[AMRadio] Pi-Net vs Link Couple


Geoff w5omr at satx.rr.com
Wed Sep 21 22:45:45 EDT 2005


SO, here we are, well past 1991 and the 'law' that went into effect 
saying that 1,500w PEP output is the maximum RF Power output that we 
hams can run, regarldless of mode.  That doesn't deter the homebrewing 
spirit, but it does suggest that acheiving 1,500w PEP output is much 
easier than producing 1kW DC input to the final.  With the mindset of 
still wanting to use the classic high-level plate modulation scheme, 
engineering a rig to use only one tube in the final (a 4-250, 250TH, 
304TH/TL, 4-400, etc), modulated by a pair seems to make more common 
sense.  That, and it's a bit more economic in filament requirements.

I've heard recently that matching the output of the Class C 
pate-modulated final to the antenna is better, and more efficiently 
achieved by link coupling, vs Pi-Net.  On the other hand, it's argued 
that Pi-Net coupling produces less RFI than link coupling does.

So, which is better?

Why?

What are the effects of nuetralizing a single tube in a balanced tank 
circuit?  If Pi-Net is to be used, does the final tube still need to be 
nuetralized?

I know of a guy who wants to build a rig using a single 450TL in the 
final, modulated by a pair.  He wants to pi-net the output, but I've 
heard that's a bad idea.

I want to build a rig using a medium powered tride, perhaps a 250TH, 
modulated by a pair of 811's.  Pi-Net, or Link Couple?

I like seeing this kind of technical discussion on the list.  I'm 
looking forward to all inputs.

--
73 = Best Regards,
-Geoff/W5OMR




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