Also those tricks with dynamic bias and drain modulation mentioned upthread can only really be done in a rig not a standalone AMPLIFIER....

I should know, I have just such a thing on the bench, but mine uses old school bipolar devices (Because I had a load of BLW96 available).
A pair of FETs should sub with only minor changes and a new PA board however.

Efficiency can be good to excellent, but it does need a fair amount of DSP support to pull it off, and I would never try it except integrated into a radio (It needs far too much integration with the baseband processing to make it work well), also the drain power supply is a complicated piece of switchmode power engineering (Making the supply swing from ~12V up to 50V at envelope tracking speeds is a hard problem, as is keeping switching noise out of the RF stage).

I would reiterate that the high power sand is really not the problem, heatsinks, and capacitors are, ATC100B (Which is about the minimum I would consider at a few hundred watts for the output filter) are ~$1 each, and you will need 3 - 5 per filter, plus the toroids, with probably 6 or 7 filters to cover 160 - 6M. Moving up to something man enough for US legal limit just makes things really expensive.

Building a truly repeatable radio is hard, my prototype makes -60dB ref one tone, but coming up with suitable BITE to make the setup for that automatic is a headache, and dialling it in manually takes tweaking a lot of parameters in the software.

Dropping the drain voltage a modest amount does NOT automatically make the IMD go to pot, as long as you keep the voltage above the level needed for whatever PEP is being demanded given the drain impedance, modulating the drain voltage does change the gain, but there are ways around that as long as you do not drop it too far (LDMOS Cdg skyrockets at low drain voltage).

Regards, Dan.

It's been discussed here before.
One thing to note is that the power device is NOT usually the major expense in a SS amp, power supply, cooling and output filtering are.

Solid state is gradually becoming a more price competitive option, at least for medium power applications, but note that cooling is a MAJOR headache with high power solid state (Far more so then with something like an external anode tube), also you will likely need to budget for an (expensive) tuner with a SS amp where the Pi match at the output of a tube PA will match anything reasonable.

It is not the case that the costs and complexity are in the same places with the two technologies, so just looking at the price of the sand is not that informative. 

Regards, Dan.

Not quite, the inductance is (to a first order) independent of frequency.

What you have there appears to be some kind of 'calculate the required inductance for a given C and resonant frequency' equation, not the same thing at all. Use it to figure out what inductor you need, or what inductor you have from the resonant frequency and C,  but that is not quite the same thing as saying that that eqn. means that the inductor varies with frequency.

Inductors are usually thought of as L = mu * N * N, where mu is the permittivity of the core ((micro)Henries per turn squared) and N is the number of turns. Mu is dependent on core material, core geometry, diameter and spacing. 

Now inductors are about the least ideal of all components so there are some second order effects, particular with very high values where inter winding capacitance can cause additional resonances (Think  supply chokes in tube linears), but to a first order inductance is independent of frequency.

Regards, Dan.

True, you got to pick the right tool for the job, and actually the major usability thing is the user interface once you get to a basically competent RF circuit.

I am far from certain that the user interfaces have improved with time recently, the buttons and menus instead of knobs feels like a step backwards to me for all but the least frequently used controls. It definitely makes for a cheaper radio, but I am not convinced it makes for a better radio.

Also I am not convinced that the move to ever smaller radios is automatically a good thing in a base station rig, dammit I like controls I can actually see and hit quickly.

A subject somewhat dear to my heart as I am working on the front panel layout for my latest set.

Regards, Dan.

Been known to extensively modify modern rigs as well, the techniques change (SMT), but I have more then one modern rig where the front end has been modified to output an IF that I then do my own thing with (And one where the micro went unobtainable, where I replaced the entire processor with a more modern part (and wrote the code)).

"No user serviceable parts inside" is supposed to be as a challenge, isn't it?

Cost effective? Not very, but then none of it really is.
The older rigs did tend to far more of an exposition of the sheet metalworkers art then the modern stuff.

And yea, the S line was considerably more recent then the 390A.  

Regards, Dan.

Thales TMR5100 might well be reasonably typical for a fixed install or a communications truck or such.
True, but would the average ham receiver from back then have done much better, the S line was high end kit, never mind the R390-A.

73, Dan.

It can be done, but the real issue is that I think people were comparing against other contemporary sets, and for most uses the variation in the quality of modern receivers is far smaller then it was back then, thus the differences are smaller.

I also think there is a little bit of 'rose tinted spectacles' viewing going on.

You get similar things said about the old Drake sets, and while they can be updated fairly easily to be at least competitive. Stock? well lets just say things have moved on.  

Also remember that the S line were not exactly cheap by any means, let alone something like an R390 which was a $2,500 proposition back in 1951 (Equals ~$20K in 2011)!

For that these days, you could buy a very nice set from Rhode and Schwartz or similar, forget the stuff marketed as amateur service.
The real issue is that nobody is prepared to pay for really state of the art performance (because almost nobody needs it), so if you do want to play state of the art in HF radio you pretty much need to build it yourself these days or look outside the amateur market.

73, Dan.

The license should not really be testing that you know how to make successful use of the kit, just that you know how to stay within license conditions and how to avoid interference to others. In this, most digi modes are broadly similar, so why license per mode?

regards, Dan.

I am not at all sure I agree, seems to me that religion (and politics (Spit!)) are at best only peripheral to ham radio so should seldom come up, but that when they do, a degree of give and take is required.

