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Antenna Impedance Confirmation

Kees T All Messages By This Member #48688 I'll make one more pass over the target................can't seem to get any interest on other threads. As far as a quick and easy "Antenna Confirmation", I still like that little circuit Don, ND6T, came up with....and maybe others out there. Just a broadband noise generator and tune for the null with the receiver part of the Transceiver. No meters, no digital values to convert (which may or may not be correct) ....just a subjectively monitored "noise dip" as you tune the receiver while the noise generator is activated. If you are in the "dip", great, hit the PTT, ......if the dip is off frequency, just retune until it's on frequency. A bit different, a bit unusual, but very inexpensive and located under the covers of the BITX with no Nano code change required.? Might be able to add a red LED to provide "null" feedback to reduce the subjectivity.? I've discussed installing it under the covers (vs externally) with Don and he tried it on his BITX-40 and says it works well.? 73 Kees K5BCQ
William Cullison #48690 Kees, I'm fairly new to the BITX group and never heard of his idea. Thanks for bringing it up again. I have always listened to the background noise to do my rough tune but like the idea. 73 Bill WA8VIH/4
Dennis All Messages By This Member #48691 Where do I find the circuit? 73, Dennis W7DRW
Kees T All Messages By This Member #48692 It's on Don's website at ND6T.com I may not be able to get some sort of visual indicator attached to it but the basic circuit and how it works is on Don's website. 73 Kees K5BCQ
Bill Maxwell All Messages By This Member #48695 开云体育 I recall building a little noise bridge, based on the 555 timer chip as I recall, for the same purpose. Worked well until one day I forgot to disconnect it before transmitting. I rebuilt it, intending to incorporate it into my homebrew atu? but never got back to that project. As I recall that would have been back in about 1979 and the original design came from an ARRL Handbook from around that time. Bill, VK7MX On 11/05/2018 8:11 AM, William Cullison wrote: toggle quoted message Show quoted text Kees, I'm fairly new to the BITX group and never heard of his idea. Thanks for bringing it up again. I have always listened to the background noise to do my rough tune but like the idea. 73 Bill WA8VIH/4
Kees T All Messages By This Member #48697 Bill, I can imaging the result of putting power to it. Activating it with a push-button and relay switching it IN/OUT of the RF line helps and is "clean". 73 Kees K5BCQ
William Cullison #48705 Kees, I guess I'll give it a try. 73 Bill WA8VIH/4? toggle quoted message Show quoted text On Thu, May 10, 2018 at 7:50 PM, Kees T <windy10605@...> wrote: Bill, I can imaging the result of putting power to it. Activating it with a push-button and relay switching it IN/OUT of the RF line helps and is "clean". 73 Kees K5BCQ
Bill Maxwell All Messages By This Member #48706 开云体育 Yes, I had planned on using relay switching to avoid a repeat, Kees. Actually I came across my rebuilt noise bridge board when packing up the shack at our old VK1 house a couple of years back. I should try to dig it out of storage and finally finish the project. 73 Bill VK7MX On 11/05/2018 9:50 AM, Kees T wrote: toggle quoted message Show quoted text Bill, I can imaging the result of putting power to it. Activating it with a push-button and relay switching it IN/OUT of the RF line helps and is "clean". 73 Kees K5BCQ
Bob KB1TEK All Messages By This Member #48733 qrpguys.com offers a noise bridge that sounds pretty similar to what you're describing... I've never tried it, but it sounds pretty nifty.
Kees T All Messages By This Member #48739 Yep, that's the idea and $15 sounds like a good price. They also have a nice write-up on how to use it. The only thing that might make it better is some sort of visual feedback. 73 Kees K5BCQ
William Cullison #48744 Yes the addition of a visual feedback gets my brain working. As a born again ham, I'm playing alot of catch up. Luckily I have been working with arduinos so I'm not lost there. 73 Bill WA8VIH toggle quoted message Show quoted text On Fri, May 11, 2018, 10:34 Kees T <windy10605@...> wrote: Yep, that's the idea and $15 sounds like a good price. They also have a nice write-up on how to use it. The only thing that might make it better is some sort of visual feedback. 73 Kees K5BCQ
ajparent1/kb1gmx All Messages By This Member #48763 Having a old Palomar noise bridge I can say its an effective and cheap tool. I also have? Daton 250 LCR bridge (can test at DC or 1khz).? Handy tools. Everyone with an antenna usually has a receiver to pair with it so a noise bridge is the? missing piece as well as a SWR bridge.? ?A wide tuning receiver like bitx as a good? tool to pair with it.? ?The beauty of a noise bridge is you can make the unknown "x" leg variable also measure the both the R and the x (or jx). As to adding a led or something other than ones ears to sense null, let me know how it works for a noise source.? The depth of the null tend to reflect two things, the Q of the masured system and to some extent the receiver. What does work well is pairing a PC/laptop with sound card/ mic input and spectrogram software and a receiver. That said an RF source and a simple resistor bridge plus a sensor (diode detector or receiver) is a hard to beat tool on the experimental bench that everyone can build and?understand. Allison
Kees T All Messages By This Member #48769 Yes, Allison, that's the idea. Thanks for your input. While we're off on other threads discussing ways to best measure SWR and power with AD8307s and S/H ADCs and trying to figure out how to minimize impact on the Nano microcontroller on the uBITX (and keep the costs down), I think it's nice to back up and think about what we really need in a QRP environment with a uBITX. Personally, I just want to know if the antenna is "good enough" and "still attached". A little circuit to accomplish this under the covers sounds like the right solution......especially if we can add some sort of visual (diode) feedback. ....some people may have difficulty with the audio null. Many hams don't understand what you can do with a noise bridge because "everyone" uses an SWR meter and assumes that is the only way to go.? ?? 73 Kees K5BCQ
Kees T All Messages By This Member #48773 What if you take the little AGC Mini-kit and drive one of those $1 three digit LED voltage readout displays they have on eBay and display the voltage. You would have to separate the power leads to the LED display from the voltage to be measured input so you can go below 2.4V (I think that can be done). You can also add a switch so it will measure uBITX battery voltage. Might work ??
