I am researching a frequency to use for Part 15 AM broadcasting. I have found RadioLocator.com and that has been quite useful. I have also been DXing on my car radio and small portable unit (Sony Walkman SRF-M37V - radio only) to see what I came up with, both indoors and outdoors on the street.
Even though I'm in a very populated metropolitan area loaded with stations, I've still found a few open spots. My question is this: everything else being equal, is it better to do a part 15 broadcast on the lower end of the AM band or the higher end? In my city there is room in the extended band (stations are on the air at 1650, and one distant station at 1700 that I pickup outdoors at night), but I wanted to avoid that since there are still a lot of old radios out there that don't go above 1610. There's room down at the bottom at 530, and another possible slot somewhere in the middle.
I am researching a frequency to use for Part 15 AM broadcasting. I have found RadioLocator.com and that has been quite useful. I have also been DXing on my car radio and small portable unit (Sony Walkman SRF-M37V - radio only) to see what I came up with, both indoors and outdoors on the street.
Even though I'm in a very populated metropolitan area loaded with stations, I've still found a few open spots. My question is this: everything else being equal, is it better to do a part 15 broadcast on the lower end of the AM band or the higher end? In my city there is room in the extended band (stations are on the air at 1650, and one distant station at 1700 that I pickup outdoors at night), but I wanted to avoid that since there are still a lot of old radios out there that don't go above 1610. There's room down at the bottom at 530, and another possible slot somewhere in the middle.
I realize the question is a bit general, and yes, everything depends upon the individual situation on the ground. But can anyone opine on this?
- Scott
A couple of things to keep in mind.
High end is an easier antenna match, and your signal might travel a little bit farther, but interference is worse and skywave at night from other stations will be intense.
Low end is less prone to interference, but the antenna match becomes more challenging.
All part of the fun, and welcome to Part15.us!
I agree with the comments of SCWIS above, but I want to add my observation.
In my home AM is almost not usable due to light dimmers whether they are on, off, or in between. However, I notice that the interference is less at the high end of the AM band (above about 1200 kHz.) If true in general, this might be an advantage to choosing a high frequency.
I wonder if anyone else notices the same difference.
Neil
The base impedance of a 3-meter x 1/4" OD Part 15 AM antenna is about 0.12 -j2900 ohms at 1700 kHz, and about 0.01 -j9000 ohms at 540 kHz.
Antenna system radiation efficiency is a function of the radiation resistance of the antenna compared to the other resistances in the antenna system (mostly in the r-f ground plane and the loading coil). The 1700 kHz antenna has over 10X the radiation resistance of the 540 kHz antenna. Radiation resistance is the first number appearing in the base impedance values above (ie, 0.12 or 0.01 ohms). The coil loss needed to resonate the 1700 kHz radiator can be significantly less, also, because its input reactance is about 2/3 less than on 540 kHz.
The end result is that the radiation efficiency of these two systems at resonance will greatly favor the 1700 kHz system.