| Welcome to my Antenna Ideas Pages. (5 IDEAS PAGES AT THIS TIME) You will see below some scans I made from Articles from Ham Radio Publications. These articles are ones that I have tried or am thinking of trying and I think they are pretty good. (PARTIAL SCANS so as not to violate copyright restrictions (QST) |
| AN INVERTED L ANTENNA WITH LOW FEEDPOINT IMPEDANCE (abt 90 ohms) on two bands of choice. (80 and 40 version or 160 and 80 version possible) SEE JULY 1991 QST or ARRL HANDBOOKS in the mid NINETIES for the original article by AE6C |
| Below is the schematic and winding details for the broadband bifilar transformer for a TWO BAND INVERTED L that will fit on an average sized city lot. Iam on a city lot now and I have an Inverted L up in the back yard. It works fairly well on 80 and 40. Right now Im just using an MFJ tuner (random wire configuration) to tune my inverted L. I have wound a T200-2 core as illustrated and tested it with a 90 ohm resistance with my rf analyser and the circuit below works. The advantage over using this circuit vs. a tuner in the shack would be to keep the RF out of the shack. I didn't have time to build the matching network at the base of my inverted L (before the snow came) so..I just used my inverted L with an Mfj tuner indoors and Ive had some good results with it. |
| Homebrew Matching System (or use an automatic tuner for all band). An outdoor end fed wire tuner would be an ideal companion with this antenna. Alternatively one can build a simple matching network or use a commercial tuner. I have outlined my design. The tuner is still on the bench being worked on. |
| Far End of the wire antenna goes into the upper branches of the large tree at the back of my yard. I used brown insulated #14 wire (it is not too visible) (good!) |
| The two band Inverted L is a 3/8 wave antenna at the lower frequency (about 90 ohms impedance with some inductive reactance (to be cancelled out with an appropriate capacitance) AND 3/4 wave antenna at the higher frequency with an approximate 90 ohm resistance impedance (the capacitance is then either shorted out (as in the AE6L version) or swamped out by adjusting the variable capacitor (in my version) with a sufficiently large capacitance that acts like a dead short almost. NOTE: I have yet to actually try this idea out. In theory..if I could have a variable capacitor with a minimum capacitance of say 50 pf and a maximum of 1000 pf..then my plan might work. In the real world ..Im not sure how Im going to achieve this!! It will take some adjustment of the antenna length to achieve a working match. I didnt have time to try it out this fall. The snow and cold weather came and I then moved on to other projects. I hope to get it done this fall b4 the snow falls or shortly thereafter!!! REGARDLESS of how it is fed; my 96 ft inverted L does seem to perform pretty good on both 40 and 80 meters. I hear DX quite well on both bands and I get fair to good reports when working North America . I DO ..HOWEVER..LOOK FORWARD TO GETTING MY TGM MINI BEAM UP TO OPERATE THE HIGH BANDS with a gain antenna and some directional coverage. |
| SEE JULY 1991 QST or ARRL HANDBOOK in the mid NINETIES for the original article by AE6C |
| CLICK ON THE BLUE FOR MORE ON THIS AND OTHER ANTENNA IDEAS page 2) go to next page >>>> |
| there are 5 or 6 pages in this little series of general ideas >>>>>>> |
| This Inverted L works pretty darn good. I feed it with my MFJ tuner in the shack. It is about 100 feet overall length. The feedpoint at the end of the antenna represents a fairly low impedance on 80 and 40 meters (where I use it most) I have a dedicated matching network in the works using a home brew torroid coil 50 ohm to 90 ohm Z match. Right now I use this wire on all bands with an MFJ tuner. When I get my little mini beam up on the tower I will use the dedicated matching network. The dedicated matching network was was described in the July 1991 article by AE6C. It also appeared in early 1990s editions of the ARRL handbook. My dedicated matching network will have a small power screwdriver motor to turn a variable capacitor to very high capacitance (effective short) or lower capacitance to cancel out the inductive reactance present on 80 meters because of the 3/8 wave length of the antenna. On 40 meters the antenna is a 3/4 wave wire with a resistive Z of about 90 ohms. |
| This toroid transformer was pretty simple to build. I tested it with an Autek RF1 Analyser and a 90 ohm resistive load. The transformer worked well. This type of transformer can be tapped for other impedances as well. I have two taps on this transformer (the red wire and the black wire). The ARRL handbook shows a scheme for 52 ohm to 75 ohm transformer for using 72 ohm cable in your antenna system. All these designs use T-200-2 cores. I used some white teflon plumbers tape to wrap my torroid above. The red tape is red electrical tape. These transformers can be used to match 72 ohm coax to 50 ohm coax or for the inverted L as per the AE6C article. |
| A 160/80 meter version of this inverted L would be about 192 ft long. It operates on the same principal as the 80/40 version. The feedpoint Z is low and can be matched by a transformer with a capacitor in series at the low frequency to tune out the inductive reactance that would be present..or an automatic antenna tuner could be used. |
| As per schematic below, I have changed the design a bit. The relay and the original capacitor changed to a large value variable that can be driven with a slow rpm motor. At minimum capacitance ranges it should match the antenna on 80 meters (which would have a slight inductive reactance), On 40 meters the Z of the antenna would be mostly resistive and about 90 ohms or so. The capacitor at full mesh..about 1200 pf, would be like a dead short on 40. I have to verify this yet in the real world. |
| IF you look real close you can see the antenna wire againsts the sky in the picture. |
| navigation links (my site) |
This simple wire antenna worked pretty well for me. My property layout would not
easily allow for a dipole antenna with open wire feed.
I have since replaced this antenna with a little TGM mini beam and I mostly work the
higher bands now. For low band casual use-- I plan to put up something this spring
2008. Not sure yet what.
easily allow for a dipole antenna with open wire feed.
I have since replaced this antenna with a little TGM mini beam and I mostly work the
higher bands now. For low band casual use-- I plan to put up something this spring
2008. Not sure yet what.
Here in the photo you see the main disadvantage
of the inverted L. It gets in the way!
I don't like wires and wire antennas. Thats just me
however!
I'm now working on a short vertical antenna
system. It will have no wire radials ..only some sort
of a counter poise ..something like the R7 and the
cushcraft series of short spoke radial antennas.
Either that or a type of vertical dipole/screw driver
antenna hybrid. To see my work in this regard
..you can click on THIS LINK
of the inverted L. It gets in the way!
I don't like wires and wire antennas. Thats just me
however!
I'm now working on a short vertical antenna
system. It will have no wire radials ..only some sort
of a counter poise ..something like the R7 and the
cushcraft series of short spoke radial antennas.
Either that or a type of vertical dipole/screw driver
antenna hybrid. To see my work in this regard
..you can click on THIS LINK
I'm working on these pages. My web site is
big. It is a hobby in itself. Sure keeps the mind
sharp doing all this kind of stuff! I have fun
with the spell check! Often times..I make
spelling mistakes and it is good for the
memory to work on this kind of thing!
I highly recommend it as a hobby you can do
in conjunction with your ham activities (and
other activities as a matter of fact).
big. It is a hobby in itself. Sure keeps the mind
sharp doing all this kind of stuff! I have fun
with the spell check! Often times..I make
spelling mistakes and it is good for the
memory to work on this kind of thing!
I highly recommend it as a hobby you can do
in conjunction with your ham activities (and
other activities as a matter of fact).