UK is /mm on the seaward side of the low water line, otherwise /m.
Maritime mobile is only available to full (Advanced) licensees, and requires the written permission of the vessels master. 

73's Dan.

Yea, but as long as the gain staging is halfway sane, power devices are usually fairly quiet.

Granted that 50+db of gain does tend to put a heavy emphasis on making the early stages of the drive chain as quiet as possible, and not all such chains seem to take as much care with matching in the mW stages as would be desirable.

Regards, Dan.

Well the big toroids Martein used in the front end box should be more or less immune to that fate anyway.

The antenna switching board will (when the rig is switched off) switch all the aerial inputs to ground so that unpleasant surprises at the aerials when the station is not in use are not shunted into the receiver.

And yea, one thing you cannot fix is the other guys radio, for all that I am thinking that there is something in the license about transmissions being as clean as the state of the amateur art reasonably permits (Have to go look up the exact wording)....... Pretty sure nobody wants to open that particular box!
 
Regards, Dan.

Your dynamic range is based on NOT having a QRO operator a few streets away who also likes to play on topband. That guy can light an LED across my aerial plug (400W? Got my doubts).

Actually his TX noise sidebands will probably be the real performance limiting factor.

Yea, I know all about the phase noise issue, lots of head scratching going on to try to build a LO that is both sufficiently quiet phase noise wise and has a reasonably low number of spurs, not an easy problem but  there are some promising approaches.

Actually, most of the build effort is in the BPF box, and that (or one much like it) I need for my transmitter design anyway to remove the image at +18Mhz from the mixer. Compared to that system the actual frontend board is almost a detail to build and I see no reason to design my own when he has done a perfectly good one (It needs a slight mod because I want to tap out an IF sample before the roofing filters for a panadaptor and a noise blanker, but that is trivial).
I probably don't need the first mixer performance, but as the mixer will only take a few hours to assemble, and the board came with the panel for the BPF, why not?

Regards, Dan.

Allowing tor to "handle" the crypto was exactly how a load of European embassy traffic turned out to be insecure a few years back. Client crypto is NOT what tor does (Let SSH handle this, it is good at it and the BSD guys did a competent security audit on that stuff).

You also need to think about how to establish a route between you hardware without using exit nodes, I am not seeing it somehow. At some point you have to inject data from machines under your control into tor and at that point you need to specify a destination IP address (which is a hard problem)..... I can think of ways to work it but they all have single points of failure.

Seriously a custom firmware image that will not support having additional applications run is very nearly trivial, and is going to be far more bug free then anything you can code up from scratch, even just replacing 'init' on a unix with your application code will do it, if it does not fork, how can anything else run?

I am off to go play radios.

Regards, Dan.

I suspect that the strong crypto cat is out of the bag ever since "Applied Cryptography" (Excellent book!) was published.

As memory serves, Zimmerman got PGP out of the country by publishing the source as a book with easily OCRed pages and a checksum at the bottom of each page.... This in the era where the US Gov was pushing for network encryption hardware with a mandatory back door!

As to not being able to use off the shelf tools, don't be too sure, take the source to your tablet of choice and rip out the ability to (easily) install software so it can only use the code built in at the time the OS is flashed, then sign the image and use the TPM hardware to attest to its validity. This should be straight forward on android at least.

You SERIOUSLY do NOT want to be implementing your own crypto routines, you WILL make security critical mistakes, crypto is subtle and you are far better off picking a known good (and widely deployed) library (Ask Sony computer entertainment about this!). 

I would not use the criminal (or even embassy) use of tor as any kind of proof of anything, both groups stuff up on a regular basis.

Further I would remind you that I can probably run a hundred thousand tor exit nodes (all under my control) on hired machines either in the cloud or on a hired botnet for very little money as these things are judged, that would give me a good chance of being able to trace most traffic well enough to do TA on it.

Regards, Dan (Who still maintains that the problem is basically solved and thus boring).

Hi all,
Just wondering if anyone else here was in the recent group buy for Marteins front end boards/crystals/metalwork, and if so what your plans are.
I am planning a transceiver build, sharing the BPF can between Tx and Rx and probably sharing the LO but with the rest basically separate.

The separation is to allow the use of a cartesian loop to improve transmit linearity, (The roofers are too narrow to allow this to work using the frontend board backwards), and I will probably fit some dsp (TMS320C6xxx in all probability) to do at a minimum group delay equalization and I/Q generation for the transmit chain, it may get more sophisticated over time.

The project is going to be a bit of a monster!

Regards, Dan.

This pretty much fails the 'interesting' test for me, take a tablet, add tor and ssh, maybe the old unix talk utility or just netcat, job done....
The key fingerprinting even provides relatively good protection against man in the middle attacks, but user identity verification is still hard.