Vince Vielhaber #48774 Those displays are extremely noisy. Vince. toggle quoted message Show quoted text On 05/11/2018 05:02 PM, Kees T wrote: What if you take the little AGC Mini-kit and drive one of those $1 three digit LED voltage readout displays they have on eBay and display the voltage. You would have to separate the power leads to the LED display from the voltage to be measured input so you can go below 2.4V (I think that can be done). You can also add a switch so it will measure uBITX battery voltage. Might work ?? -- Michigan VHF Corp.
Kees T All Messages By This Member #48778 Vince, I figure they would be noisy but just how noisy and can they be shielded sufficiently ? Series RF beads/chokes, etc ? Or take a real low tech approach and drive "3?" red LEDs depending on voltage level. All you are looking for is the "dip" and the battery voltage idea goes out the window. 73 Kees K5BCQ
Jerry Gaffke All Messages By This Member #48779 Kees, > Might work ?? I guess it works. Depends on what "works" means. And depends on what "AGC" means. I assume we're talking about this AGC:?? and not this one from the discussion the other day:??/g/BITX20/message/48670 Might work as a sort of linear S-Meter on receive, most would prefer the usual logarithmic S-meter at 6dB per tick. The relays pop the other way during transmit but I suppose you could rig it somehow to see a defined amount of? transmit signal.? Meter would show relative voltage, most would likely prefer to see watts (proportional to voltage squared) or maybe dBm (logarithmic). Or were you thinking of measuring something else entirely? I suppose you could add an AD8307 to the the AGC kit and measure the voltage coming out of that. An extra display is ok, but I'd just as soon keep to the LCD for this sort of thing If I need more room I'll move to a 20x4. toggle quoted message Show quoted text On Fri, May 11, 2018 at 02:02 pm, Kees T wrote: What if you take the little AGC Mini-kit and drive one of those $1 three digit LED voltage readout displays they have on eBay and display the voltage. You would have to separate the power leads to the LED display from the voltage to be measured input so you can go below 2.4V (I think that can be done). You can also add a switch so it will measure uBITX battery voltage. Might work ??
Vince Vielhaber #48785 Noise level was at least 10 over on the B40, based on how much signal I had to push thru from the service monitor. It was both radiated and conducted. Vince. toggle quoted message Show quoted text On 05/11/2018 05:46 PM, Kees T wrote: Vince, I figure they would be noisy but just how noisy and can they be shielded sufficiently ? Series RF beads/chokes, etc ? Or take a real low tech approach and drive "3?" red LEDs depending on voltage level. All you are looking for is the "dip" and the battery voltage idea goes out the window. 73 Kees K5BCQ -- Michigan VHF Corp.
William Cullison #48791 Kees, Well you certainly got this discussion going hot and heavy. Thanks 73 Bill WA8VIH toggle quoted message Show quoted text On Fri, May 11, 2018 at 6:42 PM, Vince Vielhaber <vev@...> wrote: Noise level was at least 10 over on the B40, based on how much signal I had to push thru from the service monitor.? It was both radiated and conducted. Vince. On 05/11/2018 05:46 PM, Kees T wrote: Vince, I figure they would be noisy but just how noisy and can they be shielded sufficiently ? Series RF beads/chokes, etc ? Or take a real low tech approach and drive "3?" red LEDs depending on voltage level. All you are looking for is the "dip" and the battery voltage idea goes out the window. 73 Kees K5BCQ -- ? Michigan VHF Corp.? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
Kees T All Messages By This Member #48909 Vince, Too bad that those little 3 digit $1 LED displays on ebay are noisy. I don't see many bypass capacitors on that thing. Turns out the analog input pin on that SOIC module they use (no ID markings) has an input capability of about "0" to 2.6V based on the 15:1 input voltage divider they use. A pair of $0.50 AD8307s connected to a Stockton Bridge Coupler each have a voltage output range of about 0 to 2.5V ....mmmmm. How could you efficiently scale that ? Let's see .....Green for Forward power (yes, in dBm) and Red for Reverse power (again in dBm).? ? Assume max power is 20W, that's 32V. Max input to the AD8307 is right at 0dBm or 0.225V so that's a reduction of 142 to 1 or a turns ratio of about 12:1 on the Stockton Bridge ferrites. I think that's correct. But then again, gotta work on the noise first. All the Bar LED readout solutions or individual readout LEDs look kinda cheezy..for a Noise Bridge or an AD8307 solution. 73 Kees K5BCQ

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