[AMRadio] Pi-Net vs Link Couple

Donald Chester k4kyv at hotmail.com
Thu Sep 22 22:34:16 EDT 2005

>I wonder though Don, while I've got your .. uhm 'ear' (eyes?)  The link 
>could use a little tuning to take a bit more load in the final.  I've 
>modified  one of my 80m B&W HDVL plug-in coils and removed two turns on 
>each side (4 turns, total), to raise the plate current a bit, because the Q 
>is a bit sharp in that circuit.  A breif excursion off-resonance, w/1.5kWDC 
>on the plates, draws around 550mA.  At Resonance (with 125mA of grid drive) 
>the thing dips to around 200mA.  That said, what value of series 
>capacitance would you suggest/recommend to tune the link?

In mine, I use a 4-turn link.  On 80m I have about a 1000 pf air variable 
directly in series with the link, and I think about 300 pf is actually 
meshed in for resonance.  On 160 I use a capacitive voltage divider formed 
by two fixed micas in series (about .002 each) with the 1000 pf variable 
bridged across one of them for fine tuning.  The load is placed across one 
of the caps.  I can get good coupling that way. When I tried a simple series 
cap on 160, I could hit resonance, but could only get about 10% coupling.  
On 40 I use the series cap, but it is almost completely unmeshed to hit 
resonance.  I duplicated the setup for my other homebrew rig, and it works 

73, Don

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