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Re: sBitx antenna-first warning

 

On Wed, Aug 3, 2022 at 10:58 AM, Ashhar Farhan wrote:
The design question is, should we go for more expensive and difficult to get RF transistors or just use inexpensive IRF series and keep many spares?
Farhan,

The answer to that question would depend on instructions or guidelines that would minimize the occurrence of the failures.? If there is no way to use a tuner without a high risk of finals failure, then we need to go to the more robust part.? If there is a method to use a tuner that reduces risk, then I would vote for the lower-cost device.? This also depends on the devices' cost difference.? A dollar or two is low enough to change.? $20 is too high to change.? Between the two is a matter of how clear the guidelines on proper operation of the radio are.

We are still in the early adopter's phase of the sBitx.? That is clear on the purchase page that risks need to be accepted by the purchaser.? It is up to us to develop the guidelines and evaluate the risks.? I believe that is what I have signed up to do.

I like that we start with lower-cost parts, as failures are likely even with more robust parts.? If I make a mistake, the cost to correct it is minimized.

Above are my opinions, which may be wrong.
73
Evan
AC9TU
Can't transmit FT8

 

The builtin FT8 reception works great.? I'm hearing stations from around the world.

However, I'm having trouble transmitting.? Software has been updated to the latest available today.? I've entered my callsign and grid square.? FT8 mode is semi-auto.

Clicking on a received CQ line doesn't seem to do anything.? Pressing the CQ button causes sBitx to exit.

Any ideas?

Thanks & 73,
John WB2OSZ
Re: sBitx antenna-first warning

 

The RD16HHF1s are no longer in production. There are some really good parts from Nexperia. They have no easy names like 807 or 6146. They have names like AFT05MP70. Why have short names when you can make up names that can't fit on the package?
- f

On Wed, Aug 3, 2022, 9:45 PM Jack, W8TEE via <jjpurdum=[email protected]> wrote:
We went through that same questioning process. Someone dinged us a few days ago because we're using the IRF510's. Out answer may be different because we are aiming the T41 at experimenters who may well blow a few while they're experimenting. Since we bought a bunch several years ago and still have some left, that's what we went with. If enough people are upset about the power drop above 20M, I'm sure someone will replace the PA board. Also, we felt a lot of experimenters have experience with the 510's and probably have some spares. Also, they're still easy to find (Mouser have 27000+!).

Your situation is different in that changing the PA would be a little harder. Also, assuming they have spares is, perhaps, less likely. Also, I searched for the RD16HHF1 at Mouser and Digikey...nada.

Jack, W8TEE

On Wednesday, August 3, 2022 at 11:59:04 AM EDT, Ashhar Farhan <farhanbox@...> wrote:


I guess the best way out is to use a robust transistor pair like the RD16HHF1 which can withstand infinite SWR, match the antenna regardless of the impedance at either end with an inline swr meter.
Remember the ol' 807 transmitters with a Pi network? You just did a dip and load until you came up to the full power.
The design question is, should we go for more expensive and difficult to get RF transistors or just use inexpensive IRF series and keep many spares?
- f

On Wed, Aug 3, 2022, 8:33 PM Jerry Gaffke via <jgaffke=[email protected]> wrote:
Not sure which statement that would be.
I've been making lots of them.

A resistive SWR meter assumes that the transmitter wants to see a 50 ohm resistive load,
but the transmitter will not necessarily work best at exactly 50 ohms.
For example, assume we are operating at 30mhz and there is a long trace to the antenna connector.
The antenna system would want to have a little bit of capactive reactance to counter the inductance of that trace.

Not much point to worry about such minor issues.
We just need a reasonably good match between transmitter and the antenna system,
doesn't have to be perfect.? You could spend a career trying to understand everything
that could go slightly wrong here, many people do.

Jerry, KE7ER


On Wed, Aug 3, 2022 at 07:45 AM, Evan Hand wrote:
Jerry,

A resistive bridge SWR meter should not work if this statement is true.

Am I missing something here?
73
Evan
AC9TU

--
Jack, W8TEE

Re: sBitx antenna-first warning

Jack, W8TEE
 

We went through that same questioning process. Someone dinged us a few days ago because we're using the IRF510's. Out answer may be different because we are aiming the T41 at experimenters who may well blow a few while they're experimenting. Since we bought a bunch several years ago and still have some left, that's what we went with. If enough people are upset about the power drop above 20M, I'm sure someone will replace the PA board. Also, we felt a lot of experimenters have experience with the 510's and probably have some spares. Also, they're still easy to find (Mouser have 27000+!).

Your situation is different in that changing the PA would be a little harder. Also, assuming they have spares is, perhaps, less likely. Also, I searched for the RD16HHF1 at Mouser and Digikey...nada.

