Harmonics. The fundamental 25 kHz signal is typically a square wave that is rich in harmonics well up into the VHF region. That is also why the accuracy of the marker decreases as you go up in frequency. The error is multiplied as well.
Anyone who has been around a while and had a .76 repeater in their area will remember the odd signal the used to be ubiquitous near 146.76. This was a harmonic of the 3.579545 MHz colorburst crystal used in analog color television sets and as a cheap master reference crystal in lots of consumer electronics (including at least one 2m HT). Not so common any more but it still can be found.
This is also an object lesson in why our transmitters have harmonic filters. :)
73
-Jim
NU0C
On Sun, 16 Jan 2022 09:27:57 -0800
andrewhege33@... wrote:
Hello,
I'm wondering how the Marker signal which seems to be a 25KHz NF signal actually leads to a signal 'received' on 14.2 MHz ...?
Any input appreciated
73
Jim Shorney