Am wanting to build a multi band dipole like in the first picture wondering if what’s in the second picture will work for these bands
Link is information on second picture
Link is information on second picture
Multi band dipole
- Thread starter DJBio
- Start date
Yes but with compromise. With a T200 core you can make a 9:1 transformer and using various lengths of non resonant wire it can work 80 through 10m with a tuner at the radio. This antenna will also use the coax as a counterpoise and the coax can be really hot with RF on some bands, requiring a good 1:1 choke balance near the radio. This antenna will also not perform nearly as well as a full size fan dipole, which has some compromises of its own.
If you swap out the T200 core for an FT-240-43 mix ferrite core you can make a 49:1 or 64:1 transformer and with about 133-135ft of wire it will work all the bands as the fan dipole plus a few more without a tuner and you won’t be able to tell any difference between the fan dipole example and your new resonant multiband end fed half wave. A single FT-240-43 core will handle up to about 400w SSB and less in higher duty cycle modes like FT8, FM, etc.
Since 80m is not exactly harmonically related to the other ham bands, if the EFHW is tuned for 40, 20, 15, 10m, then 80m will resonate around 3.55MHz, well below the 75m phone band of 3.8-4.0MHz. That can be fixed by inserting a high voltage capacitor in the exact middle of the wire and I forget the value but either a 150pf or 250pf capacitor will raise the lower resonant point to about 3.9MHz easily covering the 3.8-4.0MHz phone band and more without affecting any other band. I usually use HV doorknob caps in the 10kV range for this but an equivalent value disc cap works fine.
Do a search on 80m EFHW antenna using a 49:1 or 64:1 and you will come up with countless sites with instructions on how to make it. I’ve made dozens of 80-10m and 40-10m versions and they are very cheap and effective antennas.
If you swap out the T200 core for an FT-240-43 mix ferrite core you can make a 49:1 or 64:1 transformer and with about 133-135ft of wire it will work all the bands as the fan dipole plus a few more without a tuner and you won’t be able to tell any difference between the fan dipole example and your new resonant multiband end fed half wave. A single FT-240-43 core will handle up to about 400w SSB and less in higher duty cycle modes like FT8, FM, etc.
Since 80m is not exactly harmonically related to the other ham bands, if the EFHW is tuned for 40, 20, 15, 10m, then 80m will resonate around 3.55MHz, well below the 75m phone band of 3.8-4.0MHz. That can be fixed by inserting a high voltage capacitor in the exact middle of the wire and I forget the value but either a 150pf or 250pf capacitor will raise the lower resonant point to about 3.9MHz easily covering the 3.8-4.0MHz phone band and more without affecting any other band. I usually use HV doorknob caps in the 10kV range for this but an equivalent value disc cap works fine.
Do a search on 80m EFHW antenna using a 49:1 or 64:1 and you will come up with countless sites with instructions on how to make it. I’ve made dozens of 80-10m and 40-10m versions and they are very cheap and effective antennas.
