[ARC5] AM linear amplification

[Richard Knoppow]

    Pretty high. Curiously, KGO ran with a strange 7.5 KW transmitter 
until it was bought by ABC. This transmitter was not capable of more 
than 80% modulation. KGO was owned by General Electric (K General 
Electric Oakland) and was leased to NBC, which GE controlled for years. 
It was the the NBC Blue network station.  When Blue was sold and became 
ABC the network installed a modern transmitter, and got the power 
increased to  50 KW with the aid of a directional antenna. I have no 
idea why NBC never did this. With their directional array KGO has 
enormous coverage in central California.

On 12/19/2016 5:28 PM, spr at earthlink.net wrote:
> Folks,
>
> I think I was told that the newest transmitter at KGO (50 kW in San Francisco) has an efficiency of 90%, line in to RF out.
> That is seriously high eficiency!
>
> Regards,
>
> Scott Robinson
>
>
> -----Original Message-----
>> From: Richard Knoppow <1oldlens1 at ix.netcom.com>
>> Sent: Dec 19, 2016 5:22 PM
>> To: arc5 at mailman.qth.net
>> Subject: Re: [ARC5] AM linear amplification
>>
>> Harris introduced the pulse modulated transmitter for AM some time ago
>> but I don't remember the date. The idea is that the modulation audio is
>> sampled at some high frequency, say around 70Khz and converted to a
>> variable width pulse. The pulses are applied to the final amp plate and
>> are integrated by the tank circuit. The result is AM but the transmitter
>> is capable of very high efficiency along with wide, flat, frequency
>> response and low distortion if done right. The original pulse modulated
>> transmitters were tube amps but Harris and others have gone to solid
>> state.  The kind of thing you describe would produce the same result
>> using an array of lower level switched devices.
>
>>    A modern 50KW transmitter has a line demand of well under 100 KW.
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL