Years ago in Ham Radio magazine there was an article on high performance front ends by Ulrich Rhode. If you can find a copy (I'm still looking for you) then read through that because it gives you all sorts of layout tips. One thing I do remember is the amount of shielding he used including shields between the pins of the mixer.

If I find the article over the weekend I'll tell you which edition it's in.

Tanakasan

"Sometimes, when doing r&d for your own use it can be fun (and educational) to see just how far you can push an idea."

Oh yeah! Now why can't the majority of the amateur population think like that? As soon as I read that comment I was reminded of the 'Huff and Puff' oscillator stabilization system which started off as quite a complex piece of electronics and ended up as two or three chips.

“Everything should be made as simple as possible, but no simpler.”

Albert Einstein



Tanakasan

If you find one let me know. In thirty years of ham radio I've never found a rig with an effective noise blanker and when it came to designing my own rig I left it out without a second thought. What I HAVE found to be effective are the external boxes which use a separate noise antenna and then phase inversion to cancel out the interference. The Timewave ANC-4 is a good example of this: http://www.eham.net/reviews/detail/1138

Tanakasan

An interesting post. A long list of specifications only matters if the people reading the article can understand their meaning, and that ability is starting to wane. The latest 'product reviews' in QST seem to concentrate more on useability than anything else and they have even stopped showing pictures inside a rig so that we can get some idea of the construction quality.

I think the biggest problem is that we have reached a technological plateau and the manufacturers are either unwilling or unable to push the envelope. The same thing can be seen in the computer industry, I'm typing this on a six year old laptop that doesn't need to be replaced because it does what I want and if I should purchase a new machine it will only provide a minor increase in performance. To sell rigs (and computers, and flat screen TVs) the manufacturers therefore resort to adding bells and whistles through software in an effort to add perceived value.

So, what is the present state of affairs?

1) Receivers are about as good as they can be, although transmitters could be improved. The last truly revolutionary antenna idea was probably the StepIR.

2) Progress in technology seems to have slowed.

3) The people using these devices (computers or ham radio rigs) are being reduced to appliance operators because of the technical complexity coupled with software walled gardens.

4) The standard of technical education is falling with some purchasers of equipment unable to understand or appreciate the nature of their purchase. Specifications are ignored and new features are left switched off due to an inability to read and understand the manual.

Two weeks ago I had to explain to a licenced amateur  the difference between the emitter, collector and base connections on a transistor. This is a young man who owns a top of the line HF rig which he purchased the day after passing his exam. Something tells me he never read the specifications before purchase.

Tanakasan

I would love to find a way to add CAT control to my homebrew gear. The three DDS chips in the rig are already under microprocessor control but I have no idea where to start.

Having said that.............

It would be nice if CAT could be dragged kicking and screaming into the 21st Century with control over USB rather than an RS-232 cable. The only people I know who have come close to this are Icom with the IC-7600 but I'm willing to be proved wrong.

Tanakasan

This isn't exactly what you're looking for because the outputs to switch the bandpass filters are not in binary, but it might give you some clues.

http://www.analog.com/static/imported-files/application_notes/AN-557.pdf

Tanakasan

http://www.amqrp.org/projects/serialDDS/index.html

Go on, ask me a hard one next time 

Tanakasan

I wonder why everyone is having calibration issues this week?

This one is way too complicated to describe in a single Elmers post so you're going to have to download some stuff.

1) Make 100% certain that your 10.0000000 MHz oscillator is working properly and that it's set accurately. The oven in these devices has been known to fail.

2) If you don't have the manual then download a copy from http://www.icom-france.com/files/not-IC-7800-v2-angl.pdf and go to page 13-5 where you will find instructions for internal calibration. It's page 176 on my PDF viewer.

It's possible that the internal calibration in your rig has been wiped and maybe the CMOS battery needs replacement given that the rig is nine years old. This would explain why resetting the CPU does not cure the problem. Does it retain the correct time setting when unplugged from the mains?

Tanakasan

OK, first the good bit, "I had marked the position it was already set to and moved it back when we were finished with it". Well done, if all people tempted to align rigs would do this then the world would be a better place.

Now, RTFM (Read The Fine Manual). I'm not trying to be clever here but you're missing the important stuff and we need to put you right.

1) You will need an accurate frequency counter, Icom specify a unit that is accurate to +/- 1 part per million and an MFJ 269 probably won't cut it here. Borrow something decent or, maybe, take your rig along to a service department somewhere that has an accurate frequency counter.

2) Carry out section 5-2 PLL ADJUSTMENT. If you don't have an RF Voltmeter then a scope with a fifty ohm resistor across the input can be an acceptable substitute. Adjust L42 and L43 for maximum then connect your accurate counter and adjust X1 for 60.400000 MHz.

That's it, there are no other frequency settings to adjust inside because the IC-821H uses a PLL referenced to that 60.4 MHz oscillator to drive your first mixer and the same 60.4 MHz drives a pair of DDS chips to generate the BFO signals (bottom of page 2 section 10). Section 5-3 sets the FM Transmit frequency and won't change anything in SSB or CW.

Tanakasan

Grab a copy of July/August 2008 QEX and you'll find an article by Wes Hayward W7ZOI on building crystal notch filters. 1.35 MHz crystals will have to be ordered but with one of these filters plus some decent screened cables you should be sorted.

Tanakasan

Sorry folks but I'm still stuck here. Each of the following mixed impedances gives a line from the center of a Smith chart with a thirty degree angle to the horizontal:

R = 25.5 ohms
jX = 10 ohms
VSWR = 2.06:1

R = 82.9 ohms
jX = 31.0 ohms
VSWR = 1.99:1

So, if my scope shows that the reflected signal is 30 degrees ahead of the forward signal then which point do I pick on the Smith chart so that I can match the load to 50 ohms?

Tanakasan

Interesting problem, I played around with this until I got a reasonable solution:

1) As others have suggested you need to boost the output of your microphone as the output will be too low to trigger the counter. Any audio amp should do.

2) Place the microphone on a hard surface.

3) Strike the tuning fork then place it on top of the microphone.

Tanakasan

If I have a VSWR of 2:1 and a phase difference of 30 degrees between the forward and reflected signals how do I plot this on a Smith chart? For VSWR I use the circles radiating out from the center. Assuming an inductive load (reflected power leading), I have two alternatives for the phase line on the top of the chart, pointing towards the short circuit side or pointing towards the open circuit side.

Tanakasan

It's strange the way some people's minds work and what happens after they make their decisions. Until he died a few years ago I used to know someone who refused to fight in WWII because he was a Quaker and a pacifist. He therefore became a fireman and during the blitz saw just as much death and destruction as any man carrying a weapon.

Tanakasan

Of the two I would pick the Kenwood, I don't like that black & white display on the Yaesu.

Tanakasan