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Beacon is running

"PaulG"
 

Got the kit running on the bench still on 12 wpm with 36 ohm dummy load I am getting 5.08V p to p output on the scope. This is somewhere around 250 mw and is set somewhat below max output as max output causes the transistor to run pretty warm. I also found out that you can reverse voltage the PIC enough to cause a 2nd degree burn on the finger and it still seems to be working. I am letting it run overnight or for a few days before I put the antenna on it. Before it started working I had a bad looking sine wave at very low level. Also the final was amplifying this spurious signal. After poking and prodding and reheating some connections it starting running properly.

Pix of it on bench at

"hanssummers2000"
 

Hi Paul

Congrats on finishing the kit. Yes, the transistor can get a bit hot when tuned for maximum output and it is best to turn the trimmer pot a bit back towards the "cold" end (ground) to lower the output a bit and feel more comfortable.

5.08V p-p into 36 ohms is not 250mW according to my calcs, it's 90mW. I think you have missed a divide-by-2 somewhere.

Another thing to bear in mind is that the output low pass filter is designed for 50 ohm termination, I'm not sure what would change if you use 36 ohms.

72/3 Hans G0UPL

--- In QRPLabs@..., "PaulG" <pgerhardt@...> wrote:

Got the kit running on the bench still on 12 wpm with 36 ohm dummy load I am getting 5.08V p to p output on the scope. This is somewhere around 250 mw and is set somewhat below max output as max output causes the transistor to run pretty warm. I also found out that you can reverse voltage the PIC enough to cause a 2nd degree burn on the finger and it still seems to be working. I am letting it run overnight or for a few days before I put the antenna on it. Before it started working I had a bad looking sine wave at very low level. Also the final was amplifying this spurious signal. After poking and prodding and reheating some connections it starting running properly.

Pix of it on bench at

"PaulG"
 

Hans

Thanks for your comments. The beacon has been running for several days now and the final seems ok temp wise with the output at 5.08V. I used this table of RF volts into 50 ohms



to determine the approximate power output. I will have to find a real 50 or 51 ohm load resistor and measure it again.

One problem I am seeing is the keyer often 'locks' up after sending the call once or a few times. Once though it ran all nite and was still keying. I wonder if it is related to the supply ? I am using an old Heathkit Reg P/S IP-18 that seems stable and clean.

--- In QRPLabs@..., "hanssummers2000" <hans.summers@...> wrote:


Hi Paul

Congrats on finishing the kit. Yes, the transistor can get a bit hot when tuned for maximum output and it is best to turn the trimmer pot a bit back towards the "cold" end (ground) to lower the output a bit and feel more comfortable.

5.08V p-p into 36 ohms is not 250mW according to my calcs, it's 90mW. I think you have missed a divide-by-2 somewhere.

Another thing to bear in mind is that the output low pass filter is designed for 50 ohm termination, I'm not sure what would change if you use 36 ohms.

72/3 Hans G0UPL


--- In QRPLabs@..., "PaulG" <pgerhardt@> wrote:

Got the kit running on the bench still on 12 wpm with 36 ohm dummy load I am getting 5.08V p to p output on the scope. This is somewhere around 250 mw and is set somewhat below max output as max output causes the transistor to run pretty warm. I also found out that you can reverse voltage the PIC enough to cause a 2nd degree burn on the finger and it still seems to be working. I am letting it run overnight or for a few days before I put the antenna on it. Before it started working I had a bad looking sine wave at very low level. Also the final was amplifying this spurious signal. After poking and prodding and reheating some connections it starting running properly.

Pix of it on bench at

Arv Evans
 

开云体育

Hello

Seems that there is some confusion regarding how to measure RF power.
There are several voltage measurement methods, including:
  • Average voltage

  • RMS voltage

  • Peak volts

  • Peak-to-Peak volts.
The chart that Paul noted shows the first 3 measurements but doesn't show
power converted from peak-to-peak voltage as you would see with a full-wave
rectifier or on an oscilloscope display.? If using peak-to-peak voltages it seems
one would want to divide-by-two, then use the peak volts part of the chart.

Arv
_._


On 10/04/2010 09:52 AM, PaulG wrote:

?


Hans

Thanks for your comments. The beacon has been running for several days now and the final seems ok temp wise with the output at 5.08V. I used this table of RF volts into 50 ohms



to determine the approximate power output. I will have to find a real 50 or 51 ohm load resistor and measure it again.

One problem I am seeing is the keyer often 'locks' up after sending the call once or a few times. Once though it ran all nite and was still keying. I wonder if it is related to the supply ? I am using an old Heathkit Reg P/S IP-18 that seems stable and clean.

