HP 8753 VNA - C/D differences and LCD Upgrade

[sixtimesseven]

Hi

Need some help deciding on a VNA, both options are great but you know 
I have the option to buy a calibrated HP 8753D / opt. 006 with 6GHz with integrated S-Parameter Test Set, valid calibration or a HP8753C with the HP85047A 6-GHz test Set for 3200 USD vs 2450 USD.

I have of course seen Dr. Kirkby's nice comparison:
https://www.kirkbymicrowave.co.uk/Everything-you-wanted-to-know-about-the-HP-8753-VNA/

To sum it up the main differences are:
- Low 30khz range
- 10dB more dynamic range
- Presets
- FIRMWARE (4.13 vs 7.74) so basically the "D" variant was supported until the end! That seems to be a pretty big deal to me but maybe sombody can comment on the details?
- Floppy disk (useful?)

Some subjective differences:
- D version is much more compact (one piece, no adapters)
- More modern look and layout with the modern non clicky soft buttons

Disadvantage of the "D" verison:
- Potentially the APC-7 connectors since adapter seem to cost about 150-200USD 




I lean towards the 8753D, not surprisingly 

[TheSteve]

8753D all day long for me, especially because it has the newer/faster CPU(confirmed by firmware 7.74). With an interface box you can use ecal units with it.

[dmills]

I have the 8753C (I guess the title is a typo?), but concur that the D is better for most things.
Do make sure the screen is ok, unlike the C there is not as far as I can tell a retrofit kit available.

Regards, Dan.

[TheSteve]

The 8753D with the faster CPU is equivalent to an 8753E without the LCD. The 8753ES only adds two more buttons for direct access to S parameters but adds no actual features. So end of the day with an 8753D you're getting the same features/options as the last of a very classic series of VNA's. If the CRT is in good condition the picture might look better then the LCD anyway.
I would have preferred to have N connectors myself but the APC7 are very repeatable and you can get the adapters for reasonable prices at times.
There is a very helpful person as well that will supply option codes for either to enable software options(think 002 and 010).

[sixtimesseven]

So 8753D it is 

Now I have to figure out where to get APC-7 to 3.5mm adapters.
I'm tempted to get two chineese adapters, connect them back to back and measure them on the VNA of my university.

I'm not so sure if I should get used ones (who knows how they were threated) and new ones cost 200 USD ... 

[sixtimesseven]

I have the 8753C (I guess the title is a typo?)

Ups, thanks

[sixtimesseven]

The 8753D with the faster CPU is equivalent to an 8753E without the LCD.

Looks like my HP8753D is has not gotten the option "000" CPU upgrade. But I guess I could fit the new CPU boards: 08753-60272 for example:
https://www.ebay.de/itm/Agilent-Keysight-08753-60272-A3742-Network-Analyzer-CPU-833-PII-2-Parts/401627974128?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055359.m2763.l2649

[TheSteve]

Not the end of the world - I'd use it and enjoy it. You may not find any need to upgrade the CPU board.
I have an 8753E 6 GHz if we do need to compare anything or look for differences.

[KE5FX]

I have the 8753C (I guess the title is a typo?), but concur that the D is better for most things.
Do make sure the screen is ok, unlike the C there is not as far as I can tell a retrofit kit available.

Regards, Dan.

If I'm not mistaken, the 'C' and 'D' models used the same Sony monitor, didn't they?  If so, the Newscope upgrade will work on both.  It is so much better than even a brand-new CRT that it's not even funny.

The 'C' model also has the newer soft-touch buttons, or at least mine does.  Either of those sounds like a good deal, but personally I'd go for the C and upgrade the LCD.

The built-in floppy drive is another factor, I suppose, but it isn't especially useful.

[sixtimesseven]

I have the 8753C (I guess the title is a typo?), but concur that the D is better for most things.
Do make sure the screen is ok, unlike the C there is not as far as I can tell a retrofit kit available.

Regards, Dan.

If I'm not mistaken, the 'C' and 'D' models used the same Sony monitor, didn't they?  If so, the Newscope upgrade will work on both.  It is so much better than even a brand-new CRT that it's not even funny.

The 'C' model also has the newer soft-touch buttons, or at least mine does.  Either of those sounds like a good deal, but personally I'd go for the C and upgrade the LCD.

The built-in floppy drive is another factor, I suppose, but it isn't especially useful.

I was thinking about upgrading with the newScope 9, but then I realized that the HP8753D has a RGB output. From the frequency I would say in the EGA format (25.5khz).
So instead of the 450$ Kit + Shipping + Tax and custom fees I thought of buying this converter as an experiment and then buy a 8.4 inch LCD either with VGA / HDMI or some sort of converter in between if the converter works.



