The thicker and more robust the outer layers are, the shorter the wavelength they can refract or reflect. During sunspot maxima, the maximum usable frequency (MUF) can get as high as 30 or even 50 MHz (six meters). That is, 30 MHz signals can bounce right off the ionosphere, or be trapped between two upper layers and ducted around the world before breaking out and coming down most anywhere. That’s how CB radio “skip” works, when folks listening to the radio in their cars on the highway in Kansas hear the chat between boats working the shrimps in the gulf of Mexico. Normally a CB radio is good for 5 miles, but when the sunspots are high, all bets are off.
During a normal sunspot minimum, when the sunspot count is down around 20 or 30, the MUF stays up around 14 MHz for at least part of the day, and seldom goes below 7 Mhz.
Frequency and wavelength are related. The higher the MUF, the shorter the wavelength and the smaller the antenna that is needed to send and receive radio signals. In general, one wants to use as short a wavelength as possible, because the higher the frequency, the smaller the antenna needed. A 30 MHz transmitter uses a “natural” antenna that is only three meters long. But a 7 MHz transmitter uses a natural antenna that is about twenty meters long. [NOTE: Wavelength in meters = 300 / Frequency in MHz. A “natural” vertical antenna is one quarter wavelength long. A “natura” horizontal antenna is a half-wavelength long.] Thus, the higher the MUF, the more convenient it is to build radio installations. Most Hams therefore work the 20-meter bands, and the 40-meter bands are not uncommon. But it’s the rare Ham who works 80 or 160 meters, since the natural antenna for 80 meters is 40 meters long, and 80 meters long for the lowest common Ham band of 160 meters.
However, remember the missing sunspots? During the Maunder Minimum, during the period that Eric has set the 1632 series in the middle of, the ABC layers of the ionosphere go away to a great extent. Of course, there is always some solar wind, and there will be some ionization and some reflection. But the MUF keeps dropping and dropping until, by the year 1640, to do long-distance communications without relays you would need to be using 2 MHz for much of the day, and can get up to 4 MHz only late at night.
And remember that the DEF layers absorb the long waves, so the low MUF means that you have little if any ability to do long distance communication during the day at all.
So, the radio installations in 1632 universe end up using very large antennas. The most common antenna for a diplomatic mission will be installed this way:
Take a piece of wire, forty meters long, and cut it in the middle. Put a glass insulator in the center of it, and hook another piece of wire to each of those twenty-meter-long pieces. The “hookup” wires are held apart every few inches by a hunk of glass or plastic or wood, like a little ladder two inches wide. This ladder leads back to the transmitter. Meanwhile, take your center insulator and haul it up to the top of a tower as high as you can get. One hundred and fifty feet is really a good height. Attach the glass insulator to the tower, and then, draw a line on the ground, in the direction of the city you want to talk to the most. Stretch each of the twenty-meter-long legs away from the tower at 60 degrees up from vertical, 30 degrees down from horizontal, and perpendicular to the line you drew (crossing it). Then hook the end of each wire to a rope with another glass insulator, and pull the ropes taut so that the wire is as straight as you can get it.
Now, remember how you drew a line towards the radio you want to reach, that you want to “beam” at? Build another tower, 20 feet back away from your destination, on that line. Now, do the exact same thing with another piece of wire on that tower. (You do not need hookup wires on this one.)