I've been trying to plan out a new project for a while. It's a wideband antenna anaylyzer for radio applications. I've figured out most of the details, but the most important part – the frequency source – has me stumped.
I'm trying to figure out the best way to cover the frequency range of ~1MHz to ~1GHz, which would cover pretty much all of the communications frequencies in use today.
I was originally planning on using a DDS chip like the AD9910, which is around $40 and about the most I want to spend on a single component. The problem with that chip is that even with a 1G reference clock it still goes downhill pretty quickly after 400MHz. Analog has more options, but price ramps up pretty steep after this chip.
The Si570 series from Silicon Labs was another idea I was tossing around, but the output of the 10M-1.4G chip is LVDS which is not easily converted to a sine wave without a lot of filtering.
A PLL was something I was tossing around, but I haven't done much research into them and it seems that most chip offerings are designed for higher microwave applications.
I know regardless of what I use I'll be including switchable filter banks to cover the entire range. I would love to hear input from some people who have more experience with RF design and see what you guys think I should be using to generate these frequencies. And by all means, feel free to tell me that what I'm doing is a very tall order.
And yes, I'm aware there are commercial options that I could buy instead of building an antenna analyzer myself, but where's the fun in that? This will be used for mostly amateur radio applications, so I'd love to homebrew something together.
UPDATE:
I'm now considering using the AD9910 coupled with a frequency multiplier of some kind to reach the desired range of 1 to 800 MHz. This could be the best option, if I can find a suitable chip for a reasonable price.
Thanks for the help.
Best Answer
Texas Instruments has a component that can do the majority of your desired RF output range: LMX2571. At around $12, quantity 1, on Digikey, this will successfully implement 10MHz to >1GHz signal synthesis. It also has an internal VCO, so its output range will not be dependent on an external VCO's frequency range.
Along with a high quality, but not necessarily as high-spec as the AD9910 that you suggested, you could probably cover audio (kHz) to 50MHz effectively for HF radios, then cover 30m/10MHz and higher frequencies with the LMX RF synthesizer.