Jack, W8TEE

On Wednesday, August 3, 2022 at 11:59:04 AM EDT, Ashhar Farhan <farhanbox@...> wrote:


I guess the best way out is to use a robust transistor pair like the RD16HHF1 which can withstand infinite SWR, match the antenna regardless of the impedance at either end with an inline swr meter.
Remember the ol' 807 transmitters with a Pi network? You just did a dip and load until you came up to the full power.
The design question is, should we go for more expensive and difficult to get RF transistors or just use inexpensive IRF series and keep many spares?
- f

On Wed, Aug 3, 2022, 8:33 PM Jerry Gaffke via <jgaffke=[email protected]> wrote:
Not sure which statement that would be.
I've been making lots of them.

A resistive SWR meter assumes that the transmitter wants to see a 50 ohm resistive load,
but the transmitter will not necessarily work best at exactly 50 ohms.
For example, assume we are operating at 30mhz and there is a long trace to the antenna connector.
The antenna system would want to have a little bit of capactive reactance to counter the inductance of that trace.

Not much point to worry about such minor issues.
We just need a reasonably good match between transmitter and the antenna system,
doesn't have to be perfect.? You could spend a career trying to understand everything
that could go slightly wrong here, many people do.

Jerry, KE7ER


On Wed, Aug 3, 2022 at 07:45 AM, Evan Hand wrote:
Jerry,

A resistive bridge SWR meter should not work if this statement is true.

Am I missing something here?
73
Evan
AC9TU

--
Jack, W8TEE
Re: sBitx antenna-first warning

 

I guess the best way out is to use a robust transistor pair like the RD16HHF1 which can withstand infinite SWR, match the antenna regardless of the impedance at either end with an inline swr meter.
Remember the ol' 807 transmitters with a Pi network? You just did a dip and load until you came up to the full power.
The design question is, should we go for more expensive and difficult to get RF transistors or just use inexpensive IRF series and keep many spares?
- f

On Wed, Aug 3, 2022, 8:33 PM Jerry Gaffke via <jgaffke=[email protected]> wrote:
Not sure which statement that would be.
I've been making lots of them.

A resistive SWR meter assumes that the transmitter wants to see a 50 ohm resistive load,
but the transmitter will not necessarily work best at exactly 50 ohms.
For example, assume we are operating at 30mhz and there is a long trace to the antenna connector.
The antenna system would want to have a little bit of capactive reactance to counter the inductance of that trace.

Not much point to worry about such minor issues.
We just need a reasonably good match between transmitter and the antenna system,
doesn't have to be perfect.? You could spend a career trying to understand everything
that could go slightly wrong here, many people do.

Jerry, KE7ER


On Wed, Aug 3, 2022 at 07:45 AM, Evan Hand wrote:
Jerry,

A resistive bridge SWR meter should not work if this statement is true.

Am I missing something here?
73
Evan
AC9TU
Re: A short video of sBitx working

 

There's an excellent wikipedia article about this transmitter:??https://en.wikipedia.org/wiki/Grimeton_Radio_Station

"The Grimeton transmitter is the last surviving example of an Alexanderson alternator, the only radio station left from the pre-vacuum tube era, and is still in working condition. Each year, on a day called?, either on the last Sunday in June, or on the first Sunday in July, whichever comes closer to 2 July, the site holds an open house during which the transmitter is started up and transmits test messages on 17.2?kHz using its??SAQ, which can be received all over Europe."

The good news is that you have almost an entire year to prepare for the next transmission.

Jerry, KE7ER

On Wed, Aug 3, 2022 at 06:05 AM, Niels Jalling wrote:
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
Re: sBitx antenna-first warning

 

Not sure which statement that would be.
I've been making lots of them.

A resistive SWR meter assumes that the transmitter wants to see a 50 ohm resistive load,
but the transmitter will not necessarily work best at exactly 50 ohms.
For example, assume we are operating at 30mhz and there is a long trace to the antenna connector.
The antenna system would want to have a little bit of capactive reactance to counter the inductance of that trace.

Not much point to worry about such minor issues.
We just need a reasonably good match between transmitter and the antenna system,
doesn't have to be perfect.? You could spend a career trying to understand everything
that could go slightly wrong here, many people do.

Jerry, KE7ER


On Wed, Aug 3, 2022 at 07:45 AM, Evan Hand wrote:
Jerry,

A resistive bridge SWR meter should not work if this statement is true.

Am I missing something here?
73
Evan
AC9TU
Re: A short video of sBitx working

 

Yes, the transformer at T8 matches the extremely low impedance coming out of the IRFZ24N's
to something near 50 ohms.? There is also a discussion here about an external antenna matcher
to match that 50 ohms from the sBitx into whatever impedance the antenna presents.?

The sBitx transmitter is designed to work from 30mhz to 3mhz, a factor of 10 to 1.
Very tough to get transformers to work well across such a wide frequency range.
Since T8 has to operate at 40 Watts, that is the most critical with regard to operating at 0.474mhz.
Operating at 0.474mhz would best be done by increasing the windings on all transformers
that must work at the operating frequency, namely T2, T5, T7 and T8.

