Quote:
Originally Posted by MrBungle
Just a couple of warnings here as I've gone down this route too and burned myself a couple of times. Any measurement device will load the circuit in some way. In the case of the probe there, any stray capacitance will drag your IF measurement off and/or reduce the Q of the circuit being measured. This may or may not be an issue but it's worth remembering it.
Since discovering this I tend to adjust IF shape by injecting noise into the front end of the receiver from a noise source and using an audio FFT on my smartphone to shape it. Surprisingly effective!
I am using a clone of the noise source here, without the bridge (everything after C4 removed) to do the job: https://qrpguys.com/wp-content/uploa...ide_120616.pdf ... this is loosely coupled to the antenna with a bit of wire wrapped around it usually.
On the probe front, your standard scope probe would have 15-20pF of capacitance across it. I would build the probe as is if you want to go down that route. |
I know nothing about noise bridges but am intrigued by this and may have a go at building one. However, reading the paper you reference it says to connect the antenna to one socket on the bridge and tune using the antenna coupler. Won't this just have the effect of transmitting white noise to all and sundry?
Kind regards
Robin