Boxing Time

Well,

You may remember the 35MHz to 4.4GHz signal generator made from cheap eBay components I was fiddling with last time.

I've stuck it in a box now:

I've removed L1 from the board:

so that there is no power to the on-board 25MHz XO. I'm running mine using the shack 10MHz frequency standard I made back here. This external oscillator input simply connects to the SMA socket on the back of the board.

I've recently made a distribution amplifier for the frequency reference so  I have 8 50R outputs at 10MHz to lock a recently acquired Microwave frequency counter and also my HPO signal generator.

Good egh?

Counting Once More

Well,

Back from A71 land for a week or two and I have been looking once again at the Signal Generator that I made back here:

http://g0mgx.blogspot.co.uk/2013/10/so-hows-sig-gen.html

I was wondering about my choice of frequency counter and wondered if I could do something better. You may recall the counter I made back here:

http://g0mgx.blogspot.co.uk/2011/07/pic-n-choose-how-to-count.html

This was a PIC based frequency counter that I have blown the dust off (well re-made actually), please excuse the paws in the picture:

So, that has a gate time (right now) of 1s and a very good resolution. I have calibrated it against my 10MHz shack frequency reference from back here:

http://g0mgx.blogspot.co.uk/2011/07/ocxo-oh-you-mean-ocxo.html

and it works very well. What I don't like about it is the fact that it's coded in assembly language - I would much prefer to come up with something using a high level language that utilises Arduino.

Now, the processors on the Arduino boards dont have the same kind of timers that the PICs have and they are synchronous (this means they are gated internally to the system clock) which results in a maximum frequency that can be counted of about 40% of the system clock speed. For all the boards I have that would be about 6MHz. Also the smaller boards like the Uno have a resonator clocking the processor rather than a crystal - making the timing very hit and miss. So, I wondered if I could do something a little smarter with Arduino. I am contemplating using an external clock (based on a cheap watch crystal) to drive an interrupt on the board to control timing and an external pre-scaler to increase the maximum frequency I can count to the tune of 1024. If I use a simple CMOS 4040 chip to divide the incoming frequency by 1024 (say), the tricky bit will be not limiting the counting to a 1024 resolution - I'm still pondering that one.

Here's the watch clock running at 32.768KHz (great software number egh? 32768 is 2 ^ 15):

If I were to use one of the on-board Arduino hardware timers I could divide this 32.768KHz by 256 and crate an interrupt routine that ran 128 times per second. That should give me enough control to be able to gate an external incoming frequency to exactly one second. If I can do that then we should have the basis of an Arduino frequency counter. Seems a bit complicated though!

If I am going to go to all that trouble to generate a 1 second counter gate, I wonder why I can't use an external GPS - they can generate spectacularly accurate 1pps signals based on the US DoD atomic clocks....

Here's the mess I am working with at the moment:

And here is new Ham cat asleep on the data sheets I am trying to use:

Damn crazy cat:

Bonkers, egh?

So, How's the sig gen?

Well,

You may recall the bench Signal Generator that I started here:

http://g0mgx.blogspot.co.uk/2013/09/bench-sig-gen-any-bright-ideas.html

I also stated that I would try and find a case for the project at the HamFest; well I came home with something but it's just not quite right.... anyhow, I've found an old plastic case with a missing front (soon to be rear) panel. Here's what I've done with it:

So I've made a lash up power supply and stuck it in a box. Not made such a bad job of the rectangular cut-out needed for the display:

I need to try and find some kind of plastic see-through something or other to go in front of the readout, I also really should screen the RF parts of the circuit. I figured I could do that with more of the copper boards I have used to construct the electronics on.

The output is nice and clean:

And whilst not perfect by any means, the harmonic content is very minimal:

Geddy Cat is very pleased that I am home, he isn't allowed in the shack when I am away and his favourite sleeping spot is currently on top of the printer. He doesn't help much:

He is, however, the best cat in the world.

Bench Sig Gen - Any bright ideas?

Well,

Been fiddling around at home today and building a bench RF Signal Generator. I have a homebrew one already but it's a bit hit and miss to tune, I also have an old Avo valve based signal generator, but that's extremely heavy, very large and generates lots of heat!

I saw a schematic for a suitable bench Signal Generator a while ago in Experimental Methods in RF Design (page 7.15 Fig 7.27), so I thought I would have a go at making one.

Here's what it looks like in it's current state of construction:

The tuning capacitor on the RHS is the main tuning and the second variable capacitor on the LHS is the fine tuning; that should help make it easier to set the device.

The toroid you can see nearest the front of the picture above is a little odd; the secondary is just a single turn which in reality is the leg of the diode you can see just passing through the centre.

I then found in my box labeled "projects" a digital dial kit from QRP kits:

http://www.qrpkits.com/freqcounter.html

I've used these in projects in the past and I must have ordered an extra one some time ago, anyhow as this is a surface mount project, it was extreme soldering time again. If anyone doesn't realise how small these components are, here's one of the resistors on my thumb nail:

So, here is the underside of the project board completed:

And the display side:

Ideally you would calibrate this with as high a frequency as possible, but I have used my 10MHz frequency standard from here:

http://g0mgx.blogspot.co.uk/2011/07/ocxo-oh-you-mean-ocxo.html

And here is the counter connected to the signal generator, I've added an additional buffer output stage between the output PAD and the counter in my build:

So, the output of the new bench Signal Generator looks quite good, here's some shots of the device set at 10MHz exactly:

This now needs a case, but I am going to wait until the end of the month when I will be at the National Hamfest and see if I can find anything there. I'm away between now and then in A71 land so it will just have to wait.

There is an expression about curiosity and cats:

Good though, egh?