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Output impedance of TAPR QRPi?
3 way coax split / impedance matchWhat kind of losses do you get from an LC network matching the antenna's impedance?What is the output impedance of a typical solid state ham transmitter?Inductors for Impedance MatchingInput and output impedance of antenna/circuit: theory and measurement methods?Impedance matching using Smith Chart and relationship to reflectionImpedance matching: Why do components behave totally differently from theory?Impedance Matching between RF Amplifier StagesImpedance ratio vs. SWRHow to match low impedance of NVIS Dipole?
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I'm a newly licensed amateur and have decided to start out by trying WSPR on a Raspberry Pi equipped with TAPR's 20m QRPi. The QRPi write-ups I've read always talk about long wire antennas but I'd like to try to connect it to my Elecraft AX1. But I can't, for the life of me, find anything that specifies the output impedance of the QRPi. I'm assuming that some sort of matching will be required, for best results.
Does anybody know what the QRPi's output impedance is? If I must measure it myself, would my "Nano VNA" be of any use?
impedance-matching qrp wspr
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
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$begingroup$
I'm a newly licensed amateur and have decided to start out by trying WSPR on a Raspberry Pi equipped with TAPR's 20m QRPi. The QRPi write-ups I've read always talk about long wire antennas but I'd like to try to connect it to my Elecraft AX1. But I can't, for the life of me, find anything that specifies the output impedance of the QRPi. I'm assuming that some sort of matching will be required, for best results.
Does anybody know what the QRPi's output impedance is? If I must measure it myself, would my "Nano VNA" be of any use?
impedance-matching qrp wspr
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
$endgroup$
add a comment
|
$begingroup$
I'm a newly licensed amateur and have decided to start out by trying WSPR on a Raspberry Pi equipped with TAPR's 20m QRPi. The QRPi write-ups I've read always talk about long wire antennas but I'd like to try to connect it to my Elecraft AX1. But I can't, for the life of me, find anything that specifies the output impedance of the QRPi. I'm assuming that some sort of matching will be required, for best results.
Does anybody know what the QRPi's output impedance is? If I must measure it myself, would my "Nano VNA" be of any use?
impedance-matching qrp wspr
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
$endgroup$
I'm a newly licensed amateur and have decided to start out by trying WSPR on a Raspberry Pi equipped with TAPR's 20m QRPi. The QRPi write-ups I've read always talk about long wire antennas but I'd like to try to connect it to my Elecraft AX1. But I can't, for the life of me, find anything that specifies the output impedance of the QRPi. I'm assuming that some sort of matching will be required, for best results.
Does anybody know what the QRPi's output impedance is? If I must measure it myself, would my "Nano VNA" be of any use?
impedance-matching qrp wspr
impedance-matching qrp wspr
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
asked Sep 26 at 19:24
BezewyBezewy
1233 bronze badges
1233 bronze badges
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1 Answer
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The output impedance isn't especially important: in fact I believe it uses a nonlinear amplifier so the concept doesn't really apply.
What does matter is the intended load impedance, which for any amateur radio application you can assume to be 50 ohms unless otherwise specified.
To verify, I modelled the low-pass filter part of the circuit from the manual:
simulate this circuit – Schematic created using CircuitLab
Running a frequency domain analysis we can see this provides a nice low-pass response with a cutoff just above the 20m band, with a pretty flat passband except for some minor ripple we can expect inherent to the Chebyshev design and rounding errors in selecting common values for the components:
If the load impedance is changed to 5,000 ohms, the response no longer looks so nice:
Of course you aren't actually going to get an additional 40 dB of output power where the frequency response spikes because the real circuit isn't built of ideal components, but what this tells us is the person designing that filter assumed the attached load would be about 50 ohms.
What happens if the load isn't 50 ohms is somewhat undefined. It could be fine. It could just make less power. Or it overstress the transistor and damage it.
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
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$begingroup$
The output impedance isn't especially important: in fact I believe it uses a nonlinear amplifier so the concept doesn't really apply.
What does matter is the intended load impedance, which for any amateur radio application you can assume to be 50 ohms unless otherwise specified.
