A disk-what? Ah, a Discone!

Well,

Today has been a day of antenna fiddling. The first thing I did was put up a Discone antenna on the front of the house:

This is supposed to be a general coverage receive antenna from 25MHz to over 1.3GHz plus it is resonant for transmit on the Amateur 6M, 2M, 70cm and 23cm bands.

Here's what it looks like connected to the return loss bridge and Spectrum Analyser:

The markers at the bottom of the image above show the resonant points we are interested in and it does indeed seem to be a reasonable match to 50R at those frequencies (as is a 50R resistor, of course). How good an antenna it is remains to be seen. I am hoping this will hear more of LEO satellites than the collinear I have.

We have had some more really bad weather over the last few days and very much by luck I found a broken jubilee clip (Read hose clamp) in the garden yesterday. Looking up I could see it was off the 4M and 6M beam antenna I installed back here:

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

So I have had the antennas down again today, it's surprising how big my "mini beam" is when it's on the ground:

You can see that I have to remove the outer parts of the one element to get it past the fence next to the raised border in the garden! But I have replaced the clip and also altered the resonant point of the 4M section to be exactly at the Meteor Scatter frequency of 70.110MHz.

After adjustment the "dip" is now ~70.12MHz with a return loss of > 32dB ; the SWR at 70.11 (my target) is 1.05:1 and across the band is no more than 1.7:1.

and at 50.23MHz the SWR is a respectable 1.2:1:

Looks pretty damn fine to me!

Cat's been next to useless:

Fun, 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?