It does that, but note that most of the DDS parts from AD (that surely have their uses) talk SPI so you need both on the backplane, not a big deal if you use 64 pin connectors for the motherboard/card interface (standard subrack stuff).

Unfortunately I suspect that rewriting EMRFD & TAOE is probably not something any kit designer is up for, the elecraft stuff for example is very clear about what to do, but the underlying theory? not so much..

PA and (probably) RX BPF would need to be mounted external to the subrack frame, but that is possible. Not small, and not cheap, but it would probably be the ultimate experimenters rig.

This notion bears thinking on. 
One of my sisters kids has one like that, very similar to what I had from 'Tandy' (Think UK rat shack) at the same age 30 odd years ago, but it transpires that the thing does not survive an environmentally conscious parent putting nicads in it (At least not when the 9 year old in question does not quite get things like power dissipation!).  

73's Dan.

Tacky flux does not really work like that for the most part.
HASL is standard but does not in general provide sufficient solder to do the job, you always need to add more.

As to a common bus for the RF/IF/LO/CIO/Control, sounds like a crosstalk nightmare to me, far better to do a common bus for I2C/SPI/Power and say make the boards as eurocards that plug into the backplane with all the RF hookup being done on the front of a subrack with SMA or similar.

The metalwork is pretty much off the shelf, and the modular nature of such a rig would allow upgrades forever, it would however make a FTDX5000 seem cheap.

I might have to try it sometime.

Regards, Dan.

With a mere 120V to ground your chances of electrocution are present but fairly low. Even 240 to ground is usually just a nasty wakeup call that you were not paying attention (I hate to admit it, but been there).

What stands a FAR bigger chance of doing for you when working on a panel board is arcflash or other burns caused by accidentally shorting a supply that thinks NOTHING of putting a thousand amps into a plasma until the fuses open (which can take a surprisingly long time). Seen it, not pretty, and a far bigger danger then getting across one phase and earth (especially with dry skin and wearing shoes).

When you have seen mega VoltAmpere switchgear suffer an internal mechanical fault and short out (Loose mounting bolts caused the earth bus to drop onto a phase busbar), you gain a newfound respect for what a 1200A 400V three phase supply can do before the breakers open, domestic supplies cause smaller explosions, but it would still be enough if your face and hands were in there.

This incidentally is a good reason to use cat III test gear and (importantly) cat III probes on that stuff, folks have died when test gear failed to fail safe during a transient surge.

If in doubt get someone else to sort it.

Regards, Dan.

Most receivers these days are way more sensitive on the lower HF bands then they really need to be.

Dialing up the input attenuator until the band noise is just above the receivers noise floor will always give the best performance as the IMD drops far more rapidly then the signal strength does.

About the only time a preamp is really useful below 20M is if you have a **severely** compromised aerial system. Any other time, preamp on down there is a error as it will not help.  

Note that band noise drops with increasing frequency so a preamp  may be useful at 6M and above (but is best if placed at the mast head), and even then should only be switched in if the band noise is below the receivers noise floor.

All knobs to the right is even more of an error when running a receiver then it is when transmitting.

Regards, Dan.

Ref SMT, I actually find that as long as I stay in the sort of 1206/0805/0603 region and have a magnifier light, it is no harder then through hole.
The methods are a bit different, but harder? Not particularly.

Even the big TQFP 100+ pin 0.5mm spacing packages are actually much easier then you would expect, BGAs are a pain in the arse, as are thermally enhanced TQFP, but even these are possible.

I also suspect that many of the folks who used to build heathkit stuff probably just go on line and buy part kits from the many small companies and individuals that make them available these days. For example there are several people who sell vector network analyzers as anything from a bare board to a full kit to a kit with all the small passives fitted.....
PA3AKE sold dozens of sets of boards for his frontend design (and that thing is not cheap or low performance by anyones measure).

The thing is that what has changed is that the action in diy electronics has moved away from a single manufacturer with a very detailed set of build instructions to many small manufacturers with somewhat sketchy instructions and email lists for builders (And no real expectation that anyone will build exactly as per the design).

I don't see heath introducing anything really price competitive these days and without that incentive the number of folks building for the hell of it is I suspect rather small.
 
Regards, Dan.

