Date: Sun, 8 Apr 2018 04:57:26 -0400
From: Ward K7PO <wmwheaton@aim.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: W1VD amp help
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Paul,

I may have missed some of the previous posts, but here's my $0.02 worth. When I built my first version of the amp, I set the X2 option on the U3S and drove the amp directly from the CLK output on the U3S synth. Everything worked fine. On the next one, I had all sorts of weirdness until I removed the 50 ohm resistor on the input. I assumed the U3S at 3.3v couldn't provide enough drive across the resistor. Since then, I have left the resistor out of every amp driven by the U3S, with no issues. A level translator would probably be better, but I have thousands of hours on a couple of these amps with no problems.

Ward K7PO 

 
-----Original Message-----
From: JD <us66soft@aol.com>
To: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Sent: Sat, Apr 7, 2018 10:37 pm
Subject: Re: LF: W1VD amp help

The 74F74 is an edge-triggered flip-flop. so the correct input for the main board is a square wave at TTL voltage levels, with fast rise and fall times, but with a current requirement greater than TTL because of the 51 ohm load resistor.

As for the oscillation when the doubler is used, the issue may be whether there's enough shielding.  The phase detector input of the 74HCT4046 that provides signal conditioning is very sensitive...maybe not enough to break into oscillation spontaneously, but perhaps enough to sustain it once a feedback path has been established with actual RF through the power stage.

73
John


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<font color='black' size='3' face='Comic Sans MS, sans-serif'>P<font size="3">aul,<br>
<br>
I may have missed some of the previous posts, but here's my $0.02 worth. When I built my first version of the amp, I set the X2 option on the U3S and drove the amp directly from the CLK output on the U3S synth. Everything worked fine. On the next one, I had all sorts of weirdness until I removed the 50 ohm resistor on the input. I assumed the U3S at 3.3v couldn't provide enough drive across the resistor. Since then, I have left the resistor out of every amp driven by the U3S, with no issues. A level translator would probably be better, but I have thousands of hours on a couple of these amps with no problems.<br>
<br>
Ward K7PO <br>
</font>
<div> <br>
</div>

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<div style="font-family:arial,helvetica;font-size:10pt;color:black">-----Original Message-----<br>
From: JD &lt;us66soft@aol.com&gt;<br>
To: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;<br>
Sent: Sat, Apr 7, 2018 10:37 pm<br>
Subject: Re: LF: W1VD amp help<br>
<br>
The 74F74 is an edge-triggered flip-flop. so the correct input for the main board is a square wave at TTL voltage levels, with fast rise and fall times, but with a current requirement greater than TTL because of the 51 ohm load resistor.<br>
<br>
As for the oscillation when the doubler is used, the issue may be whether there's enough shielding.  The phase detector input of the 74HCT4046 that provides signal conditioning is very sensitive...maybe not enough to break into oscillation spontaneously, but perhaps enough to sustain it once a feedback path has been established with actual RF through the power stage.<br>
<br>
73<br>
John<br>
<br>
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