Isolation transformer for inverted-L 160 meter band with folded counterpoise. And EFHW multiband antenna based on the same wire element In the research development phase.
Prototype Isolation transformer 1:1 build on two T300A-2 toroidal cores. Silver-plated 12G wire in PTFE insulation. (Wire antenna partially described below)
The main guiding principle these projects below is simplicity and low costs. The low costs w h i l e maintaining the expected power requirements at the same time, do not give up good parameters. (Intended for use in a temporary location on a small property)
Project "Be fast and easy QRV on the 160-meter band". Plus 80-meter band (developed to from 80 to 10-meter band) on the same Inv. L / Lazy V antenna wire. Feed point 12 feet high. Counterpoise system based on K2AV FCP for the 160-meter band. Short additional counterpoise`s for 80 to 10-meter band. And/or grounding
Below two points: X = 0 (resonance) and R = 50 Ohm before tuning to the desired frequency and before matching to the transmission line.
The further tuning procedure is about moving one of these points (X0 or R=50) to the desired frequency by shortening/lengthening of the antenna wire. let's take R: Then compensate the reactance at R=50 Ohm point back to 0 (zero) to match to the transmission line, for example to a 50 Ohm coaxial cable.
While using the same antenna wire on the 80-meter (and up) band.:
A) Added impedance transformer with 56,25:1 impedance ratio between the lower end of the antenna wire, a 1:1 bifilar wound insulating transformer 20 bifilar windings on two stacked T300A-2 cores ).
B) reduced wire length by 6.6 %.
Update August 2019
In the meantime, the results show that for an EFHW antenna with the feed point at 12 feet input impedance (with a predominance of R) for the 80-meter band is much higher than for the other bands from 40 to 10 meters. This will be the subject of practical experiments. Among others, a transformer with a changeable transformation ratio, or alternatively switching between two separate transformers.
Future development/research in progress to avoid the necessity of antenna wire shortening and to select the optimal components (to keep the rule simplicity and low costs at the same time also by keeping good technical parameters at a high level )
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| 2 x T300A-2 |
The main guiding principle these projects below is simplicity and low costs. (for use in a temporary location)
(The winter season has shown that reception on low bands on the transmitting antenna is significantly hampered. Thus, the next research will be towards the development/optimization of accessories for receiving antennas and receiving antennas self, intended for a small land area. Such as short beverage, k9ay, short phased RX vertical`s. etc.)Project "Be fast and easy QRV on the 160-meter band". Plus 80-meter band (developed to from 80 to 10-meter band) on the same Inv. L / Lazy V antenna wire. Feed point 12 feet high. Counterpoise system based on K2AV FCP for the 160-meter band. Short additional counterpoise`s for 80 to 10-meter band. And/or grounding
Below two points: X = 0 (resonance) and R = 50 Ohm before tuning to the desired frequency and before matching to the transmission line.
The further tuning procedure is about moving one of these points (X0 or R=50) to the desired frequency by shortening/lengthening of the antenna wire. let's take R: Then compensate the reactance at R=50 Ohm point back to 0 (zero) to match to the transmission line, for example to a 50 Ohm coaxial cable.
While using the same antenna wire on the 80-meter (and up) band.:
A) Added impedance transformer with 56,25:1 impedance ratio between the lower end of the antenna wire, a 1:1 bifilar wound insulating transformer 20 bifilar windings on two stacked T300A-2 cores ).
B) reduced wire length by 6.6 %.
Update August 2019
In the meantime, the results show that for an EFHW antenna with the feed point at 12 feet input impedance (with a predominance of R) for the 80-meter band is much higher than for the other bands from 40 to 10 meters. This will be the subject of practical experiments. Among others, a transformer with a changeable transformation ratio, or alternatively switching between two separate transformers.
Future development/research in progress to avoid the necessity of antenna wire shortening and to select the optimal components (to keep the rule simplicity and low costs at the same time also by keeping good technical parameters at a high level )
It is better to drill a much larger diameter hole than the ones in the picture (to ensure better drainage of the condensate, But with a larger diameter, there is a risk of bugs and insects getting inside)
For size comparison. Gray toroidal core size is 240
The total length of the main antenna wire (1.8 MHz band) is about 48 meters at the starting point. The total length of the antenna counterweights is 50 meters but folded so that the maximum spread from the antenna feed point is only 10 meters to each side.
(As an experiment additional parasitic 2 elements are added for 10 MHz band.
2 elements with variable length. Two lengths of about 15.8 for Reflector and 14.4 meters for director switched by relay for change of radiation direction. Still in the development/test phase.) Mutual impedance forces changes in the feed point impedance matching transformer.
A multi-band antenna served as a vibrator. (feed element)
At this stage, the length of the main radiator is of little importance. There is no prescription for the exact length for the 80 meters and up multiband, It tells us nothing special because the length results/depends on the interreaction with the environment and the layout - way how is suspended/hanging.
This wire goes almost vertical 19 meters high into a tall coniferous tree and the rest not fully horizontally but a bit sloping.
Below three important measurement points as a starting point for further planning/selection and implementation of the matching to transmission line going to the shack.
3 Feb. 2019
The procedure is to set one of the points below on the frequency which will be in the area of interest/needs.
