SDARs amplifier spec question

[Leiser]

Hi,

I´m reviewing the specs for a SDAR LNA amplifier and I have a doubt.

The specs defines de P1dB as follows:

P1dB at 1850-1990MHz -10dBm min
P1dB at 824-894MHz -4dBm min
P1dB at 450MHz 0dBm min

The measurement is taken with respect to a -100dBm CW reference at 2333.465MHz (SAT1). The P1dB is recorded as when the wanted SAT1 tone is reduced by 1dB at the output.

Does anyone know how to do this test? I don´t undertand it.

Thanks in advanced!

 

[logbook]

P1dB is the "1dB compression point", in other words when the signal output is 1dB lower than it should be, given the input signal. The amplifier is becoming saturated and can't put out as much power as an equivalent linear amplifier would.

If you measure the output with a suitable power meter and vary the input signal using a good signal generator and/or calibrated attenuators, you should easily see at what point a 10dB input signal change gives less than 10dB output change, for example.

 

[Leiser]

Hi,

does anyone know if there is a circuit to measure CW RF power simple to built?

I am designing an antenna setup to do a open field antenna radiation plots. In order to know the power at the emitter antenna I was thinking using a coupler and measure it. I´m trying to reduce cost and instead of using a RF power meter I was thinking if there is any DIY circuit to built to measure CW RF power between DC and 1GHz.

Thanks.

 

[logbook]

Well the answer is a low bias schottky diode.

The trouble is you would need a calibrated source or calibrated power meter to calibrate the diode. There are some chips from the likes of Analog Devices which give more calibrated response than a diode, but the connectors and matching circuit would give say 3dB uncertainties and you wouldn't be much further along.

 

[Higgler]

Re: Power measurement
There are some low cost detector modules available from MiniCircuits in your frequency range. Your tx power may need to be increased to 10 watts to get accuracy at a few hundred feet. Use a high gain antenna on receive too.

Try minicircuits, they have a 10-8000 Mhz detector with -60 dBm noise floor,
this data sheet

http://www.minicircuits.com/pdfs/ZX47-60+.pdf

shows a good data linearity at -50 dBm to -5 dBm over your frequency ranges.

500 foot range at 1 Ghz is 76 dB loss with zero dBi antennas, hence you'll need a good probe (zero dBi gain).
If you expect to measure antenna patterns from your tx antenna that arrive at -50 dBm signal levels out of your 0 dBi antenna probe, you need;-50+76 = +26 dBm ERP from your antenna. ie. if you have a high gain antenna (+10 dBi gain) and want to look at patterns -30 dB down, or -20 dBi gain direction, you'll need +26 dBm + 20 dB = +46 dBm ERP - 10 dB for peak gain or +36 dBm power into your tx antenna or 4 watts.
If you Tx antenna is 0 dBi and you want to measure down to -30 dB below peak at 500 feet, you'll need 40 watts Tx power.

by the way, your antenna probe is really critical to avoid multipath in your measurements. It's tricky.


Cost is $90 each, not bad.

good luck

kch