Re: sBitx antenna-first warning
Correct David.
How come so many still believe the myth that a bunch of passive elements ( antenna system) actually changes with power level?
simple, they have a crappy SWR meter. It either has poor directivity, or the indication changes because of heating in the diode / changes in the detection circuit like core saturation at higher power levels.?
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Re: sBitx antenna-first warning
This is not correct.? The output impedance of the PA does not change
the SWR and resistance/reactance of the tuner/antenna combination.
What one is really doing is tuning out the reactance of the antenna
and setting the load resistance to the design value of the
amplifier.? A reactive load increases the dissipation of the PA
finals.? Tuning at low power within the voltage and dissipation
limits is safe.
David N1HAC
On 8/3/22 3:44 AM, Ashhar Farhan via
groups.io wrote:
toggle quoted message
Show quoted text
Many recommend tuning at a lower power. This risky
as well. That is because at lower power, the output impedance of
the PA will be different. Once you are tuned at QRP level,
increasing the power will result in a mismatch again!?
- f
Unfortunatel, no. The sbitx has no way to
check the swr (yet).?
Even if it had, as we are dealing with very
high power, fiddling with the tuner for 15-20 seconds with
large mismatch will send all the 40 watts back into the
PA, destroying it.
What will work is a resistive bridge. This
will dissipate most of the power in big resistors until
you are tuned up.?
You can paraellel up ten x 470 ohm resistors
of 1 watt to make each of the three legs of the resistive
divider of the swr bridge. A DPDT switch can bypass it
once you are all tuned up.
On Wed, Aug 3, 2022, 12:21
PM Trevor Stone < tstone@...>
wrote:
In the
operating manual I see the following warning:
```
# 1. Connect the Antenna first!
The antenna jack on the back must always be connected to a
properly
matched antenna with an SWR of less than 2 on the
frequencies you intend
to transmit on. This is a recommendation for all amateur
wireless radios
but more specifically the sBitx. The sBitx can put out
upto 50 watts of
power and if the antenna does not match, it can damage the
power
amplifier transistors instantaneously.
```
Does the sBitx have the ability to tune or check the SWR
without
damaging itself, or does one need to use an antenna
analyzer before
using the radio?
I ask because most of my operation is portable, so my SWR
changes every
time I set up my station.? SWR can be high even for an
antenna of the
right length if it's deployed in a compromised position or
if I made an
error during setup (like last month when I forgot to
attach
counterpoises to an end-fed antenna :-)
Thanks,
Trevor KF0FTJ
--
=-=-=-= Trevor Stone -=- [Flwyd] -=- <tstone @ >
=-=-=-=
Computer science, eclectic philosophy, games, wits,
esoterics, odd hats
?
? ? ? ? ?Thou brazen boil-brained malt-worm!
{embrace society}? ? ? ? ? ? ? ? ? ? ? ? ? POLAROID does
it in seconds.
Calvin: The world is a complicated place, Hobbes.? Hobbes:
Whenever it
seems that way, I take a nap in a tree and wait for
dinner.
|
Re: sBitx antenna-first warning
Please forgive my ignorance but I've never understood statements like this.?
"That is because at lower power, the output impedance of the PA will be different."
Since SSB is all about audio (no audio, no power) and the average power is about 40% of peak, what happens to the output impedance every time you speak into the microphone? Power is going to follow the audio and would be all over the place, from zero to peak power. How is this any different?
Max KG4PID
On Wednesday, August 3, 2022, 02:45:06 AM CDT, Ashhar Farhan <farhanbox@...> wrote:
Many recommend tuning at a lower power. This risky as well. That is because at lower power, the output impedance of the PA will be different. Once you are tuned at QRP level, increasing the power will result in a mismatch again!? - f
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Re: A short video of sBitx working
If the receiver goes down to 10kHz you can try to catch the sendings from the Grimeton transmitter at 17.2 kHz.
or
An impressive all mechanical radio transmitter.
