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Output impedance of TAPR QRPi?
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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 8 hours ago
BezewyBezewy
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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 8 hours ago
BezewyBezewy
1112 bronze badges
New contributor
Bezewy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment
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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 8 hours ago
BezewyBezewy
1112 bronze badges
New contributor
Bezewy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
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 8 hours ago
BezewyBezewy
1112 bronze badges
New contributor
Bezewy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
BezewyBezewy
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New contributor
Bezewy is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
BezewyBezewy
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asked 8 hours ago
BezewyBezewy
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asked 8 hours ago
BezewyBezewy
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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 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
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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 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
31.8k1 gold badge49 silver badges127 bronze badges
$endgroup$
add a comment
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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 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
31.8k1 gold badge49 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 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
31.8k1 gold badge49 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 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
31.8k1 gold badge49 silver badges127 bronze badges
answered 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
31.8k1 gold badge49 silver badges127 bronze badges
answered 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
31.8k1 gold badge49 silver badges127 bronze badges
answered 7 hours ago
Phil Frost - W8IIPhil Frost - W8II
31.8k1 gold badge49 silver badges127 bronze badges
31.8k1 gold badge49 silver badges127 bronze badges
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