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Making a replacement cable for a HP 8445B spectrum analyzer preselector

JLNY

Active Member
Thread starter #1
Hello All,
Lately, I have been working on building a replacement for a somewhat rare cable assembly for communicating between a HP 141T/8555A/8552 mainframe spectrum analyzer and a HP 8445B "Automatic Preselector" add-on box, and I thought I would document my work here for others to follow.

A bit of background first: the 8555A RF plugin for the 141T mainframe is a 10MHz to 18GHz microwave spectrum analyzer. They are very capable units, but one of their quirks is that the harmonic mixing used to achieve this high frequency range also generates a large number of spurious mixing products on the display. The best solution to this quirk, after the slightly clumsy "signal identifier" mode built into the plugin, is the 8445 preselector, an add-on box which uses a 1.8GHz-18GHz YIG tunable bandpass filter in line with the input to track the sweep of the spectrum analyzer and block out any out-of-band signals which might produce spurious mixing products, albeit at the cost of about 6dB of loss.

Here's the problem: in order to get the 8445 preselector to "talk to" the spectrum analyzer, one has to have a very special mixed-contact D-sub cable assembly to link the two boxes together, known under the the HP part number 08445-60007. Given how old these units are, probably the majority of these cables have either broken, gone missing, or been thrown out by mistake over the years. Nowadays, finding the cable that goes with the box is pretty rare, and so the cable alone can often go for as much as the preselector itself.

So I determined to make my own. From a bit of research into mixed-contact D-sub connectors, I determined that the type I needed was a "17W5P" type D-sub connector, which has 17 total positions comprised of 12 normal pins and 5 holes for either large power contacts or coaxial signal lines. In this case they are for coax lines, and it appears from the box that only 1 of the potential 5 lines is being used ("AUX B" on the spectrum analyzer side).
IMG_0130.jpg IMG_0133.jpg
First, I went and ordered some blank connectors with solder cups for the pins.
IMG_0094.jpg

Then I soldered wires into all of the solder cups and covered them in shrink tubing, being very careful to keep track of which pins were connected where. Fortunately, the bodies of the connectors I got actually have the pin numbers molded right into the plastic, which was really helpful. I wanted to use stranded wire for added flexibility and durability under repeated bending, but I only had white stranded wire, so I was extra careful to triple-check all of my connections with a multimeter.
IMG_0077.jpg

The coaxial connectors were assembled separately on some RG-174 cable, but then the bodies just pop right into the holes in the d-sub. Be careful, though, once the c-ring on the coax body pops into the plastic of the connector, it's not coming back out!
IMG_0079.jpg

I then put a few inches of some larger heat shrink tubing over the full bundle of wires around each end. This helped bunch everything together for when I had to put the backshells over the connectors. I would be careful not to use too much heat or for too long when putting shrink tubing over RG-174, as it might melt the polyethylene dielectric in the cable. My recently purchased 850D heat gun came in handy on the shrink tubing and controlling the heat.
IMG_0083.jpg

I then put some braided cable sleeving over the full length of the cable.
IMG_0085.jpg

Then I put the assembly into a backshell. It is actually a "37 position" size backshell, which is the same size shell as a 17w5P mixed contact d-sub.
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The fully assembled cable with the backshells on it.
IMG_0100.jpg IMG_0136.jpg

The cable on the back of my spectrum analyzer for a quick test. After some additional research, I later realized that the original cable was 18 inches long, so I may have been a bit too generous to make it 24 inches long. I probably could have made it 12 inches long with no problem.
IMG_0128.jpg IMG_0124.jpg

In the first image you can see the trace without the preselector for a 5GHz signal on the 2.07-6.15GHz band at 200MHz/division. The (very faint) peak on the right is the real 5GHz signal and the peak on the left is a spurious harmonic mixing product at around where 3.85GHz should be. The reasons for this are a bit complex, and require an understanding of how the harmonics of the 8555A's LO and IF frequencies add up. On the next plot, with the preselector connected now, we lose about 6dB on the 5GHz signal as expected, and the spurious signal is eliminated.
IMG_0118.jpg IMG_0119.jpg

I took my time making this, so it probably took a few hours to make. It took even longer to document my progress and set everything up to test it. In small quantities, even the parts alone to make this cable are pretty expensive, so I probably didn't save that much money in the long run, but I feel good about having increased the total number of usable cables left for these units.