73 de oz9ny, niels
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Re: Postman came with a box from hfsignals
Got it "turned ON" just for a moment before heading out to my teacher pre=planning day, today.? ?Used a safe 12V wall -based laptop power supply, will need to replace with connectors for a REAL power supply.? ?Very busy week for me with a lecture to give and many meetings and responsibilities so not? sure howmuch more I will be able to do.. But it turned ON and I got into the basic receiver/transceiver screen.? ?Hooray! Gordon
Same here..and of course I'm back traveling for an extended period starting next week, so its even more torturous that its not here by the weekend so I can at least takea peek. DHL has surprised me with early delivery a few times previous, so maybe...
On Wed, Aug 3, 2022 at 05:28 AM, Peter McCracken wrote:
I received notification from DHL today with delivery scheduled for Monday (not bad since I am in Ireland) , obviously the basic kit has started to ship, will look forward to much experimenting with this :)
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Re: sBitx antenna-first warning
On Wed, Aug 3, 2022 at 02:45 AM, Ashhar Farhan wrote:
at lower power, the output impedance of the PA will be different. Once you are tuned at QRP level, increasing the power will result in a mismatch again!?
Well that's not good!
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Re: Postman came with a box from hfsignals
Same here..and of course I'm back traveling for an extended period starting next week, so its even more torturous that its not here by the weekend so I can at least takea peek. DHL has surprised me with early delivery a few times previous, so maybe...
toggle quoted message
Show quoted text
On Wed, Aug 3, 2022 at 05:28 AM, Peter McCracken wrote:
I received notification from DHL today with delivery scheduled for Monday (not bad since I am in Ireland) , obviously the basic kit has started to ship, will look forward to much experimenting with this :)
|
Re: sBitx antenna-first warning
"Many recommend tuning at a lower power. This risky as well. That is because at lower power, the output impedance of the PA will be different. Once you are tuned at QRP level, increasing the power will result in a mismatch again! "
Interesting. Every auto tuner manufacturer's instructions I have ever seen recommend that you tune at low power. I have a remote auto tuner at the base of a wire vertical that I tune on every band change. I have always tuned with low power using several different rigs over the decades and never noticed a change in SWR. I'll pay closer attention, but if I'm getting a change it has been to small to notice.
Haven't received my sBitx yet, but it looks like there's room for a small board with SWR sensing and an absorptive bridge that you could manually switch in and out. If you wanted to get fancy you could route the measure to the Pi and integrate into the display.
--
? 73
??? Bob? KD8CGH
|
Go retro and make a collage of the old logos from the past... Collins, Drake, Harmmarlaud, Hallicrafters, etc... be sure to add the builders kits like Heathkit and Eico
On Wed, Aug 3, 2022 at 6:04 AM Alan Cooper < cqw7aln@...> wrote: ?decorations: speaking of star war and star trek....
how about a layout of our solar system some where on the radio?
Alan? w7aln
On Tue, Aug 2, 2022, 10:35 PM Thomas White AD6TW < tawhitejr@...> wrote: My $0.02 are to make the monitor case a cube with a beveled sloping front as to make it easier to view the monitor when they are on a table top.?
decorations: star wars or Star Trek spaceships !
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Re: sBitx antenna-first warning
You can also get some TO-220 non-inductive resistors of a suitable
wattage, and mount those to the heatsink. 10-watt devices should be
OK, and 50 ohms is close enough.
Those devices aren't cheap, but they're effective. I use a 100-watt
50-ohm device mounted to a heatsink with an SO-239, and it's flat to
well over 100 MHz.
73
Jim N6OTQ
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Re: sBitx antenna-first warning
You can control it in software, much simpler! The main reason for not putting in an RF sensor is that raspberry pi doesnt have an ADC
I'm wondering if we could add an SWR bridge and use the reverse sense voltage to automatically fold back the RF power?? Perhaps control the gain of Q11 to accomplish this?
(I have an sBitx on order...)
