On Sat, 4 Jan 2014 21:23:14 -0500, "Ralph Mowery"
wrote:
What I am having trouble with is the 'perfect' combiner.
I feel your pain. Many years ago, I made a similar mistake on the NEC
antenna modeling mailing list. I then processed to make a total fool
of myself and had to be corrected by the experts. Even so, I still
didn't believe it so I built a Wilkinson combiner and bench tested it
for loss. I still have the combiner somewhere as a reminder of my
mistake.
Incidentally, a Wilkinson combiner might be a tolerable solution for
combining two FM antenna. The loss is much less than a bifilar wound
toroid. I'm not sure if it will work over the entire FM band. I can
grind the numbers if anyone is interested.
My problem is where are you going to find a combiner for a broad frequency
that does not have any large (say over 1 db ) of loss ? Are the ones for
the TV frequencies built differant ?
There's only so much you can do with passive only designs. The next
step up is an active combiner:
http://www.rldrake.com/product-ac1686.php
0-3dB gain per port. 54 to 860 MHz.
Has anyone actually put one on accurate test equipment to see about the loss
like I have been trying to do ?
Yep. I have. There's very little loss between the combiner input
ports and the "sum" port. However, in the other direction, there's a
bit over 3dB loss due to the power splitting. See the specs on the
MCL splitter/combiner that you have and try it with a service monitor
or generator. Since it works down to 10 MHz, you might be able to do
the test with a function generator, a few dummy loads, some T
connectors, and an oscilloscope.
I understand phasing harnesses for antennas. They are almost loseless. Only
a few feet of coax worth. I have used them on antennas before. They are
not usually very broad banded unless the antennas are broad banded and made
so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8
dipole arays for VHF/UHF. Lots of 'tricks' used to do that.
It's low, but the phasing harness loss for stacked vertical dipoles is
not zero. I've never calculated or measured it, but this might help:
http://www.kg4jjh.com/pdf/2-Meter%20Vertical%20Dipole%20Array.pdf
"The phasing harness loss at 150 MHz is calculated to be 0.67 dB."
Scaled for 100 Mhz, I would guess about 0.5 dB. Might as well use a
combiner/splitter.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558