Up/Down Band Switching - Yaesu FT-100 Undocumented

UP/DOWN band switching

The UP/DOWN keys are intended to move up and down through the amateur bands
according to the manual. However, several users have noticed that the radio will put
additional non-amateur bands in the list if the radio is tuned to them while operating in
VFO mode. Examples of non-amateur bands that can end up in the list include the NOAA
weather station (165 MHz), and Citizen's Band (27 MHz). The FT100 will insert one
extra band on the HF side and one on the VHF/UHF side of the radio. It is not clear how
one removes the non-amateur bands from the list other than resetting the radio.
V/U MESFET pre-amp adjustment
When the FT-100 is in receive mode on VHF or UHF, now and then the squelch may
'splatter'. To clarify, what happens is this:
• The S-meter indicates brief peaks from S1 to S9++ (like there's a lot of static or
irregular spark-induced QRM)
• The green 'busy' LED goes on and off
• Lots of 'static-like' crackling sounds come from the speaker
This all looks like there's just a lot of QRM'ish noise on the frequency, but when you turn
the squelch threshold knob counterclockwise to open up the squelch, the whole
phenomenon disappears. If there really was static or QRM being received, this should not
happen. Also, if you turn the squelch threshold knob fully clockwise, the speaker remains
muted but the 'busy' LED and the S-meter still indicate irregular, intermittent and brief
signal peaks.
This is caused by spurious responses in the V/U MesFet pre-amps, the SGM2016s. The
cure is to go into the hidden F menus , hold in the ABC keys and power the radio on
and then press the function key and rotate the dial until you come to the F menus and the
first on will be F01 and once you find F01 the VHF receivers RF gain, lower the DAC
value to 115 and then go to F02, the UHF receivers RF gain, and lower its DAC value to
106. You may want to note the original DAC values and write them down just for
reference. Some users have had this problem and lowering the DAC value
for each pre-amp cured it.
IMD tests with the original values and the lowered values show no difference in
sensitivity, nor any change in 3rd order intercept point. There is however a marked
reduction in spurious response.
Apparently the radios are set up with a generic factory programmed DAC value and not
by actually measuring intercept points or by looking around the receiver range for
spurious responses. The DAC values have nothing to do directly with controlling the gain
such as controlling an attenuator value, all the DAC does is set the bias to the MESFETs
and they are borderline unstable at the bias setting with the factory DAC values.
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