Converter:

https://de.aliexpress.com/item/GBS8220-Arcade-Spiel-CGA-YUV-EGA-RGB-Signal-zu-VGA-HD-Video-Converter-Board-Dual-Ausgang/32860147000.html?spm=a2g0x.search0104.3.1.423e59922Sf7Ci&transAbTest=ae803_4&ws_ab_test=searchweb0_0%2Csearchweb201602_5_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536_10134%2Csearchweb201603_61%2CppcSwitch_0&algo_pvid=59d8db80-d42e-482d-857b-2b4f95673811&algo_expid=59d8db80-d42e-482d-857b-2b4f95673811-0

VGA LCD
https://de.aliexpress.com/item/M084-OF-Fabrik-direktverkauf-OEM-ODM-8-4-zoll-open-frame-industrie-lcd-monitor-8-4/32840853537.html?spm=a2g0x.search0104.3.31.50861ce6d7QYl6&transAbTest=ae803_4&ws_ab_test=searchweb0_0%2Csearchweb201602_5_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536_10134%2Csearchweb201603_61%2CppcSwitch_0&algo_pvid=48b3acad-a832-4076-a94b-49e2b22b9e27&algo_expid=48b3acad-a832-4076-a94b-49e2b22b9e27-5

For 100-120$ or so.

[sixtimesseven]

Not the end of the world - I'd use it and enjoy it. You may not find any need to upgrade the CPU board.
I have an 8753E 6 GHz if we do need to compare anything or look for differences.

Well it would be a lot faster that's for sure. See attached document.
Also, I assume it would add split screen capability to the 8753D.


Not sure yet. If I can get a board for let's say 100-150$ or so of Ebay I will probably try.
I would have to figure out how to transfer the calibration data to the new board though.

[TheSteve]

I installed an LCD into a 8752C using a game board and a VGA LCD. I have pictures of the install somewhere. The mod for the 8753D should be identical.

[sixtimesseven]

I installed an LCD into a 8752C using a game board and a VGA LCD. I have pictures of the install somewhere. The mod for the 8753D should be identical.

Perfect 
Any chance you could dig out the pictures 

[dmills]

If I'm not mistaken, the 'C' and 'D' models used the same Sony monitor, didn't they?  If so, the Newscope upgrade will work on both.  It is so much better than even a brand-new CRT that it's not even funny.
The built-in floppy drive is another factor, I suppose, but it isn't especially useful.

Whoops, yea, must be the E I was thinking of as the earliest one with the LCD as standard.
I am a little leery of early LCD based instruments, having been bitten by the Anritsu 8810 pathetically poor LCD thing.

The major use of the floppy drive is loading cal kits...

Regards, Dan.

[rhb]

I picked up some used APC-7 to  3.5 mm on eBay, but have had trouble finding APC-7 to N at reasonable prices.  Aaren Technology in the UK sells them for $110 which is the cheapest I've been able to find for branded product.

I'm afraid I'm slumming.  Mine is only a B model.  But at $1650 delivered with an 85046A test set, I'm not crying.  The B has been enabled to 6 GHz.  An 85047A on eBay would cost as much as I paid more. I'll suffer and swap connections above 3 GHz.

[dmills]

I actually have a 85046A going spare if someone wants to make me a sane offer for it (Someone has been in it and replaced the solid state switch with a mechanical one), works fine but annoying if you want S12 and S21 on screen at the same time!

Do you have the doubler required to make a '46A do the 6GHz thing? I thought that was a '47A only feature because while the detectors work at 6GHz (with the appropriate software option) the generator side tops out at 3GHz and the doubler is in the test set?
 
A warning about that option, when you set to do the 6GHz thing the generator output automatically goes to +20dBm to drive the external doubler, this is unwelcome if you are not expecting it (In particular the reference input really don't like that much power, the test set does the right thing, but if you have faked it out, be a little careful).

Of course the real expense with all this stuff is the cal kits, test port extensions, and connector metrology that you don't even realise you MUST HAVE until you buy a VNA....

Regards, Dan.

[rhb]

I don't have the doubler.  Thanks for the heads up on the output.  However, I made a deliberate decision to stop at 3 GHz with my test gear because the price goes up really quickly from there with all the bits and pieces you need to have.  The APC-7 to N-F connectors being but one example.

That said I did buy a Tek 11801 and four 20 GHz, 13 ps rise time SD-26  sampling heads.  So I did cheat a little. If I need to work above 3 GHz I can always use the calibrator output and do TDR to 15-20 GHz.  I just need to work out how to get data out of the 11801 and into a PC.  For a lot of things I can do the VNA with the screen cursors and a little thinking.

