New Expert 1.5K-FA and Pure Signal

[I4LEC]

Hi all,
might be interesting for the community to see how Pure Signal works together with the brand new Expert 1.5K-FA, see below link

73, Clay

http://www.eham.net/ehamforum/smf/index ... 980.0.html

[w-u-2-o]

Thanks for the look, Clay, it looks pretty good!

Too bad they chose to use a -60dB coupling factor. This puts the feedback level at about +2dBm at 1500W. That will work, certainly, but is not optimum, which is more like +7dBm. And it becomes less optimum as power is reduced. IMHO, it would be better if amp suppliers shoot for +10dBm outputs at 1500W (-50dB coupling factor), then people can fine tune the last few dB to taste with a rotary step attenuator:



They are usually cheap and plentiful on eBay.

73,

Scott

[I4LEC]

Hi Scott,

yes it looked very nice, given my input drive of 10W, the automatic attenuator settled to 21dB.
Based on your old notes, If I do recall correctly, the optimum level should be around 7db prior to over load, this latter happens at -11dBm on my unit (Att = 0), at least what I figure it out with my signal generator.

So the optimum PS input should be around -18dBm, given the 21dB of attenuation, I guess we are pretty close to your figures.

73, Clay

[w-u-2-o]

Yup, close. The 7K and 8K use 16dB pre-amp's vs. the 20dB pre-amp used on all of the other radios, so there is a 4dB difference there. There is also some kind of weird non-linearity or amplitude variation in the 8000 feedback path that I'm researching. But on all of the 10, 100 and 200 series radios shoot for +7 at the rear panel connector.