$15 Ebay Return Loss Bridge

[@dogastus]

Thanks for your extensive 'real world' demo of this return loss bridge, very useful.

[@KD0CAC]

James , thanks . I did end up finding , and I thought I found after several attempts and seem to remember a link on your channel , of the boxed one . By the time I found it , it was discounted down to $10 , pictures are different angles , but the location is the same . Thanks John

[@dannelson8556]

Hi James, I think you might want to review your DUT setup procedure, I've swept the ZFDC-20-5+ and a ZFDC-20-5 on my Agilent VNA and found them to be exceptionally flat, nothing like what you are showing here. One of the issues I see which concern me is you are using PL259 to SMA adapters, These are going to cause significant errors above 200mhz or so, I don't even like using them above 30mhz, let alone 400 and God forbid 900mhz Even the use of SMA to N connector adapters on the inputs to your spectrum analyzer is problematic and not recommended. I also noticed that you aren't using 6db pads on the input and outputs of the spectrum analyzer. The problem here is there is no way of knowing how the loading is affecting the stability of the tracking generator output. You should be using at least two 6db HP4991b inline attenuators to pad the input and the output of the spectrum analyzer, one on each. You should also be using dedicated cables with the proper terminations on each end. In this case, RG400 coax with N connectors on one end and SMA connectors on the other would be the proper setup and not that mess of stacked adapters that you are using. I believe a lot of the fluctuations you are seeing are the result of the PL259, crappy coax, and multiple stacked low-quality adapters all of which is causing unreliable erroneous readings. I'm also curious why you didn't terminate the unused ports of the directional couplers into a precision 50ohm load, leaving them open presented an infinite SWR. Like I said after watching your video I went ahead and swept my ZFDC-20-5+ and my ZFDC-20-5 using a calibrated Agilent VNA using the proper setup and found them to perform far better than spec. I don't have one of the Cheap China specials that you have so I can't test it.

[@jimeagle1]

Dan Nelson Your comments are valid but are covered in other videos I have uploaded previously and since this video as well as in my comments for this video. For those who can afford it, obviously more expensive cables, precision loads, precision cables, opens, shorts, etc. all improve performance. By the way, the only unterminated port in this video was during establishing an "open circuit" reference level. I revisited the performance of the ZFDC-20-5+ and by using a Low Noise, High Intercept amplifier after the -20dB coupled output port I was able to get much better results by getting the signal well above the DSA815-TG tracking generator's internal leakage level. I mentioned this problem with the DSA815 previously which causes the cyclic "beat note" waveform seen when the level of return loss approaches within 15-20dB of the TG leakage. My results upon doing this are now close to the specified performance for the ZFDC-20-5+. I will upload those findings in the future.

[@dannelson8556]

Hi James, It appears as though my comments may have been a bit premature. I've now had a chance to watch a few more of your videos and will say that you appear to have a good understanding of how to use the equipment you are demonstrating, I think I just overreacted when I saw the PL259 adapters which are basically useless above 2 meters Even then I prefer N connectors or BNCS at 2 meters. I just don't understand why hams are so stuck on that crappy 1930's connector. Anyhow, I've been very interested in that Rigol Spectrum Analyzer, its small and light weight. unfortunately, I have a thing for older HP / Agilent equipment and for what the Rigol costs with a tracking gen you can pick up a really nice older HP VNA , the drawback is they are much bigger and heavier. The pros , well they are much faster and much more accurate and of course, it can perform S11 and S21 tests. A few weeks ago I picked up an HP e8285 service monitor for $250 this is an older unit that covers from .1 to 2000 MHZ. I opened it up to take a look around and I have to say this thing is an absolute work of art with precision machined aluminum modules. Everything from the up converter to the downconverter are housed in dedicated machined aluminum, enclosures. On the high end, I checked its frequency calibration against our county's Motorola trunking control channel which is GPS disciplined and on the low end aginst our local NOAA broadcast. and it was spot on. By the way, I ordered one of those $7 directional couplers today. With shipping, they are now closer to $15

[@jimeagle1]

Wow. Your surplus dealers must be much better than the ones around here. I've not found any service monitor worth talking about for under $2000 and VNAs are usually over $5000. I don't have sufficient workspace to be able to use most HP spectrum or network analyzers anyway. As for frequency control, I have the found the DSA815 to be quite accurate and it is probably even more so if a precision 10 MHz frequency source such as the GPS disciplined or Rubidium unit is used. It would be interesting to see a picture of your sweep of the ZFDC-20-5+. You did not indicate which HP unit your were using or how much it cost and you would probably need to take a screen shot to capture a picture from it, I suspect. When you get the $7 RF Bridge you might take a couple of comparison shots... again realizing that the quality of the reference and DUT loads are probably what you will really be measuring.