73 Gody K3NG
On Wed, Aug 3, 2022 at 6:15 AM Ashhar Farhan < farhanbox@...> wrote: Scot, You have to build a resistive bridge like this :
Here, each of the 50 ohm resistors should be able to dissipate 10 watts. So, you make a 10 watt resistor by paralleling 10 resistors of 470 ohms each.? - f
Hi Ashhar,
I¡¯m a bit confused.? I get paralleling ten 470 ohm resistors but I¡¯m am uncertain how to use it.? How do you connect this arrangement (three legs) to protect the finals?? Is it in series with the antenna?? Can you sketch to wiring?
Thanks in advance, Scott
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?decorations: speaking of star war and star trek....
how about a layout of our solar system some where on the radio?
Alan? w7aln
On Tue, Aug 2, 2022, 10:35 PM Thomas White AD6TW < tawhitejr@...> wrote: My $0.02 are to make the monitor case a cube with a beveled sloping front as to make it easier to view the monitor when they are on a table top.?
decorations: star wars or Star Trek spaceships !
|
Re: sBitx antenna-first warning
I'm wondering if we could add an SWR bridge and use the reverse sense voltage to automatically fold back the RF power?? Perhaps control the gain of Q11 to accomplish this?
(I have an sBitx on order...)
73 Gody K3NG
On Wed, Aug 3, 2022 at 6:15 AM Ashhar Farhan < farhanbox@...> wrote: Scot, You have to build a resistive bridge like this :
Here, each of the 50 ohm resistors should be able to dissipate 10 watts. So, you make a 10 watt resistor by paralleling 10 resistors of 470 ohms each.? - f
Hi Ashhar,
I¡¯m a bit confused.? I get paralleling ten 470 ohm resistors but I¡¯m am uncertain how to use it.? How do you connect this arrangement (three legs) to protect the finals?? Is it in series with the antenna?? Can you sketch to wiring?
Thanks in advance, Scott
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Re: sBitx antenna-first warning
? Scott, where did you get three legs? ?If all the resistors are parallel there will be only two legs. ?Connect one to the ground of your transmitter and one to the antenna pin in your output connector. ?A dummy load connect just like an antenna. ?It replaces the antenna for testing purposes.
All my dummy loads have a BNC connector and I connect them to the BNC out connector of my transceivers. ?
Google dummy loads¡. ?You will find dozens of them and check YouTube for videos.
Dave K8WPE since 1960 David J. Wilcox¡¯s iPad
toggle quoted message
Show quoted text
On Aug 3, 2022, at 6:07 AM, Scott KE8KYP <scott_massey@...> wrote:
?Hi Ashhar,
I¡¯m a bit confused. ?I get paralleling ten 470 ohm resistors but I¡¯m am uncertain how to use it. ?How do you connect this arrangement (three legs) to protect the finals? ?Is it in series with the antenna? ?Can you sketch to wiring?
Thanks in advance, Scott
|
Re: sBitx antenna-first warning
Scot, You have to build a resistive bridge like this :
Here, each of the 50 ohm resistors should be able to dissipate 10 watts. So, you make a 10 watt resistor by paralleling 10 resistors of 470 ohms each.? - f
Hi Ashhar,
I¡¯m a bit confused.? I get paralleling ten 470 ohm resistors but I¡¯m am uncertain how to use it.? How do you connect this arrangement (three legs) to protect the finals?? Is it in series with the antenna?? Can you sketch to wiring?
Thanks in advance, Scott
|
Re: sBitx antenna-first warning
Hi Ashhar,
I¡¯m a bit confused. ?I get paralleling ten 470 ohm resistors but I¡¯m am uncertain how to use it. ?How do you connect this arrangement (three legs) to protect the finals? ?Is it in series with the antenna? ?Can you sketch to wiring?
Thanks in advance, Scott
|
Re: A short video of sBitx working
I understand the need for a low pass filter. That is needed for the IC 7300 also which I built a low pass filter for it which was easy enough. It produces real nice harmonic spurs right through the AM? broadcast band without one, and gives a normal watt meter fits because one cannot tell where the rf is getting produced is in the electromagnetic spectrum. It also causes an swr meter on the radio to read incorrectly since the reflected spurs power causes the rf foldback to activate and cut the transmit power way down.
the rf tranformer in the sBitx has me wondering... is the what would pass for an output matching network in the PA, that is being refered to ?
thanks
Alan
On Tue, Aug 2, 2022, 6:09 PM Ashhar Farhan < farhanbox@...> wrote: The spec sheet is on? You could transmit on 630 khz. I am not sure if the PA transformer inductance will be enough that low.? The exciter will work right down to 10 KHz or so.