Last I checked there was NO 'right not the be offended', nor a right not to have my faith questioned, if you are uncomfortable with either then either just move on,  or have a good old fashioned flame war, your choice. I doubt that many minds are changed by either option.

Freedom of religion is a good thing, but that does not imply that others cannot question your religion or even take the piss, just as you are free to return the favor (but for the most part please take both to email!).

Once you start doing the 'this makes me uncomfortable so it should not be discussed' route, you very quickly end up somewhere that is very much not good, far better just to move on (or worst case hit the 'ignore poster' button).

In any case, on a privately run website, the decision of the owner is the only one that matters.

Regards, Dan.

Don't forget that that 70% drain efficiency is probably running the device well into saturation and is far from the worst case for a mode like SSB.

Linear class AB (which is where most amps operate for SSB service) will have a drain efficiency more like 50% at 100% output, dropping rapidly with the envelope power.

600 - 700W per device might be doable for SSB service, but personally I think that pairs of SD2933 or 43  and a couple of power splitter/combiner networks looks like a better bet (Easier to cool, and should work out about the same price).
4 modules, doing say 400 - 500W each would give a nicely conservative design for 1.5KW output, with graceful fallback if a module faulted.

Apart from anything else, a lower power stage is going to be easier to get to work well at both top band and 6M (Physically smaller magnetics, so electrically shorter windings at 6M), quite apart from making the development blowups less spectacular.
Adding 6M to a all HF band amp is actually really a bridge too far in terms of the engineering compromises, designing a drain match for 160 - 10M is very much easier then 160 - 6M.

Got to love watching a chip cap unsolder itself from the board when you get the current distribution wrong......

IIRC AVX have some ceramic parts similar to the ATC products that may be worth a look in larger sizes.

Regards, Dan.

Stupidest? Not even close, try running with an open question pool for that title (it is very bad pedagogy as it tests memory rather then understanding)! Dropping a requirement for a mode that had fallen out of use as the common denominator between hams and the other users who are quite often the primary users of 'our' bands was actually probably overdue.

As for the old US advanced being the toughest in hamdom, meh!
Try the Japanese or even the UK advanced (our equivalent of the US extra), closed pool and even without study I can clock 90+% on the US Extra question pool, but only about 85% or so with study on the UK advanced (Which has design issues of its own, very subtle wording sometimes, it sets out to trick you, also poor test design, a further dirty trick is that the official practice paper is also rather easier then the real thing). 

I don't really understand the grandstanding about the historical tests that goes on. Sure you passed a different (and quite possibly harder) test, good for you, so what! Passing the test just says you have some certain minimum level of know how (Or at least could remember the answers then), other then that it means nothing.
Nothing wrong with saying ' I passed the old advanced exam' of course, until you start slating folks that could not take it even if they wanted to.

I know a couple of very expert weak signal UHF fanatics that never bothered with the top level exam because it gets them things that are of no value to their interests. I will instantly defer to them on matters of low noise preamps for 70cm or aerial noise temperature or whatever, NOT because of any exam, but because of their expertise. Pride in knowing how to do something difficult is far more worthy then pride in having passed an exam (Especially one with an open question pool that I suspect a determined 12 year old could fairly easily pass by rote).

Be proud of what you can make the radios do, or what you can build, or what the people you elmered have accomplished or whatever, not of what tests and exams you passed.

Regards, Dan.

Yep, nothing at all wrong with DSP if it is done right. Bear in mind however that a lot of the early DSP rigs did not really have the number crunching power to do it right, and that does rather show.

DSP in a transmitter provides several potential advantages over an all analogue set, and there is no real problem building almost arbitrarily sophisticated speech processors in a DSP and that things like I/Q Pair generation are really trivial where they are not in the analogue domain. Then you have some advanced tricks that DSP enables which would be very difficult in the analogue domain, error function keying, dynamic bias and envelope tracking power supplies for the finals are just the start.   

It does take a rather different design approach then an analogue rig, and there should probably still be a fair amount of tricky analogue up in the front end and IF amplifiers. Direct digital conversion is still not IMHO quite good enough to get state of the art performance, you really need a hybrid.

RF Field problems are more of a symptom of poor EMC design then any kind of inherent problem with the technology, and we can all think of radios that needed rather a lot of ferrite adding to get them to behave around high field strengths.

Picastar (A DIY Project in Radcom a few years back) is an implementation of a DSP IF rig for the HF bands that gets a very good write up for the quality of the audio on both transmit and receive.

Regards, Dan.

It means that the power combiner is seeing unequal output from the PA blocks, one of them has gone faulty or is not getting power or drive.
It could be power, it could be bias, it could be a blown FET or two.

Could be minor, is likely to be pretty major.

Regards, Dan.

Not really, do whatever works for you.
Plenty of fun to be had up in the VHF/UHF/Microwave bands if that is your thing.

Personally I wanted the whole thing, so my UK equivalent of the extra exam rolls around at the end of the month, but if VHF QRP is your thing I see absolutely nothing wrong with your approach.

You will of course get the occasional lid pulling the 'you are not a proper ham, I learned code before dashes were invented, yada yada', just ignore them and spin the dial.

Regards, Dan.

Plenty I suspect, but all they will tell you is how much past specifications they can run the chip, and that it "Hardly ever crashes".....
Not really what I consider to be good engineering.

Regards, Dan.