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Doesn't Hiroki's video disprove that?
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There's another possibility: the zener is so weak, it blows open the instant the transmitter comes on.
Here is an empirical proof to show how a single 1N4756 zener diode actually protects against high SWR.?
I ordered a bag of 10 1N4756As. I won¡¯t need all of them. Anyone who needs one would be welcome to get it from me on Friday (if they arrive before then, if not another Friday.)
Hiroki AH6CY
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My guess is, it isn't across the RF output.
Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
Here is an empirical proof to show how a single 1N4756 zener diode actually protects against high SWR.?
I ordered a bag of 10 1N4756As. I won¡¯t need all of them. Anyone who needs one would be welcome to get it from me on Friday (if they arrive before then, if not another Friday.)
Hiroki AH6CY
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On Jun 11, 2024, at 09:17, Jeff Reagan <jeffreagan@...> wrote:
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My guess is, it isn't across the RF output.
Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
There are pictures of both rigs with diode installed at the beginning of this thread.?
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My guess is, it isn't across the RF output.
Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
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Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
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Oops. I tend to give people the benefit of the doubt. It begs the question, where was that zener really connected?
Cooy and paste from above: "I? strongly encourage you to install a 1N4756A diode between rf and ground."
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I built a 6 meter rig back in high school.? I had a WA8 call and collected QSL cards from 20 states.? Then I move to CA and channel 2 TV brought that to an end.
Last year, I got motivated to get back on the Magic Band. While thinking about antennas, a local ham said he was selling his 5 el Cushcraft. Virtually the same as I once had. I put it on a 30 ft push up.? I started with my 705.? Then I found the 706 that had been sitting in a box for some years.? After several calls to West Mountain tech support, I got both rigs to do FT-8.
This was just in time for the '23 June VHF contest.? I knew from past experience that 6 tends to be good around the summer solstice and sometimes good around the winter solstice.? I couldn't believe the number of simultaneous decodes I was getting.
Now the "not so good part".? Virtually all activity on 6 is now FT-8.? I've tried numerous times without success to make any QSO's on SSB or.
Just now, I am in OR.? Grandson graduated HS this weekend.? Hope others had fun during the past contest.
On Tuesday, June 11, 2024 at 12:59:20 AM PDT, David via groups.io <dkvarn@...> wrote:
...meters, that is. I have a vintage Heathkit SB-110A 6-meter transceiver that I purchased c. 2000 and am considering selling on ePay. I was hoping to get it going for the first time this past weekend (I have a pretty good rig backlog) and using it on SSB during the ARRL VHF Contest. I did the usual vintage rig prep. Unfortunately the transmit section seem kaput, but the receive section seems to be working.?
I did not hear the expected SSB signals--did any of y'all? I did hear tones around 50.16 and 50.31 MHz--I understand the latter is FT8, yes? As to the former, online info indicates that it is used by Radio Scouts / Jamboree on the Air, JOTA. Anybody familiar with that?
A member recently mentioned that to test an SSB transmitter, one could use a phone app to generate FT8 audio, play the phone's audio into the mic of the transmitter and use PSK Reporter as a reverse beacon.?
How about the inverse, i.e., play FT8 audio through an SSB rig's speaker and use a phone app to listen and decode the FT8 signal (?) I could more fully verify the SB-110A's receiver operation that way.
I'm also thinking of doing a video including the received FT8 audio and posting the video in the eBay listing.
Thanks, and best, --David KM6RI
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I totally agree.? With the one diode as originally proposed, it would clip the waveform and generate harmonics.
On Tuesday, June 11, 2024 at 01:12:22 AM PDT, David via groups.io <dkvarn@...> wrote:
My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
https://resources.pcb.cadence.com/blog/2020-what-happens-when-you-connect-zener-diodes-in-series
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Cooy and paste from above: "I? strongly encourage you to install a 1N4756A diode between rf and ground."
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David: you would be correct, if the zener were placed across the RF output. Then it wouldn't work at all. The zener would probably blow right away.
I got the impression this zener was placed in parallel with the FET, to clamp the peak voltage.?
AC voltage can't appear across a FET. FETs have both an Avalanche-Mode breakdown characteristic (resembling an internal power zener), and an intrinsic diode (also resembling a power zener). This internal parasitic diode is antiparallel with the switching part of the device.
My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
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My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
https://resources.pcb.cadence.com/blog/2020-what-happens-when-you-connect-zener-diodes-in-series
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...meters, that is. I have a vintage Heathkit SB-110A 6-meter transceiver that I purchased c. 2000 and am considering selling on ePay. I was hoping to get it going for the first time this past weekend (I have a pretty good rig backlog) and using it on SSB during the ARRL VHF Contest. I did the usual vintage rig prep. Unfortunately the transmit section seem kaput, but the receive section seems to be working.?
I did not hear the expected SSB signals--did any of y'all? I did hear tones around 50.16 and 50.31 MHz--I understand the latter is FT8, yes? As to the former, online info indicates that it is used by Radio Scouts / Jamboree on the Air, JOTA. Anybody familiar with that?
A member recently mentioned that to test an SSB transmitter, one could use a phone app to generate FT8 audio, play the phone's audio into the mic of the transmitter and use PSK Reporter as a reverse beacon.?
How about the inverse, i.e., play FT8 audio through an SSB rig's speaker and use a phone app to listen and decode the FT8 signal (?) I could more fully verify the SB-110A's receiver operation that way.
I'm also thinking of doing a video including the received FT8 audio and posting the video in the eBay listing.
Thanks, and best, --David KM6RI
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Chelegence MC-750 vertical
Does anyone have any experience with this antenna?? I would love to hear about it.? Doug
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Re: How do I delete a group
I knew it.? After a couple of hours fiddling, I realized that you probably can't do it on the phone, and I was right.? Went to laptop and solved problem.? Sorry for troubling the group.? Doug
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I have several groups.io groups that I haven't used in a long time.? ?How do I delete them
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So glad!!? Big props for them
On June 10, 2024 1:28:37 PM PDT, "David via groups.io" <dkvarn@...> wrote:
I sent a message to Steve (Alpha pres) with full set of pix and received a reply within a few hours. Another tuning box will be sent right away along with a return label. He said that the boxes are tested at three points within the tuning range, that this process must have missed the problem and that they are revising the test procedure as a consequence. Speaks well for them IMO.?
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Re: What happened to the bands? 20m is dead
You might want to look at
Paul
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David, woohoo! 73, Eric NF6S
ex WD6DBM
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On Mon, Jun 10, 2024 at 1:28 PM, David via groups.io <dkvarn@...> wrote: I sent a message to Steve (Alpha pres) with full set of pix and received a reply within a few hours. Another tuning box will be sent right away along with a return label. He said that the boxes are tested at three points within the tuning range, that this process must have missed the problem and that they are revising the test procedure as a consequence. Speaks well for them IMO.?
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I sent a message to Steve (Alpha pres) with full set of pix and received a reply within a few hours. Another tuning box will be sent right away along with a return label. He said that the boxes are tested at three points within the tuning range, that this process must have missed the problem and that they are revising the test procedure as a consequence. Speaks well for them IMO.?
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Jeff Reagan
David
Cliff Sojourner K6CLS