On Wed, Aug 3, 2022, 3:02 AM Alan Cooper < cqw7aln@...> wrote: Ashhar and group,
is there a manual or something resembling a spec sheet on the sBitx available anywhere?
I am trying to figure out if it will operate down below the AM Broadcast band,? there is a lot of Ft8 used on our 630Meter band on 474 khz.
Thanks for any info or input
Alan w7aln
|
Re: Postman came with a box from hfsignals
I received notification from DHL today with delivery scheduled for Monday (not bad since I am in Ireland) , obviously the basic kit has started to ship, will look forward to much experimenting with this :)
On Tue, 2 Aug 2022 at 23:20, Shirley Dulcey KE1L < mark@...> wrote: Still waiting for my shipping notification. I've got one coming without the display and Pi.
?got #26!!!!? ?You beat me!!! but i still feel HONORED.? ?Gotta find a power connector and wire it all up.? Should have a logitech mouse/keyboard wireless in the car.? ?Tons of MEETING this week, but nice to have gotten this.? ?It came VERY NICELY PACKED.? ? My neighbor has theXiegu.....each has its points but this is a LARGE milestone in ham radio history, another one due to Ashhar!? (on the left is one of my primitive homebrew "go-boxes" for portable emergency deployments.
Gordon KX4Z
 
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The potentiometers has minimum at the "right" place. Lowest at anticlockwise position and max at clockwise position. Just like a volume pot.
oz9ny, niels
|
Re: sBitx antenna-first warning
Many recommend tuning at a lower power. This risky as well. That is because at lower power, the output impedance of the PA will be different. Once you are tuned at QRP level, increasing the power will result in a mismatch again!? - f
Unfortunatel, no. The sbitx has no way to check the swr (yet).? Even if it had, as we are dealing with very high power, fiddling with the tuner for 15-20 seconds with large mismatch will send all the 40 watts back into the PA, destroying it. What will work is a resistive bridge. This will dissipate most of the power in big resistors until you are tuned up.? You can paraellel up ten x 470 ohm resistors of 1 watt to make each of the three legs of the resistive divider of the swr bridge. A DPDT switch can bypass it once you are all tuned up.
On Wed, Aug 3, 2022, 12:21 PM Trevor Stone < tstone@...> wrote: In the operating manual I see the following warning:
```
# 1. Connect the Antenna first!
The antenna jack on the back must always be connected to a properly
matched antenna with an SWR of less than 2 on the frequencies you intend
to transmit on. This is a recommendation for all amateur wireless radios
but more specifically the sBitx. The sBitx can put out upto 50 watts of
power and if the antenna does not match, it can damage the power
amplifier transistors instantaneously.
```
Does the sBitx have the ability to tune or check the SWR without
damaging itself, or does one need to use an antenna analyzer before
using the radio?
I ask because most of my operation is portable, so my SWR changes every
time I set up my station.? SWR can be high even for an antenna of the
right length if it's deployed in a compromised position or if I made an
error during setup (like last month when I forgot to attach
counterpoises to an end-fed antenna :-)
Thanks,
Trevor KF0FTJ
--
=-=-=-= Trevor Stone -=- [Flwyd] -=- <tstone @ > =-=-=-=
Computer science, eclectic philosophy, games, wits, esoterics, odd hats
? ? ? ? ? ?Thou brazen boil-brained malt-worm!
{embrace society}? ? ? ? ? ? ? ? ? ? ? ? ? POLAROID does it in seconds.
Calvin: The world is a complicated place, Hobbes.? Hobbes: Whenever it
seems that way, I take a nap in a tree and wait for dinner.
|
David McGaw
Bob Benedict, KD8CGH
Jim K5KKB Steeb
David Wilcox K8WPE