Nice project Peter! I use a few of this design (slight variations) in my AM setup. I directly power headphones so I can hear my final audio... As you pointed out, also great for driving scopes :^)
+Mr Carlson's Lab Hi Paul, thank you so much! Yeah with a AM set up it is much easier as the demodulator is very easy to realise. For SSB it is a bit more effort.. Anyway enjoy a happy advent! 73
Absolutely terrific! I have been thinking of one of these for a long time. The ones available on the market are just too expensive. This is a real handy project. Thanks so much for the very useful contribution.
Great video. I really enjoy all your videos and I plan on building this project soon. I have built one in the past using a slightly different design, but this one looks very good. Thank you for the video. I always look forward to watching more videos from you!
I was going to say it’s not the easiest way to make an rf sampler but the fact it’s adjustable is a winner. I am making some videos myself on playing with RF test gear and I enjoy construction projects so will have to give this design a try. As always thanks for sharing.
TRX Bench I will be uploading my video using a simple loop in a dummy load housing later this week. When I investigated the frequency response of my rf sample it was a bit disappointing with a high pass response and 30 dB difference in attenuation between 2 and 145mhz. What was the response of your transformer coupled sampler. The idea behind my short video series will be how not to destroy your front end. My best regards Chris. I made a boob measuring a second harmonic as I had not included for the frequency response of my sampler. I would love to hear your thoughts on this and measurement errors in a future video. My very best regards Chris AKA all the gear and no idea!
Nice project, Peter. I would have built this if I hadn't bought a Kenwood SM-220 Station Monitor earlier this year. I still enjoyed watching the video. Thanks!
Nicely done Peter. If I didn't already have a Bird tap and several others I'd be warming up the soldering iron! Merry Christmas and Happy New Year! 73 - Dino KL0S
Nice 10:1 I think the hardest part was soldering that last connection lol and finding an enclosure! Really enjoyed this video, Thanks for making this! 73
Use a box with a lid so all soldering can be done easier. Stay with metal. Use a copper strap across the bottom to connect the ground side. The box has all kinds of "floating" grounding you have used. The BNC is grounded, so take advantage or that and design a proper voltage divider network. Use a coax cable and keep the shield on it except where the IRON Core toroid not a ferrite goes. Ground each end of the shield as close to the toroid as possible and at each rf connector. Use polymide tape and build up the diameter so the torrid is a snug fit and will stay in place. Use non inductive resistor for the divider network. Do not use a wire-wound resistor anywhere, especially as a trim resistor. Why is everyone still using UHF connectors. They reflect RF as low as 100 MHz. I change everything to N Type, even all my radios. Use good ones from Amphenol or King with a white bronze coating. It will not tarnish like silver. While you're at it add an AM detector to it. You will need a shield between the 2 circuits. Ig you want to go above the HF bands, you will need to use SMT and keep all leads as short as possible around the divider network and maybe shield it also if you go to 1 gig.
It's funny how things go, but I was just thinking of building some kind of device to pick off a sample signal from my transmitter for monitoring. This will certainly meet my needs. Thanks Peter
Great video enjoyed I also build one right along with you works as u said 100 watts max and resistor s in series I liked the pot. To adjust. Tnx waiting for the next one lol tnx
Just noticed the FT-747 on the bench just watched a new video #107 on The Radio Shop with you friend Buddy about the bad vari-caps on the back of the Radio that are know for failure on that radio. They are 90 degree angle and looks like good quality ones cannot be found with the 90 or as some say right angle mounting and improvised mounting is required.
Could you put a short (very inefficient) antenna on the scope input (or frequency counter or spectrum analyser or whatever) and simply Tx the transmitter close by? May be necessary to vary the distance between the two but should pick up enough signal to get a trace/frequency readout etc?
I was measuring the power output of my CB Radio simply by directly connecting my oscilloscope's probe to the dummy load. I figured that the voltage is just about 20 volts and well within the frequency range of the scope. Basically I measured the power output exactly like I measured it on audio amps, just with a different sine wave frequency (27MHz instead of 400Hz) and dummy load resistance (50ohms instead of 4ohms). So, is there something I'm missing? I understand that if you go near 50w of output power the voltages become dangerous to the scope. But couldn't I simply use a 100:1 Probe? Or does connecting the probe directly mess with the SWR? Is using an RF tap just a convenience? Or even just a well honored tradition?
