RF LNA on a budget

[brandon7861]

I have some rg316 I need to find a use for, it's kinda thin and sorta flexible. I can terminate it with bnc at the end of the enclosure or I could wire it direct into the amp. Couldn't the RF DC output be used as a relative signal strength into a volt meter?

I am emailing them asking about that pin. I don't know if it is RF with a DC offset, demodulated RF with a DC offset or demodulated RF with the audio decoupled from DC. I will update when I get a reply from them.

 

[brandon7861]

Here is their reply to me.

 

[brandon7861]

When making the power supply, start by running the probe directly on a variable supply and slowly raise the voltage until the current draw stops changing (while touching the probe tip to give it something to amplify). Design the supply for that voltage. They use a 5v regulator on the probe board and that will need more than 5v to work properly. Feeding it a higher voltage than necessary will make the probe heat up faster. It will be around 6v.

Edit: I honestly cant see what regulator they used. Maybe they used a 3.3v or something else, but I doubt it. You'll find out when running up the voltage.

I added a buffer amp to mine and made the mistake of feeding it off the unregulated side, so where the buffer is biased right is not where the current levels off. I plan to rebuild mine, fix that mistake, and add the demodulated output feature yours has.

 

[Cable Guy]

I powered one up tonight, it has the 5V regulator and current tops at 31ma with an 8V input, 5.04V out from the regulator. Increasing input voltage further, up to specified input @ 12V, creates less than 2mv increase in regulator output and zero ma current increase. These measurements conducted while touching the probe tip. Specs say:
Input voltage 12VDC 20ma.
Input impedance 0.5pf/10Mohm.
BW 100kHz-1GHz ~2.5dB
Gain -15dB

I like the buffer idea, I will consider your advice.