RF Noise Bridge: Ported Over
My next test equipment piece to build is called the Rf noise bridge. Known as the poor mans antenna analyzer. This fairly simple device can measure feed point impedance of antenna systems. It uses a wide-band noise generator which is just a zener diode that is ac coupled and amplified.
There are many circuits available. All fairly simple. I just chose one and layed out a PCB for it in diptrace. Made it fairly small for and OSHPark order. There is a transformer that has to get wound but it should be simple.
An MFJ comercial version: http://www.mfjenterprises.com/Product.php?productid=MFJ-202b
http://www.classicinternational.eu/_clientfiles/manuals/mfj202b.pdf
There are many circuits available. All fairly simple. I just chose one and layed out a PCB for it in diptrace. Made it fairly small for and OSHPark order. There is a transformer that has to get wound but it should be simple.
An MFJ comercial version: http://www.mfjenterprises.com/Product.php?productid=MFJ-202b
http://www.classicinternational.eu/_clientfiles/manuals/mfj202b.pdf
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As of today (posting date):
I have built a little PCB based on a circuit I found online. It certainly puts out an incredible amount of RF noise well into VHF from what I can tell.
I am having some issues using only a potentiometer right now finding the null even with a 50 ohm dummy load on the antenna connection. I am using my HT as the receiver for this. I will experiment with adding the parallel capacitance to see if that helps.
The transformer is using the 2 hole ferrite core commonly available. I am using a 2.4V zener as the noise source.
I will probably be posting an updates when I have some time to mess around with it more. It is lower priority.
Here is the circuit I am using:
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