[Yaesu] Anyone else with FT1500M spurious output?

2003年4月02日 22:11:39 -0800

I noticed a similar problem on a Yaesu FT-2500M, as well as on radios of
other brands. One possible cause may be related to the settling time of
the VCO when it is changed from receive to transmit. Although there are
many different ways to accomplish this task, the local oscillator must
shift from one frequency that is (usually) 10.7 MHz below the channel
frequency when receiving, to another frequency that is the channel
frequency +/- the offset. If the transmit PA is energized before the
VCO settles, some spurious signals will be radiated for a short period. 
The frequency of this "ringing" is related to the VCO loop gain and the
properties of a number of components. When the keying of the carrier
occurs at a certain phase relationship to the ringing, a sustained set
of sidebands are produced that can be well outside of the authorized
bandwidth.
It's a sad commentary on the amateur-radio industry that some radio
makers are more interested in making a radio inexpensive than in making
it stable and spur-free. Bottom Line: There are few 125ドル ham
transceivers that can match the quality and stability of a commercial
radio that costs 600ドル. Choose wisely...
73, Eric Lemmon WB6FLY
Viewing its output on an HP-8920 analyzer found that on the "initial key
up" it had spurs almost as strong as the desired frequency across a wide
portion of the VHF spectrum.