I'd sign up for a replacement board or even just the gerbers so I could get my own made instead of using your time.

In fact I'd probably just be happy with the schematic, parts list and instructions if that was easier.

TonyG

Hi Ed,
I’ve done pretty much the same thing a few times with asst SA’s. ?You’ll find that the narrow bandwidth on the SA really isn’t that useful with an SA/TG combination as the DUT will determine the resolution. ?
You could do a filter tracing with a signal generator and a diode detector, which obviously has unlimited bandwidth.
The schema I used was mixing the 1st LO with a synthesized LO at the high IF center frequency. ?I’ve used a TCVCXO as the reference and slide the frequency to get it close to the SA center frequency. You’ll need either a real good mixer and/or an isolator to keep the high IF LO from lifting your baseline. ?They’re fun projects; more an exercise in shielding than design. ? Main thing: have fun with the project and don’t do too much hair pulling.
Jeff

It's been chilly out again, and the 8568/85662 has been running stable since last night without any sweep-stopping, so I took the opportunity to work on the TG some more. I took some screen shots to record the dynamic range and look for adequate isolation. Only one came out legible after freehand shooting of the upside down display. It's at

/g/HP-Agilent-Keysight-equipment/photo/78668/0?p=Name,,8568,20,1,0,0

in a new photo album called "8568 TG project." I think I managed to get the image right side up, at least on my PC. My apologies for the poor photography or if it shows upside down.

This one shows the full ~0 to 1500 MHz span, at IF and video bandwidths low enough to get near the noise floor of the 8568 - each sweep took 500 seconds. The top A trace is the TG output near 0 dBm reference level, while the bottom one is the stored B trace maximum hold values, with the TG in its "RF OFF" mode. It exhibits better than 90 dB dynamic range between the states. The small spurious signals and ripples in the noise floor are due to leakage through the coaxial relays that rout the center frequency mixer output and amplifier output signals within the TG. When the cable from the TG out to the SA is disconnected, these disappear, leaving just the SA's noise floor. Other experiments confirm that the TG is virtually invisible to the SA, due to good isolation of all the LO signals, and proper containment of the TG's internal operating signals.

Ed

Thanks to everybody for great discussion.?

Despite initial diversion I have found that U313 Agilent 1GC1-4210 has struck yet again.? It had weird failure mode where it would change its division ratio at the bottom 30% of its input range of 4GHz..8GHz to half the intended value.? This caused its output to double in frequency and become filtered out by downstream LPFs.? So I chucked U313 out and replaced it with good honest organic grown 24GHz Hittite prescalers.? E4435B now works just how it was supposed to.? If there is enough interest I can create a drop-in PCB that will replace 1GC1-4210.
Cheers
Leo

On 11/16/18 7:44 AM, Robert G8RPI via Groups.Io wrote:

Adapting a 8922 for amateur (analogue) use would be more about
re-writing the software than changing the hardware. Another issue is
that while the signal path is fairly wideband the calibration data only
covers the celphone frequencies. I think hat the 8960 / E5515C would be
a better subject for that sort of effort.

If anyone here wants to try, I have a few spare E5515Cs here. I
bought them opportunistically; I have two in my lab which I use for
actual cellular equipment development. (*gasp!*)

I will not ship them, though. The 8922 is a one-hander compared to an
8960. Come and get 'em!

Come to think of it, from way back, I also have a fully-functional and
beautiful 8922, both halves. I'd let that go for peanuts...come and get it.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

0.050 inches.

Get a good brand, you want it to fit tightly.

-Chuck Harris

Dr. David Kirkby from Kirkby Microwave Ltd wrote:

Adapting a 8922 for amateur (analogue) use would be more about re-writing the software than changing the hardware. Another issue is that while the signal path is fairly wideband the calibration data only covers the celphone frequencies. I think hat the 8960 / E5515C would be a better subject for that sort of effort.

Robert G8RPI.

PM sent. Haven't figured out any way to confirm that in the groups.io interface; PEBKAC perhaps :-<.

