You are disregarding the low power level and short electrical length of the line. Assuming a velocity factor of 0.70, at 42MHz the 0.5m physical line is only 1/10th of the wavelength (?).
I am not disregarding it, it is simply irrelevant to my point. This has nothing to do with transmission line behavior and is simply the effect of the cable capacitance. A 600 ohm output driving 50 picofarad of cable will create a low-pass filter with a 3 dB point around 5 MHz. If you don't see its filtering effect then you are incorrect about it being a 600 ohm source.
Now I feel like a complete idiot--a 67 year old brain fart of the sort I having been having more of lately as diabetes catches up with my decadent lifestyle.
I actually have two 1300s instruments, one with a completely savaged output board converted to 600? output, and other mods, for audio console work--very easy to do because of the separate design and implementation of the output panel. It sits at the audio end of my bench right beneath a Kikusui ORC-11 low distortion generator (600? out) and on top of an old Krohn-Hite dual channel hi-low pass filter, also 600?. All of which are instruments I have used most frequently in the last several years, in maintaining older sound studios here about.
However at 'tother end of the bench, the "RF" end, is a "stock" 1300s having a 50? output; that is the one I have been using for this series, with and without the 600? pass-through, just to make sure things were really screwed up--I just had "600?" hardwired into my brain when thinking "Leader 1300".
I.e. my eyes and brain were out of synchronization and neither side wanted to yield--thank you to those that pushed me through this roadblock, I really did used to know this stuff.
I apologise to the group--I really should just sell all this crap and sit on the front porch with a shawl draped about me like a proper retired person.
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FWIW here are some FFT analyses of a 500kHz squarewave from the 600? output 1300s (limited to 500kHz output because of the hacks) using both a terminated line and low capacitance (x10) probe; and also a time domain comparison of the two connections. In both the
Memory C trace is the "600? terminated" connection, the
Memory D trace the low capacitance X10 probe.
I did these on my old Lecroy 9450A that I could operate in my sleep...
frequency domain:
![](http://www.paladinmicro.com/images/Electronics/Leader5kHzSQ-01.jpg)
Above I have used the cursors to mark the 15th harmonic at 7.5kHz, you can see the 6dB+ amplitude improvement in the "probed" trace (-17.5 in the "terminated" spectra vs. -11.5 dB in the "probed" spectra) as has been pointed out should be the case.
time domain:
![](http://www.paladinmicro.com/images/Electronics/Leader5kHzSQ-02.jpg)
Here you can see
Memory C's (the "terminated" connection) slower rise time, more rounded top edge, and slower fall and roll-off--as compared to the probed connection shown in
Memory D.
So, all it as it should be...
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I still think the OP is seeing the best his old GW function generator pushed to its max can put out...