Personally I would put all components on one side only and put feet on what you have used as a lid. Makes assembly much easier. Useful video though. The formula for the number of turns verses attenuation of the sample would have been useful but is available on another video on youtube.
The RF tap you have going to the Millivolt db meter,is it the same as the built unit other than not variable? Also is there a way I can use my Leader LBO-310A to test CB Radios with,do I need anything special to use it.
This is a great project Peter, thank you so much! Love your videos, very detailed. What would you do differently to make the device have relatively flat response from 1 to 512 MHz? N connectors for sure, but I'm wondering will the wire and toroid work at UHF?
Wow !! great job Peter. I like your Rhode & Schwarz URV5 milivoltmeter and I wonder if there is an equivalent modern device that can do the same functions?
Thank you for making this. hand made test gear is always nice to have. Very well explained and its purposes shown. Could you expand on it and add some type of visual indicator to it like the Bird unit? (Im Subscribed!)
Simple, effective and a much needed device. Thanks for sharing. One question, do the resistors have to be non-inductive? I have a bunch of 50ohms lying around, how can I test whether they are inductive or not?
Peter nice video, I was actually considering do this very thing, so thanks for confirming my approach. One thing I saw in your video is sitting odd with me. You design the tap with a 50 ohm source resistance then you directly terminated it to the oscilloscope which is a high impedance port and when you did the power measurement with the Rohde & Schwarz URV5 you terminated to 50 ohm load and took a bridge measurement, which depending on the probe that you used makes sense but should you also done the same with oscilloscope ?
+Michael Katt Hi Michael, yes of course you are right! To get the right figures you need to terminate it with 50 Ohm as I did it with my URV5. If you need to get an accurate measurement on your scope you need to terminate it with 50 Ohm. For my demonstration it was not necessary so I was able to skip it and only terminated the source with 1MOhm with the result of doubling the output voltage. Thanks for comment 73
Sir, if you still get messages here, I was curious. What wire did you use for the windings on the core that you created? I listened several times and do not believe I heard it. Thank you so much for taking your time to reply.
Nice. What is the model number of the tap you have going to your db meter...thinking of getting the same meter to set my variable bird RF sampler to -40dbm
How do you have your scope setup at the beginning of the video? i built this project and my wave forms look a bit different when modulated than yours did. Thanks for the neat design by the way. I have been looking to build something like this for a while and your circuit looked very simple yet flexible.
+afleak (KD0YTE) Hi Alex, well nothing special just to get a nice pattern only by try and error. I recorded a SSB pattern, may be you tried another mode?? Hope that helps..73
Nice Video, nice project! Would it be possible to directly use this tiny tool, to measure the output harmonics of an home brewed transmtiter? Or should one better use an dummy load, with an -40 dB output to connect the Analyzer/ Scope to? Thanks.
+MrVertigo1971 Hi, yes that is possible as the harmonic test is a relative measurement to the carrier (dbc). Therefore you can use this device. But if you need 100% accuracy you need to take a dummy load with a precision test output level with a flat gain over the entire bandwidth. Hope that helps.. 73s
+TheMidnightrdr Hi, thanks for stopping by. No this device is designed for 100W max it will work for a short while with 200W but not more. Hope that helps 73
thx for the great video - where can I get such a metal boxes ? This will be my first project in electronics ... thx for sharing. Can I directly build a wattmeter into the box as well ? Which cheap components could I use and how could I calibrate it without osci etc.
+Barnekkid Hi, we could calculate it but we don't need it here as it is simple as it can be.Just do some windings and check the output voltage. If it is okay for your needs fine if not put some more on the core. Check the output power over the frequency is it flat fine if not take another core material or put more windings for more induction. I only try to keep it simple of course we can handle this via maths as well. 73
hi sometimes we have a rf signal that it's not repeatitive sampling this signals requires a very high samle rate analog to digital converters how can we downconvert this not repeatitive signals and use low sample rate analog to digital converters ? is there anyway?
Hi Peter, in watching the vid a few times I see that there is mention of a 22 ohm resister. I have looked for the schematic that people mentioned but no where do I see that resister. Can you point it out to me.....confused i'm just not finding it.. Thanks I frequent your vidio's quite frequently.
