sig gen trying to calibrate the output - Page 1
Forum section: electronics / rf-microwave

author: m3vuv
author_rank: Super Contributor
timestamp: October 30, 2019, 02:15:27 am
content: ive a cheapo akai rf sig gen,the output just has a low and a high switch and a pot with no markings,any way to calibrate the output into dbm to set up my radio s meter,think it calls for firstly a ssg output of 1uv then 10uv,my scope only measures 5mv upwards,can any body think of a way of doing this,i also have a marconi rf voltmeter but the lowest range is 0-1mv,anyone got any ideas?,cheers m3vuv.

author: Tony_G
author_rank: Super Contributor
timestamp: October 30, 2019, 03:12:37 am
content: Without either a calibrated step attenuator, an array of calibrated fixed attenuators, calibrated splitters/dividers or some combination of those then I think you might be out of luck.What does the radio service manual say to use?TonyG

author: m3vuv
author_rank: Super Contributor
timestamp: October 30, 2019, 04:15:31 am
content: see attached info.

author: m3vuv
author_rank: Super Contributor
timestamp: October 30, 2019, 04:16:26 am
content: hope its big enough to see.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: October 30, 2019, 10:35:30 am
content: Depending on the interal architecture you might simply not be able to calibrate it in a meaningful way. Some of the cheap signal generators I've seen have no real propper ALC loop or anything - they are just a kind of VCO with a VGA after it. The range switch just ads a fixed attenuation before the VGA.As a result, with different frequencies, the VCO will have higher or lower amplitude.

author: Tony_G
author_rank: Super Contributor
timestamp: October 30, 2019, 02:49:14 pm
content: From the image, it looks like they're expecting a calibrated signal generator (I pulled up a TS-700A manual and they're looking for a generator that can do -117dBm to -7 dBm). Seeing that they expect you to hit -87dBm to set S9 I think you're not going to be able to do it.You might be able to get a very rough approximation by seeing if you can use another receiver that you trust and set the output of the generator to generate an S9 reading then transfer that output over to the TS-700A - If you had a splitter like an HPAK 11667A you could have both connected and then target ~S8 (6 dB insertion loss).Ideally, you'd use some form or power sensor such as the HPAK 8400 series to measure the output of the signal generator and then use that (measuring again at each frequency change as TheUnamedNewbie stated) but if you had that or a measuring receiver like an 8902A you wouldn't be asking. You might be able to see if you can get a HP 355D and then use that to step down the signal generator output but those things are notoriously inaccurate when purchased off places like eBay...Sorry I can't be of more help.

author: JohnPen
author_rank: Regular Contributor
timestamp: October 30, 2019, 04:38:47 pm
content: Sam Wetterlin's Leveler design could provide you with ~ -8 dB (within 0.2 dB) from your signal generator output. Then you could construct a a switchable attenuator to cover the range you need for calibration. I have some spare PCBs for the latter if you need one. As always one piece of test gear leads to another and another etc etc.Edit.The Attenuator circuit shown is for the PCB plus additional wiring that adds diodes to enable a 'power on' LED indicator. The BCDA switch in the 0 position and both the +40 dB and +60 dB switches off means the battery is not connected.