The darn internet is giving me a headache.. But I'm learning about velocity factor and how it affects things.
I'm building a dipole antenna for 137 Mhz and need to clear a few things up.
1st.. There are several instructions on the internet.. both are trying to build a double cross dipole to capture the signals coming from the NOAA satellites.. This happens at about 137.1 Mhz to 137.8 Mhz.. but lets just go with the 137 for simplicity.
The instructions on this page tell me my dipole(s) should be 38.25 inches long:
https://www.qsl.net/py4zbz/DCA.pdf
Then the instructions on this page tell me my dipole(s) should be 43.3 inches long (1100mm)
https://sourceforge.isae.fr/projects/reception-of-weather-images/wiki/_Choice_and_design/17
After a bit of reading, I followed along with the math on the sourceforge link and found indeed that the 43.3 inches seems correct.. but I don't know enough about this to know if the math is indeed correct or not.. Seems like it is though from my other dipole reading.
The only thing that these folks seem to agree on is the 21.5 inch separation between the dipoles. That's seems odd.
So what am I missing here?
I'm going to be using some 1/2 inch aluminum pipe for my dipoles. Each pipe will be screwed into a 1/2 inch threaded PVC tee at the center and I plan on drilling and tapping a hole just behind the threads to accept the coax connection point.
My first instinct is to cut the dipole length to 43.3 and cut it down if needed.. but why the difference in values from these two pages?
I'm building a dipole antenna for 137 Mhz and need to clear a few things up.
1st.. There are several instructions on the internet.. both are trying to build a double cross dipole to capture the signals coming from the NOAA satellites.. This happens at about 137.1 Mhz to 137.8 Mhz.. but lets just go with the 137 for simplicity.
The instructions on this page tell me my dipole(s) should be 38.25 inches long:
https://www.qsl.net/py4zbz/DCA.pdf
Then the instructions on this page tell me my dipole(s) should be 43.3 inches long (1100mm)
https://sourceforge.isae.fr/projects/reception-of-weather-images/wiki/_Choice_and_design/17
After a bit of reading, I followed along with the math on the sourceforge link and found indeed that the 43.3 inches seems correct.. but I don't know enough about this to know if the math is indeed correct or not.. Seems like it is though from my other dipole reading.
The only thing that these folks seem to agree on is the 21.5 inch separation between the dipoles. That's seems odd.
So what am I missing here?
I'm going to be using some 1/2 inch aluminum pipe for my dipoles. Each pipe will be screwed into a 1/2 inch threaded PVC tee at the center and I plan on drilling and tapping a hole just behind the threads to accept the coax connection point.
My first instinct is to cut the dipole length to 43.3 and cut it down if needed.. but why the difference in values from these two pages?