Difference between HP / Agilent 435A and 435B Power Meters - Page 1
Forum section: electronics / testgear

author: TimYTTT
author_rank: Contributor
timestamp: July 22, 2024, 03:10:00 pm
content: Hello HP/Agilent fans and experts,Can someone please explain me what is the difference between the HP/Agilent 435A and 435B Power Meters?Both power meters are of analog type, looking identical from the outside. For at least one sensor (HP 8484A) the HP recommends use of 435B power meter version only. I checked HP site and did not found any useful info about that.Thanks for your help!

author: johnk0gcj@gmail.com
author_rank: Contributor
timestamp: July 22, 2024, 06:02:18 pm
content: Good question. I've had a couple 435A's over the years and had seen but never had 435's, and hadassumed that the difference was the interchangeable scales on the 'A'. However, I recently obtainedanother 'A' model, and it has the non-interchangeable scale. At first I thought someone had swappedknobs with a non-working 435 until I realized that it has the marker where it belongs, just above theoutside circumference of the scale. The two 435a's are identical except one is a 1415A prefix with theold style range indicator and the other is a 1629A prefix with the interchangeable scales. Apparentlythe difference is other than what I've been able to detect without getting inside. Maybe when I get morecurious I'll do an inside examination.

author: johnk0gcj@gmail.com
author_rank: Contributor
timestamp: July 22, 2024, 06:19:29 pm
content: After giving this a little thought I remembered from years ago that the 435's select the correctindication by determining which power sensor is connected. If I recall correctly it uses 2 or 3pins and corresponding wires in the cable to indicate which sensor. The interchangeable scalesremove the need to do the math.

author: metrologist
author_rank: Super Contributor
timestamp: July 22, 2024, 08:04:09 pm
content: I think mostly you found the difference.http://www.test-italy.com/Specifiche%20strumenti%5CHP%5CHP%20435A,11683A%5CHP%20435A.pdfhttps://xdevs.com/doc/HP_Agilent_Keysight/HP%20435B%20Operation.pdf

author: johnk0gcj@gmail.com
author_rank: Contributor
timestamp: July 24, 2024, 02:40:18 am
content: Thanks a lot. Now you've goaded me into doing some moreresearch to find the difference between the A and B.

author: TimYTTT
author_rank: Contributor
timestamp: July 24, 2024, 03:10:33 pm
content: First thanks to all of you for your inputs.In the meantime I did some comparison based on the HP product leaflets for both meters. The differences that I detected are not significant:1. Frequency RangeA: 100 kHz to 18 GHz (sensor dependent)B: 100 kHz to 26.5 GHz (sensor dependent)Conclusion: Anyhow, difference between A and B, being sensor dependent, is questionable.2. Response Time (0 to 99% of reading)A:2 seconds on 3 μW range0.75 second on 10 μW range0.40 second on 30 μW range and100 milliseconds on all other rangesB:Range 1 (most sensistive range)<10.0 secondsRange 2 <3.8 secondsRange 3 <1.3 secondsRange 4 to 10 <500 millisecondsConclusion: For me not so relevant differenceEnclosed is the document with the feature comparison. I do not understand why HP introduced the B variant of the Power meter. Maybe just the commercial reasons?

author: metrologist
author_rank: Super Contributor
timestamp: July 24, 2024, 05:47:41 pm
content: The reason for the B model I highly expect is the painful process of chasing gigahertz. The 8485A is the only supported sensor to 26.5 GHz

author: johnk0gcj@gmail.com
author_rank: Contributor
timestamp: July 25, 2024, 02:19:39 am
content: That sounds logical.

author: TimYTTT
author_rank: Contributor
timestamp: July 27, 2024, 09:24:24 am
content: --------------------------------------metrologist: The reason for the B model I highly expect is the painful process of chasing gigahertz. The 8485A is the only supported sensor to 26.5 GHz--------------------------------------You are right. I went thru the HP-Catalogs from 1980 to 1997 and found following info:435A was supported till 1980 and discontinued 1981.Frequency range: 0.1 MHz to 26.5 GHz435B was introduced 1981 and discontinued in 1998.Frequency ranges:-0.1 MHz - 26.5 GHz (from 1981 to 1985)-0.1 MHz - 50 GHz (from 1986 to 1992)-0.1 MHz - 110 GHz (from 1993 to 1997)The range changes are probably related to new sensors and not to the 435B itself.