apache-labs.com

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

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

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

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.