[@sethlavinder]

Dan Nelson Good Lord how did you find any model HP service monitor for $250 , that’s amazing and could have saved me a bucket of money! Of course my dream machine is the HP 8920 but even at 25+ years old now I find properly optioned units still cost around the $3,500 - $4,500 range! I’m just a poor old ham operator, I had to settle for the Siglent SSA-3021X spectrum analyzer with tracking generator back when they cost $1,700 you can buy that model now about $1,400 being a hobbyist pretending to be an Engineer I still have a lot to learn. Think I will try one of these eBay specials before trying to understand why the cheapest “commercial grade” RLB I have seen is around $250

[@KD0RC]

Very nice video Jim. My little homebrew RLB from the ARRL circuit can't come close to what this unit is capable of. I just ordered one, and now it is advertised as a .1 - 3,000 MHz range due to a board redesign. My 815 only covers half that, but will be interesting to see how it compares.

[@allthegearnoidea6752]

Nice I have just made a video on using directional couplers to calculate return loss. That looks like a nice coupler for the cost. Is the swa display on the rigol a pay licence feature, I could not get it to work on my 815, the menu was grayed out. I hate the SMA connectors. Nice video regards Chris

[@kd5ozy]

I have a couple of these and they surprisingly compare well to my eagle return loss bridge. If they are hooked up correctly they work well

[@jimeagle1]

The latest versions (2017) of the open PCB bridge works quite well.

[@douro20]

60db.com sweep-tested one of these to 3GHz.

[@jimeagle1]

douro20 60dB.com has posted their results on their EBay posting. You can see the plot there.

[@davideisenberger6197]

Hi Jim! I would like to know how you are writing on the graphs? Is this a photo of the 2 Directional Couplers or the actual on screen graph? I am curious how you did this? Also, like you, I find a big difference between my ZFDC 20-4 and the Green Ukraine board. The Green board is either very generous or the ZFDC is a miser! Don't know which yet! 73's DAVID. K8KEM

[@jimeagle1]

Text on screen is done "post production", that is, I enter the screen shot into Photoshop then add text as needed on the screen capture photo. I also use Photoshop to reverse the image in some cases... especially when printing. Saves a lot of ink if the black background is reversed to white.

[@stevec5000]

James, after seeing this video I bought one of those RF Bridges but I've never been able to get it to work which is why I was confused. You show yours producing a dip at 2:40 into the video but mine would never do anything like that. Sometimes it produces dips but they have nothing to do with the resonant frequency of the antenna! I got a heavy duty directional coupler and it works great showing a large dip at resonance but this cheap one won't do anything. I've looked it over and can't see anything wrong with it physically so how did you get yours to work?

[@jimeagle1]

steve c. Send me a diagram or picture of how you have it connected and I might be able to figure it out. You do have a reference 50 Ohm load on the Reference Port, I presume. This does not connect the way a directional coupler connects.

[@stevec5000]

@@jimeagle1 It's connected the same as you show in the video at 2:25 with a 50 ohm terminator. If I substitute a directional coupler instead that works perfectly and gives a dip the same as you get but when I try the RF Bridge it does nothing at all. The unit looks identical to yours and I checked it over carefully and couldn't find anything wrong with the soldering, it all seems well connected but I couldn't check for shorts since all the elements are connected go ground at some point. It seems like a piece of rubbish and I will probably just salvage the SMA connectors and ferrite beads and toss the rest in the trash bin.

[@jimeagle1]

steve c The unit may be defective, then. I'd take it up with the vendor if I received a unit that didn't work.

[@stevec5000]

@@jimeagle1 I've had it several months trying to figure out what's wrong and probably can't return it now. The odd thing is I've compared it with the photos and it seems to be identical but it's not the same as the original design that had more resistors on the board. I still think it's a fraud and can't possible work. Videos showing this thing are a lot like all the fake quadcopter videos where they show some model flying beautifully when in reality it can't fly at all. Are you sure the one in the photo is what you actually used and not something else such as a directional coupler?

[@jimeagle1]

steve c What you see is what I used for the video. I have another video that shows direct comparisons between this unit, another bridge, and the MFJ directional coupler. I would suspect a cracked SMD chip or shorted turns in the. baling to be causing your problem.

[@KD0CAC]

Well thanks for trying . I did about 4-5 different searches with the info in video on both ebay & google , other stuff but not this unit .

