Line Powering

Thanks Harry
I got it to work now. I had left out the choke coil and it was passing signal back but very little.

Here is the link

http://www.sm0vpo.com/antennas/preamp-0.htm

BR Harry

The "normal" method of doing this is to connect a coax to the oscillator output as normal, but through a capacitor to block DC. Then connec an inductor from the coax centre conductor to the oscillaator battery terminals.

The DC-block and inductor is used extensively in mobile telephome where a base station amplifier (or preamplifier) is powered through the coaxial cable feeding it. They call them "Bias-Injectors", feeding "TMA" and "ALNA" type of amplifiers. Modern base stations have the function already built in the Radio Unit (RU). So there are some Googlable buzz words.

The only disadvantage is that RF coax has a huge loss at 3GHz but the DC does not. I have seen (non-engineer) testers stuffing the coaxial cable from a base directly into a receiver on the premise that 100m of cable must have a loss of 50dB (1/4" cable). They forget that DC is not attenuated.

But uin your application it should be easy. If you look at my homepages there is an antenna-mouted preamplifier that uses a powered relay at the antenna feed-point. The diagrams and description should give you exactly what you are seeking - RF and DC down the same cable.

Best regards from Harry - SM0VPO

Thanks Ivan
Yes it is a remote oscillator. I did try to raise the value of the resistor to get a stronger signal but then the oscillator stopped running as it only runs on around 5 volts. This is something I haven't tried before so I didn't know much about it.  The power and signal are through a piece of video coax about 4 feet long.  I am trying to pick up enough signal to drive a PLL chip (LM567)  It locks intermittently so I think I only need a bit more input.

Hi Jalex,
why you do not pick the signal from the oscillator output as usual ? Is it a remote oscillator and you attempt to use the same wires both for power and for signal ? If this is the case, you must avoid any filtering of the power line and minimize its stray capacitance. The signal voltage on the resistor is Us = Is*R , where R=22 ohm in your case. Increasing Is will increase the Us, too.
I have no idea why to use a diode. If Is<<Icc, the above formula is valid, R means the dynamic resistance of the diode at Icc. If Is were comparable with Is, you would get a very distorted signal with much of the second harmonic, making it unusable.

BR from Ivan

Hi
I have an oscillator powered though a 22 ohm resister and I am trying to pick up the signal from the resister but it's too weak. Would it get a lot more if I power it through a diode and maybe use a follower at the oscillator end.  I would like to be able to get maybe around 100mv or so.