[caption id="attachment_713" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2010/03/IF- Amp-3.jpg) Completed IF Amplifier[/caption]
The I.F. Amplifier exists to boost the strength of the final intermediate frequency before it reaches the final filter. It is really 2, 20 dB, amplifiers chained together. The design of the PCB is such that one side is simply the mirror of the other.
[caption id="attachment_712" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2010/03/IF- Amp-2.jpg) Fix for the slight error in the border[/caption]
There was a change order for this version of the PCB. There is a short section that was missing. The fix is really simple, all I had to do was bridge it with some solder wick.
[caption id="attachment_908" align="aligncenter" width="540"]!(http://alternet.us.com/wp-content/uploads/2010/05/if- amp-1-2.jpg) I.F. Amplifier test setup[/caption]
The test setup for the IF amplifier is shown above. I'm using a SMA jumper from the amplifier output to the log detector. Later, the final filter will live between them. Later still, I'll build and install the filter switch and have a few different filters.
[caption id="attachment_906" align="aligncenter" width="473"]!(http://alternet.us.com/wp-content/uploads/2010/05/IF-Amp- dummy-load.jpg) Analyzer input with dummy load on I.F. Amp input[/caption]
I performed a similar set of tests with the I.F. amplifier that I did with the Log detector. The first, shown above, is with a dummy load attached to the input. Now, the noise floor is 10 dB higher than the log detector alone, at -75 dBm.
[caption id="attachment_907" align="aligncenter" width="473"]!(http://alternet.us.com/wp-content/uploads/2010/05/IF-Amp- antenna.jpg) I.F. amplifier with antenna[/caption]
With the antenna installed to the I.F. amplifier the noise floor is higher, still at -62 dBm. An interesting artifact on this plot is the strange shape on the right. I couldn't make an image without this feature because it is sensitive enough that it signal changes when I clicked "save image" on the spectrum analyzer software. I have to admit that's pretty cool.
[caption id="attachment_905" align="aligncenter" width="473"]!(http://alternet.us.com/wp-content/uploads/2010/05/IF-Amp- transmitter.jpg) Transmitter signal with I.F. amplifier.[/caption]
Again, I keyed my radio near the antenna. This time you can clearly see the 25 dB difference between 'off' and 'on'.
At this point, my hope is that the noise floor begins to lower once I get some filters installed. :)