Non-HP RF MW meters capable of using HP-478A Type Bolometers - Page 1
Forum section: electronics / testgear

author: Dawn
author_rank: Regular Contributor
timestamp: August 24, 2014, 02:26:55 am
content: I have a trusty, analog, 432A with cable and mount that I've had for years.It sure would be nice to have something that has both digital and analog combined hopefully with an internal cal source.My understanding is that there were several alternatives that would work with the '478 and similar family.I certainly can't afford or dream of having an N432A, nor would I need anything like that. Something of the capability of a HP-436A or Boonton-4200 with hopefully a cable compatible connector. Prices of these newer units with a cable and mount are still way out of my price point. I'm hopefully looking for some similar alternative that's compatible within my budget.Anything out there that docs can be reasonably obtained for?

author: G0HZU
author_rank: Super Contributor
timestamp: August 24, 2014, 02:58:16 pm
content: I'm not aware of any but your 432A + 478A is a classic piece of engineering.You can always produce a real time digital display remotely, eg on a laptop by logging the rear of the 432A and displaying the data on a laptop or mini notebook.You also don't really need a cal source with the 432A + 478A as they self calibrate (unlike modern t/c power meters that require an internal 0dBm cal standard to achieve short term calibration)I have a HP431C + 478A head that was made in the 1960s and I've never ever 'calibrated' it in the 20 odd years I've owned it. But it still maintains very good accuracy.Maybe your best option is to stick with the excellent meter you already have and just make better use of the rear output for logging/display purposes

author: Dawn
author_rank: Regular Contributor
timestamp: August 26, 2014, 02:04:33 am
content: I've looked around on Ebay and noticed that a 432B without a cable and sensor goes for around $200usd while a 436A sans cable and sensor is around $50. What gives? What makes the older 432A or 432B more desirable then the 436A or a similar Boonton without a cable or sensor?I'm just trying to move my bench out of the 70's and early 80's now that there's a lot of industrial surplus flooding the market of later vintage while the prices are still low due to oversupply.

author: swingbyte1
author_rank: Contributor
timestamp: August 26, 2014, 11:56:08 am
content: HiWhat makes the 432+478 more expensive is a demand of course! This demand is due to several reasons including: the ability dc calibrate them to high accuracy one can then use them to calibrate 848x sensors. 8v8x sensors can be vey expensive and bargains hard to acquire in working condition.The 432 series unlike the 432 series used chopper stabilised inputs to reduce noiseThere was a 432c I think had a digital disiplay.Thats all I can recall at the moment.Good luck,Tim

author: G0HZU
author_rank: Super Contributor
timestamp: August 26, 2014, 04:21:27 pm
content: QuoteI agree with what Swingbyte1 said. Note that the 478 is still available from Agilent/Keysight simply because it offers remarkable accuracy when used with a 432A. The meter also operates in closed loop with the 478A thermistor head unlike the modern (open loop) t/c meters that have to rely on the 0dBm 50MHz cal source to provide a reference calibration.The trick with the 432 and 431 series is to use the recorder output at the back because this is where the real accuracy lies. The analogue meter at the front is very limiting in resolution by comparison. You can also use the dc substitution method (at the rear) to enhance the accuracy of the meter but I've never bothered with this.My 431C + 478A is still my gold standard power meter although I did buy an Anritsu ML4803A t/c meter a few years ago simply because it is so easy to use and it was so cheap.http://www.anritsu.com/en-US/Products-Solutions/Products/ML4803.aspxI got it for £200 with a fully working 18GHz t/c head. The other advantage of the Anritsu was that Microlease in the UK/US were recently selling off all their surplus t/c heads for this meter for £100 each so I bought a low frequency head from them. i.e. 100kHz to 5.5GHz.They may still have some left today. So maybe that is another option. Look at Anritsu?

author: edavid
author_rank: Super Contributor
timestamp: August 26, 2014, 05:24:16 pm
content: Quote from: Dawn on August 26, 2014, 02:04:33 amI think you are mistaken about that, 432Bs don't cost that much. Here's one that included a 478A and sold for $91:http://www.ebay.com/itm/HP-432B-RF-Power-Meter-with-478A-thermistor-mount-and-cable-/141378637822Anyway, I think 436As are cheap because there are a lot of 437s and 438s out there too.

author: G0HZU
author_rank: Super Contributor
timestamp: August 26, 2014, 07:34:19 pm
content: If that 432 and 478A were both functional then that was a real bargain at $91 !I got my 431C + 478A for free about 20yrs ago because somebody dropped it at work and bent/jammed the fine/coarse zero vernier.I rescued it from the refuse skip and straightened the vernier and it has worked ever since. The only issue with it is that the meter dial has developed the classic 'flakey death' where the silkscreen on the dial has aged and lifted and it sometimes jams the meter needle movement. I believe the same issue can affect the 432A.But this doesn't matter because you are supposed to use it via the recorder output at the back anyway. It is possible to set the zero very accurately this way and get very accurate readings via an external DMM even for low signal levelsThe HP432 + 478A really is a wonderful bit of engineering despite its age and I would rather have this combo than a HP436 and a modern HP84xx t/c power head. The only real downside is that it only works down to about 20MHz because the 478A sensor VSWR starts to creep up a lot below this.That's one advantage of the modern t/c meters because there are various sensors available that work down to a few kHz.

author: Dawn
author_rank: Regular Contributor
timestamp: August 26, 2014, 10:56:15 pm
content: I seen that 432B combo and also there was a recent 432A with a military subsitute sensor on the cable. That one sold for 111 a few weeks ago. Looking through the completed listings, both appear to be outliers and most sets posted wind up being re-listed until the price gets around $200. The B wasn't tested operational and sold as is. The A you'd be taking a chance with whatever limitations that sensor had if any. Neither would be a choice for someone needing a working meter, but more of a gamble.