I have found several other “kindred spirits” who have worked on variations on the Bobtail Curtain – that have some things in common with my “Mod Bob”. This one came up with a Google search on Bobtail Feed, and this link will give you hours of joy looking at creative antenna ideas – especially the Low Band Antennas:
What is most interesting is that unlike the higher bands – 20M on up, there are quite a few people out there who have experimented more on the low bands with all kinds of interesting ideas. I am sure its because if you want an antenna that works “reasonably well” as a DX antenna on the bands 160 – 30M, its quite a challenge. But that – just like making any QSO on 160M – is what drives me. The day that the challenge is gone is the day I will hang up my key. Luckily, I don’t see that happening, because just trying to understand 160M propagation could be a life time journey, and I will never work them all on 160M – but will try to keep my “count” climbing. For me – that’s far more interesting than the DXCC Challenge.
I think this is called an NRY antenna, but it does look like a “Lazy H” antenna. In any case, the dimensions can be modeled, and you can even try variations, especially looking at height above ground. One antenna that works well with the bottom at least 8′ above ground is the Bruce Array, and Rudy, N6LF has written the best articles about this fine antenna:
OK – so I have wandered a bit away from the Bobtail Curtain feed – but that’s precisely why this is so much fun – grab a nice beer, sip slowly, and you can get lost tracking down these wonderful antenna ideas. Since its 4 AM PST right now – I am listening to very low noise but no signals on 160M, drinking a nice cup of Sumatra coffee, and blogging. Beer will have to wait!
Here is an interesting “Inverted Bobtail” which can be found at:
Finally, here is a hybrid idea:
I remember seeing an article in QST that was written by Hal, N4GG where he created a “fan dipole” version of this. I think he said its usable, but not a great DX antenna. Its a good place to start as far as trying to experiment with Bobtail Like antennas and feeds.
What is so interesting to me is that there are just enough variables in trying to create a resonant (or perhaps a non resonant) antenna for one or all of the low bands. There is the actual dimensions of the antenna and where you might put such an antenna on your property. If you have minimal space like I do – the equation can be quite tricky:
I have a narrow strip of land that is right next to a creek that wraps around two sides of my house. Its a very pleasant and calming environment, and with my new landscaping that I worked on with my son Trevor, its a great place for everything (except being able to put lots of antennas up). But I took that challenge and still made Honor Roll and am closing in on 160M DXCC.
Two of three elements of an antenna that is 41 feet high and 70 feet wide – not bad for a small suburban and wooded lot.
Two of the three elements of my Mod Bob antenna. The creek is just to the right – so you can see that my space is tight. The wires on the left go into an Array Solutions Rat Pack remote antenna switch. I have my Mod Bob and DXE 40M phased array plus 2 element 20M yagi attached to the Rat Pack and thus have only one (transmitting) coax line coming into the shack. I also have a coax line coming in from the Wellbrook ALA1350LNP receive antenna, plus several control lines.
I will be replacing the 1:1 current choke with this:
And will have it in a very nice weatherproof utility box. I’m doing this because right now my Elecraft KAT-500 does not like the Mod Bob on 80M. It will be a little bit of a hassle to go out and tune manually for each band – but this might get me to try to build a remote control circuit using stepper or other synchronous motors and also remote switching for the two relays:
The relays switch in Hi Z or Low Z double L circuits.
OK – hopefully this blog post gives you some ideas – just thinking and reading and drinking coffee is fun. I just spun the dial on 160M – and hear ZL2OK quite well on 160M SSB.
Not bad for being a couple weeks away from the Summer Solstice – right at our sunrise. He was a good S7 here. The noise is much lower than it has been – which gives me hope, and ADXO says a team will be on T8 soon – which I need on 160M.
I sure love the Low Bands!