Type of Signal Output from an Agilent ESG 44XX Series Signal Generators - Page 1
Forum section: electronics / testgear

author: LPS
author_rank: Contributor
timestamp: February 04, 2020, 05:04:07 pm
content: A pretty basic question, I would like to know if the output wave from any ESG series signal generator, without any type of modulation applied, is a sine wave? Across the whole output frequency spectrum?I was looking at information wanting to purchase an inexpensive ADF4351 based signal generator and seen a video which showed the large amount of harmonics on the output signal and realized that a square wave is produced from these cheap types of signal gens.I was wondering if i got a used (eBay) name brand synthesized RF signal generator such as an Agilent ESG series, is the output also a square wave, or a cleaner (less harmonics) sine wave.thanksLen

author: nctnico
author_rank: Super Contributor
timestamp: February 04, 2020, 05:09:24 pm
content: These generators output a sine wave. However the harmonics are at around -35dB (IIRC) so it is not an exceptionally clean sine wave.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 04, 2020, 07:50:53 pm
content: Spec says -30dBc typical below 1GHz, in practice it's not that bad.Brochure attached for your info.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 04, 2020, 08:11:20 pm
content: Basically every dedicated RF generator will be a sinewave output with no modulation, as this is a CW tone and as harmonics can be extremely problematic in RF applications. That said, generating a clean tone can be very difficult when you're also optimizing your generator to have a wide frequency range and a quick settling time so you can sweep quickly, so it never works out to be perfect. ESG specification of 30dBc means that there is 1/1000th of the power in the second harmonic and above than is in the primary tone - the irregularity is definitely measurable, but if you put the signal on a scope it would just look like a sine wave. Very good generators can manage 50dBc or better, but they become reliant on external filtering much beyond that.As a comparison, AD specifies the second and third harmonic content in the ADF4351 datasheet (and these will be most of the power in the harmonics), and they're about 10dBc worse (10x worse) or more than the ESG's specification. it will still look like a sinewave, but it's a much less sinusoidal signal than the ESG or another full generator will produce.Harmonic distortion at these kind of frequencies can come down to tiny imperfections in cable and connector geometry, so it's not realistic to expect performance as you'd see in the audio band (for example) without heavy filtering.

author: nctnico
author_rank: Super Contributor
timestamp: February 04, 2020, 08:43:01 pm
content: Quote from: DaJMasta on February 04, 2020, 08:11:20 pmProbably the second harmonic is -10dB but the third won't. The ADF4351 outputs a very nice square wave (which only has odd harmonics).

author: DaJMasta
author_rank: Super Contributor
timestamp: February 05, 2020, 12:29:16 am
content: My mistake, so in that case the output of the ADF4351 won't look or act anything like an ESG