Looking for probe for Hp 8591a

[turkalp.kucur]

Hello
I have just bought a Hp 8591a spectrum analyzer. unfortunately I could not get the probe, just device. I searched internet I could not find a suitable probe for it . note that I live in Turkey so I could not buy any product from ebay, just aliexpress or temu.. Is there a link to obtain probe?thanks.

[jwet]

Unlike oscilloscopes, Spectrum Analyzer don't typically have standardized probes.The input to your analyzer is just 50 ohms which is the standard for RF gear.  The input power should be kept low usually below 1 mW (0 dBm) and less than a volt.

A common practice in a lab is make a simple probe some times.  This "probe" is a series 950 ohm resistor and a piece of 50 ohm coax directly to the SA.  This will give a 950 ohm DC impedance and an attenuation of 10x- this can be AC coupled by adding a series cap.  Spectrum analyzers have wide dynamic range so throwing away a decade isn't so bad.

There are fancy Hi Impedance probes for SA's but they are really expensive and only a well stocked lab would have one.  A couple representative ones are the HP 41800, good to 500M IIRC and the HP 85024 good to 3GHz.  The latter is about $3000!

Good Luck

[PGPG]

This "probe" is a series 950 ohm resistor

I would rather use 450 ohm resistor.

[jwet]

You're right- 450 is for 10x my mistake.  I've used the 950 in the past but  it will knock off another 6 db. 1K is often a better value if you don't want to load bias circuits too heavily.  I went back and looked at prices for the 41800, its now over $6K and the 85024 is over $8K.  I think I have one of each in a drawer- I'm going to sell them off and go to Paris!

One other thing that HP sold for a while was a "buffer" type gadgets that you could put on an SA that gave it a standard scope like interface- 1M 13pf.  You could use standard scope probes generally at fairly low frequencies (<200M).  The HP number was 15709- I had one, may still, lost to the mess.  I built something like it with a hot FET op-amp (OPA656) based roughly on the circuit of the link below.  It worked well up to about 75M with a pretty sloppy lab construction.

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.edn.com%2Fhigh-impedance-fet-probe-extends-rf-spectrum-analyzers-usable-range%2F&psig=AOvVaw1L3agh1A7oStgJXMk94V8t&ust=1733760973026000&source=images&cd=vfe&opi=89978449&ved=0CBQQjRxqFwoTCJDa_YnJmIoDFQAAAAAdAAAAABAE

Have fun.