Well? You must have played a little by now?

Well,

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:

http://g0mgx.blogspot.co.uk/2012/10/well-since-progress-i-discussed-last.html

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:

http://g0mgx.blogspot.co.uk/2013/04/well-further-to-my-musings-last-time.html

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?

Antenna Complete!

Well,

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:

http://g0mgx.blogspot.co.uk/2013/05/thatll-never-work-will-it.html

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?

That'll Never Work - Will it?

Well,

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?

A what-un? ah, A Balun!

Well

Whilst musing about being able to run SO2V or SO2R back here:

http://g0mgx.blogspot.co.uk/2013/04/so2v-so2-what-ah-2-vfos.html

there are quite a few things to consider. If I am going to operate with 2 radios at the same time, the most important factor will be protecting the radio in receive from the high RF generated by the radio in transmit - this could result in some very expensive damage if not catered for correctly - more on this later.

The other thing I need to accomplish is a second antenna for the higher bands. Lets say I want to run on 20M and 15M at the same time, clearly I can use the MA5B on one radio, but I don't currently have a second antenna for either of these bands. The simplest solution (as very much a starter for 10) is to cut and hang up a simple common multiband antenna - a G5RV. I've cut one using some hard drawn copper wire I had here, some 450 ohm ladder line and a commercial balun...... hence the confusion and lack of understanding.

I've always been bothered by baluns - what do they do and how do they do it? Whats the difference between a current balun and a voltage balun - whats a 4:1 balun for? Whats a 9:1 balun for? Why don't I just go out more and not worry?

Over the coming weeks I plan to run some experiments to answer these questions, to run some tests against a commercial 1:1 balun, and to construct some baluns for myself and see what they actually do.

So, starting with the newly strung G5RV which I've included a commercial balun between the 450 ohm feedline and the coax to the shack, I see this with my newfangled antenna analyser thingamabob:

Now, I only plan to really use this antenna connected to a second radio, but as a starter for 10, the antenna looks like it's OK ish. As a quick test (clearly the SWR on my dummy load will be better!) I left the antenna and radio WSPRing on 30M last night:

So, I conclude that the antenna radiates and it looks like I can transmit a signal using it.... so it's not just a dummy load. This is a good start.

So, the next project will be some kind of band stop filters for the radios so certain radios can only be used on certain bands - this should allow me to experiment with SO2R in an RTTY contest.

Now, back to baluns.... A balun should be used where we go from a balanced arrangement (e.g. a dipole) to an unbalanced arrangement (e.g. coax cable). I would therefore expect that the output of the two balanced ports of a balun would be out of phase with each other when compared to the ground point of the input port. Here I am feeding a 10MHz signal into a commercial balun and measuring the two terminals of the balanced output:

So, the yellow and the blue (please ignore amplitude) are the two output ports and the green is the sum of the two signals.... they look to me to be about 45 degrees out of phase - this is not what I was expecting at all! I thought they would be 180 degrees out of phase such that the sum of the two was as close to zero as makes no odds.

Unfortunately (or fortunately, depending on how you look at it), I'm heading back to A71 land again today.... I'll be picking this up in about two weeks when I get back.

I'd like to hear from anyone who understands the 'scope output above though, confusing - egh?

My antennas got no nose; well no decent SWR anyhow!

Well,

Further to my musings last time about SO2V, I've been making some changes here with a view to getting a second HF general purpose antenna up in the air - the idea being that this can be connected to the second V!

I took down the 30M (10MHz) dipole that I had here and put up a half size G5RV - this was something I had kicking around anyhow and it's fed with 400 Ohm ladder line. It's good and clear and up quite adequately high. I was rather horrified and/or surprised to find that signals on 40M were way stronger on this G5RV than on my 40M/80M dipole - something was not right!

So here's what I did:

• Checked the antenna SWR to find it close to infinite everywhere....
• Replaced the feedline (RG213) between the shack and the ground level under the dipole centre.
• Replaced the feedline (RG58) between the end of the RG213 and the dipole centre.
• Checked the SWR with the analyser at the end of the RG58 feeder and there is a clear SWR curve around 7 MHz ish
• Then checked the SWR at the shack end of the RG213 cable and its 10:1 flat….
• Went for a curry
• Decided to look again at the dipole centre so I dropped the antenna again
• Centre looked OK, so tried to pull the antenna back up and broke the bailing twine in the pulley at the top of the pole at the bottom of the garden
• Gave up completely and went to bed 

Today I've replaced the pole at the bottom of the garden and made an alternative antenna, here is the design I came up with:

The inductors ("L") in the design calculate out at about 80uH.

The first thing I did was to just construct the two 33' legs of the antenna and get them tuned to the RTTY/Digital segment of 40M - that was a doddle. Then I added the coils and the stubs, the calculation was aimed at 3.050MHz and here (using my new fancy analyser thingamabob):

So not bad at all! Here's the plot for 40M now I've added the stubs - clearly there has been some slight de-tuning of the 7MHz part of the antenna, but I can live with it for now and fiddle some more with it later:

The only other thing I have to report was that following my being a good boy at work I have bought myself a gift:

The picture doesn't do the radio justice; it's quite nice looking and has a shiny finish (not the normal Yaesu matt). The good things are that the radio includes a CW decoder, plus in-built decoding for PSK and RTTY - you can also send all three modes without any external equipment.

All in all I think it will be an excellent second radio for me - it has replaced the TS-590 - too early to report fully but early signs are good!

Fun, egh?