Rather than easiest or hardest, how about luckiest?
I was given a 50" plasma tv once where the top half of the display was dead and the bottom half worked fine. Once I got inside I could see that the power supplies and all of the driver hardware came in duplicate. It was like there were 2 TVs inside. With no schematics but knowledge of how plasma and LCD TVs are designed, I was able to compare working and non-working components until I found a string of 4-5 diodes that were shorted. Though they were SMT, I kludged 1N914s in place and the set has been working ever since!

Kevin

Sent from kjo iPhone

I have a number of tracking generator projects in the works, over years, for the 8566 SAs. When I acquired a couple almost-working 8568s a few years back, I figured I'd make one for them too, if I got them fully working, so started design and parts collection, and rough layout and construction. This was a low priority project, until I acquired a couple more 8568s and 85662s this summer, which led to the fix-a-thon I mentioned earlier - to get some fully working. Having three usable SA systems, I restarted effort on the TG project, and was really close to done on the design and build, until this 8568 sweep-stopping etc problem showed up.

The TG isn't quite done, but is usable and works well. It started life as an HP8444A, which was part of a large HP141T SA system I got many years ago, but have since decommissioned and parted out, except for a few pieces. Now, this isn't your typical 8444A - all that remains of the original is the chassis/case, power supply, output amplifier, leveling system, and a bandpass filter. The original 8444A type was used for a number of HP SAs that had pretty much the same frequency plan as the 141T system, such as that in the 8555A, which was the main plug-in. The 8568 is quite similar, and the 8444A has been used with it too, but with limited capability - it can't normally match the high resolution and narrow spans the 8568 can provide.

I wanted this TG able to allow the 8568 to be all it can be, and do all it can do, TG-wise, so I built a whole new frequency control system into it. It uses all three of the local oscillators present in the 8568. Normally, only the the first LO is accessible externally, so simple mods are needed to get the second and third LOs out and delivered to the TG for processing. I had planned all along to use the second LO - it allows for seamlessly using spans below 1 MHz, and is available inside on an SMB coaxial test point that just has to be brought out.

When I started the frequency control design years ago, I didn't have detailed info for the 8568, and I naively and wrongly assumed that all the LOs were fully synthesized and "exact," but recently discovered that wasn't the case. All my work on this part of the plan (I'll explain later) was down the tubes, and I had to incorporate the third LO information. This required another, fairly simple mod to pick off a little bit of power from the third LO in one of RF modules - adding an SMB connector, a couple resistors, and cabling out to the rear panel. The third LO info is what allows the system to reach the narrowest IFBW resolutions all the way down to 10 Hz.

So, to reconstruct the center frequency, the third LO (nominally 280 MHz) is mixed with the second LO (nominally about 1750 MHz +/- a few MHz) to make 2050 MHz. This 2050 MHz, mixed with the first LO (2050 to about 3550 MHz) provides the center frequency ~0 to 1500 MHz as the difference, which is low-pass filtered out, amplified, and leveled. The tricky part is that the second LO includes the fine tuning info for narrow spans, and info from the third LO, used in its synthesis.

The third LO is not directly controlled or synthesized - it's a crystal oscillator that may vary quite a bit, say +/- 50 kHz - but since it is used in the overall second LO synthesis, the variation gets cancelled out at the last conversion from 301.4 MHz IF to 21.4 MHz IF. This was the crucial piece of info that I was missing way back when I started. I thought the 280 MHz was right on, and simply making 301.4 MHz to mix with the second LO would do it. I had a slick arrangement all rigged up, with an oddball OCXO I happened to have, that was close enough to modify to run at 100.466666... MHz, then run through a cool amplifier-SRD frequency tripler from a 1960s PLO unit. I spent countless hours on these two pieces, perfecting it to make a precise, clean, 301.4 MHz, only to find that it wouldn't work, because the 50 kHz or so variation in the 280 MHz was hopelessly beyond even the coarse tuning range of the OCXO, let alone the fine tuning for tracking.

I realized that even if I could have made a new oscillator setup, or put in a DDS system, it still would not accommodate and correct for the possible drift in the 280 MHz XO - there are no specs on this, so all I would know is that the actual frequency can be pretty far off nominal, and drift an unknown amount. The only simple way to go then, is to get that third LO signal and use it to make the proper approximately 301.4 MHz that includes the error.