Jerry, KE7ER


On Wed, Aug 3, 2022 at 03:04 AM, Alan Cooper wrote:
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
Re: sBitx antenna-first warning

 

My first guess for having different values of SWR reported at different power levels would be that the SWR measurement device cannot accurately measure the two power levels.? This does make sense to me.? So If you use a meter that can measure down to the low power level, it should be good to tune the tuner.

NOTE that the SWR meter is not part of the tuned circuit.? It is measuring at the cable's connector to the tuner.? The "measurement plane" in S Parameter terms.

Am I missing something?

73
Evan
AC9TU
Re: sBitx antenna-first warning

 

Jerry,

A resistive bridge SWR meter should not work if this statement is true.

Am I missing something here?
73
Evan
AC9TU
Re: Drive potmeters?

 

Good to hear!
If so, then all should ignore my previous post:??/g/BITX20/message/94334

Jerry, KE7ER


On Wed, Aug 3, 2022 at 01:52 AM, Niels Jalling wrote:
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

 

I would tune up any antenna matching network (if you have one) at low power,
that should be close.? Then increase power and tune again.
Alternantely, use something like an Antuino or nanoVNA to do the initial tune up.
If you have an antenna you know to be somewhat tuned, a matching network is not needed.
But you don't want to start at 40 watts, only to find that a windstorm took it down
and you have a 10:1 SWR.

For those who actually read my comments, it should be clear now.
I started out this morning by reading the most recent post and am working my way back.

Jerry, KE7ER



On Wed, Aug 3, 2022 at 04:50 AM, Bob Benedict, KD8CGH 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! "

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.
Re: sBitx antenna-first warning

 

If it works well, it's good.

This does not strike me as all that odd.
I wouldn't worry unless it somehow caused significant distortion in the transmitted signal.

Jerry, KE7ER


On Wed, Aug 3, 2022 at 05:21 AM, John AE5X wrote:
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!
Re: sBitx antenna-first warning

 

There is room for doubt here.
An SWR meter assumes the transmitter wants to see a 50 ohm resistive load.
A uBitx/sBitx might work a bit better into a load that is somewhat different than assumed.

Jerry,? KE7ER


On Wed, Aug 3, 2022 at 06:20 AM, David McGaw wrote:
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
Re: sBitx antenna-first warning

 

David,

Here is the explanation as I see it.
First, the impedance. It is the ratio of voltage to current. Let's skip RF and only consider DC, then we will expand this to DC.?
Ex 1: Consider a 12 supply?that is delivering 40 watts of power to a resistor across it's terminals. It's current should be 3.3A, so that 12v x 3.3A = 40 Watts. Now, which also means that the resistor is 12V/3.3A =? 3.6 ohms. This is also the case of the full power of sBitx.?
Ex 2: Now, consider that we have decreased the output of the power supply's current?only such that we are producing? 12 watts of power. The current will now be 1 A (as 12v x 1A = 12 Watts) and the load resistance required will be 12 ohms (12V / 1A). Hence, the load impedance is changed. If you still put a 3.6 ohm resistor, the voltage from the power supply will drop down and become unregulated and unstable, the power supply is overloaded.

Now, let's switch to an RF 'power supply', that is, a transmitter.?
The output impedance of a power amplifier, derived from the above explanation is given as (Vcc * Vcc)/ (2 * Po). That is, output impedance of the power amplifier is calculated as square of power supply voltage divided by double the output power.

Ex 3: Consider a QRP transmitter like the BITX20 or QRP labs QCX. The Vcc is 12v and the output power is 5 watts, hence, the PA output impedance is (12 * 12)/ ( 2 * 5) = 14.4 ohms.?

Ex4: In the above Ex 3, now consider that you have reduced the power to 1 watt. The Vcc is still 12V, hence, the output impedance is (12 * 12) / (2 * 1) = 72 ohms.

In case of regular SSB transmitters, they are tuned to match at the maximum output to protect the transistors from excessive power remaining in the device at the peak output, it also makes sense as for CW and other continuous carrier modes like FT8 and RTTY, the output power doesn't vary but remains the same as the peak ssb envelope power.

- f??


On Wed, Aug 3, 2022 at 6:50 PM David McGaw <david.g.mcgaw@...> wrote:
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 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

On Wed, Aug 3, 2022, 12:52 PM Ashhar Farhan via <farhanbox=[email protected]> wrote:
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

John Cunliffe W7ZQ
 

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.?
Re: sBitx antenna-first warning

 

¿ªÔÆÌåÓý

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:

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

On Wed, Aug 3, 2022, 12:52 PM Ashhar Farhan via <farhanbox=[email protected]> wrote:
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
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
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


On Wed, Aug 3, 2022 at 8:15 AM Don--AE4DW <AE4DW.Don@...> wrote:
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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