Dsa815 tg frequency counter generator#

Transformers on this core have worked very well for me in the past, but that has all been in the HF range or 50 MHz. I think the first thing to try is a different input transformer. The magnitude drops off precipitously between 90 and 100 MHz, right where the input stage stops working. I think this is due to reflection from the transformer performing poorly at these frequencies. Although the input level drops off slightly up to 90 MHz, it picks back up afterwards, becoming very large between 140 and 160 MHz. But, the shape of the traces shows the real problem. The difference in levels between the two is in part due to the transformer boosting the voltage. The yellow trace is the signal right at the input jack, while the magenta is after the transformer (across R1), shown here for reference: The vertical is set to linear mode to show the problems more clearly. This is always a little scary since the SA input is a bit delicate, but I was very careful. To capture these traces, I plugged a 10:1 oscilloscope probe into the input of the SA. I was poking around hopelessly at the front end with the oscilloscope when I realized I had a spectrum analyzer in front of me!

The first find took much longer than it should have. I spent a little quality time at the bench this morning, trying to diagnose the issues with the first prototype board. I have 3 copies of the PCB from OSH Park, so I'll make one of them for I/Q outputs up to 70 MHz, one of them for a single clock up to 296 MHz, and maybe one that skips the PLL to go below 300 kHz.ДЄ DC-296 MHz logic clock will do for the immediate future. I think based on this experiment, I won't re-spin the board. With lower frequencies, the scope can render the true shape more accurately, as shown here for 56 MHz (14 MHz input).

Dsa815 tg frequency counter generator#

The input frequency from the tracking generator was 74 MHz (=296/4). That's what you get when you look at a signal near the scope's bandwidth - everything looks like a sine wave, since none of the harmonics make it through. The highest controllable frequency I was able to get was 296 MHz, shown here on a 300 MHz scope: I cranked the TG frequency up until the PLL stopped following at 4x (at that point the PLL's VCO just stuck). With this mod, the input signal is buffered, the frequency is multiplied by 4, and the result output on one of the ports. It only took a few mm of wire and a steady hand. I finally got around to reworking the PCB to route the 4x PLL directly to one of the output drivers.

Dsa815-tg frequency counter