Edit 7/12/2018:
Here is my parts list for these cables (IIRC, I believe I used the crimp-type coax connectors, but the solder-type should also work if you don't have access to hex crimp tools for the contact):
17W5P housing, solder cups (male) --mouser/digikey (3017W5PCM99A10X)
17W5S housing, solder sups (female) --mouser/digikey (3017W5SCM99A10X)
37 position size die cast backshell --mouser/digikey (165X02639XE, 8655MH3701BLF)
female coax contact (crimp type, female center contact) --mouser/digikey (131J21019X)
male coax contact (crimp type, male center contact) --mouser/digikey (132J21019X)
female coax contact (solder type, female center contact) --mouser/digikey (131J20029X)
male coax contact (solder type, male center contact) --mouser/digikey (132J20029X)
22AWG stranded wire (19x34) --mouser/digikey (400R0111-22-9, 55A0111-22-9)
2mm, 5mm, and 10mm shrink tubing -- ebay/amazon (from kit)
PET expandable braided cable sleeving -- ebay/amazon
 
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JLNY

Active Member
Thread starter #3
Tidy work; thanks for sharing it.
Thanks! I have a soft spot for these old 140-series analyzers, so I wanted to make something that would look the part and hopefully last a while. This procedure could basically apply to any of the non-standard D-sub cables used on various types of older HP equipment like the cables for the 141, 8566, 8510, etc.
 
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JimB

Super Moderator
Most Helpful Member
#4
Here is mine:

HP141T.JPG


As you see, I have a Tracking Generator which is most useful.

I also have an 8553B 0 to 11/110MHz RF section which seems to take for ever to warm up so that it is stable and will stay in lock.

As it stands the analyser could do with some TLC.
I spent some time working on it a year or so ago and found that whenever I switched anything, there would be a transient on the 10v (?) line in the IF section and the YIG oscillator would jump to lock on the next MHz setting.
Rather annoying when you are trying to look at something close in.

JimB
 

Attachments

Mikebits

Well-Known Member
#5
The 141T was the first analyzer I used after I got out of the Navy. It was soon replaced by the 8566 I think that's the correct model number but alas my memory often fails me. Oh, nice work by the way.
 

JLNY

Active Member
Thread starter #6
Here is mine:

HP141T.JPG


As you see, I have a Tracking Generator which is most useful.

I also have an 8553B 0 to 11/110MHz RF section which seems to take for ever to warm up so that it is stable and will stay in lock.

As it stands the analyser could do with some TLC.
I spent some time working on it a year or so ago and found that whenever I switched anything, there would be a transient on the 10v (?) line in the IF section and the YIG oscillator would jump to lock on the next MHz setting.
Rather annoying when you are trying to look at something close in.

JimB
Nice. Very clean looking unit you have. The 8444 tracking generator is a fine piece of kit. I have an 8553 plugin along with a 8443 tracking generator. It has the option for the counter (with nixie tubes in the display!). maybe I'll take some photos when I get home.

I think I may have had a similar issue with the frequency stabilizer on mine, although I have never really looked into it. I think I usually just turn it off and keep a steady hand on the fine tuning knob while I fight the frequency drift. :p

The 141T was the first analyzer I used after I got out of the Navy. It was soon replaced by the 8566 I think that's the correct model number but alas my memory often fails me. Oh, nice work by the way.
That sounds about right. The 8566 was a 100Hz-18GHz SA from about the early 1980's to maybe the mid 1990's or so, and I wouldn't be surprised if there were units still in service to this day (they say 22GHz on the panel, but that's kind of a lie given that 22GHz is above the moding frequency of an airline type N). Excellent units, and the synthesized sweeper gives it much better frequency stability than the 8555A plugin for the 141T. I actually picked up one of my own for not too much, but I use it sparingly as I am much better at doing repairs on the 141T. It seems these units are reaching an age where they are starting to crop up on Ebay for semi-reasonable prices. Many are suffering from faded CRTs and issues with phase locking, but I imagine they are well worth taking in and repairing for the right price.
IMG_8682 resized.jpg
 

JLNY

Active Member
Thread starter #7
My 8443 tracking generator/counter. The counter actually contains an Ovenaire OCXO frequency reference, so it is quite accurate, perhaps even more accurate than it needs to be for a 10Hz resolution counter. The marker function on mine doesn't seem to work 100% correctly, but I don't use this unit much, and it isn't really necessary for using it anyway. I plan to fix it up at some point, but it isn't anywhere near the top of my list right now. This too uses a unique D-sub connector, but right now I am just using the bare coax lines without a shell on them. At some point I will assemble together a proper cable for this.

IMG_0144.JPG
 

JimB

Super Moderator
Most Helpful Member
#8
Very nice.

I also have an old Marconi Instruments spectrum analyser, this one only scans up to 110MHz, but it has built-in digital storage for the trace, and a built-in tracking generator.

In the picture here it is displaying the response of a 65 MHz LPF.

Marconi Spectrum Analyser.JPG

Due to strobing effects between display and camera, there is an awful bright band across the CRT and digits missing from the counter.
The read-out from the digital memory to the display is odd, it is done with a raster like in an old crt tv, but the lines are vertical and the frame is horizontal.
The thing was designed in the mid 1970s and uses lots of good old TTL in the display and logic sections. The memory for the display is pure unobtainium.

