HP8753C VNA Sampler Teardown & Reverse Engineering - Page 1
Forum section: electronics / rf-microwave

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 14, 2025, 12:07:58 pm
content: I'm planning to build a VNA that mimics the architecture of the HP 8753. But due to budget limitations, I bought a broken 8753C. While repairing it, I ran into some fairly common problems. Two of the samplers were damaged — one of them had already been opened by a previous repair attempt. So I used that opened sampler to start investigating the issue and began reverse engineering it.I first looked at the LNA in the RF input path (I think it’s an LNA — if I’m wrong, feel free to correct me). I tested it separately. The test results showed that it was no longer functional.Next, I started reverse engineering the main part of the sampler itself. I first found the schematic of the sampler’s control board, which showed the pin definitions. Then I started measuring with a multimeter and ended up drawing the following schematic.There’s one part of the operation I don’t quite understand:In Figures 6 and 7 — how is the band switch implemented? What type of diode is used there, and what’s its function?Also, I’m not very sure about what some of the components actually are:In Figures 2 and 3, at first I thought the part was a transistor, but something felt off. So I measured its diode voltage, resistance, and capacitance, and even removed it to check the pads underneath. Turns out the bottom pad wasn’t connected, and the measured resistance was the same as the one below — 39.1K — so I think it’s probably a resistor.In Figure 1, the golden component at the bottom — I saw a similar part before when reverse-engineering a YTO, and someone told me that it was a capacitor. I’m not quite sure if this one is also a capacitor.Any suggestions are greatly appreciated — I’d love to hear your thoughts and discuss these interesting problems.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 15, 2025, 02:24:52 am
content: For figure 2 and 3, the part is a resistor.The golden component is most likely a capacitor. Is there a bond wire connected to the top?According to the service manual, in low band the diodes are constantly biased so that they're on. This means the signal passes through unimpeded. In high band the diodes are biased off, so a strong pulse is needed to turn them on (which comes from the LO). Your sampling bridge probably has a mistake, the diodes should all be schottkies not SRD. (The 100pF capacitor seems weird but actually makes sense given the IF frequency out is 1 MHz, and its job is to filter out all the other harmonics). There is probably nothing special about D1 and D8 other than having low capacitance. Try measuring the forward voltage of the diodes again.You are going to have to send a clearer picture of the LNA.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 15, 2025, 04:41:27 am
content: Really, really appreciate your reply, EggertEnjoyer123!1. You're absolutely right — the sampling bridge does useSchottky diodes, not SRDs.2. The golden component is indeed a capacitor. I measured it using a 4291B impedance/material analyzer. There’s a bond wire on top of it, and it connects to pin 1 of the amplifier on the left. This pin is then connected to ground through a 50 Ohm resistor. I suspect the left side is some kind of pseudo-differential amplifier.3. Regarding the bandswitch circuit: when the diodes are forward-biased, the four-bridge configuration basically acts as an analog switch that stays on continuously, allowing direct sampling of signals below 1 MHz. It's honestly a brilliant design.4. Apologies, I don’t have a detailed photo of the LNA. By the time I opened up the sampler, the LNA was already completely destroyed, so I didn’t get a chance to take a proper picture. However, I can confirm it had a complete biasing circuit for an amplifier — please refer to the top-right corner of 8753C_sampler_5.png.Thanks again for your insights and clarification — I really appreciate it!