--- In QRPLabs@..., "hanssummers2000" wrote:
>
>
> Hi Paul
>
> Congrats on finishing the kit. Yes, the transistor can get a bit hot when tuned for maximum output and it is best to turn the trimmer pot a bit back towards the "cold" end (ground) to lower the output a bit and feel more comfortable.
>
> 5.08V p-p into 36 ohms is not 250mW according to my calcs, it's 90mW. I think you have missed a divide-by-2 somewhere.
>
> Another thing to bear in mind is that the output low pass filter is designed for 50 ohm termination, I'm not sure what would change if you use 36 ohms.
>
> 72/3 Hans G0UPL
>
>
> --- In QRPLabs@..., "PaulG" wrote:
> >
> > Got the kit running on the bench still on 12 wpm with 36 ohm dummy load I am getting 5.08V p to p output on the scope. This is somewhere around 250 mw and is set somewhat below max output as max output causes the transistor to run pretty warm. I also found out that you can reverse voltage the PIC enough to cause a 2nd degree burn on the finger and it still seems to be working. I am letting it run overnight or for a few days before I put the antenna on it. Before it started working I had a bad looking sine wave at very low level. Also the final was amplifying this spurious signal. After poking and prodding and reheating some connections it starting running properly.
> >
> > Pix of it on bench at
> >
>
Stephen Farthing
 

Guys,

FWIW the formula for calculating RF power into a 50 ohm load from the peak to peak voltage observed on a scope is :-

Power = 2.5 x (Peak to peak voltage squared) milliwatts

So if you have a peak to peak voltage 0f 5 volts :-

Power = 2..5 (5x5)

Power = 2.5 x 25

Power = 62.5 milliwatts

I am happy to post a graph of Power vs Peak to Peak voltage in the files section if it makes things simple for the numerically challenged..

72/3 de Steve G0XAR





On 4 October 2010 16:52, PaulG <pgerhardt@...> wrote:
?


Hans

Thanks for your comments. The beacon has been running for several days now and the final seems ok temp wise with the output at 5.08V. I used this table of RF volts into 50 ohms



to determine the approximate power output. I will have to find a real 50 or 51 ohm load resistor and measure it again.

One problem I am seeing is the keyer often 'locks' up after sending the call once or a few times. Once though it ran all nite and was still keying. I wonder if it is related to the supply ? I am using an old Heathkit Reg P/S IP-18 that seems stable and clean.


--- In QRPLabs@..., "hanssummers2000" wrote:
>
>
> Hi Paul
>
> Congrats on finishing the kit. Yes, the transistor can get a bit hot when tuned for maximum output and it is best to turn the trimmer pot a bit back towards the "cold" end (ground) to lower the output a bit and feel more comfortable.
>
> 5.08V p-p into 36 ohms is not 250mW according to my calcs, it's 90mW. I think you have missed a divide-by-2 somewhere.
>
> Another thing to bear in mind is that the output low pass filter is designed for 50 ohm termination, I'm not sure what would change if you use 36 ohms.
>
> 72/3 Hans G0UPL
>
>
> --- In QRPLabs@..., "PaulG" wrote:
> >
> > Got the kit running on the bench still on 12 wpm with 36 ohm dummy load I am getting 5.08V p to p output on the scope. This is somewhere around 250 mw and is set somewhat below max output as max output causes the transistor to run pretty warm. I also found out that you can reverse voltage the PIC enough to cause a 2nd degree burn on the finger and it still seems to be working. I am letting it run overnight or for a few days before I put the antenna on it. Before it started working I had a bad looking sine wave at very low level. Also the final was amplifying this spurious signal. After poking and prodding and reheating some connections it starting running properly.
> >
> > Pix of it on bench at
> >
>




--
It is vain to do with more that which can be done with less.
"hanssummers2000"
 

Hi Paul

Thanks for your comments. The beacon has been running for several days now and the final seems ok temp wise with the output at 5.08V. I used this table of RF volts into 50 ohms

As others already noted, the table is peak voltage, not peak-to-peak. That's where the missing division by 2 comes from.

Also bear in mind that table is for 50 ohm load. You were using 36 ohms so it needs to be adjusted.

One problem I am seeing is the keyer often 'locks' up after sending the call once or a few times. Once though it ran all nite and was still keying. I wonder if it is related to the supply ? I am using an old Heathkit Reg P/S IP-18 that seems stable and clean.
This seems to happen sometimes and I think is due to the floating inputs. My recommendation is to ground any of the pins 5, 6 and 7 which you haven't tied to +Vcc. That normally will address this problem.

73 de Hans G0UPL

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