HP8656B: To calibrate or not to calibrate - and where to go in Sydney? - Page 1
Forum section: electronics / general

author: Brumby
author_rank: Unknown
timestamp: May 24, 2019, 05:59:43 am
content: I have an HP 8656B that I picked up. It had a problem which I fixed, but I can't really tell how well it is working and if it is up to spec.My limited gear can confirm basic functionality, but nowhere near good enough to give me an accurate indication. ThingslookOK on the scope, but I can't measure frequency accurately (yet) let alone check attenuator accuracy or distortion - and I don't have any means to check its communication abilities.It's more kit than my bench and anticipated needs will require, and since it could probably command a fair price,it is destined for sale. As such, while I want to maximise the sale price, I don't want to misrepresent the item.SO ... what would you do? Calibrate? Not calibrate? Sell as is, showing what testing I have been able to perform?... and if to calibrate - where would be the place to go in Sydney (preferably western suburbs)?

author: tkamiya
author_rank: Super Contributor
timestamp: May 24, 2019, 03:24:20 pm
content: I wouldn't calibrate unless buyer asks for it and willing to pay for the cost.Anyone serious enough will have it hooked up to lab frequency standard and level wise, have an ability to measure that anyway. aaaaaand, if I were the buyer, I'd prefer taking it to my cal house, rather than seller taking it to some place unknown to me.

author: Brumby
author_rank: Unknown
timestamp: May 25, 2019, 01:29:18 am
content: That sounds reasonable.As a minimum, I was planning to try out as much as I can, make notes, take photos and include this in the listing.I had wondered about making a video showing incremental changes for frequency, attenuator and maybe modulation, but I'm not really set up for video and I'm not sure how much it would help. Any thoughts?

author: tkamiya
author_rank: Super Contributor
timestamp: May 25, 2019, 02:14:44 am
content: I don't think video is really necessary. You can't possibly show all functions anyway.Just demonstrate it turns on, signal is seen on oscilloscope, frequency is reasonably accurate, etc. If there is a self-diagnostic, show the results. Then take photos of all sides to show it's clean. Show inside to show it's clean.I typically don't buy unless the seller at least shows it turns on and something in coming from output. Rest, I won't know until I get it on my bench and test it for few days anyway.

author: Brumby
author_rank: Unknown
timestamp: May 25, 2019, 12:54:33 pm
content: What you're saying is what I was originally planning to do. Seems I'm starting to overthink things.

author: IconicPCB
author_rank: Super Contributor
timestamp: May 26, 2019, 06:01:22 am
content: Brumby,Think about the step recovery diode and build your own transfer oscillator.An audio signal mixing with RF signal in a step recovery diode will set up "birdies" on a scope screen.Adust audio oscilator for two adjacent frequencies which produce birdies.. and from there on you can calculate the frequency of RF source... a bit old school... but then who is not!

author: Brumby
author_rank: Unknown
timestamp: May 26, 2019, 04:06:21 pm
content: Are you enticing me into the RF world? I've kept my distance so far - but if you do manage topervertconvert meI'll probably want to keep this box!The question is, though: What accuracy can be achieved?

author: IconicPCB
author_rank: Super Contributor
timestamp: May 26, 2019, 08:23:54 pm
content: Slightly worse than the accuracy with whihc the audio oscillator frequencies are measured.The slightly worse part is due to user interpretation of the "birdie" frequency on the scope display. and accuracy of audio frequency counter.

author: Brumby
author_rank: Unknown
timestamp: May 27, 2019, 04:48:20 am
content: Are you sitting down? If so .... continue...

author: Brumby
author_rank: Unknown
timestamp: May 27, 2019, 04:48:57 am
content: Have you put your coffee cup down and out of the way? ... If so, continue.....

author: Brumby
author_rank: Unknown
timestamp: May 27, 2019, 04:50:56 am
content: I put in a web form enquiry for calibration of my 8656B .... and here is the response:Cost for Traceable Calibration of your HP 8656B is $1350.00 + GST.Return freight to metro area is usually $25.00 + GST depending on size & weight of package.If you would like to go ahead please contact me and we can arrange the details.Have a great day.Ahhh, that will be a "No".In all fairness, though, it was just a random calibration lab from a Google search.

author: IconicPCB
author_rank: Super Contributor
timestamp: May 27, 2019, 09:31:49 am
content: Random local mob?

author: beanflying
author_rank: Super Contributor
timestamp: May 27, 2019, 09:54:13 am
content: 'Traceable' adds a chunk to Calibration over and above the standard one and will come with some extra stats (uncertainties).Just buy a GPSDO you know you 'need' one and think of what you will have 'saved'

author: EEVblog
author_rank: Unknown
timestamp: May 27, 2019, 10:02:20 am
content: I wouldn't get an old function gen like that calibrated. I'd just spot check basic functionality and sell as spot tested.

author: MadTux
author_rank: Frequent Contributor
timestamp: May 27, 2019, 12:19:51 pm
content: That thing was rather low class when new, so every penny spend for calibration is a waste of money IMO.Also the calibration manual is rather bad for this one, if I remember correctly.Just check for functionality on spectrum analyzer and sell it as is.

author: warrjon
author_rank: Newbie
timestamp: June 01, 2019, 10:27:24 am
content: If you do decide to get it cal'ed, TR Calibration in Prestons Sydney have the capability to Cal this, The RF guys are very experienced I worked there until I retired.

author: Brumby
author_rank: Unknown
timestamp: June 01, 2019, 02:09:00 pm
content: Might see what they would charge...

author: bdunham7
author_rank: Super Contributor
timestamp: June 02, 2019, 03:10:52 am
content: Just to give you something to think about, I actually want to buy one of those if I can find a decent one cheap enough. Shipping would be ludicrous, so I'm not your potential customer, but the ones that are may think as I do. I would not want to pay a lot more for a calibrated HP 8656B, I'd rather buy a cheap, fixable one. I might pay a bit more for a good, tested, guaranteed one, but I certainly am not going to shell out big bucks for a calibrated one. The only thing I can't check myself is the lower levels of attenuation and the distortion and levels over 500MHz--and even those things can probably be worked out. I would guess that most people that want a calibrated instrument are not going to be wanting that old boat anchor.