Saturday, January 15, 2022

An off centre fed dipole antenna for more bands

It's been great having a dipole up high in the trees but I wanted to be able to use more bands so I made an off centre fed dipole, cut for 80, fed with a 4:1 balun. This gives me a number of bands with a low enough reactance that the IC-7300's tuner can match it. Here's a plot using AntScope2 on macOS.

The grey bars are ham bands. I'm sweeping from 3MHz to 30Mhz. As you can see I get low SWR on 80m, 40m, 20m, and 11m. With a manual tuner I've been able to use 30m but it's quite a stretch.

Speaking of stretch... The antenna wire is half of a figure-8 speaker wire and I think it is slowly stretching. I had a doublet for 160m up but the wire broke.

I did notice that 40m on the OCFD was not as good as it was on the dipole cut for 40m but the extra bands and convenience make it worth while.

The shack is improving! I ordered a 2m bench, a gas chair, and a 4 draw unit from Ikea. Delivery cost almost as much as the furniture. 


The afternoon sun hits the other side of the corrugated iron in front and it gets very hot. Next step is to insulate and line that wall at least. 

Update: Winning at WSPR reception

It's a combination of height, antenna and of course the low noise location. I'm pleased to see that after 24 hours of WSPR reception on 40m I'm at the top of the global chart by accumulated distance.

The WSPR challenge is a wonderful idea. I love the concept of competing by reception rather than transmission.


(Of course it's a bit unfair as we VKs are very distant from most stations so we have an advantage).

7 comments:

Grant said...

Sounds like an ideal location for HF, any plans to remote so you can work from your home QTH?

Unknown said...

Like the bare bones shack. Its gonna be cold in there in July! 8^) -- VK3HN.

Peter Marks said...

Yes, it's going to be very cold in there. My plan is to install some insulation and a lining.

* said...

Nice clean workbench Peter, I can't say the same for mine. I have the same Ikea table and gas seat :) Looking forward to seeing the new shack improvements. Andrew VK1AD

PE4BAS, Bas said...

The OCF dipole does well Peter. I was surprised to see you've spotted my 1W signal over there on 40m today during your and my greyline. This event might give it some extra boost of course.
But still I think such things are miracles. 73, Bas

Peter Marks said...

Hi Bas,

I received spots from you 18 times over night with the best SNR being -16dB. As you say, a miracle given that we are 16,000km apart and you are running 1W.

The antenna is working well but my location is very low noise.

73

Peter
VK3TPM

PE4BAS, Bas said...

Nice Peter, the antenna I use is a doublet in inverted-V configuration. Apex is about 12m down to about 3m above the ground. The entire antenna including the balun right behind the tuner is homemade. 73, Bas