I would have guessed an impedance bump , going through the box to dummy load ? My reasoning is the dimensions of RF path , coax impedance is partially made up by the dimensions between dielectrics ? Thanks again John
+KD0CAC Hi, yes you are right this is valid for coax cables. In this case it is no problem as we are far below critical frequencies where it indeed matters. Thanks for comment 73
sadly peter didn't mention the value of the pot, when i calculate 2x22ohm paralell i get 11. somethig ohm???, what is the value of the pot ,gues paralell whit the 22ohm should be 470ohm in paralel whit 22ohm, you get 22
Hi Peter, I cheated and made a separate output for my scope from my isolated SWR Meter Header box . I could then observe the RF into or out of the mobile Amp. This was for my /M CB setup before I got my ticket.
I saw in Ine of your later video's test you had a stabilblock instrument? Right? Or EM i mistaken, IG you have one, would you demonstrate IT for us? I have one here But i'm not so known to it
TRXBENCH, Can you suggest a different resistor combination ? A 22 ohm wire wound pot is rather odd, I'm trying to build your project without special ordering parts. Great videos and thanks !!
+Phil Spargo Hi Phil, well you can go down with the pot to let me say 18Ohm but you need something rough. If you can get a pot with more power just use it. The wire wound is simply the cheapest solution. But again you can use what you want material wise. Hope that helps. 73
I don't understand. The through conductor is not coaxial. Therefore, it's a step impedance change in the transmission line. Won't it send strong reflections back into the radio? How does this project avoid doing more harm than good?
Hi Peter can you put together a parts list of your projects. It will be great if you can just for reference.... Great job my friend. I will be building the project soon myself....
+Chris „Sir Cable“ Ortiz Hi Chris, not completely sure what you mean. What is missing in my schematic? Thanks for watching and good luck with the project.. 73Peter
Did you by chance check your coil with an inductance meter to see the result. I used a 22 gauge wire and got 25 actual coils on the outside of the core and it gave me 5.35uh and was able to use the center conductor from a piece of 58U Coax with a good fit.
I am building one of these samplers myself. Most all I understand. Got me Rigol products for test and measure. Was there 50 ohm terminator on scope? I could not see. Second, more important.... Can I put this sampler directly on the back of dummy load with a watt meter and use a short coax for connection to transmitter? How much coax effect? This me much easy for connecting and testing radios.
John Cundiss Hello John. The basic thing with RF wiring is that cable lengths only really matter when the wavelength of your signals approaches that of your cable. For example at 3mhz your wavelength is around 80m so a couple of meters of cable won’t effect anything. However if you working at 145 MHz your wavelength is no 2m and cable lengths have an affect and correct termination become more important. If your working in GHz everything matter. So for working in the HF bands provided you use good quality cables and connectors and terminate reasonably carefully your going to be fine. Hope this simplified explanation helps.
Has helped some and does make sense. Thank you. Built my box and got a nice flat response from the Rigol up to around 80 Mhz and that is more than good for me currently. Yea very true, the highr the frequency, the more things get very "touchy".
Why are you using a wire wound resistor (pot)? This adds unwanted inductance. Also where did you find a 22 ohm pot? I checked and they are unobtainable, at least I couldn't fine one.
+TRXBench Peter most audio applications the impedance is around 600 ohm? You state that this will not work because it is not good for low impedance, but the 600 ohm is higher than 50 ohm?
+Doctor Forbin yes supposing you are talking about PA output, as this application is designed for RF output around 100W. 600Ohm is the input impedance of audio applications with low level output...
+Doctor Forbin Well there are some dependences in RF circuits but to make a long story short let me try to simplify as much as possible. We have to fight with changing independences over the frequency, with stray losses and saturation issues this and some more effects makes it nearly impossible to control it without a toroid. As I said this answer is simplified but may give an idea on the hole challenge. 73
just found your channel a few videos ago. Very good and unique content and your english is fine - but you kind of repeat yourself, making the videos longer than needed. as a result I have ended up watching them in 1.5x mode :) Btw i'm not interested in HAM radio but electronics in general, but I watch anyway! Keep up the good work!
Thanks for feed-back. I know that there is room for improvement but it is the price I have to pay not being a native speaker. BTW I'm watching my videos for editing in 2.0x mode. Cheers
18:13 Ha, that's not a 50ohm resistor, that's only 47ohms. And what does that additional resistor across the potentiometer do? It looks to be 15ohms or something like it.
