Lets talk about power amplifiers solutions for AO-100

The successful launch and commissioning of the AO-100 has been a real rule-change in the story of amateur satellites. Although foreseeing since the very beginning of Oscars story and classified as “phase 4”, we had to wait for more than five decades to have the very first geo stationary amateur satellite in place and fully available.

But why it’s referred as “phase 4”? Let step back to the origin, when the continuous technological development led the history of amateur radio satellites to be divided into "phases", each of which is characterized by clear objectives and technical or structural characteristics.

The following table includes the distinctive characteristics of each “phase”.

Since its commissioning, the QO-100 demonstrates of being even more sensitive than expected. I personally succeed to run some QSOs with only 400mW and a 10dB horn antenna and I believe this is probably one the most QRP way to use the bird. For a more reliable and comfortable traffic some more ERP is needed. As rule of thumb, it’s preferable to start investing on a good and big antennas, but not always space, cost and other constraint let us reach to the ERP wished in that way. Thus the only chance comes from an higher transmit power.

The market is now plenty of offer of smalls, compact and (often) cheap amplifier modules, mostly intended for WiFi, Cellular, WiMax, ISM and Bluetooth applications. But how do they perform? Which pro and cons? Let see my experience with some of the most popular ones.

An important note prior to moving on: I do not have a certified ISO 17025 radio frequency lab at home, but a “regular” ham one. So, all the figures you will find on the following pages have been measured with my best effort to minimize errors but of course, are not “official laboratory grade” ones.

SBB5089Z + SZA2044

Figura 1: SBB5089 + SZA2044 amplifier

This is a very compact module, advertised for a 1W max output. The supply may range from 6 up to 30Vdc and this makes it very convenient also for portable operation. The idle current of the whole device is about 210mA @ 12Vdc; please note that the current drowned from the power supply decrease with the increase of the voltage due to the internal switching power supply that try to keep the input power constant across all the input voltage range.

The circuit use a couple of well known devices. The one at the input is theSBB5089Z, an high linearity gain block for applications such as PA Driver Amplifier, Cellular, PCS, GSM, UMTS, wideband instrumentation, wireless data, satellite terminals. It is internally matched to 50 Ω at input and output over a very broad range.

Following in the chain, we found the SZA-2044, a modern product specifically designed as a final stage for 802.11b/g and 802.16 equipment in the 2.0GHz to 2.7GHz bands.

The module shows an overall very high gain, in the order of 39-40dB, with a bandwidth a -3dB that ranges from about 400MHz up to 2.7GHz. This is something to concern for our application: in order to prevent a lot of spurious emissions over the air, it’s mandatory to feed it with a very clean signal and perhaps also to filter its output upon the cases.

Here its response curve at my bench:

Figura 2: Gain response (S21) of the two stages, 1W amplifier. Note: add 10dB to the measured figures

“Out of the box” my specimen was not able to deliver more than 550mW @ 2400MHz with saturated input (-5dBm). At lower frequencies, let say 2380MHz and downward, I could see up to 29-30dBm with no problem and with -10dBm at the input. If you wanna squeeze up some half dBm you can just remove the component marked R7 and C17.

Surfing the web, you could find also a version with a pair of SZA2044, which I guess able to deliver some 1-1,5W.

Final advise: when operated at “high power”, the case of the final device may become pretty warm, so watch your fingers!

SZM2166