So, mixing the third LO with 21.4 MHz from a regular VTXO is what finally made it all work - beautifully.

That's all for now. I hope you can appreciate why I used all three LOs, and that it's not all that hard to get them. Next time I'll explain the details of how I did it. The frequency plan is just how to make the desired output frequency, but there's a lot more to making it good, and making the TG operation invisible to the SA.

Ed

I think it would work more than fine as a little bit of JavaScript running in the browser on mostly anything. After all, the era of intelligent terminals is back with vengeance. You can program them even in assembly (asm.js). And asm.js is exactly like IBM’s mainframe hardware abstraction – I’m almost identical fashion, it is translated to the platform’s machine code. And you get it for free with a cellphone :)

Cheers, Kuba

On 11/15/18 5:44 PM, Brad Thompson wrote:

As one of the first programs of its kind, IBM's ECAP (Electronic-Circuit
Analysis Program) included many of the features found in modern analysis
programs
(e.g., TINA) and a user-interface that's painful by today's standards
(punched cards, anyone?). If you're curious about ECAPs innards and
applications, I have a book for you.

I have one copy of "IBM Electronic Circuit Analysis Program: Techniques and
Applications" by? Randall Jensen and Mark Lieberman; published by
Prentice-Hall,
Englewood Cliffs, NJ, 1968 first edition hardcover, 402 pp.. EX-LIBRARY
copy
in good condition (card pocket, spine label, library markings). Library of
Congress catalog? 68-18515.

I'm asking $5.00 which includes USPS media-mail postage and a cuppa coffee
for yours truly.

Questions welcomed, PayPal honored.

Great stuff. I have a copy of that book, and am looking for the
actual software.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

On 11/15/2018 6:14 PM, tmillermdems wrote:

Hi Brad,
I don't have any need for the book but did use the ECAP program on an IBM 1127 system back in the late 60's. The element nodes were entered on punch cards and a printout of results came pretty quickly. It was very good for filter design.
The original program ran from a removable disk pack.

Hello, Tom--

I encountered ECAP via an university's IBM 1620, which offered 24- to 36-hour
turnaround. That made for slow debugging.

Maybe someone with time on their hands could recode ECAP for a Raspberry Pi<g>.

73--

Brad AA1IP

I've got the 8568 "working" now with a different IF/display unit, and it's pretty much the same behavior - OK when nice and cold, then the sweep stopping and other problems if it's warmer. I'm taking a break from it for a while to let my unconscious work on all this info. I'll be talking about the related TG project for a bit to get my mind off of this 8568, which definitely now counts as one of the most difficult cases I've encountered.

Ed

开云体育

From what I see the differences in models is mostly in the power handling of the front end. There are other cell phone features between model variants, but, those do not concern me too much. I am trying to trace out the mother board module interconnects. I guess I just do this for the challenge.

I have bought a few in the $100.00 range. For me to buy one it must have option 006 and 010.

Just wish I could find the component level info on this to try and adapt it better for ham use.

73
Glenn
WB4UIV

Which 8922? There are several suffix letter variants. Some commonality with the 8920 and 8924 but not much.
As a dedicated digital cellphone test set it has poor mass and volume to functionality. Some models have a spectrum analyser (for some it's option 006) which is useful but has a maxium span of 10MHz? Other than that it's a CW signal generator going to 1GHz.
I hope it was cheap, they cost around $40,000 new but I would not pay more than a couple of hundred for one. They do have some useful bits depending on model. I don't like breaking modern equipment but hve to admit breaking a couple. They provided a spectrum analyser upgrade for a 8920A, new monitor for a 8920B and parts for a RF input module repair on another 8920B plus some switched attenuators connectors etc.

The smilar looking 8924C is much more useful as it's basically a 8920B with spectrum analyser option and a CDMA adaptor in a big box. The difference is it retains all the analog functions of the 8920B.

Robert G8RPI.

-- 
-----------------------------------------------------------------------
Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv@...    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"