V
VK2RK
Guest
The new VNA and Amidon FT240-61 ferrites have arrived, first thing was to validate that the new VNA was accurate and not all over the place as the old one was.
The FT240-61 ferrite are very large, requiring to look for another container with large enough dimensions to accommodate the transformers.
I chose 80 mm OD PVC pipe (Thick Wall DN80) with end caps.
All other hardware was obtained from Bunnings.
I used the Guanella topology to minimize the common mode currents as I did with the previous prototypes.
Due to the erroneous VNA I was using I still obtain useful data to compare results with, thus I kept the design the same.
There is split opinion on using the Guanella either on single core or double core, as to the effectiveness on which one is best for common mode rejection.
All my windings are 8 turns each, on the previous ferrites I found that increasing or decreasing the number of turns made little difference to the wanted inductance, only evident change was on the highest applied frequency.
I concluded that the ferrite material favored the low frequencies at the cost of the high frequencies, and the number of turns favored the high frequencies, (too many turns reduced the operational high frequency.
I found eight turns to be the sweet spot.
The analysis of the new system using the FT240-61 shows a large improvement on the response from 3 to 20 MHz
This table shows measurements taken in each band.
80 Meter scan
49.5 Ohms J6.89 (Inductive) @ 3.65 MHz
VSWR- 1:1.49
BW- 3.5 to 3.8 MHz
40 Meter Scan
50.5 Ohms J7.0 (Inductive) @ 7.1 MHz
BW- 7.0 to 7.2 MHz
30 Meter Scan
51.3 Ohms J8.2 (Inductive) @ 10.125 MHz
BW- 10.1 to 10.15 MHz
20 Meter Scan
52.8 Ohms J9.68 (Inductive) @ 14.178 MHz
BW- 14.0 to 14.35 MHz
17 Meter Scan
53.4 Ohms J9.69 (Inductive) @ 18.12 MHz
BW- 18.01 to 18.17 MHz
15 Meter Scan
51.7 Ohms J15.2 (Inductive) @ 21.23 MHz
BW- 21.0 to 21.45 MHz
12 Meter Scan
56.5 Ohms J17.1 (Inductive) @ 24.94 MHz
BW- 24.89 to 24.99 MHz
10 Meter Scan
60.25 Ohms J18.4 (Inductive) @ 28.86 MHz
BW- 28.0 to 29.7 MHz
6 Meter Scan
77.35 Ohms J7.96 (Inductive) @ 51.0 MHz
BW- 50.0 to 52.0 MHz
The data above shows that the transformer starts to become more reactive above 24 MHz,
3 MHz to 30 MHz sweep shows what is happening to the BALUN impedance.
The VSWR response is at worst case less than 1:1.5, so this should work, but been here before, need to stick it up in the air and see what happens.
As a reflection regarding permeability, the T200-2 has a Permeability (ui) 10
The FT240-61 has a Permeability (ui) 125
The Jaycar LO1238 Ray measured to be mix 43 has a approx Permeability (ui) 800
In my case the LO1238 worked best on 80 meters and 40 meters but overheated at the higher frequencies.
Thus the FT240-61 system should provide a good response up to 30 MHz with power in excess of 1KW
A smaller Mix 61 can be used for lower powers.
The FT240-61 ferrite are very large, requiring to look for another container with large enough dimensions to accommodate the transformers.
I chose 80 mm OD PVC pipe (Thick Wall DN80) with end caps.
All other hardware was obtained from Bunnings.
I used the Guanella topology to minimize the common mode currents as I did with the previous prototypes.
Due to the erroneous VNA I was using I still obtain useful data to compare results with, thus I kept the design the same.
There is split opinion on using the Guanella either on single core or double core, as to the effectiveness on which one is best for common mode rejection.
All my windings are 8 turns each, on the previous ferrites I found that increasing or decreasing the number of turns made little difference to the wanted inductance, only evident change was on the highest applied frequency.
I concluded that the ferrite material favored the low frequencies at the cost of the high frequencies, and the number of turns favored the high frequencies, (too many turns reduced the operational high frequency.
I found eight turns to be the sweet spot.
The analysis of the new system using the FT240-61 shows a large improvement on the response from 3 to 20 MHz
This table shows measurements taken in each band.
80 Meter scan
49.5 Ohms J6.89 (Inductive) @ 3.65 MHz
VSWR- 1:1.49
BW- 3.5 to 3.8 MHz
40 Meter Scan
50.5 Ohms J7.0 (Inductive) @ 7.1 MHz
BW- 7.0 to 7.2 MHz
30 Meter Scan
51.3 Ohms J8.2 (Inductive) @ 10.125 MHz
BW- 10.1 to 10.15 MHz
20 Meter Scan
52.8 Ohms J9.68 (Inductive) @ 14.178 MHz
BW- 14.0 to 14.35 MHz
17 Meter Scan
53.4 Ohms J9.69 (Inductive) @ 18.12 MHz
BW- 18.01 to 18.17 MHz
15 Meter Scan
51.7 Ohms J15.2 (Inductive) @ 21.23 MHz
BW- 21.0 to 21.45 MHz
12 Meter Scan
56.5 Ohms J17.1 (Inductive) @ 24.94 MHz
BW- 24.89 to 24.99 MHz
10 Meter Scan
60.25 Ohms J18.4 (Inductive) @ 28.86 MHz
BW- 28.0 to 29.7 MHz
6 Meter Scan
77.35 Ohms J7.96 (Inductive) @ 51.0 MHz
BW- 50.0 to 52.0 MHz
The data above shows that the transformer starts to become more reactive above 24 MHz,
3 MHz to 30 MHz sweep shows what is happening to the BALUN impedance.
The VSWR response is at worst case less than 1:1.5, so this should work, but been here before, need to stick it up in the air and see what happens.
As a reflection regarding permeability, the T200-2 has a Permeability (ui) 10
The FT240-61 has a Permeability (ui) 125
The Jaycar LO1238 Ray measured to be mix 43 has a approx Permeability (ui) 800
In my case the LO1238 worked best on 80 meters and 40 meters but overheated at the higher frequencies.
Thus the FT240-61 system should provide a good response up to 30 MHz with power in excess of 1KW
A smaller Mix 61 can be used for lower powers.
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