HP/AGILENT 54701A 2.5 GHz Active Probe - Page 1
Forum section: electronics / testgear

author: pherdie
author_rank: Contributor
timestamp: October 02, 2016, 06:51:05 pm
content: I am interested in purchasing a used 54701A probe and have several questions.1) Are most of the internal components proprietary?2) Are there any issues/vulnerabilities common to this series?3) Are there any secondary sources for accessories such as tips and grounding leads?4) Is the power connector a LEMO type? If not, what type is it?5) Any other helpful information relative to this product?

author: Someone
author_rank: Super Contributor
timestamp: October 02, 2016, 10:01:48 pm
content: It looks like the spectrum analyser version of the more common 1152A, they're hot in operation and can be broken if dropped. The tips are screw in and I've never seen or needed to look for extras, grounding is easily done with wire looped around the tip. Lemo type power connection but you'll need to confirm the exact voltages, google suggests +15V/-12V but it may work on +/-12V.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: October 02, 2016, 11:13:07 pm
content: The schematics are online for both the power box (thing with type N connector attached to probe) and for the power supply (as in the thing you plug the power box's LEMO connector into). The schematics include the pinout and voltages of the LEMO connector. Instead of buying the separate power supply I unscrewed the LEMO connector (you can do this without damaging it) and soldered 0.1" +/-17V supply wires to the appropriate back pins (it draws 100mA from each, haven't looked to see if most of it sinks to ground or if it's going from + to -). The LDOs in the power box bring it down to +/-15V before sending it off to the probe. This works well enough for me.

author: rastro
author_rank: Frequent Contributor
timestamp: March 05, 2017, 02:08:51 am
content: Quote from: jjoonathan on October 02, 2016, 11:13:07 pmI'm looking into doing something similar with an HP 54701A probe. The used adapter/power boxes seem over priced.The +/- 17VDC power looks pretty easy to build. I found a lower cost LEMO EGG.0B.307.CLL ( 7 PIN FEMALE) source on ebay. These are ~$30.00 at mouser/digikey!!Question: Did you do anything for the offset adjustment?-rastro

author: jjoonathan
author_rank: Frequent Contributor
timestamp: March 05, 2017, 04:21:44 am
content: Not really -- I brought it out on a 0.1" pin like I did for the +-17V and I had one occasion to use it, but I just drove it with my power supply. Contrast to the power pins which I feed with a pair of cheapo USB supplies. The linear regulator in the power box does a good enough job of chopping off the ripple. I can still see feed-through ripple on a spectrum analyzer, but I don't use my 54701 to look at 120kHz ripple, so that's fine. It doesn't seem to modulate on to my signals.

author: rastro
author_rank: Frequent Contributor
timestamp: March 05, 2017, 04:23:51 pm
content: I'll probably make an adapter powered by my HP 6235a for the +/- 17 VDC. It's analog so minimal ripple.I'm still not clear on how the offset works. It appears current driven.Maybe I can tap between the +/- 17 VDC with a 100-ohm potentiometer using the sweep as the offset. Also use an appropriate value resistor (3.4K) from each supply to limit current to 5mA?Basically there is only 4 connections used:1. +17VDC2. -17VDC3. Ground4. Offset Current +/- 5mA.-rastro

author: Chris_ayc
author_rank: Newbie
timestamp: September 10, 2021, 09:58:26 am
content: I have one of those. I am now considering either making an adapter to connect LEMO to a traditional probe port, or creating a simple circuit that can be powered from a 5V charger. But before I even start down this path, let me ask... did anyone already come up with DIY circuit to drive this probe?