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 15, 2025, 05:29:23 am
content: I suspect you can just bypass the LNA entirely. The performance would probably be reduced but it should still work.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 15, 2025, 01:22:43 pm
content: The sampler It's working now, but there are still some issues. The sampler is operational, but it still has some serious problems. At first, I thought the issue was with the A3 source, but after testing its YTO and mixer separately, the output was normal, with the amplitude reaching up to 18 dBm. I also tested the fixed frequency output, and all frequency points were output normally. Even when I bypassed the power amplifier and connected directly through the sampler, the same issue occurred in the middle of the frequency range.Strangely, the frequency sweep function isn’t working properly. I also tested analog bus input 16 on the 8753 series, and I found that the signal level suddenly drops between 1320 MHz and 1620 MHz. I’m not sure what’s causing the problem—I only have one sampler that might still be functional. Can anyone help me out?Attached is an image of the LNA.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 15, 2025, 01:46:17 pm
content: This is the image of the test results.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 16, 2025, 02:43:16 am
content: Your LO is no longer phase locked.Let's say your frequency is 1501 MHz. The LO might be set to 300 MHz (the comb generator part generates the 1.5GHz signal). Normally, this would result in an IF of 1 MHz. However, if your LO is not phase locked then the LO could be a little off, which would cause a different IF frequency to be generated. Because the VNA only listens for 1MHz it will miss this signal.To fix it you should probably just set the measurement frequency to a frequency which causes the LO to not phase lock. Then debug the phase lock loop circuitry. The usual suspects are tantalum capacitors or high ESR capacitors.

author: W4PJB
author_rank: Regular Contributor
timestamp: April 20, 2025, 10:54:38 pm
content: You may want to try reaching out to Joel_Dunsmore on this forum, he was involved in the 8753 design.https://www.eevblog.com/forum/profile/?u=772320]https://www.eevblog.com/forum/profile/?u=772320

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 21, 2025, 10:07:56 am
content: I think it's most likely due to the YTO's current and frequency not matching properly. I'm not entirely sure what's going on, but the sampler I built myself is working flawlessly. It might look like there's some frequency leakage, but that's actually because I haven't added a low pass filter yet. I tested this sampler all the way up to around 3.2 GHz, and it maintained excellent performance, It's super clean and stable. Honestly, this result turned out way better than I expected!

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 21, 2025, 10:14:25 am
content: Thanks for the referral, W4PJB!I’d really love to get in touch with Professor Joel Dunsmore. I still have so many questions about his coaxial directional coupler design. I'm currently trying to build one that works from around 300 kHz up to 26.5 GHz. Unfortunately, it seems like he’s no longer active on the forum… or maybe he’s just on vacation.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 23, 2025, 02:11:45 am
content: Just wondering, have you gotten anywhere with the coupler project?I am having trouble getting things to work in simulation... but then again I don't have the same materials that HP does.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 23, 2025, 10:50:12 am
content: Hi EggertEnjoyer123,Please refer to:https://hforsten.com/designing-a-low-cost-high-performance-10-mhz-15-ghz-vector-network-analyzer.htmlThis person completed the design of a directional coupler and successfully used it in their project. However, I have a few questions for them, and unfortunately they haven't replied to my email.My question is:I have a question regarding the directional coupler you used in the project. In the conceptual diagram in your article, the "coupled forward" and "coupled reverse" ports are left unconnected. However, in the PDF schematic you provided, these are connected to pin 2 and pin 5 of J2. Could you kindly explain where these pins are routed to, and what their function is in the overall design?

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 24, 2025, 02:59:19 am
content: First of all, his coupler design doesn't work as well as you would expect. Look at his uncorrected S parameters. With high directivity, the short and load S11 traces should not cross. If the uncorrected S11 is the same for a load and a short, then you have zero directivity. You can calibrate it out, but it leads to a lot of error because your correction term is large. It is much easier to build a multimeter which can distinguish between 0V and 0.001V than it is to build a multimeter that can distinguish between 100V and 100.001V (even though theoretically you just need to calibrate it at 100V first). If anything drifts by 0.01% it's over for the second multimeter, but the first multimeter can still reliably distinguish between the two cases.Without looking at the PCB files I can't be sure, but my guess is that he put extra pads in his footprint to help keep the spacing between the resistors consistent.If you want to see an example of a working 40GHz bridge you can take a look at my 22GHz VNA thread. Some Russian guy posted the internals of a 40GHz R&S VNA there.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 24, 2025, 07:26:24 am
content: I noticed that the bridge in the 8753 has a similar structure, so I thought I'd post it here as a reference. The design from this person actually has several issues:When the source is acting as a load, they used something like a GVA-93+ as a buffer amplifier. But after testing the parameters, I found that it doesn't really work well as an output impedance matching buffer. At higher frequencies, around 4~5 GHz, the S11 drifts to around 20 Ohms, and it gets even worse beyond that. So in my opinion, this design isn’t very professional. I ended up redesigning the whole architecture, using an RF switch chip I designed myself to properly switch between a 50 Ohm load and source.Also, I'm planning to tear down a ZNA43 soon for research purposes—I'll share that here once it's done.One more thing EggertEnjoyer123 could you please share the link to your project? I’d really love to check it out, but I can't to find all your posts. I'm still getting used to how the EEVblog forum works.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 24, 2025, 08:01:44 am
content: Quote from: JoeyDeng on April 24, 2025, 07:26:24 amThat doesn't matter in this case because he's not measuring the S21 in the uncalibrated plots. The measurement of the short/load is only done with the port acting as a source.Also how are you designing chipsQuotehttps://www.eevblog.com/forum/rf-microwave/building-a-22-ghz-network-analyzer-for-under-$1000/75/

