Adventures in the 8m band

Recently, in addition to 3cm projects and HF digital, I’ve been monitoring WSPR in the 8m (40 MHz) band. This an ISM band with some experimental licenses issued in the US, Canada, and other countries, as well as a few secondary amateur allocations in Europe and in South Africa. There are proposals to make this a secondary allocation in the US, at least.

This is a very low VHF band, and shares propagation characteristics with both 10m and 6m. It’s a potential indicator of Sporadic E openings on 6m, and with the good sunspot conditions lately, there’s been an uptick in folks transmitting and receiving.

You can find out more about 8m at EI7GL’s blog, which is a fantastic resource for this and many other amateur radio topics.

I started listening a couple of weeks ago with a simple wire dipole strung up in the back yard. I’ve now built an aluminum dipole which can self-support and be more readily tuned, and put up above the roof line with a shorter and better feedline. This has shown marked improvement, and I’ll keep experimenting to see what works best. It may turn out to be better further from the house, even if closer to the ground.

8m dipole test & tune.

I adjusted element lengths for about 12ft off the ground to simulate over-roof mounting. The resonant frequency of a dipole changes greatly with height due to capacitance with ground. It’s close enough for now.

There was some great great propagation happening today between Australia/NZ and USA/Canada, on 40.68 MHz.

In the above, there’s a 15642 km report for VA2CY from VK4OTZ:

2023-03-03 22:44 VA2CY 40.681527 -11 0 FN46lw 50 VK4OTZ QG62jo 15642 284 W-2

This is just short of the current record for 8m for any mode, but I think is actually the record for WSPR on 8m.


I had been posting radio/electronics updates to Twitter instead of this blog for some years, but I’m not as active there since the ownership change and I’ll try and update this more instead.

I’m also now on the Fediverse (“Mastodon”) here: . There is not currently seem to a critical mass of radio & electronics experimentation folk on there, but it is growing. If you’re reading this and on there, consider adding me. The real value of this kind of social media is the network graph, so I’m adding anyone with similar interests currently to help build that.


Author: w7txt

W7TXT, also VK2TXP Currently located in the PNW.