To verify, I modelled the low-pass filter part of the circuit from the manual:
simulate this circuit – Schematic created using CircuitLab
Running a frequency domain analysis we can see this provides a nice low-pass response with a cutoff just above the 20m band, with a pretty flat passband except for some minor ripple we can expect inherent to the Chebyshev design and rounding errors in selecting common values for the components:
If the load impedance is changed to 5,000 ohms, the response no longer looks so nice:
Of course you aren't actually going to get an additional 40 dB of output power where the frequency response spikes because the real circuit isn't built of ideal components, but what this tells us is the person designing that filter assumed the attached load would be about 50 ohms.
What happens if the load isn't 50 ohms is somewhat undefined. It could be fine. It could just make less power. Or it overstress the transistor and damage it.
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
$endgroup$
add a comment
|
$begingroup$
The output impedance isn't especially important: in fact I believe it uses a nonlinear amplifier so the concept doesn't really apply.
What does matter is the intended load impedance, which for any amateur radio application you can assume to be 50 ohms unless otherwise specified.
To verify, I modelled the low-pass filter part of the circuit from the manual:
simulate this circuit – Schematic created using CircuitLab
Running a frequency domain analysis we can see this provides a nice low-pass response with a cutoff just above the 20m band, with a pretty flat passband except for some minor ripple we can expect inherent to the Chebyshev design and rounding errors in selecting common values for the components:
If the load impedance is changed to 5,000 ohms, the response no longer looks so nice:
Of course you aren't actually going to get an additional 40 dB of output power where the frequency response spikes because the real circuit isn't built of ideal components, but what this tells us is the person designing that filter assumed the attached load would be about 50 ohms.
What happens if the load isn't 50 ohms is somewhat undefined. It could be fine. It could just make less power. Or it overstress the transistor and damage it.
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
$endgroup$
add a comment
|
$begingroup$
The output impedance isn't especially important: in fact I believe it uses a nonlinear amplifier so the concept doesn't really apply.
What does matter is the intended load impedance, which for any amateur radio application you can assume to be 50 ohms unless otherwise specified.
To verify, I modelled the low-pass filter part of the circuit from the manual:
simulate this circuit – Schematic created using CircuitLab
Running a frequency domain analysis we can see this provides a nice low-pass response with a cutoff just above the 20m band, with a pretty flat passband except for some minor ripple we can expect inherent to the Chebyshev design and rounding errors in selecting common values for the components:
If the load impedance is changed to 5,000 ohms, the response no longer looks so nice:
Of course you aren't actually going to get an additional 40 dB of output power where the frequency response spikes because the real circuit isn't built of ideal components, but what this tells us is the person designing that filter assumed the attached load would be about 50 ohms.
What happens if the load isn't 50 ohms is somewhat undefined. It could be fine. It could just make less power. Or it overstress the transistor and damage it.
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
$endgroup$
The output impedance isn't especially important: in fact I believe it uses a nonlinear amplifier so the concept doesn't really apply.
What does matter is the intended load impedance, which for any amateur radio application you can assume to be 50 ohms unless otherwise specified.
To verify, I modelled the low-pass filter part of the circuit from the manual:
simulate this circuit – Schematic created using CircuitLab
Running a frequency domain analysis we can see this provides a nice low-pass response with a cutoff just above the 20m band, with a pretty flat passband except for some minor ripple we can expect inherent to the Chebyshev design and rounding errors in selecting common values for the components:
If the load impedance is changed to 5,000 ohms, the response no longer looks so nice:
Of course you aren't actually going to get an additional 40 dB of output power where the frequency response spikes because the real circuit isn't built of ideal components, but what this tells us is the person designing that filter assumed the attached load would be about 50 ohms.
What happens if the load isn't 50 ohms is somewhat undefined. It could be fine. It could just make less power. Or it overstress the transistor and damage it.
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
answered Sep 26 at 20:24
Phil Frost - W8IIPhil Frost - W8II
34.7k2 gold badges51 silver badges127 bronze badges
34.7k2 gold badges51 silver badges127 bronze badges
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