[@jimeagle1]

Searching on Ebay seems to be platform specific. I had no problem finding these offerings every time I used the search phrases that I provided using my Mac computer with the Safari browser though I note that on my iPad the $15 unit was not always found for some reason. It sure would be nice if KZbin allowed links to other sites or if I could find a work around to their link filters. The $15 units are now $20 + $5 shipping. Search "RF Bridge Ukraine" on Ebay The $36-56 Boxed units that are listed by different vendors all seem to be from the same source and its performance is superior to the $15 unit. However it can only be used at 50 Ohms while the other unit could be used to check match from 30-75 Ohm (maybe even 100 Ohms) simply by changing the load on the Reference Port.

[@jimeagle1]

I thought I should mention that while this video shows the performance capabilities of the 046 RF Bridge using standard precision loads and attenuators, this particular bridge relies on the precision of the Reference Dummy Load for its calibration accuracy. Since that was a 30dB attenuator used as a load that was only specified to be better than 1.2:1 over its full range, the Return Loss shown by the 046 RF Bridge in this video should not be taken to be representative of the best performance that can be achieved using the unit. Use of ultra precision loads for both Reference and DUT ports without the use of any adapters will likely show even better performance than that demonstrated in my video. I don't have access to such a calibration kit since they are very expensive... almost as much as the Rigol DSA815-TG, in fact. However for Hobby and Amateur Radio use below 1GHz, this RF Bridge should be accurate. It should be useful even at 1296 MHz (23cm) for most requirements. (PS. I will be uploading another video soon showing the performance of a $40-50 RF Bridge that will work quite well to 1500 MHz and probably even higher.)

[@stevec5000]

James, I can hardly believe it but I finally got the unit to work after reversing the connections! Didn't you notice that problem with yours since they are also reversed in the photo at the beginning of your video? I contacted Serge at transverters-store.com who claims his units work properly but the fake Chines ones don't and asked him why the ports on his units are reversed the same as the Chinese ones but he refused to answer and blocked me with a spam filter. I think he's actually selling Chinese made ones too since the photos on his website are identical to the ones being sold from China on Ebay right down to the same bad solder joint on the Input connector SMA center pin!

[@jimeagle1]

The swept signal source (Tracking Generator) attaches to the connector labeled "Input" exactly as shown in my video. The "DUT" and "REF" ports are for Device Under Test (your antenna in this case) and Reference (50 Ohm Load) respectively just as shown in my video. "OUT" goes to the Spectrum Analyzer input as shown. (By the way, it will make no difference if the DUT and REF ports are swapped.)

[@stevec5000]

@@jimeagle1 It DOES make a difference if the ports are swapped since they work differently! The original design with the ports correctly labeled can be seen here: hiqsdr.com/index.php?title=Bridge-Circuit

[@jimeagle1]

I've looked at the article mentioned and the unit I show in the video is identical... Input on Left, DUT on Bottom, REF on Top, and Output on the Right.

[@vidasvv]

tnx for the informative video ! oh, unfortunately the RIGOL 815-TG has LOTS of bleed thru above 1GHz which looks like "ripple". Using same setup with the Siglent 3032X its pretty flat up to 1.5GHz 73 N8AUM

[@jimeagle1]

vidas v Yes this is a problem with the Rigol DSA815-TG... especially the earlier units. I know that Rigol has made at least one hardware change but I don't know if they fixed that particular problem that I showed in one of my videos quite some time ago. What are your impressions of the Siglent 3032X? Apparently it does not have the same level of leakage as the Rigol unit but it is also twice the price. However there is the 3021X which compares more Apples to Apples with the 815 though priced about $200 more. Since their Tracking Generator add on is probably separately shielded I would expect it won't have as much leakage as the Rigol unit. I did get better results from the Rigol unit by using an LNA between the Bridge output port and the 815's analyzer input port to raise the level from the 60dBm.com's output port to a level 10-15 dB higher than the 815's internal leakage.

[@stevec5000]

>Clifford Heath: This page shows the PCB tracks with the missing connections! www.ebay.com/itm/0-1-3000MHZ-RF-SWR-Reflection-Bridge-Antenna-Analyzer-VHF-VSWR-Return-Loss/253947491090. I can't see any difference between that one on Ebay and the one on the transverters-store website. Actually it looks like the one from there was also made in China! There is a note on the website about fake items from China (which seems odd for an open source device) so I emailed them about it and got a reply from Serge saying: "They have a mistake in the PCB." He wouldn't tell me what the mistake was however and his unit also has the silk screen for the Ref and Dut reversed like the Chinese ones.

[@jimeagle1]

Theoretically there should be no difference but this depending entirely on the balance capability of the Balun used on the output of the unit. I tried my unit while swapping the REF and DUT ports using a quality SMA 50 Ohm Load and the same 439 MHz Patch antenna and I got the same exact results at the Output port either way.

