Rhode and Schwarz SMK - UK Vintage Radio Repair and Restoration Discussion Forum

Draker4c · 4th Sep 2020, 6:39 pm

Anyone got any experience or comments in uses / applications ofthe R&S SMK signal generator. Only covers up to 140 MHz but the specs look great. I am concerned about future availability of memory chips , IC and semiconductors as well.
Many thanks
Hugh G1AUR

G0HZU_JMR · 5th Sep 2020, 12:27 am

I've not used one but I've seen the datasheet and the basic block diagram.

The AM and FM specs for modulation distortion are really impressive and it also operates down to just 10Hz and this sets this sig gen apart from most others in these areas.

The main downsides with this generator appear to be the lack of a common rotary control (it only has up/down keys) and also the far out phase noise seems to be quite high. At 100kHz offset it's going to be about 15dB noisier than something like the little Marconi 2022 for example. Closer in the phase noise will be better than the 2022 but worse than the Marconi 2018/9.

In my opinion this sig gen would make an excellent companion to something like a HP8640B or a Marconi 2018/19 because of its LF operation down to just 10Hz and its excellent FM and AM modulation specs. I'm not so impressed with the far out phase noise and this generator would be a poor choice for doing receiver blocking tests at 100kHz offset for example. At an offset of just 10kHz the SMK would be OK for doing adjacent channel testing because it has fairly good phase noise here.

Note that the block diagram suggests that this sig gen generates signals from 10Hz to 140MHz using a UHF mixer. In other words it generates signals across a 140MHz slice up in the 440-580MHz region and then it downconverts to 10Hz -140MHz using a mixer. This explains the compromised phase noise although it is still much cleaner than some modern sig gens that use a similar synthesis scheme.

These generators are quite old now. I think some will be over 30 years old but R&S equipment is very well built.

Draker4c · 13th Sep 2020, 8:54 pm

Jeremy thanks for you reply I got waylaid with work and have just seen it. I can see that there is no perfect piece of kit out there for receiver measurements as per your exhaustive and greatly valued comments on my earlier questions re TF2002B! I just happened to come across one at a good price ..together with a HP 8640B ( read lots here about plastic gears etc ) would the latter be a more versatile choice particularly around 100 KHz offsets?

G0HZU_JMR · 13th Sep 2020, 9:30 pm

If I had to choose between the SMK and the HP8640B for LW/MW/FM receiver work I'd choose the SMK despite the far out phase noise limitation. Few people will want to do high performance receiver blocking tests at 100kHz anyway.

The HP8640B will generally have a phase noise of -150dBc/Hz at 100kHz offset and I think this is due to the noise floor of the dividers it uses to get the lower frequency ranges. This will be about 15dB better than the SMK at this offset but I'm not sure how significant this will be for most users.

They are both very nice generators and they would complement each other if they were on the same bench. However, the HP8640B is a big and heavy generator and reliability is becoming a major problem.

The SMK should be more reliable but it might be much harder to repair if something exotic fails because spares will be rare. There should be loads of spares for the HP8640B and lots of people around who can help with advice etc.

4th Sep 2020, 6:39 pm	#1
Draker4c Pentode Join Date: Jun 2017 Location: Basildon, Essex, UK. Posts: 188	Rhode and Schwarz SMK Anyone got any experience or comments in uses / applications ofthe R&S SMK signal generator. Only covers up to 140 MHz but the specs look great. I am concerned about future availability of memory chips , IC and semiconductors as well. Many thanks Hugh G1AUR

5th Sep 2020, 12:27 am	#2
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: Rhode and Schwarz SMK I've not used one but I've seen the datasheet and the basic block diagram. The AM and FM specs for modulation distortion are really impressive and it also operates down to just 10Hz and this sets this sig gen apart from most others in these areas. The main downsides with this generator appear to be the lack of a common rotary control (it only has up/down keys) and also the far out phase noise seems to be quite high. At 100kHz offset it's going to be about 15dB noisier than something like the little Marconi 2022 for example. Closer in the phase noise will be better than the 2022 but worse than the Marconi 2018/9. In my opinion this sig gen would make an excellent companion to something like a HP8640B or a Marconi 2018/19 because of its LF operation down to just 10Hz and its excellent FM and AM modulation specs. I'm not so impressed with the far out phase noise and this generator would be a poor choice for doing receiver blocking tests at 100kHz offset for example. At an offset of just 10kHz the SMK would be OK for doing adjacent channel testing because it has fairly good phase noise here. Note that the block diagram suggests that this sig gen generates signals from 10Hz to 140MHz using a UHF mixer. In other words it generates signals across a 140MHz slice up in the 440-580MHz region and then it downconverts to 10Hz -140MHz using a mixer. This explains the compromised phase noise although it is still much cleaner than some modern sig gens that use a similar synthesis scheme. These generators are quite old now. I think some will be over 30 years old but R&S equipment is very well built. __________________ Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 5th Sep 2020 at 12:33 am.

13th Sep 2020, 8:54 pm	#3
Draker4c Pentode Join Date: Jun 2017 Location: Basildon, Essex, UK. Posts: 188	Re: Rhode and Schwarz SMK Jeremy thanks for you reply I got waylaid with work and have just seen it. I can see that there is no perfect piece of kit out there for receiver measurements as per your exhaustive and greatly valued comments on my earlier questions re TF2002B! I just happened to come across one at a good price ..together with a HP 8640B ( read lots here about plastic gears etc ) would the latter be a more versatile choice particularly around 100 KHz offsets?

13th Sep 2020, 9:30 pm	#4
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: Rhode and Schwarz SMK If I had to choose between the SMK and the HP8640B for LW/MW/FM receiver work I'd choose the SMK despite the far out phase noise limitation. Few people will want to do high performance receiver blocking tests at 100kHz anyway. The HP8640B will generally have a phase noise of -150dBc/Hz at 100kHz offset and I think this is due to the noise floor of the dividers it uses to get the lower frequency ranges. This will be about 15dB better than the SMK at this offset but I'm not sure how significant this will be for most users. They are both very nice generators and they would complement each other if they were on the same bench. However, the HP8640B is a big and heavy generator and reliability is becoming a major problem. The SMK should be more reliable but it might be much harder to repair if something exotic fails because spares will be rare. There should be loads of spares for the HP8640B and lots of people around who can help with advice etc. __________________ Regards, Jeremy G0HZU