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From: Jan Panteltje <alien@comet.invalid>
Newsgroups: sci.electronics.design
Subject: Re: "Sampler??"
Date: Wed, 31 Jul 2024 10:54:58 GMT
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On a sunny day (Tue, 30 Jul 2024 15:11:35 -0000 (UTC)) it happened Cursitor
Doom <cd999666@notformail.com> wrote in <v8avr7$13368$1@dont-email.me>:

>On Tue, 30 Jul 2024 14:51:10 GMT, Jan Panteltje wrote:
>
>> On a sunny day (Tue, 30 Jul 2024 11:20:47 -0000 (UTC)) it happened
>> Cursitor Doom <cd999666@notformail.com> wrote in
>> <v8aiaf$10lqo$1@dont-email.me>:
>> 
>>>On Tue, 30 Jul 2024 10:36:51 GMT, Jan Panteltje wrote:
>>>
>>>> On a sunny day (Tue, 30 Jul 2024 08:58:35 -0000 (UTC)) it happened
>>>> Cursitor Doom <cd999666@notformail.com> wrote in
>>>> <v8a9vr$v9r2$1@dont-email.me>:
>>>> 
>>>>>On Tue, 30 Jul 2024 05:16:24 GMT, Jan Panteltje wrote:
>>>>>
>>>>>> On a sunny day (Mon, 29 Jul 2024 09:29:04 -0700) it happened john
>>>>>> larkin <jlarkin_highland_tech> wrote in
>>>>>> <72gfajl8ke966lsu54bpajpang9dvgmt63@4ax.com>:
>>>>>> 
>>>>>>>On Mon, 29 Jul 2024 05:19:06 GMT, Jan Panteltje
>>>>>>><alien@comet.invalid> wrote:
>>>>>>>
>>>>>>>>On a sunny day (Sun, 28 Jul 2024 21:40:41 -0000 (UTC)) it happened
>>>>>>>>Cursitor Doom <cd999666@notformail.com> wrote in
>>>>>>>><v86dsp$3n74$1@dont-email.me>:
>>>>>>>>
>>>>>>>>
>>>>>>>>>I still can't see where the 'sampling' bit comes into it.
>>>>>>>>>AFAICT, there's are two signals into this thing and one signal
>>>>>>>>>out. The signal from the LHS is passed through a very fast diode
>>>>>>>>>which generates harmonics from that fundamental. The signal from
>>>>>>>>>the RHS is unmodified and mixed with the desired harmonic to give
>>>>>>>>>the necessary output signal which is then filtered to get rid of
>>>>>>>>>the unwanted mixing products. If that's all correct, as I believe
>>>>>>>>>it is,
>>>>>>>>>where does any *sampling* come into it?
>>>>>>>>
>>>>>>>>A 'sampler' is fact a non-linear mixer.
>>>>>>>
>>>>>>>In the audio world, a "mixer" is a linear summer.
>>>>>>>
>>>>>>>In RF, a mixer is usually a multiplier, typically a 4-quadrant diode
>>>>>>>thing or a Gilbert cell type circuit. Or a 2-quadrant thing like a
>>>>>>>pentode. Or even a single diode. All do some flavor of multiplying.
>>>>>>>
>>>>>>>Some mixers inherently multiply a signal by a square wave, which
>>>>>>>resembles other multiplier-type things once you lowpass filter the
>>>>>>>output. That's a "synchronous detector", which we usually do in an
>>>>>>>FPGA.
>>>>>>>
>>>>>>>A sampler is a signal multiplier too.
>>>>>>>
>>>>>>>These are all variations on the basic idea of multiplying two
>>>>>>>signals.
>>>>>> 
>>>>>> A the word 'mixer' in RF is not the same as a multiplier,,
>>>>>> Multipliers are like harmonic generating stages say you have a 1 MHz
>>>>>> distorted sine wave and then a second stage tuned at 3 MHz,.. turned
>>>>>> to third harmonic.
>>>>>> 
>>>>>> mamamatical speaking RF mixing is indeed multiplication.
>>>>>> 
>>>>>> Like Shakepierce once said:
>>>>>>  "What's in a name..." CocaCola wihout coke
>>>>>
>>>>>I think in this context, HP is using the term "sampler" to mean
>>>>>something which 'sniffs' a small amount of a signal for testing
>>>>>purposes. Like a few turns of wire around a transmission line will
>>>>>'sniff' a small sample of what's going on in the line.
>>>>>Where I went wrong was rigidly thinking HP meant 'sampling' in the
>>>>>manner a sampling oscilloscope works. That's what threw me. I tend to
>>>>>interpret things very literally. :(
>>>> 
>>>> Would be nice to see a real circuit diagram of that thing.
>>>> What is the model / type number?
>>>> I am curious.
>>>> So far I have been able to find circuits for most stuff I came across
>>>> with google.
>>>
>>>It's the HP8566B - a very well known lab-grade analyser of the day which
>>>many RF designers still use. There is a *ton* of service info on this
>>>model online. However, I have not been able to see a *proper* schematic
>>>for the "sampler" in the A11A5 board which is where the issue is.
>> 
>> OK, thank you, I will google a bit..
>> I got the user manual now:
>>  https://elektrotanya.com/
>hp-8566b_spectrum_analyzer_100hz-2.5ghz_2-22ghz_usr-
>programming_1984_sm.pdf/download.html#dl
>> Then trouble shooting manual part 1
>>  https://xdevs.com/doc/HP_Agilent_Keysight/
>HP%208566B%20Troubleshooting%20&%20Repair%20Vol.%201.pdf
>> Seems to have at least some circuits (just a quick look)
>> and part 2
>>  https://xdevs.com/doc/HP_Agilent_Keysight/HP%208566B,
>%208568B%20Troubleshooting%20&%20Repair%20Vol.%202.pdf
>> also has some circuits I will have a look at the hundreds of pages, will
>> take some time.
>> I presume you have these?
>> Took 10 seconds to find with google
>
>Yes, I have all of those and more. I think altogether there are 7 very 
>large manuals for this analyser. However, I've not been able to find a 
>single actual schematic which gives component level detail of what they 
>call the "sampler" - and that's unusual, as they've given a great deal of 
>attention to providing very full service details in all other respects.

