I think at present I need to build the following;
An RF 2 tone oscillator, this should be two separate xtal controlled oscillators, each possibly pulled to be 20kHz apart (maybe a series coil in one and series cap trimmer in the other as I don't have many Xtals in my junk box). Each of these will be built ugly style using PCB board soldered up as boxes. The two boxes must be very well screened from each other, Each will feed a 6dB attenuator and then into a return loss bridge wired as a combiner into a low pass filter, 3 coils, 4 caps. (see the separate posts)
Maybe a second RF weak signal oscillator to measure sensitivity. (see the separate post)
Actually might divert into making a grid dip meter as this would pay dividends - with jigs to measure C and L. I could build in a PIC based digital frequency meter into it as well as an analogue meter.
A switchable step attenuator. 0-70dB, low power
A return loss bridge - I'll just use this with my scope and see how I get on. I wonder how I could do phase as well as return voltage across 50 Ohm. (maybe make a more sophisticated bridge with hi-q air capacitors - assuming a two channel scope can detect zero phase (add/subtract scaled voltages - minimum if in phase)
A "sampler" to allow feeding from a 10W or 100W Linear into the SDR(acting as a spectrum analyser).
Dummy loads: I do have ham radio SWR meters and ATUs with dummy loads as well as a Elecraft K" 10W transceiver and a Kenwood TS530 Valve Transmitter, but I will try and test with simpler (cheaper) equipment.
Farnell have 3W 1% metal film and even 30W or 100W metal film 1% (100 Ohms) FEC2396003, FEC2328286(30W/1%/100R@£2) or EC1114422(100W@£5.74)Need a heat sink on the last two, maybe <0.7degreesC/W
These should allow testing the receive path - measuring sensitivity (MDS= Minimum Discernable Signal) and third order intercept/1dB compression/IMD (Intermodulation Distortion). I will also need to measure noise figure but have yet to learn the theory of how to do that! (I have postponed that for now).
When I build the transmit chain I will have a chain of amplifiers/drivers, each of which should be 50 Ohm i/p and o/p; I would think outputs of the 100mW, 1W, 10W and finally 100W should be ok. With a 20W return bridge I can do return loss measurements of the input of the 100W amp. I will use a conventional SWR on the output, at least on the 10W and 20W.
At present I can see how to use a return bridge to measure amplifier inputs - best done at normal running power. I have read they can be used to measure output return loss by injecting signals into outputs whose inputs are grounded. Sounds risky to me, a spurious oscillation destroys the sig gen. And the test is better done at full power output, hence I think outputs should be tested just by measuring their SWR feeding into a dummy load. Measuring "SWR" of a 100mW amp can be done using a bridge - or just drive 50, 60 and 70 Ohm resistors? When I get experimenting I'll see what things look like.
An RF 2 tone oscillator, this should be two separate xtal controlled oscillators, each possibly pulled to be 20kHz apart (maybe a series coil in one and series cap trimmer in the other as I don't have many Xtals in my junk box). Each of these will be built ugly style using PCB board soldered up as boxes. The two boxes must be very well screened from each other, Each will feed a 6dB attenuator and then into a return loss bridge wired as a combiner into a low pass filter, 3 coils, 4 caps. (see the separate posts)
Maybe a second RF weak signal oscillator to measure sensitivity. (see the separate post)
Actually might divert into making a grid dip meter as this would pay dividends - with jigs to measure C and L. I could build in a PIC based digital frequency meter into it as well as an analogue meter.
A switchable step attenuator. 0-70dB, low power
A return loss bridge - I'll just use this with my scope and see how I get on. I wonder how I could do phase as well as return voltage across 50 Ohm. (maybe make a more sophisticated bridge with hi-q air capacitors - assuming a two channel scope can detect zero phase (add/subtract scaled voltages - minimum if in phase)
A "sampler" to allow feeding from a 10W or 100W Linear into the SDR(acting as a spectrum analyser).
Dummy loads: I do have ham radio SWR meters and ATUs with dummy loads as well as a Elecraft K" 10W transceiver and a Kenwood TS530 Valve Transmitter, but I will try and test with simpler (cheaper) equipment.
Farnell have 3W 1% metal film and even 30W or 100W metal film 1% (100 Ohms) FEC2396003, FEC2328286(30W/1%/100R@£2) or EC1114422(100W@£5.74)Need a heat sink on the last two, maybe <0.7degreesC/W
These should allow testing the receive path - measuring sensitivity (MDS= Minimum Discernable Signal) and third order intercept/1dB compression/IMD (Intermodulation Distortion). I will also need to measure noise figure but have yet to learn the theory of how to do that! (I have postponed that for now).
When I build the transmit chain I will have a chain of amplifiers/drivers, each of which should be 50 Ohm i/p and o/p; I would think outputs of the 100mW, 1W, 10W and finally 100W should be ok. With a 20W return bridge I can do return loss measurements of the input of the 100W amp. I will use a conventional SWR on the output, at least on the 10W and 20W.
At present I can see how to use a return bridge to measure amplifier inputs - best done at normal running power. I have read they can be used to measure output return loss by injecting signals into outputs whose inputs are grounded. Sounds risky to me, a spurious oscillation destroys the sig gen. And the test is better done at full power output, hence I think outputs should be tested just by measuring their SWR feeding into a dummy load. Measuring "SWR" of a 100mW amp can be done using a bridge - or just drive 50, 60 and 70 Ohm resistors? When I get experimenting I'll see what things look like.
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