Re: PM demodulation

On Fri, 05 Nov 2004 10:11:08 +0800, Steve Underwood <steveu@dis.org>
wrote:

>Allan Herriman wrote:
>
>>
>>All "solid state" finals for broadcast FM have been around since the
>>'80s.  At the time, they were better in terms of reliability, but not
>>initial purchase price.
>>
>>I don't know how the comparison stands today.
>>
>>Regards,
>>Allan
>>  
>>
>I said big FM transmitters. 100kW ERP from a silicon final stage? I 
>haven't seem that used

You're right.  At 100kW, valves (tubes) still rule.  Can't license
anything like that around here though.

Here's a 40kW solid state job from Harris:
http://www.broadcast.harris.com/product_portfolio/product_details.asp?sku=WWWZDD40CD
I think that's about as powerful as they get.

>Up to a couple of kW things are OK, but you need to stack too many well 
>matched transistors to keep scaling things. Minor mismatches cause a lot 
>of stress, and reliability tends to be rather poor.

Interesting.  Usually solid state transmitters are used because they
are *more* reliable (= more cost effective in the long term) that the
valve units they replace.
That was certainly the case for the microwave SSPAs produced by a
company I used to work for.

Regards,
Allan