Extending the grounding pin of a RF probe

I have a high frequency RF probe that is used for up to 6GHz RF module. This is a probe fabricated by order and it is very very expensive. The problem is the grounding pin is loose and is too short to reach for the best grounding point. Is it advisable to have a longer grounding pin? How will this affect my readings? As long as the deviation is the same, I suppose that wouldn't matter? Comment from all of you is much appreciated.

Thanks,
dionysus

At 6 GHz wavelenght is 5 cm.
this menas that, if you don't want any trouble in reading the maximum lenght is about 1/20 of wavelenght (means 2,5 mm ).
Any lenght higher than this will affect your measurement, also considering that the parasitic capacitances make changes in your measurement depending the position of the ground, hands, ecc.

I have something similar but till 2 GHz and the ground connection is made through the screen of the probe; thismeans you have to have a ground ( shield, box, PCB ground plane, ecc ready available.

Mandi

Hi Mandi,

Very helpful indeed. Thanks very much. May I ask why we need to be confined to 1/20 for the pin length? If a longer ground pin is used, will the conductor contribute to the unwanted inductance and filter?

Can you explain this : "..and the ground connection is made through the screen of the probe..." -- the screen of the probe?

Cheers,
dionysus

Great! This is a very usefull question for me too!
I am a tenderfoot for high frequency probe,Can anyone give me some advice on using it?

Hi'
Does high frequency probe can measure the actual power in RF circuit?
I use HP 85024A to measure power in RF circuit, it seems the measured power is not the real power.
Furthure, I try to measure the relative power at DUT input and output to estimate power lose, it looks using high frequency probe is not a accurate measure.
I didn't use GND pin cos it's not easy to touch GND and test point at the same time.
If I use GND ping, should I always touch the same GND point?

I'm don't have a good idea but i think this link very good for emc general

hxxp://www.elmac.co.uk

S 8O KRAT

Hi guys
some notes:
HP Rf probe measures voltage and displays the results in the spectrum as 50 Ohm equivalent power.
Consider the old problem of loading: RF probe input capacitance (that is the most relevant for HP) is something like 0.7 pF, that means something like 100 Ohm @ 2 GHz. you cannot define this exactly as a "high impedance". The result is that you will afect the signal you want to measure.
In my opinion all these stuffs are not usable for frequencies above 1 GHz if you want a good accuracy.
Bye
Mazz

My probe is self-made and characterized with a HP8510.
Until 2 GHz is quite flat, then drops .
Hope in the week-end to make a drawing of it and to load.
It is quite simple, completely passive and with about 20 dB attenuation.
At low frequencies the roll-off is at 1 MHz.

Mandi

Mandi,

Will you include step-by-step instruction about how to characterize the probe too?

Cheers,
dionysus