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Monday, 27 May 2013

Well? You must have played a little by now?


Last time I mentioned that I had bought myself a Rigol DSA815 Spectrum Analyser with the built in Tracking Generator. I'm just about to head back to MAN for a flight to A71 land but I have had a bit of a fiddle this morning. First off, I made myself a very simple SWR bridge using some bits and bobs lying around, it's similar to the one I made back here for the power meter:

but smaller and not designed for the power, it looks like this:

What we have here at the top of the photo is a LH connector for the RF source, the top RH connector for the load (antenna). On the bottom the 2 parallel 100R resistors form a 50R termination for the forward power sample port and the reflected power sample port is connected to the bottom connector.

So, if I now connect the output of the Spectrum Analyser tracking generator to the top left (RF source), an antenna under test to the top right (RF Load) and the input to the Spectrum Analyser to the Reflected power sample port, we have a very expensive antenna analyser thingamabob!

With my recently constructed 40/80M dipole from here:

coupled to the RF Load port and the instrument appropriately configured, here's what we see:

Now, I've used the built in marker capability within the Spectrum Analyser to do a few things here:

What does this all tell me?

  • The 80M part of the antenna is nicely tuned within the band at 3.533MHz
  • The 40M part of the antenna is a mile out at about 7.765MHz
  • The 5dB width of the 40M resonant point is about 165KHz
I haven't done the maths yet so I don't know if my selection of a +5dB measurement is appropriate to see the bandwidth of decent SWR - I will do that later. But a summary of the summary?

It's too damn short!

Interesting though, egh?

Friday, 24 May 2013

Antenna Complete!


Perhaps you remember the antenna I started to put together last weekend and then realised that the bits for the 6M sections were the wrong size? It was back here:

The correct parts arrived today to complete the antenna, so the tower has been down again. I've just flicked through the archive from "Antenna Cam" and here's me up the ladder fiddling with the top bracket prior to dropping the tower down:

If you look closely in the above image you can see me fiddling, but you can also see that the closest element on the HF beam is a bit "out of bonk". Here's the antennas back up again and I've fitted the parts to the 4/6M beam and also straightened out the HF element:

And finally here's an image of the antennas back up with the weather a little clearer and them pointing back to the SE:

The 6M part of the top beam is no longer resonant at 55MHz, but seems to be a good match on the 50MHz amateur band!

It's perhaps just a little too short but it's more than acceptable for my requirements; the resonant point on 4M or 70MHz hasn't moved.

Good, egh?

Really, More Baluns - Now What?


You may recall my musings on the topic of Baluns back here:

A Balun is a kind of transformer to take a BALanced signal and convert it to an UNbalanced signal (or vice verse).

So, in my traditional have a bash style, I've made this:

Now, the schematic of the thing looks like this:

Now, the B2/C1 junction is ground and C2 and A2/B1 are the balanced outputs. The unbalanced port is between the same ground point (B2/C1) and A1 for a 1:1 and A2/B1 for a 4:1.

So here I am injecting a 4MHz signal into the 1:1 unbalanced port and monitoring the two balanced outputs with the 'scope:

This looks exactly as expected - the purple line is the sum of the two balanced outputs and for two signals perfectly out of phase should be a flat line. Here is the same thing at 7MHz:

Again - nothing short of perfection!

Here at 14 MHz:

the signals are still out of phase with each other, but the amplitudes of the two balanced ports is no longer equal, and here at 18MHz:

The two ports are no longer anything like out of phase....

So this homebrew device looks like it's good to about 10MHz and not much further. Its been made using FT240-61 ferrite material.

I need to now make something similar using a different material and see what the difference is.

Interesting though, hug?

Thursday, 23 May 2013

The Most Dangerous Thing Ever?


Funny the way things work out, isn't it?

Here's the main subject of my post:

This devices are known as "helping hands" - they get a lot of use here - especially the magnifying glass. This thing was just left on the bench wherever I happened to have last thrown it.

This afternoon, whilst in the shack, actually occupied by some activities for my employer, I suddenly became aware of smoke rising from the bench. You guessed it, the May sunshine was beaming through the window, through the magnifier and was superbly focused on my wooden bench. Now, as I was in the room, the very small smoldering patch was soon extinguished. However had I not been here the consequences could have been significantly different - doesn't warrant thinking about really.

But here's some good news: I've got myself one of these:

It's a Rigol DSA815TG Spectrum Analyser. I have been looking at them for quite a while, there was a recent review of the device in RadCom which was the decision maker for me. The one I have includes the tracking generator.