[TheSteve]

I had always planned to do a post on how I did the LCD mod to my 8752C but never got around to it. I have since sold the 8752C but I still have notes on the mod.
I used a LED backlit 8 inch 1024x768 LCD screen with a VGA driver - $50 shipped from ebay
The 8752C video signal was converted to VGA using a GBS-8200 - $17 shipped from ebay
The stock CRT is powered by 65 VDC so I used a 120 VAC to 12 volt adapter that happily worked with the 65 VDC input to power everything.
The stock video driver has separate horizontal and vertical signals that need to be joined together for the GBS-8200 to sync, that is done using 2 gates of a 74AC86 XOR in DIP format. The AC version is used so it can be powered by the 3.3 volt supply on the GBS-8200.
The stock backlight in the LCD I used was a little weak and driven well under spec so I powered the LED backlight from the 12 VDC supply through 15 ohms of resistance.
The above mods let me keep all changes in the CRT unit only which is easily removed and connected only by a single ribbon cable.
The boards were mounted to a piece of copper clad that was cut to fit on the bottom of the original CRT cage.
The LCD adjustment button PCB was mounted on the top of the CRT cage - they are only used once for the initial setup, same with the buttons on the GBS-8200. Once setup the top cover of the CRT cage is screwed in place.
Here are two pictures, a top view looking into the CRT cage after the mod was done and of the LCD mounted with the original tinted shield glass installed.
I was very pleased with how it turned out. I wouldn't doubt the newscope LCD is even nicer but this mod was very affordable and still looks/works great.

Any questions let me know.

edit - added the correct schematic of the sync combiner I used.

[rhb]

That looks really useful for any CRT replacement that does not already have a VGA port (e.g. some  LeCroys).

There is a discrepancy between the text and the schematic. 

that is done using 2 gates of a 74AC86 XOR in DIP format. The AC version is used so it can be powered by the 3.3 volt supply on the GBS-8200.

The schematic shows a 74HC86 and 74HC32.  And the switch at the CSYNC is puzzling.

Would you please check that.

[TheSteve]

rhb - thanks for noticing that! I have attached the correct schematic in its place.
Note again that a 74AC86 should be used with the 3.3 volt supply on the GBS-8200.

[rhb]

Thank you!

Would you consider writing a post about the general case?  There is a *lot* of old gear from the 80's and 90's with very fine performance, but failing CRTs.

Something along the lines of "Replacing  instrument CRTs with a cheap VGA LCD" in Repair.  My 8560A, 8753B and Tek 485 & 11801 all have fine CRTs.  But that can change in a heartbeat if an HV PSU part fails.  While there are kits offered for particular instruments, there are none available for most.

[TheSteve]

That might be a little tough as the video interface differs so much between the various machines.  The GBS-8200 does handle a variety of inputs but there are some it specifically excludes(on purpose) to entice you to purchase a more expensive version. I have only spent time looking at LCD conversions for three specific machines.
The HP 8752C, an 8714C and an HP 8920B

The 8714C mod is documented here:
https://www.eevblog.com/forum/testgear/upgrading-the-hpagilent-8714c-from-green-crt-to-color-lcd/

The 8920B I can get to work with an LCD but the original green CRT is amazing and mine is like new. It is also monochrome so the LCD upgrade isn't quite as enticing.

I did upgrade the backlight in an 8753E to LED as the original CCFL's all crap out:
https://www.eevblog.com/forum/testgear/8753-screen-upgrade-replacement/msg2043622/#msg2043622

I don't have any LCD upgrades planned for the future as my current 26.5 GHz VNA is LCD from factory, but should I come across an HP 8722 at the right price it will come home and get upgraded.


Hopefully sixtimesseven has his 8753D and it is working well - maybe he can post a few pictures.

Also for loading cal kits I highly recommend a GPIB interface - as a bonus it can be used to grab screenshots. The Agilent 82357B USB interface works great for the task.

[sixtimesseven]

Just got my APC7 to SMA adapters and attached them to the ports.
I noticed that both ports have a fair amount of wiggle in them 

On closer inspection it seems as if the coupler assembly is loose 

Edit: It actually seems as if the assembly is meant to slide a bit - At least from the mechanics of the attachment. The plastic part will not allow the screw to press the metal together and the assembly will slide in the oval slot.
Weird I would have thought that this would stress the semi-ridgit (lookded pretty ridgit to me but the service manual says otherwise) with time?

[rhb]

One connector is intended to slide over a small range to avoid binding between a fixture and the instrument so that very small errors in the position of the connectors on the fixture don't damage the connectors.

 On my 85046A it's the left connector

[sixtimesseven]

One connector is intended to slide over a small range to avoid binding between a fixture and the instrument so that very small errors in the position of the connectors on the fixture don't damage the connectors.

 On my 85046A it's the left connector

Interesting. Well I have only really worked with a R&S ZNB20 and a HP3577 which both have all solid connectors. But I guess it makes sense.

However, I do not see how one side could be fixed on the HP8753D since all eight screws and their 3D plastic washers / offsets are the same.