VK1JA wrote:Thanks for the replies everyone, muchly appreciated!
I've been offered the use of a AA-170 analyser to measure the VF of the cable I have which is going to make the process so so much easier to determine the VF of this particular piece of cable
So, just to check I have the correct thinking - I wish to use two
half wave lengths of cable to the combiner, so the formula should look like this (?)
300 / Frequency x VF x .5
Assuming the VF is .695, the formula would be;
300 / 432.15 x .695 x .5 = 241mm
?
I have had some doubts whether RF Supplier coax uses Teflon or not, so after reading your post decided to made a measurement of the remaining length I have in my stock.
Test was a length terminated in a SMA at one end and short at the other and measuring the electrical delay to the short on a VNA.
The physical length from cal plane is 944mm with an electrical length of 4.53ns
Free space length = 4.53E-9 x 300E6 = 1.359m
VF = 0.944 / 1.359 = 0.6946
Therefore the VF is that of Teflon, 0.69 as you have predicted.
Also if the power combiner is for 50 ohm in and out you don't need to worry about the length, you just need to maintain the same lengths.
On a side note I recently got a Chinese power splitter for 800MHz to 2500MHz and they are excellent value for money. I paid less than US$10 shipped for mine (shop around as the same item lists for $20 at other places). The insertion loss was less than 0.1dB from the theoretical 3dB with good directivity and match over the design range.
It is now installed on the ZL2WHO/b 23cm beacon feeding the North and South antenna panels.
73
Wayne ZL2BKC