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 24, 2025, 09:48:23 am
content: Quote from: EggertEnjoyer123 on April 24, 2025, 08:01:44 amThanks for the clarification EggertEnjoyer123. I understand now that you're saying S11 and S22 correspond to the load and short respectively, but the issue is that they can no longer be distinguished. I found this image from his test that illustrates the problem.Here's a test I did using a directional coupler I pulled from an HP 8350B. It has good directivity, which helps to better understand what’s going on.Quote from: EggertEnjoyer123 on April 24, 2025, 08:01:44 amI'm majoring in economics, but I'm currently working as a PA in an EE lab. Kind of a long story

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 25, 2025, 01:38:51 am
content: So, EggertEnjoyer123, do you have any ideas on how to make an ideal directional coupler?I found a schematic of the directional coupler from an old version of the E5071C, but it's from the 4.5 GHz model. I'm not sure if the 20 GHz version uses the same kind of coupler. Here's the video link:

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 25, 2025, 02:14:19 am
content: No way the 20 GHz module is using the same coupler as this one. This is just a resistive bridge coupler, and the directivity on these things is honestly pretty bad.It works fine at 4.5 GHz, but once you go higher, things like parasitics, resistor tolerances, and small layout differences start to mess with the performance. You just don’t get good isolation or directionality beyond a few GHz with this kind of setup.They’re definitely using something like a stripline or Lange coupler at 20 GHz — proper RF structures, not this resistive bridge.That said, I haven’t seen the higher-frequency version of the E5071C myself, so I’m not sure what kind of coupler it actually uses.Also, I don’t really know why the directional coupler of the 20GHz version still manages to work pretty well at low frequencies. The 2~18 GHz directional coupler I took down doesn't work well at low frequencies the coupling is basically gone.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 25, 2025, 02:30:24 am
content: The same circuit is used, just with smaller components.Couplers based on EM waves (like directional couplers) have high directivity but don't work in the low frequency range, which means you can't do lowpass TDR.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2025, 03:03:59 am
content: go resistors !

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 25, 2025, 03:27:50 am
content: Does that mean the directional coupler in the Keysight E5071C also has poor directivity?So why can the 5071C still correctly distinguish between a short and a load? Is it because it uses some special calibration?

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2025, 03:35:16 am
content: Directivity is measured in dB's and while something might be less sensitive it does not mean its not functionalIf you understand the effect of directivity and its proportional magnitude of error because of different directivity then you can understand what measurement error it will have on what loadshttps://www.allaboutcircuits.com/technical-articles/finite-directivity-of-directional-couplers-a-source-of-uncertainty-in-power-measurements/I suggest sitting down with the math for a few hours to get an idea of what is actually going on because you will easily go bankrupt if you try to use loose terminology like "poor" for complex measurement tools like directional couplers.... they get very expensive quickly. It might be essential or have little relevance depending on what you are doing.Though, it never hurts to get a few 'premium' solutions on the radar in case you luck out and can score a deal, which is worth while even if you are not exactly sure of what you needAs you can see, it can be hit or miss.. and you might be surprised how bad your results might be, even with the best equipment, if you have a difficult load.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 25, 2025, 03:51:40 am
content: Coppercone2, thank you so much for your reply and the link you provided. I’m really sorry for my non-professional terminology.I’ve also been curious about how directional-coupler errors are removed algorithmically, so I foundhttps://helpfiles.keysight.com/csg/pxivna/S3_Cals/Errors.htm.But it’s so late now and I’m completely exhaustedI think tomorrow I’ll have to sit in the school library and study all of this carefully.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2025, 03:54:31 am
content: the problem is that someone is going to be working with something specific and their 'scale' works for that but it might be totally irrelevant or misleading to you