Will read some of it and let you know what I come up with ..

OK have flipped through all circuit diagrams in the thing.

It looks to me like a heterodyne down converter followed by a narrow filter IF stage
tuned over the whole frequency range.
No sampling on the input signal at all.
Just a RF mixer.
PLLs in the tuned oscillator that are used to scan the band.

Like an old AM shortwave radio where you turn the big tuning knob really fast mechanically to see the amplitude of each station
on the cats eye as you tune over the whole receive spectrum.
spectrum width set by the 450 kHz or so IF filter stages in those radio days....
To get the IF narrow enough I did notice some crystal filter?, multi stage RC filters?
Scanning the band takes time that way... horizontal deflection scope, amplitude on vertical deflection scope..
Does it have a long persistence screen?
That way you can point at any small section of the input like long wave / medium wave / shortwave in the old radios.
Also because I do not see any Fourier transform / computah / computation..

That thing is from 1987? enough computah power back then for Fourier transform? 

I could be wrong though, more than a 1000 pages read in... lemme see... an hour.
Need to sleep on it and look again.
Rest is just scope trace drive and power supplies..
Its all so easy:
 https://panteltje.nl/panteltje/scope_tv/index.html
HP should have added a teefee mode, but alas, analog teefee is dead in most of the world these days. 

This is more fun: 
>> OTOH my 1.4 GHz RTL_SDR sticks cost 30 dollies($$) or so,
>>  https://www.ebay.com/p/22032165355?iid=335019807057

Use a Raspberry Pi or a PC ..

I remember when I build a frequency counter with nixy tubes and TTL and 100 kHz crystal
took it to work (tube days) it blew the guys away..
Then demoed it at the local ham group connected to the local oscillator of a shortwave receiver
Explained 'subtract the IF frequency from the indicated frequency to get the real frequency'
Most radios have that now with nice LCD screens and PLL local oscillators.... Or now even direct sampling
like that SDR_RTL stuff.


I personally would dump the HP thing.. or maybe donate it to some museum..