Відео

Take more heat away from this design? I would think it would.

The cable/test leads are the ones in the video. Sorry, but I am not clear on how you explained your test setup.

Good to hear that! Hope it works out for you.

Please do that Mike and let us know what you find out! 73's

I agree if the common leg is open. I am guessing its by design. The manual has a contact for tech support. I just may give them a call and report back. Thanks for the comment!

@@rfburns3472 Did you open the box and confirm with a VOM?

You have a very good question. Look at the video starting at 4:00. Here you can see the device impedance is flat from 1 MHz to 30 Mhz. It's 49 Ohms and with basically no significant reactance indicated on the VNA. So, shortening the length of the connectors does not affect the test results in any negative way. What does improve shortening the distance is a better response from 30 MHz to 650 Mhz. After 650 MHz the return loss goes off the rails as shown below. The terminator is good to 650 Mhz. These measurements were the worst case at 650 Mhz. Return Loss: -20.6 dB SWR: 1.206 Z = 44.6 ohms -j7.1 S21 Insertion Loss: -3.93 dB

Hi Joe. Got them from DigiKey. www.digikey.com/en/products/detail/fair-rite-products-corp/0444164181/8594097?_gl=1*lkn6ue*_up*MQ..&gclid=EAIaIQobChMI2feL75D_iAMVMjYIBR0fsAFTEAAYAiAAEgJvxPD_BwE

@@rfburns3472 Thanks for your novel approach with this project and expedient response. Joe

@@joes6718 Your welcome Joe. I am working on a tester with a amplifier for folks who have very low common mode currents.

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. ua-cam.com/video/KTCMJNP9fUw/v-deo.html 73's

@@rfburns3472 That is one of the most helpful responses someone has given me on UA-cam. 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.