How to not blow up spectrum analyzer - Page 1
Forum section: electronics / testgear

author: Dan Moos
author_rank: Frequent Contributor
timestamp: August 18, 2020, 02:11:58 am
content: Just won a HP 8590d on eBay. Price was right. Anyway, I know that the front end of these things are easily damaged. I suspect I should get an attenuator. Am I correct? I'm new to rf. I just want to be safe.

author: 0culus
author_rank: Super Contributor
timestamp: August 18, 2020, 02:23:43 am
content: DC block too.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 18, 2020, 02:36:10 am
content: I treat my SAs the same as my scopes. I don't normally do anything additional beyond wearing a wrist strap and make sure I discharge what ever I am hooking them to. For the older SAs, I would normally leave the 10dB attenuator selected.If I need more protection, say I am working with higher voltages, I will use some combination of Citel GDTs, diode clamps and attenuators. If I am looking at higher power devices (amplifier for example) I have a small 50 ohm load with a tap built-in.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 18, 2020, 02:38:44 am
content: A DC block can be a good idea to have onhand, unless you're working with really high power signals you shouldn't really need an attenuator, and leaving it connected all the time just removes your low noise/low signal performance.Proper spectrum analyzers should be pretty durable in terms of desktop generators and signals. If you're connecting up to homebrew then the external stuff can be there to make sure, and if you're dealing with broadcast then you want a beefy attenuator... but they are designed to be failure resistant, at least. The specs say it can tolerate 1W continuous (+30dBm) and 25V DC, which at least for desktop stuff where a signal generator's maximum output is probably +20dBm or less, you really don't need extra protection equipment.The most important thing is to know the devices you're measuring and being careful/using appropriate protective equipment when you think there's a risk.

author: Dan Moos
author_rank: Frequent Contributor
timestamp: August 18, 2020, 02:53:07 am
content: Ok, good info.The thing was advertised as "working, but not calibrated" . Got it for $300 plus $98 shipping. I bid the minimum, and was the only bidder. Being the only bidder on an instrument that was cheaper than every other similar one I saw concerns me. As a hobbyist, how concerned about not being calibrated should I be? And out of curiosity, how much does a cal for such a thing usually cost?

author: 0culus
author_rank: Super Contributor
timestamp: August 18, 2020, 03:12:24 am
content: It may be "close enough for government work" as it were...you aren't going to be doing anything that requires traceable cal I'm betting, so just see how it performs when you get it. The main thing now is to hope that the seller packs it right.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 18, 2020, 03:22:51 am
content: Quote from: 0culus on August 18, 2020, 02:23:43 am+1DC block lives on the SA

author: Dan Moos
author_rank: Frequent Contributor
timestamp: August 18, 2020, 03:23:41 am
content: "Close enough for government work" is all I need.Is adding a tracking gen to one of these expense/difficult/with the hassle?

author: Dan Moos
author_rank: Frequent Contributor
timestamp: August 18, 2020, 03:26:10 am
content: DC block seems to be a recurring theme here. I presume you mean more than just a coupling cap. Any specific suggestions?

author: 0culus
author_rank: Super Contributor
timestamp: August 18, 2020, 03:28:42 am
content: Quote from: Dan Moos on August 18, 2020, 03:26:10 amI use Mini-circuits DC blocks. They make a range of them...I have some 18 GHz ones that I always use on my 8566B. A true dc-block is indeed just ac coupling the signal to protect spectrum analyzers that can't be dc coupled at all. However, quality ones will have a nice flat frequency response across the specified bandwidth. Definitely one thing to buy new and not used.

author: 0culus
author_rank: Super Contributor
timestamp: August 18, 2020, 03:30:37 am
content: Quote from: Dan Moos on August 18, 2020, 03:23:41 amHonestly? Tracking generators aren't that useful anymore when you can purchase a NanoVNA v2 for under $100 and then you also get to have vector measurements.

author: Dan Moos
author_rank: Frequent Contributor
timestamp: August 18, 2020, 03:36:52 am
content: On tracking gens...Remembering I already bought the HP, let's say I want to look at the freq. response of a filter I've built with it. I have a few sig gens. Tracking gen not needed? Can the HP be synced to the sweep trigger pulse of my Siglent 40 MHz arb gen for instance? Does it need to be?

author: 0culus
author_rank: Super Contributor
timestamp: August 18, 2020, 03:42:27 am
content: Depending on the connections available on your other stuff, you could probably cobble something together with a few mixers and things. FWIW, I have an old version of this:https://www.dsinstruments.com/store/products/tg6000-rf-tracking-signal-generator-usb/It works very well, and the new ones don't need an external CW source like mine does. It should work on any spectrum analyzer that provides a 1st LO output (most do).

author: Dan Moos
author_rank: Frequent Contributor
timestamp: August 18, 2020, 03:49:17 am
content: Ha! That thing is $700! I have only $400 into the SA!Is there no way to sync my Siglent to the sweep on the HP? Some combo of using the sweep trigger signal on the Siglent arb gen, and setting the span/rbw on the HP?

author: tkamiya
author_rank: Super Contributor
timestamp: August 18, 2020, 01:16:16 pm
content: Lab I use charges somewhere around $200 to $250 to calibrate 859x series.To check filters, etc, you don't necessary need a tracking generator. Output of a sweep generator goes to filter and its output goes to SA. Since they are not synchronized, it will take a while to fill the screen. But it can be done.Better, yet.... if you are going to do that, it'll be easier to do sweep generator to filter to a detector into an Y axis of oscilloscope. Then drive the X axes by ramp signal from sweep gen.