Yeah, well, it seems you don't get what 'rated' means. If a part is 'rated' up to 18GHz it merely means that it's properties up to 18GHz are known. It doesn't necessarily mean 'guaranteed to work great at' or 'zero loss at'.
You can rate a piece of string to 100GHz, no problem. It doesn't mean it's any good at that frequency, though.
As to what the manufacturer rating is worth, I certainly wouldn't trust a cheap part from a Chinese ebay seller but I an tell you from quite a bit of personal experience that the stuff you get from manufacturers like Huber & Suhner is pretty much spot-on. In fact, Huber & Suhner is one of the most renowed manufacturers for RF cables and stuff, and that's for a reason.
While you are both to'ing and fro'ing somebody should state a load impedence which WILL make a massive difference at those frequencies.
While you are both to'ing and fro'ing somebody should state a load impedence which WILL make a massive difference at those frequencies.Load impedance is only part of a transmission line system.
Source impedance, termination-load impedance, connectors and transmission line all matter. If the currently common BNC worked past 110 Ghz, there would be no reason for connectors like N, TNC, SMC, SMB, SMA, WSMA, APC-7, APC-3.4, K, 2.92mm, 2.4mm, 1.85mm, V, and others.
When Ghz systems are discussed, connectors and the entire transmission line system performance matters.
Bernice
Lol, that's basically a glorious Jim Williams pulse generator sold in a TM 5000 box, although the 50kHz rep rate generator is a nice addition to the original free running version, if you don't want too much jitter.
Please take the covers off, I'm seriously wondering how they managed to get 10m of coax charge line inside a TM 5000 box. The 60ns/15m delay line in the HP 215A fills the complete lower part of a 19" rack box.
Finally got around to setting up my 54120B on the bench, first time using this scope, this is what I got up and running about five minutes from switching on. I'm using a 54121A TDR test set with a short on the TDR/Ch1 channel for the pulse. Total of $700 of TE from ebay, in three separate auctions for the 54120B, 54121A and interconnecting cable, the cable cost almost as much as the 54120B.
Finally got around to setting up my 54120B on the bench, first time using this scope, this is what I got up and running about five minutes from switching on. I'm using a 54121A TDR test set with a short on the TDR/Ch1 channel for the pulse. Total of $700 of TE from ebay, in three separate auctions for the 54120B, 54121A and interconnecting cable, the cable cost almost as much as the 54120B.
Nice scope, which brings back fond memories of using them when they were the dog's bollocks, and of chatting with the digitiser's creator. They are still useful on this forum, since they are a clear demonstration that the "samples/s" spec is completely different to the "front end MHz" spec
Finally got around to setting up my 54120B on the bench, first time using this scope, this is what I got up and running about five minutes from switching on. I'm using a 54121A TDR test set with a short on the TDR/Ch1 channel for the pulse. Total of $700 of TE from ebay, in three separate auctions for the 54120B, 54121A and interconnecting cable, the cable cost almost as much as the 54120B.
Nice scope, which brings back fond memories of using them when they were the dog's bollocks, and of chatting with the digitiser's creator. They are still useful on this forum, since they are a clear demonstration that the "samples/s" spec is completely different to the "front end MHz" spec
Unfortunately, for directly measuring eye diagrams of many of today's high speed interfaces such as USB 3.x and HDMI, I find the 54120B and its additional modules less than perfect.
The problem is that the p-p voltages are fairly low, and typically you need to split off the signal you're measuring into both a scope channel and the trigger input. If your signal has a longer term DC component in it (or is bursty) then you need to use a resistive power splitter to maintain DC adding to your probe loss, so that's typically 26dB down in total with a typical x10 probe. When the single ended p-p is only 300mV or so, that doesn't leave much for the scope's channel front end.
If you use a directional coupler to reduce losses into the channel input, with the trigger sampling off the coupled port, then that improves things a bit but only if the signal has no DC component: the coupled port will be AC coupled so this will show up as jitter on signals with much DC component.
At least with HDMI there is a clock/10 signal, so using that to trigger is usually a reasonable option but it makes casual browser probing much harder as you're almost certainly going to have to solder in a tap to make it work logistically.
Still, the biggest problem is that the scope front end lacks sensitivity for a lot practical use cases on many of today's low level high speed serial signals. Sure, you could add a broadband amplifier block, but that in itself introduces its own problems, not least that you're no longer measuring the actual signal.