J. Freed
The reason we picked the ZFL-500HLN amp for SPI's Double Mixer was that it was an amp that met requirements from minicircuts
-frequency range contains 80MHz (our operating frequency)
-Operates at voltage supplied by Low Noise Power(15V, 17V, 24V etc.)
-Has a P1dB well above our output power of 10dBm (to remove non-linearity)
-No heat sinks (to fit in a 1U chassis.) (This requirement actually doesnt matter, the ones discussed here are still the best even compaired to amps with heat sinks)
-sma connections
-Low noise
-Low gain (we only need ~8dB of amplification)
The ZFL-500HLN was chosen because it fit all those requirements, with the cavieat of having to attuniate before amplification (adding noise). Though if I am correct and the Low noise power board 5V Vcc port is capable of supporting a 63mA load, another option would be the ZX60-P105LN+ instead due to the lower gain and lower noise. This would remove the need for an attinuator before amplification but its low input return loss means alot of power is reflected back towards our mixers (Also causeing noise). So it becomes a pick your poison of adding noise by attinuating before amplification vs by reflections back into our mixers. In practice, I believe both would operate about the same. Will add a comment if something changes
Double-MixerAmpComparison.png shows a quick comparison of the 2 amps
Acording to this term definitions manual I found on minicircuts:
"Directivity (active) is defined as the difference between isolation and forward gain in dB. It is an indication of the isolation of the source from the load, or how much the load impedance affects the input impedance and the source impedance affects the output impedance. The higher the active directivity (in dB), the better the isolation."
So directivity is just a measure of Isolation - Gain. Which isolation is just a measure of how much power is sent through the amp to the input port with power applied on the output. This would really only affect the amp when there is a large impedance mismatch on the output (load). If there is little to none, directivity doesnt really matter. But if it did come up, the ZFL-500HLN would do much better. The greater concern I believe for the ZX60-P105LN+ is the large input return loss, which is the power of the reflections off of the ports back the way it came. This would cause a standing wave on our input. To reduce it, we would have to add an attinuator on the input anyway. Probably less than the 10 dB attinuator which we currently have, but still something to consider.
P.S. VSWR and Return Loss(RL) are the same thing with different units, the conversion between them is VSWRvsRL.png. A VSWR closer to 1 is better, while a higher return loss is better. Converting the ZFL-500HLN aproximate 1.04:1 VSWR to Return loss gives 34.15dB. This means the reflections power are about 20dB greater on the ZX60-P105LN+. Really not sure if it is worth it excpecilly since mixers are sensitive to these reflections.
