RF Explorer & Signal Generator - Page 1
Forum section: electronics / testgear

author: videobruce
author_rank: Frequent Contributor
timestamp: July 30, 2021, 05:14:02 pm
content: I have a RF Explorer. I'm aware of their RF Signal generator and I'm wondering if I could use the two in a slightly different way.https://www.seeedstudio.com/RF-Explorer-Signal-Generator-RFE6GE-p-2074.htmlWhat I want to do is be able to test existing RF cable runs, mostly 50 ohm RFC (LMR) 400 for problems without using a Spectrum Analyzer since the opposite ends can not be within reach of a single device as one would when testing 'jumper cables' of shorter lenghts using the Tracking Generator function of a SA.Anyone out there familiar with this could tell me if my quest would work with these two devices? This would be instead of just placing a dummy load at one end and comapre they with the result of whatever antenna is normally connected. Hopefully, all of that made some sense.

author: tautech
author_rank: Super Contributor
timestamp: July 30, 2021, 08:00:20 pm
content: They claim addition of the RF gen can offer some VNA capability however ideally TDR could better suit your needs.Maybe it's time to upgrade your SSA to an SVA ?

author: videobruce
author_rank: Frequent Contributor
timestamp: July 30, 2021, 08:41:54 pm
content: How & why would that solve the problem of not being able to access both ends of a coaxial cable??But, for it to be a VNR doesn't both devices have to 'talk' to one another?

author: tautech
author_rank: Super Contributor
timestamp: July 30, 2021, 09:06:31 pm
content: Quote from: videobruce on July 30, 2021, 08:41:54 pmTDR can display faults and total length of a coax feed line with just one end of the coax connected.In SVA models in DTF mode you have a menu of settings to optimize accuracy of measurements.From the Siglent NA website:Attached is a screenshot from my SVA1032X with an open Port 1 (TG port) in DTF mode and showing some previous settings. Only the TG port is used for DTF and in S11 VNA modes. S21 measurements use both ports.Here DTF can show cable joints with a antenna connected:https://www.eevblog.com/forum/rf-microwave/what-really-is-this-antenna/msg2680419/#msg2680419

author: videobruce
author_rank: Frequent Contributor
timestamp: July 30, 2021, 10:44:51 pm
content: What are you tiring to do, get me to spend more money??Fast questions since you brought it up, that 1st chart, can I assume that the 1.00 means a dead short? And the bottom chart, I assume that's loss, but what is the scale representing?

author: tautech
author_rank: Super Contributor
timestamp: July 31, 2021, 12:37:40 am
content: Quote from: videobruce on July 30, 2021, 10:44:51 pmLOL, now you know what it feels like for me when Siglent releases more new equipment !QuoteDTF mode, using Port 1 only.Here's something you can relate to as I've just done this quickly using ~5M of RG213/U with M-F terminations and a N-BNC and a BNC short. Note the further reflections at multiples of the coax length.No settings adjusted from default to allow for velocity factor or other cable characteristics.0- 3.2 GHz sweep although this can be adjusted to your needs as the second screenshot displays when the sweep is limited to 500 MHz.

author: gf
author_rank: Super Contributor
timestamp: July 31, 2021, 08:17:45 pm
content: What properties of the cable do you want to test/measure?What is the the cable length? (at least what magnitude)What is the frequency range of interest?What is connected to the far end of the cable?Is the far end completely unaccessible, or do you have the opportunity to connect anyting different to the far end (e.g. open or short)Do you happen to have a scope and a function generator already, or a NanoVNA?A NanoVNA V2 is just ~$50. Yes, it were an investment, too (but only 1/4 of the price of the RF Explorer Signal generator that you linked).NanoVNA can also do TDR. Depending on you exact use case, it may or may not suffice. You need to tell more details.

author: videobruce
author_rank: Frequent Contributor
timestamp: August 01, 2021, 01:45:50 am
content: Cables around 50'or so,Up to at least 1GHz,Antennas, but those would be disconnected for the tests,Far ends accessible,I have a SA w/ a TG, but that won't work (using the TG) of course w/o pulling the cables back into the 'shack' which is impracticable.The cost of that SG isn't any issue. The Siglent SVA kinda is thou. if I didn't already have their SSA, I wouldn't be posting here as I would of already bought oneI think you are off on the price;https://www.tindie.com/products/hcxqsgroup/4-nanovna-v2-plus4/noVNAV2See here;https://nanorfe.com/nanovna-v2.html#buyingQuote

author: gf
author_rank: Super Contributor
timestamp: August 01, 2021, 09:04:24 am
content: Quote from: videobruce on August 01, 2021, 01:45:50 amYou mean the cost of the Siglent is an issue for you?This was my understanding of your statement, and that's why I bring the NanoVNA into the play, as potential alternative.QuoteWell, I wanted to buy a V2 plus4 at the beginning of this year, and it was out of stock everywhere. Then I though "so what - better than nothing" and ordered a V2.2 from China for 52€. Likely I got a clone, still it does work basically. Even if an original V2 plus or plus4 are supposed to perform better, I do not consider it wasted money. It was just 52€, and I still got a lot of functionality for the money. Maybe I just had good luck with the clone? I don't know. In the meantime there is also an (even better)NanoVNA V3in the pipeline, but again it will be more expensive than its predecessors. Now thtat the V3 is announced, I'm even glad that the V2plus4 was out of stock, and that I did bridge the gap (until V3 becomes available) only with a cheap V2.2 clone which was still good enough for me so far. What's good enough depends of course in the individual requirements and use cases. For many use cases a V2.2 clone is good enough, and for other use cases even the Siglent SVA is not good enough.Which properties of the cable do you actually want to measure/test?Do you just want to detect a broken cable and distance to fault?