Yep, where there is specific advice from the manufacturer that should be followed.

I would be very surprised to see the chassis bond run that close to overload, simple voltage drop issues make that a bad plan, but still following the manufacturers advice is probably best in the cases where it is available.

Regards, Dan.

This is getting waay off topic, but you will not build a PA with that performance, you will build a **transmitter** with that performance....
The PA is standard and is linearized by the envelope feedback to the modulator.

One gotcha is that things like VSWR foldback have to involve the modulator as otherwise it will just ramp the drive power to try to maintain the set gain level. 

Actually with a collection of pads and a suitable power sampler head you could probably bring most external solid state PAs inside the loop, but that is a sort of advanced topic and I have not tried it yet. I suspect however that valve external PAs are right out with this system however (Too high a tank circuit Q).

Regards, Dan.

Yea a large face mill followed by polishing should be good enough, as long as the contact area does not cross two passes of the cutter (where any tilt in the mill head will result in a ridge (and there is always some)).

Sure you get voids with solder, and it is not a great heat transfer material, but it is one hell of a lot better then white gunk, or air. 
The other approach is to use more PA devices and so increase the area of the heat transfer, as the power flux density drops so does the delta T.

I do wonder about just sticking a bit of indium foil in there, and clamping down, it is VERY soft and should flow to gap fill quite effectively. Might want to power on and heat the interface before re tightening to make sure nothing comes loose as the indium flows.

On that point, use a torque wrench on the device mounting screws! Over tightening can actually distort the base of the device and cause poor contact.

PAs are all about attention to detail.

Regards, Dan.

If you do run wire back to the battery negative, there is one important gotcha....

If you connect this to the battery negative terminal then there is a risk that should the battery negative to chassis strap come adrift and an attempt be made to start the car then the starter current will try to find its way back to the battery via the coax outer, radio and radio negative return.... Smokey at best!

In a high power installation even fusing this connection may not help as the fuse will likely need to be rated high enough that the coax braid will melt first.

UK best practice is to connect the DC return from the radio to the chassis near the point where the battery negative strap connects to the chassis, not to the negative pole of the battery, this connection is unfused. This does make the battery negative strap a common impedance, but also means that this strap coming adrift will not potentially start a fire.

The DC feed can reasonably be fitted with a common mode choke to keep RF off the supply cables (and thus out of the engine compartment), large binocular cores are good for this. 

The standard to google for is FCS1392 (a free download), which also includes the advice that vehicle manufacturers specific advice should be followed if available.

Of course US custom and practice probably does differ, as did ours (used to be the old 2 fuse thing until the standard was revised). 
You pays your money and takes your choice.

Regards, Dan.

Oh all the manufacturers you mention know exactly how to do it, it is not rocket science.

But doing it right costs money, and space, and weight and potentially efficiency, and you really do NOT want to do it with 12V parts, so possibly you need a boost converter in there if the rig really must run off 12V.....

 Big heatsinks, 400W devices in 200W PA strips, power rails that stay put under full modulation, magnetics and wire that are man enough under 3:1 VSWR, audio stages rated at 0.1% THD instead of 10%, it is enough to bring a beancounter out in hives!

Also you do it this way and you get ONE receiver and one transmitter in a $5,000 radio, not popular these days.

Regards, Dan.

The trick is all in the feedback!

basically I am using cartesian envelope feedback with the group delay in the PA compensated by using two DDS chips (one for the forward IQ modulator carrier and one for the reverse), then by tweaking the phase control registers I can bring the returned signals into phase with the forward path, add a suitable band limited error amplifier and close the loop when the measured values come right and the distortion just vanishes.....
36dB of overall loop gain cures a lot of ills if you can make it stable.

As long as the group delay causes less then a few tens of degrees of phase shift change over the loop bandwidth (~70Khz in my design) no further loop compensation is needed.

This is all in 20+ year old literature, I found a paper about a design done for IIRC Racal that was doing this in the late 80's (Granted DDS makes it easier), so there is no excuse.

My biggest pain at the moment is (because the loop runs at baseband) dc offset drift, I might need some sort of chopper arrangement.

