New Expert 1.5K-FA and Pure Signal

I4LEC
Posts: 5
Joined: Sun Apr 09, 2017 2:58 pm

New Expert 1.5K-FA and Pure Signal

Postby I4LEC » Sat Dec 02, 2017 9:42 am

Hi all,
might be interesting for the community to see :roll: 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
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w-u-2-o
Posts: 784
Joined: Fri Mar 10, 2017 1:47 pm

Re: New Expert 1.5K-FA and Pure Signal

Postby w-u-2-o » Sat Dec 02, 2017 11:46 am

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:

Image

They are usually cheap and plentiful on eBay.

73,

Scott
I4LEC
Posts: 5
Joined: Sun Apr 09, 2017 2:58 pm

Re: New Expert 1.5K-FA and Pure Signal

Postby I4LEC » Sat Dec 02, 2017 1:54 pm

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
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w-u-2-o
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Joined: Fri Mar 10, 2017 1:47 pm

Re: New Expert 1.5K-FA and Pure Signal

Postby w-u-2-o » Sat Dec 02, 2017 2:28 pm

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.

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