Thanks, John. How do you have the AV-620 mounted?

Thanks for all of the suggestions. I agree that the Hy-Gain AV's sound like good antennas, and particularly with the current trend in the sunspot cycle, the AV-620 seems interesting. However, MFJ and DX Engineering both list only a "new" AV-620 "Patriot" for about $600. Is there a version of this antenna still on the market for about a third of that price?

Ralph, I'd agree that the Mid version (covering 40, 30, 20 and 17 meter bands) is a good starting point, because those are the bands most consistently open to DX opportunities at various times of day, at least in the current phase of the sunspot cycle. Personally I'm also interested in lower bands, but they tend to be best in winter months. As for upper bands, if you are interested in DXing on the 6-meter band during sporadic E openings in spring/summer, WSPR is one of several ways to watch for opportunities.

@toryglenn I have an existing 130-foot wire antenna, so as an initial experiment I made an LC circuit for it that resulted in an SWR of only 1.1:1. I ran the WSPR transmitter on 630m for two or three night, but got no spots. Hams active on 630m advised me that horizontal antennas are not practical for most people -- the 30-foot height of my wire antenna is such a small fraction of the 630m wavelength that I may as well have the wire laid across the ground. So an inverted-L (vertical with a horizontal cap-hat wire) seems to be the way to go. One fellow I contacted is experimenting with a large loop about 40 feet in diameter, but that's a more advanced design.

Yes, I registered with the utility group in the U.S., and they said there is no problem for me to transmit on either 630m or 2200m from my location. An update on my 630m project: I contacted some hams who are active on that band, and they all recommended an inverted-L antenna (the vertical portion is the radiating element, and a horizontal wire attached at the top acts as a capacitance hat). The antenna also requires a substantial inductor (usually called a "variometer") for loading and impedance matching purposes. While I started collecting components for this, I also noticed that band conditions gradually worsened as we moved into spring in the northern hemisphere. So I'm going to wait until autumn and work on the antenna and variometer then. Ultimately, higher transmitting power may also be required. In the meantime I'm working on a few other projects, including the frequency measurement testing that I mentioned in my original post above.