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 25, 2025, 04:00:14 am
content: The old HP VNAs had over 40dB directivity. They accomplished this by having good balancing with the resistors (I know R&S uses laser trimming to get the resistances just right). Parasitics are mitigated by using extremely small resistors (the patent says <1/10 wavelength). On top of all that, the CMRR of the coaxial balun has to be very high. To accomplish this HP used lossy material to kill any common mode signals at high frequency. R&S uses a resistive ground plane to accomplish the same thing.The relevant patents are here:https://patents.google.com/patent/US4588970A/enhttps://patents.google.com/patent/US20150130554A1/enIf you want to know how error correction works, go look at the 12 term error model. The math has already been done and I suggest you use already existing solutions like scikit-rf or this:https://github.com/NanoVNA-Saver/nanovna-saverYou can calibrate out the errors to an extent. If you want to know the actual directivity go look for the words "Uncorrected directivity" in the spec sheet. For your VNA see here:https://nscainc.com/wp-content/uploads/2017/05/Keysight_E5071C_ENA_Network_Analyzer_datasheet.pdf(page 13). Higher directivity is always better, and calibration can only get you so far. It is much easier to distinguish between a 1mV and 2mV signal than it is to distinguish between a 100.001 and 100.002V signal. Even though you can calibrate out the second measurement by subtracting 100V, any gain errors or drift in your circuits would cause you to get a garbage result.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2025, 04:01:19 am
content: resistive ground plane is right what I was looking for, another fascinating aspect of advanced DIY PCB manufactureI hit a dead end for applications of resistive wire inductors (i.e. mix R and L for RLC, so its just physically a L and C), but resistance ground plane sounds like something that can involve thick film resistor pastes, nichrome PCB's or other weird things

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 25, 2025, 04:33:35 am
content: Thanks so much for all the information, and for being so patient with a non-professional.I’ll need to dive into these resources first. Here’s the article I found:https://www.rfmentor.com/sites/default/files/NA_Error_Models_and_Cal_Methods.pdfHonestly, without studying this I couldn’t hope to build a VNA myself. Luckily I’m comfortable with mathI really enjoy it. I’ll start out using an open-source solution, and eventually move the whole thing onto an FPGA.

author: Bud
author_rank: Super Contributor
timestamp: April 25, 2025, 05:46:30 am
content: Then you need Dr Joel's bookhttps://www.amazon.com/Handbook-Microwave-Component-Measurements-Techniques/dp/1119477131/

