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Agreed

Thanks Patrick! I been burned plently of times by RF.

I purchased mine on eBay. The AM broadcast band radios are a bit rare, but they come up every now and then for auction.

That's a very good question. The problem is connecting anything to the resistor termination leads would cause a massive disturbance in the desired impedance. You might have a better chance using a thermoelectric system to transfer heat into electricity. The fan I used with a 9.1 volt battery draws .240 amps. That's 2.2 watts of power.

Agreed. They are new to me so I need some time to prove their reliability.

Your welomce Bill and thanks for your comment.

Glad you liked the tester! Stay tuned to the channel as I will be adding an RF amplifier to increase the sensitivity for use with low power transmitters.

Welcome to the channel! As demonstrated in the video, the two resistors can be whatever wattage you have on hand as long as they are noninductive. But, let's say instead of using the NanoVNA as the source, and you use your transmitter, you may easily burn up those resistors that only have a 1 watt rating. This would depend on how much power you apply to the UNUN's 50 ohm connection point.

Thank you kindly Arnold! The best way to get the diagram would be to contact Charles Smith, KV4JT. His email is good in ORZ.com. Charles says, "I have manuals...... The cost is minimal. If you want a manual please contact me at my email address and I will arrange to send you one. I only mail manuals. I do not post them anywhere else.

Hi Dean. Let me know how your tests work out. I extended the 4 screws on the SO-239 to make a pressure fit on the flange resistors just below. I was somewhat disapointed to find thre was no improvment noted on the NanoVNA. It's possible the copper clad bridge connecting the 4 spacers to the heat sink was still having an affect on the measurement's even with a more direct connection. 73's

Thank you Andrew! Take a look at some of the CPU coolers that could be used for a heat sink. Just be careful when mounting the flange resistor to not drill into the "heat pipes" that run through the sink's mounting plate. I like this one for dissipating lots of heat. Might be overkill however. www.amazon.com/Thermalright-Peerless-SE-Aluminium-Technology/dp/B09LGY38L4?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&smid=A1BCKG4OE2CKC4&th=1 The problem with this one is you cannot drill into the plate due to the 6 heat pipes running through it. Some other means of pressure mounting must be used. Let me know how your project works out. 73's

Thank you Clems. Wish I would have figured that one out before I did the video! Live and learn. LOL

Boy did I mispeak! Thanks John for kindly bringing that to my attention. I did a correcton using a subtitle in that segment of the video.

Glad you liked it Bob! Stay tuned to the channel as I am coming out with a improved version which will have an RF amplifier to increase the sensitivity for low power transmitters. The frequency I used was 14.25 MHz I only intended it for use between 1 to 30 Mhz.

Hi Andrew and welcome! From my testing in the video you can see how poorly the DL performs above 60 Mhz. I have come up with a much better design based on what you just stated...reducing the physical distance from the resistor flange to the coaxial connector. SWR is now 1:0:1 from 1 MHz to 220 MHz and 1.1:1 at 450 MHz. Part 3 video coming out this weekend.

You certainly can do so. I use them too but wanted to experiment with incorporating it into a smaller SMA package. As an aside, when you use a BNC tee (or any external adapter), you are adding a stub to the signal. You will see the impact of the stub at frequencies greater than 1 GHz which is certainly beyond the reach of my o-scopes.

Thank you Hman! Something to keep in mind. Keep the coax leads short as possible. Additionaly, I am using 100 watts of transmitter power for this demonstration. You will need enough power to get a full scale meter deflection when calibrating the tester. QRP power will not work. With low power, a active amplifier should be incorporated in the test device. I may do this in a future video. Let us know how it works out for you!

Thanks a lot for the tips. Looking forward to seeing the active amp.

@@handyman7147 Actually, I just purchased the Surecom S11 FS Meter and will do a video on it. It has an rf amplifier built in. www.amazon.com/Mcbazel-Surecom-Portable-Strength-Antenna/dp/B092SCDDWH/ref=cm_cr_arp_d_product_top?ie=UTF8

I appreciate your comment Arnold. More video's to come.

Go for it Robert! And, thanks for the tip on IR false readings.

Please see my new video Part 3 soon to hit the channel with an improved version of this DL. It has much better performance from 60 MHz to 600 MHz. So far, the heat pipes are doing well but I will keep an eye on them going forward. Thanks!

I agree. The two resistors measure 100 ohms and in parallel the dc resistance is exatcly 50 ohms. So, each resistor should dispate the same amount of heat. It could be I was not getting a good placement of the IR gun on each resistor.

Thank you. I appreciate your kind comment!

