HPSDR Alex Filter Bank Prototype Test Results

These screenshots show the frequency response and return loss of the individual filter elements in the prototype HPSDR "Alex" filter bank product.

Note that these are not directly comparable to the production unit measurements as the receive plots here show only the RX board without the contribution of the TX board's low pass filters. Scales may also be different.

S-parameter and magnitude files, as well as analyzer parameter files, for these measurements are available here.

Receive Filters

RX 1.7 MHz High Pass Filter

RX 6.5 MHz High Pass Filter

RX 9.5 MHz High Pass Filter

RX 13.0 MHz High Pass Filter

RX 20.0 MHz High Pass Filter

RX 51.0 MHz Low Noise Amplifier/Band Pass Filter
(Drive level -40dBm to avoid compression)

System 55.0 MHz Low Pass Filter

Transmit Filters

TX 160M Low Pass Filter

TX 80M Low Pass Filter

TX 60/40M Low Pass Filter

TX 30/20M Low Pass Filter

TX 17/15M Low Pass Filter

TX 12/10M Low Pass Filter

TX 6M Low Pass Filter
(Network analyzer calibration did not support higher stop frequency; will rerun after recalibration)

System Response

10M - ANT 1 to RX OUT

6M - ANT 1 to RX OUT; source level -40 dBm

Note that there is a significant hump in the frequency response at around 110 MHz. This was due to lack of a low impedance ground between the Alex RX and TX boards. Adding a ground strap significantly improved the ultimate rejection; this plot shows before-and-after frequency responses:

Below are the original analyzer screenshots from which the combined plot was generated so you can see the marker values.

Note that the hump in the above shot is significantly sharper than in the earlier plot. That's because the analyzer settings were changed here to improve the noise floor, and among other things the bandwidth was reduced. It's also worth noting that the hump tended to move around and was influenced by the position of the test cables.

Here is the plot after adding the ground strap:

Penelope and Mercury Source Match

Penelope source match, at output BNC.

Mercury source match, at input BNC.