Initial connection setup is also problematic as you need to know a target IP address which is easy if connecting to say a newspapers servers, but much harder if say trying to call someone else without a trusted intermediary to provide the fixed point for both users to connect to.
Do it right however and this intermediary does NOT need to be able to decode what is being said, and in fact is ONLY involved in call setup.

Certainly I don't see any need for custom hardware here, off the shelf stuff will do, but on the software side you would want to do some very involved security auditing and would probably want to have some integrity attestation stuff (TPM) involved to ensure that no keyloggers or such had been installed.
On the radio front, there are some known attacks using rf emissions or even fluctuations in power consumption or packet timing that would need consideration, and entropy generation for the crypto sub system would want thinking about. 

I would also note that tor is vulnerable to parties controlling a sufficient number of the exit nodes, an attack which has been used in reality.

Nothing that has not been done a hundred times on a hundred different laptops out there.

Regards, Dan.

I also view it as one of a long list of things I want to play with some day, but there are more interesting engineering problems....
Some day!

Regards, Dan.

Yep, and it is worth noting that even if you have narrow selectivity filters immediately behind the roofing filter, these often sacrifice IMD3 performance for shape factor so a good roofer helps even then.

All of this does of course only show under contest conditions,  and even then everything else needs to be spot on to make the IF filters the weak point.

Regards, Dan.

Back in the day when the throttle and clutch were controlled mechanically by wires run in spiral metal tubes, you sometimes used to see these tubes heavily burned where the link between the engine block and chassis had come adrift and the starter current had found an alternative ground path!

In the UK there is actually a standard relating to this, http://www.fcs.org.uk/my%20files/fcs_pdfs/codesofpractice/fcs1362_2010.pdf aimed mostly at business radio rather then ham but the principles are the same.

Regards, Dan.

These amps seldom run anywhere near the optimum drain load point anyway, for the simple reason that the match will only really be right at ONE power level (PEP), everywhere else the thing will be matching the drain at a lower then optimum impedance, so no with a power level 20db down, the optimum match for the harmonic energy would be to a drain impedance 10 times what the network will get you.

On 'mixer' behavior, I would not that the devices clearly are non linear as we need output filters, which we wouldn't if the stage was truly linear, and with a third harmonic typically being somewhere around -15dBc or so unfiltered, we even have a reasonable indication of how non linear.
S21 obviously != S12, but still clearly gain and Vds are related so there is a mixer mechanism there.

Further,  in VHF PMR service where multiple transmitters often share a single hilltop tower, spurs produced by PA intermod (with received RF from colocated transmitters) is a well known issue and it is common practice to store a before and after spectrum to be able to demonstrate that nothing has gone pearshaped when a new transmitter is installed.

I think some experiments are in order.

Regards, Dan.

Are you sure about that?

Most solid state HF amps use broadband matching networks (which after all is why we need the output filter) which are typically designed to provide something approaching a match from 1.8 - 30Mhz or so. Certainly if operating on a low band the harmonics will fall within the designed range of the broadband match.

The win (if there is one) with diplexers is probably more to do with reduced circulating currents (or peak drain voltage) and getting some heat away from the devices then IMD (at least on aggregate, there will be cases where significant improvement is measured).

Regards, Dan.

For us legal limit, I personally would be looking at multiple devices with power splitters and combiners, MUCH easier to cool and you can test each amplifier separately at maybe 4 or 500W output.
I do this even for UK legal limit (400W at the feedpoint, so maybe 500W TPO), 4 * BLW96 (Two, two transistor amps) makes a nice 500W set that is robust (800W nominal transistor rating). I have a bucket full of the things but would not otherwise recommend them for a new design.

The lower per device dissipation means the heatsinks can run hotter (because the drop from the die to the heatsink is smaller), and the lower power per device makes the output match a lower ratio, so easier to build and more efficient.

4 * 600W PEP modules will run at the required ~400W reliably into a much bigger mismatch and will be much easier to cool (As well as having lower IMD and giving you a fall back to half power if one module goes south). Design the output match for the intended PEP power, not the maximum the sand is capable of, it will help the efficiency. I never like to exceed 75% of a devices data sheet rating, and 60% is happymaking.
My homebrew also tends to be designed assuming CCS not ICAS service, so it tends to be a bit big......

Do pick a 50V device, the matching tends to be less painful and you need rather more reasonable supply currents.

A LOT of the RF manufacturers have taken to rating devices at 25 degrees C case temperature, the derating to something you might actually sustain is painful (IXUS looking at you!).

Regards, Dan.

For SSB and non keydown modes I can think of a few good ways to shrink the power dissipation as well (A variation on polar loop modulation), but that does not help when you put the thing into CW or rtty mode.

Personally I like my homebrew CCS rather then ICAS, it makes for a big radio that runs wonderfully cool (And the higher rated magnetics and less stressed finals help the IMD figures too).

Regards, Dan.