10 years delay.Example isHP 334A(1966) and TeslaBM 543A(1977)Please excuse me for spamming.Is it even possible to discover how many units of these (8645A) were built ? Was it available for everyone ? Or some embargo in that years ?

author: G0HZU
author_rank: Super Contributor
timestamp: July 30, 2013, 05:07:08 pm
content: At a guess the big long transmission line that is coiled up and wrapped with tape will be part of the synthesiser system.It's precise and well controlled phase shift will introduce a precise time delay and is probably used as a frequency discriminator in an FLL (Frequency Locked Loop).At a guess that coax will be about 50feet long so if we assume 1ns a foot then that would mean a 50ns delay line.The accuracy of the FLL synthesiser will be determined by the precision of the delay line when running in agile mode. It probably has to calibrate or learn the accuracy of the delay line for each mission programmed into it.So I doubt it will be truly phase locked to a reference in its most agile modes and the frequency stability will be defined by the delay line stability and whatever else is within the FLL section. So maybe that is why the temperature of the delay line (i.e. the frequency discriminator) is controlled by an oven.It certainly is an interesting old generator and the build quality is excellent.

author: free_electron
author_rank: Super Contributor
timestamp: July 31, 2013, 01:54:01 pm
content: I found an HP catalogue from 1991. List price : 32000$ without options.... This was their flagship

author: vaualbus
author_rank: Frequent Contributor
timestamp: August 01, 2013, 01:02:36 am
content: Where you get the schematics? I've checked on artkemanuals but I haven't found nothing. I want to have the schematics ti know all this advanced mudulation has done.Best regards, Alberto Vaudagna.

author: free_electron
author_rank: Super Contributor
timestamp: August 01, 2013, 01:05:44 am
content: 8643A is the base machine. artekmedia has that service manual.

author: vaualbus
author_rank: Frequent Contributor
timestamp: August 01, 2013, 02:16:45 am
content: thank you.

author: vaualbus
author_rank: Frequent Contributor
timestamp: March 04, 2014, 01:04:31 am
content: For every body that want to go more inside the instrument design an theory of operation, I have this HP journal about this series of signa generator.Link:http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-10.pdf

author: echen1024
author_rank: Super Contributor
timestamp: March 04, 2014, 02:06:49 am
content: Gorgeous microwave black magic. I think for the logic boards they just set up the autorouter and let er rip.

author: TerraHertz
author_rank: Super Contributor
timestamp: March 04, 2014, 03:00:46 am
content: Quote from: free_electron on July 29, 2013, 01:19:39 pmI do hope you captured the firmware, and plan to upload it to bitsavers or BAMA or ko4bb.Since those EPROMS must be getting close to bit evaporation by now.What an awesome machine! (Attempts to resist feeling jealous, fails miserably.)

author: TiN
author_rank: Super Contributor
timestamp: March 04, 2014, 07:28:30 am
content: Great score. Dead battery failures are for sure a popular thing in old gear. Got my R&S generator fixed exactly same way.