The thing was given to me as a non-working pile of scrap.
Several months of head scratching got it working. It is far from perfect in some areas but it can do useful work when required.

JimB
 

Attachments

#9
Unfortunately I have a 141A instead of 141T so I don't have the external connectors. Does anyone know if something similar is accessible from inside the unit? Also, do you know of any HP 141(A/T) specific owners forum? Seems like there is a lot of scattered information across the net and there is enough going with these units that it could deserve its own niche place. I got my 141 serial# 819-03060 several years ago with 7 modules including the 8555a for a steal at a hamfest from a retired FCC lab engineer, so I know it was taken well care of before it got in my hands.

For those that don't want to go through the pain of making their own cables I found http://www.glkinst.com/cables/hp_cables.htm#141T. What is the specific coax connector that you used on the RG-174?
 

JLNY

Active Member
Thread starter #10
Nice, sounds like you've got a pretty nice set. Out of curiosity, what specific plugins/modules do you have?

Yes, the 141A doesn't have the auxillary D-subs on the back. I don't know if you will be able to use a tracking generator or preselector with it in that case. I believe the 8444A tracking generator runs off the IF outputs on the front of the unit, so you may be able to use that without any kind of D-sub. It should also be possible to use the 8445A/B in manual mode to looks for spurs manually if yours has the option installed, but it won't be able to track the sweep automatically without the D-sub.

I believe that the back of the plugins themselves have some kind of D-sub on them, that relate to the auxillary functions, but I don't believe that they correspond 1:1 with the rear d-subs on the 141T display section. You would probably need to really study the manuals for both the upper and lower plugins, as well as for the tracking generator/preselctor you wanted to connect to and splice something together, but that seems pretty ambitious if you ask me.

If you have more than one set of plugins, it may make sense to keep an eye out for a 141T display section. I've seen empty mainframes for reasonable prices on ebay from time to time, and fixing them up isn't usually that hard as long as the CRT is intact and not cracked.

As far as I know, there isn't any kind of dedicated forum for the 140-series analyzers, but I've seen plenty of good info and some very knowledgeable folks on the EEVblog forums. I also did a (somewhat amateurish) series of videos on Youtube for doing the display section calibration procedures a few years ago (They're a bit embarassing, if I'm being honest).

Here is my parts list for these cables (IIRC, I believe I used the crimp-type RF connectors, but the solder-type should also work if you don't have access to hex crimp tools):
17W5P housing, solder cups (male) --mouser/digikey (3017W5PCM99A10X)
17W5S housing, solder sups (female) --mouser/digikey (3017W5SCM99A10X)
37 position size die cast backshell --mouser/digikey (165X02639XE, 8655MH3701BLF)
female coax contact (crimp type, female center contact) --mouser/digikey (131J21019X)
male coax contact (crimp type, male center contact) --mouser/digikey (132J21019X)
female coax contact (solder type, female center contact) --mouser/digikey (131J20029X)
male coax contact (solder type, male center contact) --mouser/digikey (132J20029X)
22AWG stranded wire (19x34) --mouser/digikey (400R0111-22-9, 55A0111-22-9)
2mm, 5mm, and 10mm shrink tubing -- ebay/amazon (from kit)
PET expandable braided cable sleeving -- ebay/amazon
 
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#11
Wow thanks for the parts list and the videos which I stumbled on and watched a couple weeks ago :) Check out my recent comment on
.

I have the 8445B, 8555A, 8552B, 1402A, 1421a, 1415a, 1410a, 1425a, & 1416a which came with the 140a. Shortly after I acquired the unit I got the 8555a's external mixer and the 3 sized waveguides, and patiently waited for two 10241A 10:1 voltage dividers to surface on eBay for a reasonable price. One of the probes doesn't work on the 1410a which I intend to repair someday, but even one probe on an oscilloscope that goes up to 1GHz for the price is pretty amazing.

I think I will get a 141t display section for the 8555a and then I can keep the 140a with the 1410a permanently installed. The spurs have definitely been an annoyance. Having access to that third LO would also be nice.

Any experience with the storage normalizer unit? Just came across that for the first time last night.
 

JLNY

Active Member
Thread starter #12
Oh wow, that is a very nice set of plugins indeed! A 1GHz sampling oscilloscope is a superb piece of kit. Those external mixers for the 8555A are not easy to come by, either.

