Default AM Frequency 1610 Update
New station on 1610 in Toronto 1kw, CHHA. Licensed April 29 2005
Anyone hearing this yet?
Hope this will not be a trend in U.S.
Part 15 people using this frequency might want to think about trying to secure this channel through legislative action, if there are enough of us?!!? Along with other L/P users!
That is bad news for part 15ers. Certain frequencies like 530, 1610, 1620, 1630 are used by traffic and parks for information in the US. These are great for part 15ers who aren't near one of these short range info stations. Encroachment from commercial stations is not welcome for part 15ers OR the information stations.
The FCC and the international radio lawmakers should clean this up and reserve some frequencies! There are some commercial radio stations on these frequencies even inside the US. What a mess for any government agency that needs an info station. They should not have to compete with commercial stations for an available frequency.
Just wondering, why do people use the upper end of the AM band? You can get a MUCH better signal on something like 560, 610, etc.
The reason Part-15 operators use the upper end of the band is because of our antennas. The 10 foot antennas are more efficient there. Yes, the low frequencies cover better, but our antennas really lose efficiency on the low end. It's good for carrier-current, though. Our college radio station, KEWC (may it rest in peace!), was on 640 and covered pretty well.
The radiation resistance of a 3 meter antenna at the upper end of the band is about 0.1 ohm. At the low end it is about 0.01 ohm (10 times less). Higher radiation resistance is better. This is a measure of how well an antenna radiates relative to ground loss resistance. These antennas are severely crippled at both ends of the band, but at the high end, the antenna is slightly less crippled. A quarter wave vertical by comparison has an RR of about 50 ohms.
As an aside, the very low radiation resistance of these antennas is why a very good ground is so important. The radiation resistance is in series with the ground loss resistance. If you have 10 ohms of ground loss resistance (pretty good), at the high end of the band, your signal will go mostly to ground and the ratio of lost signal to radiated signal will be 10 ohms/0.1 ohm = 100:1. If you could sweat out achieving a 0.1 ohm ground loss resistance, the ratio would be 1:1. Even then half of your signal would be lost and the other half radiated, but you would be 100 times better off than with a 10 ohm ground.
With a full quarter wave vertical and 0.1 ohm ground loss, your ratio of lost signal to radiated signal would be 0.1 ohm/50 ohms = 1:500! Essentially all the signal is radiated.
The FCC obviuosly had low radiation resistance in mind when they wrote the 3 meter rule. They may not have expected that innovative users would install very elaborate ground systems to overcome the crippled 3 meter antenna.