part filter bandpass testing

Made a transformer to match the 100 Ohm output impedance of the Adruino controlled AD9850 DDS board  to the 50 Ohm input of the filter. the output is loaded with 50 Ohm (parallel two 100 Ohm resistors)

 Fired up the RF generator and used my $20 dollar ham fest bought  20Mhz oscilloscope as the detector.

look like the  band pass is around this frequency.

the reading was barely there on the scope . the sensitivity of the scope at max 5mV/cm and the 20Mhz range at the edge. Boy, this is  going to be unusable data collecting.

                I just step through the RF generator range at 100 Hz steps from 19.994 to 19.999 mhz.
the scope blurr shows it blinked very fast indicating the filter is sharp.
                I must add an amplifier to this  to buffer and amplify the signal.

Took a quick reading  on the input side of the filter and the output side readings. te input was 150mV and the output was 60mV.



        20 Log 60mV/150mV=-7.96 db  loss

time to build an amplifier with 50 Ohm in and 50 Ohm out. remembered VK5TH site has one circuit.

http://vk5tm.com//homebrew/dds/dds.php

click on the schematic to enlarge and click back to the blog

click data t o view

built the amplifier and added the diode detector to get a finer reading. the scope was useless with 5 gradient to a centimeter in reading the changes.

The Arduino RF generator  from AD7C's site

http://www.ad7c.com/projects/ad9850-dds-vfo/

 here is the result plotted. It has a huge ripple  but the sides looks impressive . and the bandwidth is too narrow for  SSB use.

                so back to more experiments  testing loading . Maybe the cause of the ripple from the input and  output side and change the capacitor bypass C to adjust the  band pass width .
            need a amplifier with more gain and high input impedance without loading the filter so that the filter is terminated with a plain resistive load.
mean while had enough today "BASTARD" as in Soldersmoke Blog . Feel like going to was some dishes and relax. I am suppose to be retired.

TO BE CONTINUE..