The PA  at the moment is nothing more then a pair of old BLW96 driven by BLW50F, nothing exciting (-30dBc or so open loop @250W), I am sure a modern SD whatever would do as well. Yes I know my intermediate license only allows 50W at the feed point, not using it on air yet, relax.

One trick I am working on is based on the realization that with all this feedback in place I can afford to vary the gain of the finals (slowly compared to the loop bandwidth) as long as the drive power stays within limits, this opens up the possibility of going to a sort of partial polar loop wrapped around the cartesian loop, in that the collector/drain voltage can follow (and lead on just a bit) the envelope, which with a DSP modulator is trivial (delay the audio a ms or so, and ramp the switchmode PSU as appropriate). The win is improved load matching at all power levels and less heat in the finals. The inner loop will compensate the gain changes automatically allowing the PSU modulation to be open loop.

Further for key down modes (or CW) I can start off with the PA bias in class AB, once full carrier power is achieved, bias can be ramped down to improve efficiency (the inner loop will automatically ramp the drive to compensate), possibly all the way to zero bias class C, with the reverse being done just before key up to allow the decay to happen.   

Getting both the bias control and the supply voltage control laws right is proving a bit nasty (they interact in horrible ways, especially on 10M, miller effect I suspect).

A key realization is that for SSB, it really does not matter what the efficiency is at PEP, what matters is the efficiency at 30% of PEP as the rig spends far more of its time down there then it does at full power.

Oh, also ALC between amps and the rig sucks, bad idea, don't do it, you know the amps rated power and the amps gain on each band, so just program the correct rig output power for each band..... AGC between gear which was not fairly carefully designed to work together will always suck as the composite transfer function will not have been designed in any sane way (Splatter city). 

Transmitters really are the low hanging fruit in ham radio at the moment, particularly as the HF receiver is fairly close to being at the point where QR{N,M} is the limiting factor in most situations (LO Phase noise is really the last part of that puzzle).

My problem is I am never satisfied, I really should just stop, design some nice boards and write this thing up for QEX/Radcom/DUBUS or whatever.

Regards, Dan.

IIRC Within territorial waters you should be operating under the CEPT reciprocal licensing arrangements for the country whos waters you are in (with whatever that countries rules for /mm are), so no, claiming .jp while sailing off la is not really cricket.

Operating in international waters should be done with your home call sign with an optional /mm (Helpful to tell operators with beams not to point them in the usual direction).

73's Dan.

It may, /mm is an optional suffix in the UK, and once in international waters the frequencies are per the IRU regions IIRC.
You have me now, I cannot remember if the permission is needed from the captain/skipper or the master (not  always the same person!).

And no, tidal is NOT quite the same thing as 'seaward side of the low water line' on the admiralty charts!

I suspect that while this all tends to be subject to minor national variations, the general idea is going to be the same in most places.

I should know this, it is in the advanced exam that I am studying for.
Regards, Dan.

IMD3 twenty below PEP, OUCH!

30dB below ONE TONE is about the minimum anything around here does, any worse then that and it gets fixed (-30dB ref one tone is not that hard if you design everything conservative like, as long as big and heavy does not bother you).
I have a rig on the drawing board that should manage better then -60dB ref one tone at competitive power levels and efficiency.

Note that the use of PEP rather then ONE TONE level for the test gives the manufacturer a 6dB free pass!

I should design a digital mode with a constellation diagram that only a really clean PA can reproduce, and try to get it popular, maybe get my full license and go and do some DX with it from a **REALLY** rare location.

Regards, Dan.

Personally I have a few things that I would think about publishing, but ONLY if there was a good way to get some peer review first!

I am not a fan of mandatory peer review in this context, but being able to submit a possible article for review would be (in my view) a good thing for those who wish to take advantage of the facility (And, at east for technical articles, I would wish to take advantage).

I am not bothered at all by technical (or even stylistic or grammar criticism), but would rather know where I screwed up before public distribution followed by needing to issue a retraction (Which is a little embarrassing).

Peer review is not always appropriate, opinion pieces in particular seldom benefit from it, but having a review committee and having it be an option for those who want to take advantage of it would be useful.

Even having a short list of specialists in particular areas who would be willing to informally look at the odd pre publication draft would be useful and would reduce somewhat the amount of folk law unintentionally repeated as truth.   

Regards, Dan.