Thanks Kult! In video Part 2, I pushed 340 watts into the DL for 2 minutes. The ambient temperature was 85 deg F. The highest resistor temperature was 188 degrees F. The temperature delta was 103 Degrees F. About all my amplifier can put out is 400 watts with a new set of tubes so, for now, the DL is handling the power quite well. 73's

That's a very good question Jason. Most commercially produced radios "should" meet the minimum emission standards of 47 CFR § 97.307. But.....after WWII, many hams purchased surplus military transmitters that were rich in harmonics and caused terrible TVI and harmonics of the fundamental frequency. There are many in use today. Therefore the need for an external LPF. Today, there are many home brew transmitters and linear amplifiers that may require a LPF. See my video where I purchased a DIY linear amplifier kit from China. It definitely needed a LPF. ruclips.net/video/KTCMJNP9fUw/видео.html 73's

@@rfburns3472 That is one of the most helpful responses someone has given me on RUclips. Thank you so much for replying. I appreciate this so much. Very kind to share your knowledge and time in such a helpful way to a “newer” ham. Thx.

@@KD9ZHF Your welcome Jason. Glad to have you aboard!

You might be correct to some degree Jerome. High quality 259/239's are rated to 300 MHz while Type N's are rated to 11 GHz. SPOILER ALERT! Part 3 video will be a TYPE N female connector and a somewhat different construction arrangement.

Good for you Sawyer! Getter done and lets her about it soon! 73's

Same here Ben. Amazing stuff we now can get our hands on these days!

@@rfburns3472 hunh ... not the first time: YT just evaporates my comment when my Edit fails. Anyhow: when I see stuff on having Arduino feeding digital readout my mind got into a whirl! cheers

Thank you kindly John. I have a new improved version coming out soon in Part 3. Maybe in a week or so.

Thanks Mike for your positive comments! I still hope do a video on how I constructed the toroidal sensors.

Thank you! It's a HP desktop CPU fan from eBay. www.ebay.com/itm/155725388653?epid=16019326502&itmmeta=01J4A7VFB81Y6JG9Y2WPMBKV2X&hash=item2441f4db6d:g:UW0AAOSwAkpk35kT&itmprp=enc%3AAQAJAAAAwPqwypUvCxpBPw%2BrJ47ipAppoGxF5B8PR3pQeFbSZslJh0c7oSDOa8He2VOZNlnHtsVzX9Us59x%2F8E4h%2F5wsTvor8w8MnmnMAtlSwrsQMijsrnEv0Y0R9XsjfJrPgjqGAs%2BC%2FbVisrqnfk%2FNFqm6QIH8Zhjjkf99xDnmXSZMko6Uk9P2tyoWTE5xxzwX8kYa9Ys5PMGJby3GuAH3fbAUAwtRqnyI6W5wPi9fqd9D32bXf%2Fvg2UNa%2FXrIyYbyeeCqog%3D%3D%7Ctkp%3ABk9SR-r17ceiZA

73's

100% agree and I will test the fan with 12V in the next Part 3 video.

Thank you Dean. I am glad it was brought to my attention so I could do the test the correct way.

I placed the parts info in the "Description" in both video's. Thanks for your nice comment!

@@rfburns3472 Thanks again. Great video. I think I'm gonna try this build too. Possibly propose this as a project for our Build a Thon we have monthly at our ham radio club.

@@deanberglund2332 You might want to wait a bit as I am building up what I think will be an improved verison of this DL. The same type CPU heat sink/fan will be utilized with a much better UHF/VHF resistor. I should have the parts in a few days and will have the Part 3 video published up soon. Thanks for watching!

@@rfburns3472 Thanks for the heads up but I already ordered the resistors. They aren't that expensive so not all is lost. I will try to wait till you come out with Part 3 to see what happens. Thanks again. 👍

@@deanberglund2332 Your welcome Dean and hope to get that video up next week or so.

I just added the source for resistors and CPU heat sink in the "description". I believe you are correct that adding the solder wick will improve the SWR. Standby for that change in video Part 3.

Oh boy, how did I miss that! Sure enough I was on S21 and not S11. The RL did look too good to be true. Thanks OM for pointing that out! I also agree with you about the ground situation. Additionally, I would like to try resistors that do not have the double tabs like I used. Not sure that would help the SWR at VHF/UHF freq's. But the length of the grounds certainily can be addressed. A Part 3 video will be forthcoming after some aforementioned adjustments. 73's

@@rfburns3472 I noticed it because it was a bit too good (1.05 VSWR is -33dB, 1.01 is -46dB, 1.0001 would be around that -90dB. I used an online calculator for those, I only know that 1.5 is around 13dB), and that it did not change at all, even when the SWR got very bad. I'm not that familiar with those resistors (altough a friend of mine also ordered some, might build a similar thing in the future), is the bottom of it also ground? If yes, using a proper 50 ohms feed (maybe on a PCB) it can even go to microwave frequencies. Well, even without that, but I'm not sure.

