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Author Topic: Finals?  (Read 1415 times)
KD6OJG
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Posts: 38




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« on: October 23, 2013, 07:19:18 PM »

I am trying to learn as much as possible but there's a lot of terminology that loses me.

Could you please explain what finals are.  I know they are a part of a transceiver but every time I come across this word it is in a sentence along with "burn up".  Does it have to do with antennas or power being supplied to the radio?

What causes finals to be burned up.  I don't want to burn up my finals.  This doesn't sound good.  I have a Yaesu FT-840 that I bought back in the late 90's that I've taken good care of and it's practically in new condition and I don't want burn it up while I'm learning about station building and equipment.

When people talk about their Yaesu FT-817D they always mention burning up their finals.  Why does this happen easily to a FT-817D?

One more thing...What is a paper chaser?  I heard someone say that on 20 meter about another Ham today but didn't elaborate so I'm clueless.
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KD0REQ
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« Reply #1 on: October 23, 2013, 07:38:27 PM »

finals = the final stage of power amplification in a transmitter.

if your antennas aren't matched well, and the reverse voltage is too strong, that's one way to roast the finals.

another is inadequate heat sinking on transistors.  the story I've seen is that for best results, you need to lap-grind the back of the transistors and heat sink face for complete contact before you put on the compound and bolt the transistors down.  heatsinks are extruded aluminum, and transistor backs are stamped out of a sheet of metal.  neither is a fine-grained process.  rule of thumb is half the DC input power is wasted as heat.

rigs with heat issues also include tube jobs like the CX7, which infamously killed power transformers.  black tranny was right next to the RF compartment, and the tube was conduction cooled.  not much air circulation in that chassis.  whack, the primary winding was shorted.  the independent CX7 newsletter recommended a small fan facing the heatsink as one help, another was a sheet of plain shiny aluminum between the transformer and the RF cage.
« Last Edit: October 23, 2013, 07:43:57 PM by KD0REQ » Logged
NO2A
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Posts: 824




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« Reply #2 on: October 23, 2013, 07:49:32 PM »

"Finals" are simply the last stage in a transmitter that amplify a rf signal so it`s strong enough to be heard "on the air." Without finals,a signal would be extremely weak,though maybe still able to hear. They must be operated within limits to keep heat down,which can damage them. The problems with the FT-817 might be a design flaw,possibly. Though today`s transistors are well made,they can still suffer damage if not cooled properly,or constant transmit duty cycle (like on fm) (or long key down on cw)which causes heat very quickly. Simply allowing time for finals to cool down between transmit time is usually all that`s needed to insure years of good service from them. A "paper chaser" most likely means someone who operates in contests for awards.
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N1UK
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« Reply #3 on: October 23, 2013, 08:05:34 PM »

Quote
A "paper chaser" most likely means someone who operates in contests for awards

..or just works new DX for the QSL card and doesn't rag-chew with non-DX stations very much.    



Mark N1UK
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KD6OJG
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« Reply #4 on: October 24, 2013, 08:42:56 AM »

Thanks for the replies and information.  I understand better and I'll be able to do some research.

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