Friday, August 13, 2010

No improvement

I know that one of the purposes of my website is meant to be to demonstrate that you can play ham radio even if you can't have outside antennas. But sometimes the frustrations of not quite being able to achieve what you want to make become almost too much.

On Tuesday I replaced my home made ribbon cable Slim Jim 2m antenna with a commercial dual band colinear from Moonraker. I wasn't sure the home made antenna was working as well as it possibly could. Originally I planned to replace the Slim Jim with a single band 5/8 wave Sirio, but after a month waiting for Radioworld to deliver it I cancelled the order and gave up. Then I got the Kenwood TM-D710 which is a dual band transceiver, so I decided I should have a dual band antenna to give me the option of running a public Echolink node on 70cm.

During the last few days I have been searching for signs of improvement in my 2m receive capability, but the signs haven't been good. I'm hearing a frustrating number of APRS "braaps" that are just not strong enough to decode.

The antenna certainly works. I'm getting almost end-stop signals from the repeaters GB3DG and GB3LA, whilst GB3AS is about S5 with a bit of noise on it. I have had a couple of solid contacts using the antenna but nothing to form a basis for comparison until today, when Noel G4PEW drove past.

On the left of the screengrab you can see his track on Monday, when I was still using the Slim Jim. On the right you can see today's track, received using the new antenna. It's a lot shorter. I certainly heard a lot of packets after the last one shown by the grey blob, but none were strong enough to decode.

If only I could have the antenna outside the attic, up above the apex of the roof, I'm sure that extra little bit of height would make all the difference.

4 comments:

S.o.a.I said...

This will sound totally crazy but go turn that antenna 30 degrees one way or the other and try it again.

Reason I say to do this is I was helping a new ham put up his Diamond 2m antenna (I forget the model number). Once we got it up he couldn't hit a repeater that was about 20ish miles away but I could hit it with my mobile rig. So on a lark we turned it a bit. What do ya know he could hit it.

Now if you look at the E-plane pattern for these antennas turning it shouldn't make any difference but the longer I'm a ham the more I start to wonder about all this antenna "theory".

Good luck
Jay aka KD8EUR

Noel said...

Hi Julian,
Just read your blog tonight. So it was a like for like comparison!
Cheers Noel
ps I do increase my beaconing frequency when I think you I may be heard. Was 3 min when leaving Newcastle then 15 or 30 sec when near Cockermouth, for reception interests when reaching home.

K9CHP said...

Perhaps a more directional antenna might help, try something like the tape measure antenna there is a link to it here: http://www.work-sat.com .
It is so light that anything could rotate it, but you may just want it in the direction where your signals generally come from, IE the main road there... I made a few satellite contacts with that antenna, cheap to build, doesn't take much time either.

Amir K9CHP

Fenris said...

If the new antenna has a reduced vertical radiation angle because of increased gain, then you'll find this sort of problem.

While the extra gain is handy if the distant points you want to be able to receive from are in the main lobe, if they're not then you lose signal earlier.

But if you have bits of building in the near field of the antenna, then that narrower lobe can make things even worse. You definitely want that extra height!