author: henrikf
author_rank: Newbie
timestamp: April 26, 2025, 09:08:05 am
content: Quote from: JoeyDeng on April 23, 2025, 10:50:12 amIn the coupler schematic symbol pin 1 is the coaxial cable signal conductor, pin 2 is the coupled output, and pin 3 is the coaxial cable shield. See the attached image of the coupler footprint.Quote from: EggertEnjoyer123 on April 24, 2025, 02:59:19 amYou are comparing port 1 and port 2 traces which have different frequency responses. Attached is a measurement of the coupler breakout PCB (Input port to thru, coupled, and isolated ports). Unused ports are terminated with about -20 dB return loss loads and the connector return loss is about -15 dB. Coupling drops at higher frequencies due to 0402 packaged resistor parasitics. 0201 resistors and smaller diameter coaxial cable should be used to optimize the performance above 10 GHz.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 26, 2025, 06:30:52 pm
content: Quote from: henrikf on April 26, 2025, 09:08:05 amHmm, I just assumed the two ports were identical, and I guess I shouldn't have done that.I believe that the directivity is still close to zero in the plot you sent. At 15 GHz if you had a short, the source would get attenuated by 10dB before making it to the short, and then after reflection it would be about 30dB lower when it reaches the coupled port. With a load the isolation is about 30dB, so a short and a load would look almost the same.Also for the mixers you might want to consider looking into building your own. In my otherthreadI was able to make a 2-18 GHz mixer for a few bucks with decent performance. I think you can extend the performance down to DC if you used ferrites to increase the bandwidth of the microstrip baluns.I'm also curious as to whether you measured your calibration kit with a professional VNA (since you did do measurements with a professional VNA + cal kit). I don't really think the calibration load you made is good to 15 GHz, but I could be wrong. There are Chinese loads on Aliexpress that go to 18GHz with low VSWR supposedly (they're only $20), I bought two 40GHz ones and my friend at a lab found out that they were good.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 26, 2025, 11:43:29 pm
content: After getting a basic grasp of error models and working through them (btw, this article is really explains things clearly:https://www.rfmentor.com/sites/default/files/NA_Error_Models_and_Cal_Methods.pdf), I realized something I totally missed before:Even the strongest error model can’t fully separate data where the strace is completely tangled up with no extra parameters to fix errors.It took me almost a whole afternoon staring at this to finally click!Turns out, the graph from heneikf shows the short and load setups for different ports...

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 27, 2025, 12:17:27 am
content: btw,I really wouldn’t recommend relying on this stuff made in china for anything mission-critical. thinking back to when I was in middle school in China, I bought a LibreVNA set, hoping to use it myself. But after testing the included load with the VNA in our lab, I found it totally failed to meet specs. The open calibration piece literally had no internal pins — the leakage was terrible. There are so many shady sellers in China... Youmightget one decent unit, but the rest in the batch are probably junk.Just my opinion

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 27, 2025, 05:44:39 am
content: And also the rf source I designed. Hope it works.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 27, 2025, 07:06:02 am
content: Quote from: JoeyDeng on April 27, 2025, 12:17:27 amI measured some cal kits too, the results are also in the 22GHz thread.The open is almost ideal (it has some fringing capacitance), the short is basically ideal. The load can just be thrown away, it's garbage. There are honest sellers on Aliexpress though. I bought a 40GHz load for $30 and it measured within spec (had a friend measure it for me with his lab equipment).Have you also looked into the LMX2820? It is twice the price of the LMX2594 on LCSC but the frequency goes up to 22.6 GHz.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 27, 2025, 07:13:55 am
content: Im new to microwave. I saw that lmx2594 only sales for 35cny(abt 4.79$) on alibaba, so I asked my friends to get some for me, and the appearance of the chip looks fine and brand new.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 27, 2025, 07:52:51 am
content: $5 a chip seems way too low to be believable. Then again, I have won chip roulette on Aliexpress before so they might be real (but if they are they're probably factory rejects).

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 27, 2025, 08:51:59 am
content: yeaaa thats true, but if they sales the fake chip, the chip out of spec or the second hand chip on alibaba, u can just get ur money back and keep the goods by providing evidence.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 29, 2025, 05:18:45 am
content: The load I got from alibaba looks not bad

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: April 29, 2025, 07:12:03 am
content: Link?

author: szoftveres
author_rank: Regular Contributor
timestamp: April 29, 2025, 02:41:00 pm
content: Quote from: JoeyDeng on April 29, 2025, 05:18:45 amWhat type of (how high quality) cal standard you used to calibrate the VNA before measuring it?

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 30, 2025, 12:41:17 am
content: The measurements utilize CETC 41st Institute's 2024-calibrated VNA calibration kits with full NIST traceability.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 30, 2025, 12:58:37 am
content: and also the best cal kit I could get🥲

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 30, 2025, 01:03:39 am
content: My friend got it for me in the Chinese market.If you need it, please dm me, I can send you some.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 30, 2025, 09:20:24 am
content: I truly regret using 01005 components. I tried soldering one capacitor and one resistor, and it felt okay, but still...

author: khach
author_rank: Contributor
timestamp: April 30, 2025, 09:36:47 am
content: What is real bandwidth of HP8753 Sampler? Does anybody measure sampler response at third harmonic of VNA source and hack firmware to expand frequency range?

