Wow Gianfranco! You've swept me away! I wonder how can I best contribute to your efforts! I've never modelled a Beverage before so it's a great time to try.
Fundamental frequency of operation: 7.05MHz
Construction:
#1 vertical wire 0.78m high, feed point at the bottom of this wire, driven against ground
#2 horizontal wire 90.6m long, 0.78m above ground, connected to the top of wire #1 and the top of wire #2
#3 vertical wire 0.78m high, connected to ground via a 500 Ohm non-inductive load
The table shows it is remarkably flat across the bands from 40m up, with a radiation resistance around 400 Ohms and little bothersome reactance.
The next two pics show radiation pattern and angle of take off at 7.05MHz and 51.0MHz. As you would expect the other frequencies range in between.
- beverage-calcs.jpg (103.7 KiB) Viewed 24276 times
- radiation-7.05.jpg (119.93 KiB) Viewed 24276 times
- beverage-51.jpg (121.24 KiB) Viewed 24276 times
I would simply feed it with 450 ohm ladder line. If you have a problem bringing ladder line into your shack because of bad close contact with metal parts of the building, then you could use twin lengths of 70 ohm TV coax as a shielded balanced line.
At the radio, if it is an RSP2, I would connect it straight to the HiZ input through a common mode choke. A simple twisted pair on a toroid. In the picture of my chokes from my previous post the toroid with the orange twisted pair was built explicitly for 450 Ohm ladder line.
Here is a point that has always seemed to me to be important; please find fault or I'll keep on being wrong!
If you use a toroid to transform impedances then your frequency range and efficiency will be limited by the ferrite, which of course is why you're chasing 73 material. That limits your received signal bandwidth, eg. no single ferrite material goes from DC to 70cm.
If you don't go that way and instead use the inductance of the core to provide as high an impedance as possible just so as to reduce common mode signals over the frequencies of interest, then you are *not* limiting your received signal bandwidth. What you are doing instead is limiting the effectiveness of the common mode rejection and balanced to unbalanced performance, but only outside the ferrite's range. Neither of those characteristics matters nearly as much as losing all that frequency response!
Also (imho of course) I'm willing to suffer a non-perfect impedance match. If you use a balanced feed line of simple 300 ohm, 450 ohm or twisted pair (where necessary I use home made twisted pairs or home made ladder lines so I can create an impedance to suit my antenna) then there is negligible power loss caused by the poor SWR in your feed line, especially at HF, because as you know the losses caused by standing waves are because of additive feed line loss, principally in coax. Not only that but a balanced line and antenna inherently helps reject the common mode signals that plague coax.
So I've come to choose and design antennas and feed lines so as to require as little as possible impedance transformation: impedance transformation whether it uses L and C, coax stubs, etc must always be frequency dependent because we are dealing with reactances. Ferrites are not as bad but I've found I really need three different mixes to effectively cover from 100KHz to the top of 6m
Your Beverage seems like a great candidate for that approach with it's broad flat response.
It's great to compare notes Gianfranco, I used to be shy about putting myself out there to be knocked down but as I got old and didn't care as much I found it was the fastest way to learn from others and be presented with things I'd never seen or been able to do as you have done with your work, thank you.
Best regards, Phil VK7JJ