[Amps] Solid State Amps

Carl km1h at jeremy.qozzy.com
Sun Oct 19 15:59:16 EDT 2014


With all your spare time how about coming up with a substitution chart plus 
what changes are needed for a wide range of RF devices that are no longer in 
production with some unobtainium? This would include VHF/UHF brick amps.

Carl
KM1H



----- Original Message ----- 
From: "Manfred Mornhinweg" <manfred at ludens.cl>
To: <amps at contesting.com>
Sent: Sunday, October 19, 2014 1:53 PM
Subject: Re: [Amps] Solid State Amps


> Roger,
>
>> Small, generic LCD screens could be produced for pennies, or at most, a 
>> few dollars as you can now purchase a 40" smart HD TV receiver for 
>> $300-$400.
>
> It's a matter of checking what a simple cellphone costs these days. Two 
> years ago I got my latest one, an old-style dumbphone in clamshell style. 
> That one has two displays, a monochromatic one outside and a pretty decent 
> color display inside. The whole phone cost like $30, including shipping 
> from China, and that's a price that wasn't subventioned by a phone 
> company! So the displays really must be cheap, when bought in the quantity 
> a cellphone make buys them.
>
> > How many
>> transistors used in SS rigs over the last two decades are no longer 
>> available?
>
> That's not a problem, because essentially any transistor can be replaced 
> by a different one. But the problem does exist with specific ICs. A famous 
> (or rather, infamous) case is the DDS chips of the Kenwood TS-450, 690, 
> 850, that seem to rot from the inside out due to some fabrication mistake. 
> Those ICs are specific, discontinued, and presently unavailable except 
> perhaps from someone who has a few stockpiled, and sells them at a very 
> stiff price. And there is nothing that can replace them in a plug-in 
> fashion. One would have to cook a new board with a different DDS chip and 
> a MCU or other circuit to translate the commands, to revive any of these 
> radios whose DDS chips went bad.
>
> Mine went bad in time, when I still could get replacements without the 
> fabrication mistake, so I'm fine in this regard. But I know of several 
> hams who have dead radios of these models, and no way to fix them.
>
>> However, HRD and other Graphical interfaces can replace most of the front 
>> panel, let alone the individual  displays on today's rigs.  If using HRD 
>> you might not even notice a failed, non essential display.
>
> It's true, but when you tie a radio to a computer, it's getting twice as 
> expensive, 5 times larger and heavier, and the power consumption is 10 
> times higher. So it's really good to be able to operate a radio without an 
> external computer!
>
> And now, let's go to really interesting matters!
>
>
> Warren,
>
>> ** It seems to me that it's probably much easier to optimally implement 
>> pre-distortion in a DDC/DUC (digital up-conversion / digital 
>> down-conversion) software defined radio than in other radios.  There are 
>> simply very few places that errors can creep into the required 
>> processing.  The required precision and accuracy increase exponentially 
>> as the desired reduction in IMD increases. So, having few error sources 
>> and the benefit of double-precision floating point become important.
>
> What does "double-precision" mean in this case? 32 bits, 64 bits, or how 
> much?
>
> To have errors down 60dB, even 16 bit should be OK, for a single 
> operation. But I wonder how many math operations are involved in a radio's 
> whole processing. That surely calls for more bits of resolution in each 
> operation!
>
> I saw that a DSP chip with integrated CODEC, aimed at mid level HiFi 
> applications, has a 56 bit processor! They strive to put any errors about 
> 100dB down from the peak signal.
>
>> ** 50V LDMOS amplifiers are probably the "most correctable" solid state 
>> amps.  Tube type amps also correct very well.  13.8V amps are more 
>> difficult due to "memory effects."
>
> What memory effects do you mean here? Dielectric absorption, thermal 
> effects, or what?
>
>> ** No problem to correct an entire amplifier chain, at legal limit. No 
>> extra hardware or software is required.  One just feeds back a sample of 
>> the output from the last stage to calculate the correction.
>
> That's the nicest thing about SDRs. Once you have the interfaces to the 
> analog world up and running, and a good chunk of processing power, you can 
> do pretty much _anything_ at no additional cost.
>
>> ** You cannot successfully correct by pre-distorting the MIC input to a 
>> radio UNLESS you have VERY wide bandwidth from the MIC through the entire 
>> transmitter. The IMD frequencies that you want to correct must be within 
>> the bandpass of the correction path.
>
> Here you caught me in a shaky position. It's where I touch the limits of 
> my present theoretical knowledge about the matter. If I set up an 
> amplifier that corrects amplitude nonlinearities, with a loop bandwidth of 
> 30kHz, does this mean that any amplitude-error-caused IMD more than 30kHz 
> away from the center frequency will not be corrected at all? But that 
> could still be quite useful, given that IMD so far away from the center 
> frequency should anyway be pretty low.
>
>> At Ham Radio Friedrichshafen this past June, I gave a talk (approx. 30 
>> min.) on the openHPSDR solution for pre-distortion.  It's posted on the 
>> openHPSDR web site.  If any are interested, here's a link:
>>
>> "*Warren Pratt,*NR0V, 2014.Digital Predistortion linearizes RF amplifiers 
>> <http://video.openhpsdr.org/HRF2014/PureSignal1.2.mp4>(MP4)"
>
> Is the contents of that video available in written form? Due to internet 
> connection limitations, I cannot download videos...
>
>> I hope this helps explain a little more about this technology and sparks 
>> more interest in finding ways to reduce IMD!
>
> It does! For several years I have been wanting to get seriously into DSP 
> and really do something myself in the area, but never have found the entry 
> door. Warren, can you perhaps suggest a practical, inexpensive way to set 
> up a kind of DSP breadboard, that would allow me to mount a processor, 
> suitable A/D, D/A sections, and then go along getting my feet wet 
> programming it? So far my only attempts at incorporating DSP into my own 
> projects has been by basic digital filtering functions in low frequency 
> applications. Mostly power line frequency. And implemented in integer 
> math, on 8-bit PICs!
>
> Years ago I tried my hand with a DSP-93 kit that I got for free, but never 
> found out how to even start doing something useful with it.
>
> Roger seems to be in the same boat I am.
>
> Manfred
>
> ========================
> Visit my hobby homepage!
> http://ludens.cl
> ========================
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2015.0.5315 / Virus Database: 4181/8416 - Release Date: 10/19/14
> 



More information about the Amps mailing list