[@jimeagle1]

Ah! I looked online on EBay and found what appears to be a Chinese copy made by someone who doesn't know how a 1:1 Balun is supposed to be made. It is connected totally wrong thus would probably not be balanced or matched correctly. Sloppy soldering, as you indicated. It is marked as being from the transverter-store but probably isn't since it ships from China directly! Fake item for sure.

[@pottshillsanctuary5414]

Is this thing made for use of multiple receiver antennas and you don't lose gain using this device

[@jimeagle1]

This is not an SDR or a VSWR meter to be used inline between a transmitter or receiver and an antenna. It is a test instrument used to test one item at a time, It is used to check the match of an antenna, filter input, dummy load, etc. I hope I understand the nature of your question.

[@dennisqwertyuiop]

would it work better in enclosed in metal box ?

[@jimeagle1]

Probably not. 30 dB RL when measuring a precision load is adequate performance for most uses. 40 dB is typical performance for RLB bridges considered Professional Grade.

[@Cisco8484]

Can you provide a link to the ebay page? I can't seem to find it.

[@jimeagle1]

See the edited version of my video comments just below the video.

[@BerrieSchuurhuis]

searched for this on ebay.com without success. further pointers would be appreciated!

[@jimeagle1]

See the edited version of my video comments just below the video.

[@kevingray707]

James Eagleson I was wondering what function on your spectrum analyzer allows you to put the extensive text on the screen. I haven't found that function. Thanks for the videos. I find them so helpful. Kevin

[@jimeagle1]

Kevin Gray I do the extra text using a photo editor (Photoshop Elements) after saving the screen shot and transfering it to my computer. If I only want the text in the video, I simply use the video editor to add a title over the clip. If I need to print an annotated copy of the picture, I usually reverse the Color image to save ink. (That gets rid of the solid black background.).

[@dennisqwertyuiop]

is this better than your other one ? before i order one thanks

[@jimeagle1]

DENNIS N In order of performance: Boxed 1500 MHz RF Bridge $45 (Video being worked on), 046 RF Bridge $15 (Present video), then ZFDC-20-5 Directional Coupler $85 (Previous video). Other issues: ZFDC is the most rugged and smallest. ZFDC uses BNC connectors. The other two have SMA connectors. 046 is just a PC Board and requires the addition of a good Reference 50 Ohm Load (additional cost). Boxed RF Bridge has the best range and accuracy up to 1500 MHz. If you have the money, I'd get the 500kHz-1500 MHz boxed unit. You may need to buy several adapters to match the unit's SMA connectors (female) to Type N, BNC or "UHF" connectors depending on what you are evaluating.

[@dennisqwertyuiop]

I do have the boxed bridge with bnc connectors, I think your new bridge should be enclosed

[@jimeagle1]

There are a number of offerings available on Ebay. I also got a boxed unit that I will probably be using for most things that I do (video to follow). I didn't see one that has BNC connectors though this would be a good choice for much of the work I do with such a unit. BNCs are good up to about 2000 MHz with better ones reaching 3000 MHz. The advantage of the PCB 046 version is that the Reference Load can be changed to evaluate things that might be other than 50 Ohms. Examples: 35 Ohms (typical HF or VHF natural beam impedance), 75 Ohms (for TV/FM antennas) as well as 50 Ohms.

[@dennisqwertyuiop]

the one I have is a mini circuits, 15542 ZFDC-20-5

[@jimeagle1]

I cover this at 3:59 in this video. Assuming you use a good Reference 50 Ohm load on it, the 046 RF Bridge works much better than the ZFDC-20-5 for this purpose.

[@PowderMill]

😷 👍🏻 Thank you. You have a great channel . RF & duplexer tuning and you have the same spectrum analyzer that I had as my first jump into test instrumentation. This channel is ideal for CCP Chinese Communist Party Virus PLANdemic Binge Watching!! 😷🦠🤓🤣

[@KD0CAC]

Why no link ?

[@jimeagle1]

KD0CAC I can't seem to put up a link that works on You Tube. I see that others have this problem as well. Anyone know how to get around You Tube's filters?

[@DonDegidio]

Let's see if this link works. 73 WB3BJU www.ebay.com/itm/RF-SWR-Reflection-Bridge-0-1-1500-3000-MHZ-Antenna-Analyzer-SDR-VHF-UHF-SHF-/222080291102?hash=item33b504511e:g:4KQAAOSwjDZYkBFo

[@davideisenberger6197]

Thanks for taking the time to make this video Jim. I have several questions. Do u have an email ? 73's David. K8KEM

[@michaelnobibux2886]

Cascaded adapters ...not good!PL259...very bad !!!

[@jimeagle1]

Michael Nobibux See my other videos for support for what you are saying. This is the earliest video I made using this set of products. Also note my disclaimer about likely Return Loss error in my comments under the video.