Here you will find information about our antenna tuning device. It is made to be able to adjust a V-Star antenna for frequencies from 1MHz-32MHz.
Schematics
Galery
( as PDF) (1MHz-32MHz)
Description
For antenna tuning we experimented with all kinds of publications so far in literature and Internet websites. We tried symmetrical tuning devices for an antenna with a symmetrical line T, L at the exit with baluns for symmetry and the standard LC with inductances. Out of the long samples, which we made in power of about 200W, all worked, but for us the results were insufficien.
The first problem with tuning devices L and T at the exit with symmetry chains, the so-called baluns for different power of 10W and a 1kW, there were quite a lot of losses. To enable the tuning device to work with 1000W and for the baluns to not radiate, they should be quite bulky. However using the same balun and operation at 10W, there are very large losses at the exit of the tuner. At 10W at the entrance with a balun for 1kW for the exit with a symmetrical load of 600Ω, there is an output of only 1.5W power. So if an amateur wants to work with small and large powers, they must have different tuning devices.
Then we experimented with a standard balancing device of LC type. Indeed, the efficiency is greater than 90% there, but has the following disadvantages. The transferring elements must be very large at the exit of the two capacitors must be enormous. There runs nearly 3000V of output voltage. And if you make a small mistake in the tuning, this becomes fatal for the whole tuning device and the final step. The second drawback is that at the low frequencies there is a very narrow band. And you have to constantly rotate the tuner at 1.8MHz over 5kHz, and in 3,5MHz over 30kHz. And finally, at certain places in the scope in the resonant tuning of the tuner, the harmonics are amplified, and no matter how neat final step is, they are broadcast at higher power and TV interferences occur.
We have placed my antenna through neighbouring yards and near the lines of cable TV operators, and it is unacceptable to cause television interference, both for us and for any radio fan. So finally we decided to try a low-pass collins filter, which is given only in theory for the antenna. After many experiments the following structure was created, which works from 1.5MHz to 32MHz. With this the antenna is tuned most easily. It turned out to be quite a wide bandwidth of 1.8MHz – 25kHz to 3.5MHz – 100kHZ. And for me, the most important result is better suppression of higher harmonics. At 1kW of maximum power the antenna does not interfere with TV broadcasting at all.
We just want to emphasize and not bother anyone with theory, a lot of material has been published in textbooks. A Collins filter is a low-pass filter, which passes only the operational frequency and suppresses all higher frequencies above it. In other words, it cuts out higher harmonics. In fact, the double Collins filter tunes optimally the final step in the antenna. The efficiency of the tuner we use is about 98%. So this can be used for tuning of 1W, as well as tuning of 1kW.
What we publish here is the result of many years of experimentation. If the manufacturing is repeated identically and it complies with all data, we guarantee success, as well as avoiding the headaches I’ve had with previous tuners.
Notes to Scheme
Coils L3 and L4 are compensating inductances, which are used only for 1.8MHz and 3.5MHz for increasing the inductance of the input transformer. Coils L3 and L4 can also be rolled without a body, I’ve used PVC pipe. For tuning of 1.8MHz and 3.5MHz bands, we used the total inductance of L5 and L6. Efficiency at 1.8MHz is 93%, at 3.5MHz it is 95%, and from 7MHz to 32MHz it is 98%. This is measured relative to the input power of 1W at 50Ω and at the output in percentages at 600Ω.
| L1 | 5 – turns of copper pipe 4mm diameter L1 is within L2 |  |
| L2 | 5 – turns of copper pipe 4mm diameter L1 is within L2 |  |
| L3 L4 | 4 – turns of copper wire 2mm diameter PVC body 62mm diameter |  |
| L5 L6 | 27 – turns of copper wire 2mm diameter ceramic body 52mm diameter outlets of these turns: 2nd, 4th, 6th, 8th and 13th |  |
| L7 L8 | 4 – turns of copper pipe 4mm diameter outlets at 1st and 2nd turn |  |
The next picture shows the dimensions of the line Lx which is used for both indicators for setting the output signal of the tuner.
