On 5/3/2012 6:20 PM, W2XJ wrote:
> A good portion of this has already been done. Check the HPSDR group.
> Also look at the ADAT. The final hurdle is to do this at the legal limit.
Viking had a legal limit transmitter (Invader 2000?) while Hallicrafters
had a legal limit transceiver, the SR2000.
I have a top of the line transceiver the Yaesu FTDX5000MP and what was a
leading transceiver in its day, the Icom 756 Pro.
I have an Emtron DX-2sp amp which is a legal limit amp that will run 24
X 7 any mode and the Alpha 76 which was a nice amp for it's day. I even
have reconditioned a hallicrafters HT-33B amp which was also considered
to be one of the "good ones" back in its day. However, I didn't
purchase the transmitters and amps at the same time. Far more hams are
able to get one or the other even if they are top end, but not both at
the same time. Yes there are hams who can plunk down ten grand for a
state of the art, legal limit transceiver although they are a very small
percent of the existing hams. That's no more than the cost of the top
end Icom or Yaesu transceivers.
This approach reminds me of the old "entertainment center" of the 60s
and 70's with a stereo, TV, and record changer. As soon as the TV gave
out or was outdated the entire system ended up out by the road even
though the record change and stereo were still good. These things were
big! Fairly expensive too. We think today's large screen TV are
expensive. Back then a huge 21" CRT color TV cost over $4,000. They'd
give two body builders hernias to move.
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.
The more complex the piece of equipment the more likely it will have
problems. Many of the transceivers suffer from teething problems, some
times for years. Those ten to thirteen thousand transceivers are
already being replaced by better equipment for roughly half the price.
The manufacturers have to limit the features on some of these new
transceivers to maintain the market for the expensive stuff, but as
demand falls off the old, but expensive will fall by the wayside. OTOH
they just go whole hog on the new ones because they expect to make more
money selling a lot more of the rigs that run only half the cost of the
ones they only sell a few of.
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.
73
Roger (K8RI)
>
> We did have transmitters back when AM was dominant. I fondly remember
> the Viking 500 but I do not think such an approach is practical for
> commercial production as not everyone can use a full limit TX and would
> not pay for it.
>
> On 5/3/12 6:03 PM, Dan Mills wrote:
>> On Thu, 2012-05-03 at 17:29 -0400, W2XJ wrote:
>>> I agree. A complete transmitter would solve many technical issues and
>>> depending on the implementation, could drastically improve performance.
>>> Solid State broadcast transmitters that transmit digital carriers along
>>> with analog and therefore must run in linear mode can achieve IMD under
>>> -80 DBC using techniques most easily implemented in a composite unit.
>>> For an I/Q interface, I think SDR has evolved to the point that Ethernet
>>> is all that is required. Any control or tuning can use the same Ethernet
>>> connection.
>> I was thinking in terms of taking the data (possibly as ethernet frames)
>> straight into a modest FPGA and then doing the upsample followed by
>> cordic carrier generation thing in the gate array.
>> Something like a very modest cyclone III should suffice I would have
>> thought.
>>
>> Output could be either full on EER/PWM or partial EER with cartesian
>> feedback via a high speed ADC with the loop closed right in the gate
>> array.
>>
>> Regards, Dan.
>>
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