[Amps] Why are we building amps rather then transmitters? (Tubes vs. Solid State)

[Dan Mills]

On Thu, 2012-05-03 at 23:52 -0400, Roger (K8RI) wrote:
> On 5/3/2012 6:20 PM, W2XJ wrote:

> When we combine the transmitter or transceiver with the amp we now have 
> a very sophisticated amp that has just had its MTBF most likely cut in half.
> If you follow the Icom and Yaesu reflectors you will find that these top 
> end transceivers are not trouble free and they are very complex pieces 
> of equipment.

I was only advocating the transmitter being integrated (and only part of
it at that!), adding the RF signal generation and I/Q modulator to the
amp housing seems to be to be fairly trivial small signal electronics if
the amp is simple minded, or something more if the amp is trying to be
clever, but look at what it does to the other box:

It removes the heat from the 100W PA. 
It removes now redundant LPF networks and their associated relays (not
exactly a trouble free area!).
It removes the 100W PA (so making more space for a better RX).
Probably the fan can go.
As the 'amp' is now a transmitter, that stupid gain limitation the FCC
impose on amplifiers goes out the window so we do not need to make 100W,
then attenuate it to 15W before driving a 20db gain power stage.

Note that if the input to the exciter is an I/Q pair of reasonable
bandwidth, then that power section can operate any mode nearly
trivially, dependent only on what the DSP in the front end can produce
as the I/Q pair. 

Back in the day, separate transmitters were sold because the transceiver
as we know it did not really exist, then the transceiver as a package
became the go to option because much of the (then) expensive signal
processing path could be shared between transmit and receive and sharing
things like the VFO was a operational convenience. 

My contention is that the sand has now advanced enough to make the low
level modulator and RF stages of a transmitter an almost irrelevant part
of the cost of a rig (never mind an amp), so if it allows the amp to
play it smarter it surely makes sense to provide the signals from the
basic radio to allow an external modulator/amp to work with input as
something other then 100W or RF power. 
A 100W packaged radio would require an extra connector to support this
style of operation as well as a menu option to turn off  its internal
transmit path, and it might be that the internal 100W transmit path
could be an optional module....


> I do like the idea of amps that can be integrated *with* the 
> transceivers so they operate as if they were part of the transceiver, 
> but physically seperate so  they don't have to be purchased at the same 
> time and neither piece of equipment depends on the reliability of the 
> other. In this case the amp doesn't have to be driven by the output, but 
> from a much lower power intermediate stage.

I am advocating forgoing the RF drive to the amp and sending it a
baseband pair and data about what frequency to translate it to. 

RF as input to an 'amp' has only downsides as far as I can see given
that generating the RF inside the 'amp' is so nearly trivial these
days.  

73, Dan (M0HCN)