Then depending on whether man chooses one of 2 points: with Rs 50 or with X0, a different method of matching to the transmission line be used.
Homemade FCP wire. Hand electro drill twisted copper wires 2 x 1.5mm2. Painted with UV resistant varnish (Copper oxide plus skin effect are not good friends for conductivity). Antenna wire in PE not PVC Insulation. DX-Wire made in Germany. Not a budget solution, but I already had one. For multi band use from 80-meter band and up its length was 141 ft. Plus a home brew EFHW transformer
The 160-meter band antenna after a.m. modification to 80 meters and UP feed-thru a broadband EFHW transformer.
SWR after re-tuning for 14 Mhz band
Starting point
Broadband impedance transformer version v. 1.0
In version v. T1.1 PTFE sleeving is omitted on the primary twisted winding.
For the final usable version when it is certain that the winding will not be unwound again it can be wound with enameled wire without Teflon tubing.
Teflon tubing served as thermal protection of the wire against core high temperature rise during testing. And as mechanical protection so as not to damage the insulation when winding and unwinding several times.
Tests have shown that the loss of properties (Permeability) due to temperature occurred much earlier than the risk of thermal damage to enamel insulation.
In the (final) version with fewer cores, a better coupling may be considered if the winding wire adheres more to the cores. But in test versions of with 4 cores and more, this factor was of little importance
4 x FT240-52 Ferrites. Still under testing.
This transformer has worked well from 3.5 to max 18 Mhz. It requires a slightly larger capacitance parallel to primary winding to compensate for +j reactance. I used 120 - 180 pF. It should be chosen experimentally to obtain improvement in higher bands but at the same time not to spoil the parameters on the 3.5 MHz band. In future plans is a different separate transformer design for the Higher bands.
Generally, it should be stated that for high power EFHWtransformers would be best to divide them into two separate transformers. Lower and upper bands separately.
Then switching them. But of course, it adds complexity.
Calculations have shown and subsequent tests have confirmed that the power dissipation of the transformer on five FT240 toroid cores, material 52 is still quite large.
For the possibility of using the EFHW antenna with QRO, I am planning a new project using material 61. Or cores with a larger diameter = FT300.
For example. Calculations have shown that using FT240-61 cores at least six cores and three turns on primary winding will be needed to achieve optimal input reactance.
I will present the results of practical measurements here in the near future.
The shape of the antenna is slightly different from the letter L towards the letter V
The easiest way to add 5 MHz without influence to the other bands is to add a horizontal tuned counterpoise (perpendicular to FCP from the 160-meter band as possible). Experimentally selecting the length because the length is influenced by the antenna environment and the counterpoise height over the ground) Reflection coefficient, Return loss / SWR was measured using VNA directly connected to the antenna feed point and observed remotely while adjusting the length of the counterpoise. (A metal reel measuring tape works well for this. You have to solder a piece of electric wire to the tape using a special flux or use a compression connection with screws.)
Broadband impedance transformer version v. 1.0
In version v. T1.1 PTFE sleeving is omitted on the primary twisted winding.
For the final usable version when it is certain that the winding will not be unwound again it can be wound with enameled wire without Teflon tubing.
Teflon tubing served as thermal protection of the wire against core high temperature rise during testing. And as mechanical protection so as not to damage the insulation when winding and unwinding several times.
Tests have shown that the loss of properties (Permeability) due to temperature occurred much earlier than the risk of thermal damage to enamel insulation.
In the (final) version with fewer cores, a better coupling may be considered if the winding wire adheres more to the cores. But in test versions of with 4 cores and more, this factor was of little importance
4 x FT240-52 Ferrites. Still under testing.
This transformer has worked well from 3.5 to max 18 Mhz. It requires a slightly larger capacitance parallel to primary winding to compensate for +j reactance. I used 120 - 180 pF. It should be chosen experimentally to obtain improvement in higher bands but at the same time not to spoil the parameters on the 3.5 MHz band. In future plans is a different separate transformer design for the Higher bands.
Generally, it should be stated that for high power EFHWtransformers would be best to divide them into two separate transformers. Lower and upper bands separately.
Then switching them. But of course, it adds complexity.
Calculations have shown and subsequent tests have confirmed that the power dissipation of the transformer on five FT240 toroid cores, material 52 is still quite large.
For the possibility of using the EFHW antenna with QRO, I am planning a new project using material 61. Or cores with a larger diameter = FT300.
For example. Calculations have shown that using FT240-61 cores at least six cores and three turns on primary winding will be needed to achieve optimal input reactance.
I will present the results of practical measurements here in the near future.
The shape of the antenna is slightly different from the letter L towards the letter V
The easiest way to add 5 MHz without influence to the other bands is to add a horizontal tuned counterpoise (perpendicular to FCP from the 160-meter band as possible). Experimentally selecting the length because the length is influenced by the antenna environment and the counterpoise height over the ground) Reflection coefficient, Return loss / SWR was measured using VNA directly connected to the antenna feed point and observed remotely while adjusting the length of the counterpoise. (A metal reel measuring tape works well for this. You have to solder a piece of electric wire to the tape using a special flux or use a compression connection with screws.)