author: JoeyDeng
author_rank: Regular Contributor
timestamp: April 30, 2025, 12:31:37 pm
content: I saw someone managed to upgrade an 8753C to 6GHz by modify the EEPROM data, but haven't seen anyone push it further. Here's y I think there's a hard limit:1. The directional coupler in 8753C was only designed to work well at lower frequencies2. While you could technically use multipliers to get higher frequencies (signal loss isn't even the main issue here...)3. The real showstopper: The RF diodes in the sampler simply can't handle higher frequencies anymoreIf you want to hack a similar architecture VNA for higher frequencies, I'd recommend getting an hp8720

author: hendorog
author_rank: Super Contributor
timestamp: April 30, 2025, 11:31:27 pm
content: Quote from: JoeyDeng on April 30, 2025, 12:31:37 pmThe 8753C receivers work perfectly well up to 6GHz - they have to, as there is a 6 GHz software upgrade for the 8753C. The RF Out only goes to 3GHz, so the 85047A test set contains a doubler to get to 6GHz.The directional coupler you have there looks like one from a 3GHz test set. Those do not work well above 3GHz.Getting a 8753C working at 6GHz requires at a minimum.* A frequency doubler. I made my own. (https://github.com/hendorog/8753_modules/tree/master/hw)* The 006 option enabled in the 8753C (The simplest way is to execute the POKE command here:https://www.eevblog.com/forum/repair/repair-hp-8753c-network-analyzer/msg989541/#msg989541)* A directional coupler, bridge or some other three port device. A splitter works at a pinch.* Another three port device - ideally a splitter - to feed some signal back to the R input

author: JoeyDeng
author_rank: Regular Contributor
timestamp: May 01, 2025, 12:16:56 am
content: Quote from: khach on April 30, 2025, 09:36:47 amHe means the 3rd harmonic (3GHz*3=9GHz).

author: hendorog
author_rank: Super Contributor
timestamp: May 01, 2025, 12:59:53 am
content: Quote from: JoeyDeng on May 01, 2025, 12:16:56 amAh gotcha

author: khach
author_rank: Contributor
timestamp: May 01, 2025, 10:19:19 am
content: Yes, I am looking for 9- 12 GHz operation mode of HP8753. Of course, S-parameter test set is completely different then original and directional couplers with wider bandwidth. At my HP8753C signal source is degrade by power and not excited 85047A internal freq doubler. Maybe, if implement some active or PLL like doubler or tripler the possibility of extendimg freq range is good solution. Of course, bandwidth of sampler harmonic generator SRD need check for higher harmonics present. And sampler schottky diode freq range is critical too.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: May 03, 2025, 03:23:21 pm
content: all the things works fine

author: JoeyDeng
author_rank: Regular Contributor
timestamp: May 03, 2025, 03:25:31 pm
content: But my spectrum is dead :pdead, Next plan is to make a spectrum analyzer with the components in this anritsu ms710.

author: JoeyDeng
author_rank: Regular Contributor
timestamp: May 03, 2025, 03:27:17 pm
content: the noise figure of source is in spec and acceptabel😆

author: JoeyDeng
author_rank: Regular Contributor
timestamp: May 03, 2025, 04:09:32 pm
content: After spending a longgg time washing this sh!t spectrum analyzer which with a large amount of juicy battery.I just want to gave up, almost all the logical parts and AFE are dead. The IF generator is dead and the front att and sw also has get damp…

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: May 03, 2025, 06:28:21 pm
content: Are you using the KHD-23 connectors?Have you simulated the transition yet for those yet?

author: JoeyDeng
author_rank: Regular Contributor
timestamp: May 03, 2025, 06:43:43 pm
content: I use sma-kcd47. And I’ve done the simulation in ads with a paltry number of parameters, I bought a lot of magnetic ring, but none of the seller provides the exact parameter for simulation.and also I’m really curious abt how HP make their directional coupler have that high directivity. So I did some research on “Joel P. Dunsmore "Dual directional bridge and balun used as reflectometer test set," US Pat. Nº 4 962 359, Sept.10, 1990.” But I haven’t got any inspiration yet