@@rfburns3472 I'd enjoy seeing a part 3 video when it comes out. Thanks.

@@deanberglund2332 It's in the works....thanks!

@@HA7DN After reading your first comment, I changed the return loss from S21 to S11 and got results in line with your online calculator and this conversion chart www.amphenolrf.com/vswr-conversion-chart The bottom flange is NOT grounded. The resistor has two tabs and the flange is "floating". I may replace these with the grounded flange type to see if there is any improvement in the SWR.

I came here to say that.

And I'd enjoy a follow up video with it calibrated

@@jonathancotner7040 I will demonstrate that in the next Part 3 video where I will also build another DL using a single higher frequency Aneran flanged resistor and Type N connector. Please stay tuned as this might be an interesting improvement at the VHF/UHF frequencies.

@@jonathancotner7040 And you would be correct! Thanks

Thank you for the nice comment. There is always some room for improvement such as using one resistor instead of two. This might give better VHF/UHF SWR performance.

I agree. The dynamic range of the NanoVNA was exceeded and appearing almost too good. I also should have recalibrated the VNA for the 220/440 MHz range and possibly got a better SWR. Your cantenna is a great way to go with your 100 watts.

Thank you so much for the complement!

You are correct. But, there are occasions when transmisions into the dummy load may require some extended time. Let's say I want to run a audio frequency sweep on my AM transmitter. This may require quite a bit of extended key down time. Thanks for your kind words!

​@@rfburns3472 You should redo the video. The s21 for s11 mistake is terrible.

@@jspencerg I acknowledged my "mistake" in CC (closed caption). "Whoops! He made a misktake. The return loss was not on S11. It was later measured at -32 dB @ 30 MHz." I am working on a Part 3 video which will display it correctly.

Thank you! I got these on eBay....Normally Open Thermal Switch Temperature Sensor Thermostat KSD-01F 50

I'd be happy with just the part number. :)

@@deanberglund2332 I added it in the "Description".

@@deanberglund2332, you remind me of when I got a job testing spy satellite subassemblies, and each of the 1k pull-up resistors on the board (through-hole days,) had a tiny serial number on it and a 24 hour burn-in thermal curve document, all time annotated, room temperature logged, dated, signed, and stamped with the stamp of the person certifying the results, plus the make, model, and serial number of the piece of equipment that recorded the results for that 1k pull-up resistor. That was when I knew I'd made the big-time in the electronic-test world. :)

@@johnwest7993 Awesome and productive post. I'm sure you feel better about yourself now. :)

Funny you should say that as I thought about it when I was watching the fan during the first test. Good idea WECB640! Has anyone tiried that?

@@rfburns3472 I think you'd be the first. Give it a try when you have time to experiment. The beauty of the RF power running the fan is twofold. 1. No more dead batteries that leak. 2. The fan is on when RF is applied, so there is no wait time for the thermal mass of the heatsink to trip the sensor and enable the fan. It should run cooler overall as a result. 73 OM

​@@WECB640 Your idea sounds "cool"❄but I'm afraid tapping onto the resistor network may cause a prohibitive change in the desired 50 ohm impedance. How about a thermoelectric generator that turns heat into electrical energy? Probably not enough heat to run the muffin fan though. 73 to you!

Lm317 and some fat resistors can fit all in the battery box

@@MichaelOfRohan That would work. I found some rechargable lithium-ion 9V batteres that outlast the alkaline one I was using. www.amazon.com/Quzmo-Rechargeable-Lithium-ion-Multimeters-Walkie-Talkie/dp/B0CRYS8NYH/ref=sr_1_38?dib=eyJ2IjoiMSJ9.cEZnn1YZw9BvOkaWPQtAURTu01r4O5FAWpMbsHUpmjHGQvWCO1VuevpA6LTRUbwLPsI50NI3FnyxlhnhnlRiFpDPtsuvA7FgHIU8ZQ1jVU_oSRim8jA6-BTbELzKXYtcBOIzNS6eOIpcN3cbL18AardEpXSPatY4gTvDAeYO8NIurWU65_nRmiKpn6XYk0TqoIDzY8JYP33SsFKDTaN-O3Rup4ZwAw22MWx0jjMEk0sU4E9oWZ5ZlKpJtAkGppA-Yz1ehgMSTPjCAkLrj0WW9KQI430ErQVaYGpToIkoap0.svWl3QCfyw-MuM9R7HDW98LJd3S968CjUp6opabvKdE&dib_tag=se&keywords=9%2Bvolt%2Blithium%2Bbatteries&qid=1722625501&sr=8-38&th=1