I've only starting playing with it today, and have hooked it up to a crystal filter I had lying around here. This is what I find:

This is telling me lots of things about the filter - none of which I could have measured before. This is going to come in very handy....

Good egh?

Saturday, 18 May 2013

That'll Never Work - Will it?


The VHF antennas here have always been somewhat of a compromise. Recently I moved my 4M or 70MHz antenna from the side of the house and put it on top of the HF antenna on the main mast. I also took down and filed (in the hedge) a 6M or 50MHz antenna. I saw this a while ago and wondered... could this really work:

InnovAntennas 4 & 4 ele

So, you guessed it, I bought one.

Here's the antenna as it starts to go together:

As you can see, there are 4 elements for 6M and 4 elements for 4M on the same boom. The thing that I didn't (and still don't) understand is how the thing works electrically as the 4M elements are all parasitic (there's no wires connected to them from the RF supply). The antenna has a direct coax connection without any kind of connector:

There's plenty of self amalgamating tape under the white PVC tape you can see, the connections themselves were then coated with Copper grease. The antenna also needs a coax wound balun - this is preventing me from feeding the antenna directly with Westflex 103 - it's just too thick to wind tight enough. I've had to connect a length of RG213 to the antenna, use that for the balun then have a join to the 103 close to the boom.

I then brought the tower down and changed the antenna on the top for this one:

While the antenna was in this position I attached the analyser thingamabob; the 70MHz resonance looked really good, but the 50MHz resonant point was more like 55MHz.... hmm I thought, perhaps I should raise the antenna and see.... no change at all.

I scratched my head for a while and re-checked all the dimensions - they seemed correct to me, here's the diagram I was following:

Suddenly I realised that the element centres that are labeled as 1800mm on the diagram are only 1500mm on the antenna! A quick email to InnovAntennas confirmed that I had indeed got the wrong parts.

The antennas are back in the air:

But the 6M or 50MHz elements on the top antenna are currently exactly 300mm too short.

Useless, hugh?

Tuesday, 14 May 2013

Is this what I was waiting for?


I'm still in A71 land, but I have been checking my WSPR beacon that I left running on 4M from time to time. I mentioned about it here:

But here's what I found this time:

So my 20 watts on 4M has made it all the way to PA0O - clearly there has been some propagation while I am away (typical).

Good, egh?

Friday, 10 May 2013

Wow, that's a long way down...


I'm back in A71 land and have finally got the appropriate approvals to use A71/G0MGX whilst in region. This is good news indeed.

To coincide with the timely arrival of this approval I have also moved into an apartment within the centre of Doha. This will be my residence whilst I am in this part of the world between now and the end of the year.  I already know where the buddypole will be sited, it's a long way down though:

This is the view that the buddypole will have, it's kind of looking West:

So, all I need now is some equipment. I'm planning to bring my FT-450 and Buddypole with me next time I travel back here.

I've also sent the appropriate evidence to the ARRL and have already received the certificate for my A71 callsign for LOTW:

Interesting times, egh?

Friday, 3 May 2013

Movements are afoot.... It's all go you know...


Been fiddling with antennas a bit whilst home this time, I've moved the 4M antenna from the side of the house and put it on top of the HF antenna on the main tower.

Here's a picture from "Antenna Cam" at dawn this morning:

and here's one from just a bit later on:

You should be able to see that the 4M beam is now sat happily on the top of the tower. Inspired by the site of Brian, G0MJI:

I've set up a WSPR beacon on 4M.... time will tell but it sounds like a lonely kind of activity to me....

I've also been fiddling with Ham Radio Deluxe (HRD), my internet router, the FT-5000 and various other bits and bobs to try and see if I can control (and operate) the Yaesu FT-5000 radio remotely (read from A71 land).

So, HRD runs on the shack PC, this communicates with the radio over the conventional Yaesu CAT interface. As is well documented the modern radios allow control of just about everything via this interface.

Now, you then set HRD running in remote mode and then run the client application on the remote PC (in my case this is a laptop). With a bit of fiddling and a port open on the router I can now control the FT-5000 remotely, this is what HRD looks like on the client PC:

So this will be something interesting I can fiddle with next time I am away from home. I've also set up a remote desktop access to my shack PC so in theory, I should be able to connect and run RTTY via logger as if I was sat here.... shouldn't I?

You might remember an episode of "extreme soldering" from quite a while ago:

Well, I've been fiddling with this SDR again, It's really quite good fun, here's a screen grab from the Software, my waterfall is a little too intense, but you get the idea:

Fun, egh?