PA-100D output

General discussion

PA-100D output

Postby EA3IN » 23 Mar 2021 23:29

Hello

I have a SunSDR2 pro radio that gives 15-20 w out max.
I would like to raise the power to 40-45 w in order to drive my amplifiers (KPA-500 and ACOM2000)
Is the gain level control of the PA-100D able to grant 40-45w out with let's say 5-10w in?

I know that the answer should be to upgrade to a different radio or to go for a low drive amplifier. But ....

Thank you
Marcel
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Re: PA-100D output

Postby 5B4AIY » 24 Mar 2021 11:42

Hi, Marcel,

The PA-100D is fitted with a stepped input attenuator, having 4 settings. The nominal maximum power gain of the amplifier is between 14dB and 15dB. By setting the gain to its lowest setting, G1, with an input power of 5W (37dBm) you will have a power gain of about 9dB to 10dB giving an output power of between 46dBm and 47dBm, in other words between about 39W and 50W. So the short answer is, yes, by using the minimum gain of the PA-100D, and a drive of about 5W you will be able to get an output power in the range you require. Make sure you set the gain for each band, as the gain settings are memorised for each band, and if you were to accidentally select the G4 gain setting 5W of drive would saturate the PA-100D and overdrive your linear!

One benefit of using the lowest gain setting, the highest attenuator setting, is that the input match is excellent over the entire frequency range, giving a very low input VSWR.

73, Adrian, 5B4AIY
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Re: PA-100D output

Postby EA3IN » 25 Mar 2021 23:26

Thank you Adrian

I have ordered one unit from rowaves

Might be is it posible to increase a little bit more the level of attenuation?

Let's see if it does the job
Sunsdr -> PA100 -> KPA500/Acom2000

I guess I can put in parallel the 2 PTT outputs
EA3IN
 
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Re: PA-100D output

Postby 5B4AIY » 28 Mar 2021 07:09

Hi, Marcel,

Since the input attenuator uses discrete components it would certainly be possible to increase the attenuation. For example, if the attenuation steps were increased so that the 2dB attenuator was 3dB, and the 4dB attenuator was 5dB, then this would give steps of 0, 3, 5, and 8dB. With 8dB attenuation the amplifier's gain would reduce from 15dB to 7dB, and for an output power of 50W, +47dBm, you would need an input of +40dBm, or 10W. If you opt to do this bear in mind that the power rating of the resistors forming the attenuator would need to be sufficient to dissipate the input power.

As for the PTT switching, the amplifier repeats the input key line to the output socket, so connect the SDR PTT keyline to the amplifier, and take the amplifier's output key line to the linear. There is no need for a parallel connection. Have a look at the Juma MAIN BOARD, T/R, ATTENUATOR, CURRENT SENSE schematic. The NOT_KEYIN line, active low, switches TR1, which repeats this by switching the NOT_KEYOUT line with TR2. The T/R switching is connected via a 3.5mm socket on the rear panel. This uses a stereo 3.5mm plug, with the NOT_KEYIN line wired to the tip, and the repeated NOT_KEYOUT wired to the ring.

Adrian, 5B4AIY
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