Thanks for the suggestions Bonnie. My tests were performed into a dummy load at low levels but I don't have a calibrated signal generator. I do have a scope so will do some testing to see what the amplitude from the Sound card/Signalink looks like but I am fairly certain it is flat for this range - this interface & sound card was in use with my FT-897D and I performed similar tests with no dramatic roll-off. LSB on this FT-450 behaves identically by the way.
The irritating thing is that as soon as I got the rig I upgraded to the latest firmware from Yaesu's website and wish I had run the tests on the version it came with. I asked Yaesu about the possibility of rolling-back the firmware and they said sure, if you've saved the previous version... the joke here is the software they provide to do the update has NO facility to save the previous version! I have asked the Yaesu engineer to take another look at the graph but I am reluctant to send the radio to them if all he is going to say "it is within design parameters" and charge me for the privilege. At the end of the day it was $616 new and it works fine for PSK31, CW and SWL which is 90% of what I do. 73 Sholto. expeditionradio wrote: > > > One more comment for Sholto on conducting tests of > the measured response of audio frequency vs. power > output of the SSB transmitter. > > The test must be conducted into a dummy load > at power levels well below any ALC action, > such as 1 watt. > > You must use a low impedance calibrated audio > signal generator to do this type of testing, > or all of your measurement results will be invalid! > > Your generator must have a source impedance of > 600 ohms or less. > > Use of a computer soundcard as the signal generator > and/or a ham radio audio interface, may cause > tilt errors in your measurement. There are ways > to use a computer soundcard, with an external > audio low impedance amplifier driver, but this > also must be calibrated. If a cheapo interface such > as a Signalink or other interface with small > audio transformers are part of your test system, > all of your measurements will be invalid. > > Use of an oscilloscope to monitor the constant > level of peak-to-peak audio voltage to the transmitter > audio input provides verification of the generator > source. > > An oscilloscope may also be used with a power > attenuator (or dummy load -20dB tap) to measure > the power output. > > 73 Bonnie KQ6XA > > >