A current transformer arrangement, identical in concept to those used in power distribution, except this one is for RF!! I am going for a stupid comment record here: 0:05 - As long as you're not doing a HowToBasic video in your lab. I would cry. 3:29 - Indeed yes, everybody's heard about the bird. watch?v=aPrtFxd9u9Y
I'm confused about the 50 ohms in line series resistor as a matching device. My understanding is that a spectrum analyzer will have a 50 ohm load on the input in the analyzer and with max output of less than 1W that would be okay for most analyzers. For an oscilloscope with high impedance input then the current drive at 10 dBm could create a high voltage on the input so it would need to be pre-loaded. Aren't the 22 ohm resistors in parallel performing the actual loading to limit the potential output voltage?
+W3AMD US Hi John, oh be careful by far not all analysers can take 1W=30dBm and if they could do you are close to the rated maximum which will already create intermodulation. So never feed a SpA with that high input power!!! This game is all about Ohms law and inner resistors of a source and termination a source with a load. I would recommend you to watch my video about the Siglent SDG 1025. Although it is a product introduction I show a bit about the inner resistor and termination. 73
+TRXBench Hi Peter, I reviewed the other video. I can see why we have this conclusion. I think though that the Siglent SDG 1025 doesn't have a series 50 ohm resistor inline but is just doing math based on expected dBm to load impedance and then sets a digital to analog voltage output based on the expected load. Am I still wrong? Do signal generators and spectrum analyzers have both a series resistor inline on the output and a load resistor of 50 ohms on the input of the spectrum analyzer? This would cause half the voltage on the measuring circuit because there is a half voltage divider circuit created?
+W3AMD US Now you are right all sources like generators have a series resistor along with it's source and all SpA have a termination resistor to ground. In this network both resistors are in series and thus the voltage is split 50:50. This is called power adjustment. 73 Peter
+TRXBench Okay let's see if I am right again Peter. Danke for your answers. I think radio TX section to the antenna does not have 50 ohms in series and the radio RX section has a termination resistor to ground? This is what confused me because I assume the radio transmit is direct to the antenna so power is not wasted in a series resistor. Merry Chrismas!
+W3AMD US Ahh John now I see what you are struggling with. You should not consider the 50 Ohm to be a real resistor it is more a complex component of the TX amplifier. Any Transistor with it's inner output resistor and all the components around needs to be designed to be at least 50Ohm. A tube amplifier needs a transformer in the outputstage to convert the high inner resistor of a tube into the 50 Ohm needed at the coaxconnector. The same is valid for a RX and yes there is a (complex) 50 Ohm resistor to ground. Hope that helps. Merry Christmas! 73
Neat project! I've been inactive in amature radio for a while now, but interested in getting back into it, so I'm getting ready to upgrade my ticket. Could someone fill in a few build details for me? I seem to count 13 turns on the core. What would a recommended core be? I have a couple small ones sitting on the bench now, but am not sure if they would be suitable for this build. I also believe I saw that the pot was a 10K ohm. Would this be linear or log taper? And lastly, it was hard on my screen to see what the value of the parallel resistor to the pot was. I'm kinda leaning towards 15 ohms, but the second color band was hard to see clearly. These appear to be maybe 1 or 2 watt resistors - is that something I should be concerned about? I think I would like to really run with this design and include a single pole, multi throw switch where I can have a calibrated fixed attenuation for each band, plus a variable attenuation option as well. Thanks in advance for any suggestions! 73's KF4JXP
+Donald Ohse (W5DRO) Hi Donald, this is a RF current transformer and we need to keep the impedance low to get together with the 47Ohm series resistor a more or less stable 50Ohm output over the entire frequency rage. Hope that helps 73
Hi Peter ... I will be building this kit … could you please tell me the requirements (toroid size, pot, resistors, wire for toroid … ) Hope you can help me Peter … Mike M0csi ...
Hi William, that comes from the past when a scope only had very limited bandwidth or a scope was totally missing. With demodulating the hf you was able to hear the af tone and thus it was proven that hf is going through the circuit...hope that helps 73
Thank you very much that really helps,Sincerely William C. Colvin. I was going to use an SC-239 Tee and come off the side connection of the Tee with a straight through RF Sampler, but did not know if I needed the Demodulation Circuit.
Good one Peter. I plan to build one. Question! Do you see any problem with installing an additional toroid for VHF frequencies and using a selector switch to switch between them. Keep up the good videos. I really look forward to them. 73s, Dave
+wb8vqv Hi Dave, well this unit is designed to work up to 30MHZ if you go over 100MHZ it becomes critical as all frequency above 100MHZ needs a special handling. All is getting worse if you have a switch in between... no way with 100MHZ. It is of course possible but it needs to be designed different. Hope that helps 73