author: tautech
author_rank: Super Contributor
timestamp: August 01, 2021, 10:05:52 am
content: Quote from: gf on August 01, 2021, 09:04:24 amVB already has an older SSA3021X3032X and a SVA would be an all in one upgrade that could do his SA, cable and antenna analysis work if he were to flick his SSA and have a hard look at all the options available to him.SVA1032X is a great tool and if anything were to happen to mine I would replace it in an instant.Still it's his choice when he's done the necessary homework.

author: gf
author_rank: Super Contributor
timestamp: August 01, 2021, 10:18:21 am
content: I have no doubts that the SVA1000X is a nice device, if it fits the available budget. For pure hobby usage, it still may be too expensive.OTOH, there do exist microwave use cases, where it does not suffice, and where you rather need a $100k device. Everything is relativeIn the first place it were necessary to know the exact requirement -- i.e. what exactly is supposed to be measured/tested.

author: tautech
author_rank: Super Contributor
timestamp: August 01, 2021, 10:28:54 am
content: Quote from: gf on August 01, 2021, 10:18:21 amYes of course but in this case it can be offset by quitting the SSA he already has and as Bruce is familiar with the UI the SA mode in an SVA is identical which in itself has some benefits.Then there are ways to get a SVA for a lower outlay too......Bruce can hunt out my SVA and antenna threads and decide if its capability will suit his needs.

author: videobruce
author_rank: Frequent Contributor
timestamp: August 01, 2021, 11:02:22 am
content: The SA I had previous to my 3032 was Rigol which was my 1st 21st century scope. All the prior models were from the 90's for the most part and the Rigol was a huge step, mostly in the display. The Siglent was another step, again with the display since that was the major change other than frequency range 3M vs 1.5M IIRC).Much of my additional research has been done right here.Quote from: gf on August 01, 2021, 09:04:24 amNot the cost, but the hassle of selling a similar piece of equipment for a step-up especially when what I have is current and functional (minus a few features).As to the tests; for cable loss & for bad fittings for the most part.

author: videobruce
author_rank: Frequent Contributor
timestamp: August 01, 2021, 11:14:03 am
content: BTW, that Explorer signal generator used is $150 (new it's $220US).

author: gf
author_rank: Super Contributor
timestamp: August 02, 2021, 12:01:01 pm
content: Quote from: videobruce on August 01, 2021, 11:02:22 amDamping can be measured from one end, if the other end is open or shorted (i.e. 100% reflection), and if it is granted that no other reflections occur along the cable (e.g. due to defects, or bad matching). Both, the forward and reflected wave are attenuated by the damping. Therefore the one-way damping is 1/2 of the observed |S11| (in dB) then. If there are other reflections too, besides from the open/shorted far end, then it becomes difficult to separate their contributtions to S11, and damping is no longer |S11|/2, of course.Scalarreturn loss measurements are basically possible without VNA, but in addition to SA and tracking generator a directional coupler/bridge (with good directivity) ist required.This method (and its limitations) was recentyl discussed here:https://www.eevblog.com/forum/rf-microwave/can-a-siggensadirectional-coupler-be-used-as-a-poor-mans-scalar-analyzer/[ For this purpose, Siglent obviously offersthis kitas accessory for the SSA. 20dB directivity is a bit meager, though. For a scalar analyzer, good directivity is essential (for a VNA this is less important, since the vector error correction can compensate it mathematically). ]If the aim is to localize a bad connector, or a cable damage somewhere in the middle (i.e. "discance to fault"), then you need TDR. Traditionally, TDR is done in the time domain (-> fast pulse generator + fast scope), but alternatively it can be also calculated from S11 measurement in the frequency domain via IDFT. The S11 measurements must bevectormeasurements, though. It is not possible to calculate it from scalar measurements (i.e. magnitude only). Chapers 1-5 in thisapplication notegive an overview how it basically works. The presentation of the results may vary between different VNA models, but the underlaying principle is basically the same. It is also possible to calculate an impedance profile (i.e. impedance vs. distance) from the S11 measurements (no magic either -- just a variation of low-pass step processing). NanoVNA V2 firmware supports this display mode, too. I don't know if the Siglent SVA does?

author: gf
author_rank: Super Contributor
timestamp: August 02, 2021, 12:09:08 pm
content: Quote from: tautech on August 01, 2021, 10:05:52 amI missed that. In the original post he said:Quotewhich I associated withthis device. No Siglent SA was mentioned initially.@videobruce:But why do you consider a signal generator for the RF explorer, if you already own a SSA3032X, which includes a tracking generator anyway?Is there anything the RF explorer with signal generator can do, which the SSA3032X with its tracking generator could not do?