The 1416A is also a rather interesting plugin to me. Used in conjunction with a sweep oscillator like an 8690 and a slotted line, it can be used to effectively form a scalar network analyzer. I'm pretty sure it should also be possible to connect it up with newer sweepers like an 8350 or 8340 series sweeper, which would allow for much wider-band sweeps rather than having to swap out the plugins for each band as in an 8690. Pages 14 onwards in this document explain the procedure for taking swept SWR measurements, but I suspect that the sweep adapters mentioned for connecting back to the ALC may be hard to come by. I can't really say with certainty how amplitude-stable those older sweepers are without one, or even something like an 8350 for that matter. Taking S21 measurements should be as simple as connecting a detector in place of the slotted line setup.

I have seen VK2SEB's video before. I'm definitely interested to see if he does more development on his project. Aside from that, I haven't done much research in the way of storage normalization, but I believe that Azur Electronics also mentions on his site that the 8750A storage normalizer can be used with the 140-series SAs via a special adapter. At a glance, the 8750A's currently on ebay don't seem to be excessively expensive, but purchasing the adapter needed and/or figuring out how to make one yourself could be a challenge. I believe they mention having the correct 08750-60035 cable on that website you mentioned above, and I see one listed on ebay right now for about $50.

In favor of tracking generators and such, I personally made the investment to get hold of a proper vector network analyzer. Through a series of strategic ebay purchases of the individual boxes at low prices, I was able to piece together a working 8510C network analyzer, complete with the Option 10 TDR mode. I've since replaced the free-running 8350 sweeper in the picture with an 8340 synthesized sweeper for greater frequency accuracy. I probably spent nearly as much piecing together a working APC-3.5 calibration kit for it. It is the jewel of my collection.

HP 8510 testing.jpg
 
#13
Funny, you've caught me in a bit of a buying frenzy and this morning acquired a 8690B, 8695A, 8696A, and 8697A which match perfectly to my aforementioned waveguides. I considered the newer models but from what I could tell the plugins don't go above 18G. I will actually be using the CW mode more than the sweep most likely and will be attempting to sync it up to my GPSDO sourced distribution network for frequency stability. Up to now I can get upwards of 13 GHz from a cheap Chinese ADF5355 programmable source but it produces a ton of splatter.

That is a very nice piece of equipment and outside of my current budget range. I would definitely have to have a need before I could justify the cost. I don't mean to take this thread way too off topic, especially since we could probably continue to wax poetically about the other items in our labs, but I am now more curious about what you're using your home lab for more than what is in it (besides repairing 141T's of course). I have an interest in radio astronomy, the lesser used ham bands (we've got to use them or lose them), and am also experimenting with creating phase-based logic gates in the mmW RF domain using GCPW techniques. Most of the research out there is in the optical domain which is currently not very accessible due to exotic materials and construction techniques (not sure if you've ever priced out an aftermarket optical table). I have done some preliminary simulations that are promising. I plan on using VK2SEB's ultra cheap prototyping techniques on a PTFE dielectric starting with 10 GHz and working my way up in frequency. I admit I may have interpreted the PTFE dielectric constant effects for GCPW at high frequency wrong and it may be the more inferior material to use, but its a lot cheaper than alumina ceramic for experimentation.
 

JLNY

Active Member
Thread starter #14
Ah, very cool! Yes, I think an 8690 may be the most sensible option if you are shooting for bands above 18 or 26.5GHz and have the needed waveguide adapters already. I believe that the 8350 also has a 26.5-40GHz plugin called the 83572B (I looked at this for the full list of plugins), but I have no idea how common they are, or if they can be obtained at any kind of reasonable price. Other than that, you are basically into the 8360 series and other "modern" equipment that would likely not be even remotely affordable at the hobbyist level.

Hehe, all I will say on my 8510 is that I paid quite a bit less than you might think. :happy: By purchasing it from the individual boxes, as well as some lucky breaks with local pickups and saving on shipping costs, I was able to assemble a working 8510 for about as much, if not less than what a working 8753 VNA would have cost, especially compared to one of the ones with the highly-desirable 6GHz option installed. The 1.3GHz and 3GHz 8711, 8712, 8713, and 8714 network analyzers would be another viable option at the hobby level, especially if one knows about the firmware upgrade hacks for converting an 8711 or 8713 scalar network analyzer into an 8712 or 8714 vector network analyzer, respectively.

In my own lab, I dabble in a few microwave circuits, and on rare occasions I do work with equipment for a VHF contesting group I work with. Most of what I work on is relatively low frequency at the moment, especially compared to what it sounds like you are working on. I also have an interest in metrology and all things test equipment. In all honestly, I have yet to really exercise my VNA's full capabilities, but I know that I have it available if I ever do start experimenting in the higher bands.

Lately, though, I have been doing a lot of stuff with audio circuits and microcontrollers, so much of my microwave equipment has been somewhat dormant.

I suppose we can start a separate thread if we just want to talk about our test equipment. :p
 

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