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Saturday, 26 January 2013

Hows the Interfacing?


Following my acquisition of an FT-450 to take on my travels, I've been making a digital modes interface for the radio today; I ended up with this design (like 0/10 for originality!):

I've built the electronics into a small plastic enclosure that I had here and eventually I've got it working 100%.

I struggled with FSK RTTY; it just didn't want to work for some reason. I tried re-making the switching circuit, tried swapping it for the (working) PTT switch - all attempts failed.

I then realised that I had never tried an FSK transmission from a PC using a USB to Serial adapter. Bingo! A quick search on the interweb soon revealed that my goal was in fact impossible! A bit more research on the MMTTY Yahoo! group revealed the fact that there is a software fix for this - it's called EXTFSK and is a dll that you drop into the same directory as the MMTTY exe file.

Bob is now my Uncle and all is working well; tricky though - may never have found that and was close to giving up!

Cat's as impressed as normal:

Good though, egh?

Friday, 25 January 2013

My God, Your Obsessed!


A little while ago I was talking to Dave at Lam Communications; I happened to show him a picture of my shack – his reaction amused me suggesting I was completely obsessed!

Hmm, I can see how he may have a point!
It looks like I may be going to spend some working time in A7 land, so I have been in contact with the Qatar ARS and also the local authorities to find out about getting a license to operate from there. It looks very much like it may be possible as there is a reciprocal licensing agreement between Qatar and the UK.

I was planning to take a newly acquired FT-450D plus a small switch mode PSU with me and see what I can manage to set up. I need to build a small digital mode interface so I can connect it to my laptop; so that is the project for this weekend - its also the BARTG RTTY sprint contest too.

I've put my IC-7410 up for sale and the box has come down from the attic ready for it's departure. Cat's not impressed:

Interesting times, egh?

Friday, 18 January 2013

The Old Dog is Up and Running


Following my last post about the FT-1000MP Mark V I found, I've managed to purchase a SMPS from eBay. This PSU has 2 x 15V @ 15A and 2 x 14V @ 15A; as SMPS are good in series it wasn't hard to manufacture a replacement for the FP-29!

It even fits in the FP-29 case!

The radio is working FB:

There doesn't seem to be anything wrong with the radio itself. The PSU is a bit noisy and running a little warm - I will keep my eyes open for an alternative, in the meantime I'll stick it up on a shelf and run the cable to the radio.

I want to use this instead of the IC-7410 I have here, it will be employed for AFSK type digital modes mainly - and as a second radio to my FT-5000 RTTY contest machine!

Not bad, egh?

Sunday, 13 January 2013

There's life in the old dog....


That "sold without warranty given or otherwise implied" FT-1000MP Mark-V that I picked up from Lam Communications, as I showed last time, the power supply was all sorts of broken.

However, today I've stuck 13.8V in the appropriate place for the radio, and that seems to spring into life quite nicely:

The PSU provides the 13.8V to the receiver and other parts of the radio, the 30V supply is just for the linear amplifier MOSFETS, so the radio won't transmit right now. I've taken the bottom off the radio - mainly to investigate if I had been lucky enough to inherit any of the optional filters - alas not:

but the radio does look very clean and tidy.

So, I'm now on the look out for a SMPS with about 28V output at 15A for the PA, this will have to be at, what us radio hams refer to as, "the right price", but something will turn up soon I'm sure.

Good though, egh?

Saturday, 12 January 2013

5MHz Short Dipole


Having had my 5MHz NoV renewed in early January, I decided to have a go a fitting a dedicated (shortened) dipole into the garden.

I started with my preferred on-line calculator here:

A truly magnificent tool, and ended up with this design:

I've managed to fit this antenna into the back garden today without getting it too close to anything else. My MFJ Antenna Analyser thingamabob suggested that the SWR and impedance of the antenna was good at the target frequency; after getting some RG58 and running it back to the shack, the radios seem to agree also. Time will tell, but it seems that I have a dipole for 5MHz!
I also payed a visit to Lam Communications today, rummaging through their shop a FT-1000 took my eye, the PSU for the radio was described as broken and the radio was sold with "no warranty implied or given"... so I've had a punt. Here's what I found inside the PSU:
 So I very quickly concluded that the PSU is all sorts of broken.
The radio requires 13.8V at 3A and 30V at 15A (for the PA), so a replacement shouldn't be so hard to manufacture from something.
Watch this space, I'll keep you posted.
Here's the Geddy cat mid tea munching the other night:
All good fun though, egh?

Monday, 7 January 2013



Had a play in the ARRT RTTY roundup this weekend, conditions seemed quite poor, 10M wasn't open at all and most of these contacts were on 20M and 15M. I'm a bit dissapointed really, would have hoped for a bit better:

What do you think?

Wednesday, 2 January 2013

Calibration Finaly Complete (Really)


You may remember the musings from a while ago where I made the dBm meter for the shack:

I wasn't overly convinced of my calibration, the 'scope, spectrum analyser and this meter didn't align, especially at low power levels. There is always a risk that the old test equipment I have (the spectrum analyser) is well out of calibration, but I was curious. The calibrator that I made (Design courtesy of Mr Kopski, K3NHI) didn't quite look correct on the 'scope either - it was described as a square wave, but mine looked kind of triangular like this:

But it did look full of harmonics when viewed on the spectrum analyser:

So, I started by asking some suitably dumb questions on a forum or two, and ended up in a very educational and excellent email exchange with my new found chum Kerry who lives down under.

To cut a long story short, Kerry has some very accurate test kit (accurate read expensive!) and has kindly fed some known signals into an AD8307 RF front end (like the one in my power meter) and noted the voltage output by the device itself, here are the values:

So, I took these values and plotted them as a X-Y scatter plot in good old Excel, then added a trend line to each set of data and got the spreadsheet to include the equation on the graph:

Now, hopefully you will be able to see that using the equation on the graph, we can now calculate any dBm value that the meter should be displaying from the actual voltage on the device output (pin 4).

So, using my good faithful Avo signal generator and some of the attenuators I made earlier, plus the attenuator on the Avo itself, I have fed a load of different RF signals into the meter, read the voltage on pin 4 of the AD8307 and then used the equation to calculate the dBm value that the voltage represents:

Once this was complete (ignore the yellow above for now), I then used the lowest and nearest to 0dBm to calibrate the meter. The yellow values are the meter actual display readings once the calibration was complete.

My confidence is now very high in this homebrew instrument and I suspect it may become the most useful device yet.

So, feeding a -30dBm signal (as measured with the calibrated meter) into my Spectrum Analyser with the reference level (top line on the display) set to 0dBm, the fundamental 5MHz signal in this photo is shown -30dBm down from the 0dBm reference level i.e. they agree! Sorry about the wonky photo:

Here is the dBm meter with the Avo signal generator set at 0dBm and a -10dB attenuator (pad) in line with the feeder; 0.3dBm is really very close indeed:

Oh, and the suspect Kopski calibrator? That now reads 19.9dBm - can't be bad! It was the -50dBm version that I concocted myself that was highly suspect - it reads -39dBm!

I've started an Analogue equivalent of the meter, initially because this would only require a single calibration point, but now I have found a better way to calibrate the digital meter, the project is rather redundant. I'm rather pleased with the meter scale though:

And all this because I became suspicious of the readings I was seeing from the attenuators I created as part of this project:

Hey, Ho. Perhaps now I am happy with the dBm meter, I can progress that project? Unfortunately I've run out of holiday and have to go back to work. I suppose there's always next Christmas.

Fun though, egh?