Dave wrote:
Replies interspersed
"starman" wrote in message
...
Dave wrote:
Starman,
I am no longer intending to use a folded dipole, or a dipole of any
kind. I am currently planning to connect the conductors at the far end of
the 300 ohm twinlead but only connect one side of the near end to the
300/75 ohm matching transformer. Will this not work? I don't need
perfection, just reasonably good (I think.)
Thanks,
Dave
So you're going to use the twinlead as if it was a single wire. In that
case, you might as well connect the two wires in the near end too. There
isn't any advantage to keeping the wires of the near end seperated.
Connect the twinlead's near end to one wire of the high impedance side
(300-ohm) of the matching transformer (balun).
I'm not clear on this. It sounds like you are saying to make a loop out of
the twinlead, only to connect both near ends to the center conductor of the
300/75 ohm matching transformer (I guess.) Is that right? What would that
accomplish?
Since you're using twinlead as the horizontal antenna element, there is
no point in keeping the two wires in the twinlead seperated at either
end. The twinlead will act like it's one wire if you connect both of
it's wires together at each end. The near end (both wires in the
twinlead) will go to one wire of the high impedance side of the matching
transformer.
I forgot to mention in another post that the high side of a shortwave
balun should be about 500-ohms. This is another reason why the homemade
transformer is better. It's wound for an impedance ratio of about 9:1.
The TV balun in 300-ohms on the high side.
The other wire on the
300-ohm side should go to a ground rod, IF you're building the antenna
design on the website I gave you.
Do you mean the low-noise inverted L? If I did that, one leg of the L would
be hanging near my A/C compressor, which I fear would induce a great deal of
EMI. That's why I went back to the higher-up random-wire idea.
I figured you were going to use just a horizontal antenna section with
the coax going up to one end. That end is where the matching transformer
should be.
Otherwise connect the remaining
300-ohm wire to the shield of the coax.
Ramaining 300 ohm wire? You just lost me. When I connected the two 300 ohm
twinlead conductors together on the near end, I came up with one wire, which
I already connected to the pigtail going to the center conductor of the
300/75 ohm matching transformer. What remaining wire? Where did I go
wrong?
The TV balun should have two wires on one side (300-ohms) that may look
like a short length of twinlead or they could just be two pigtails. One
of those wires goes to the end of the antenna, which in your case is the
two wires of the twinlead connected together at that end. The other wire
of the 300-ohm side must go to the coax shield. That's why some kind of
adapter is needed with a grounding screw on the 75-0hm side which has
the threads, so you can connect the remaining 300-ohm wire from the
other side to the coax shield and threads via the screw.
This will require some kind of
adapter, if the balun has a threaded female F-connector for the coax on
the low impedance side. A standard coax inline grounding adapter (block)
would work. These are made for connecting a ground wire to the coax
shield in a TV installation. This adapter has a female F-connector on
each end and a grounding screw on the outside of the 'block'.
I *think* I understand up to this point.
Connect
the remaining wire on the 300-ohm side to the ground screw on the
adapter block.
Is this the same "remaining" wire as before? Do you mean to connect
whichever side of the antenna I grounded to the ground screw on the adapter
block?
The shield of the coax will be grounded at some point near the earth
ground. At the antenna end of the coax, the shield needs to be connected
to the remaining wire on the 300-ohm side which did not get connected to
the twinlead. I assuming you are not going to run a seperate ground wire
(don't) up to the end of the antenna where the coax connects to the
matching transformer.
If you use this kind of adapter you will also need
another adapter with a male F-connector on each end to connect the
ground adapter block to the threaded female side of the balun. You might
be able to find a coax grounding adapter which has a male F-connector on
one end and a female on the other end, along with the grounding
terminal. Then you wouldn't need two adapters.
Have some trouble following this, but let me see if I have it at the end.
The center wire of the coax goes to the low impedance side of the balun
which is the center hole of the threaded female F-connector on the
balun. The coax shield connects to the outside threads of that
F-connector, which would also go to the ground rod from the grounding
adapter, if you're making the website antenna.
That's right except you are not making the website antenna, so the coax
shield at the TV balun just goes to the 75-ohm threads and to the
remaining wire from the 300-ohm side as I explained above. You need the
grounding adapter so you can connnect that remaining 300-ohm wire to the
coax shield and threads on the 75-ohm side. Unfortunately that adapter
will probably have a female threaded F-connector on each end, so that's
why you might need a second adapter to connect the grounding one to the
threaded connector on the balun. It's just a matter of getting the right
combination of male and female connnectors to do it.
All of the above assumes you're using a standard TV balun which has a
threaded female coax F-connector for the low impedance side and two
wires (pigtails) on the high side. You should install a male F-connector
on the balun end of the coax. In the previous post I advised against
using a TV balun because it will most likely attenuate signals below
about 10-Mhz. This means the lower shortwave bands and also the regular
AM(MW) band would be somewhat weaker but this might not be a problem,
depending on what frequencies/bands you want to hear best.
Okay, let me see if I have this right. 50' of 300-ohm twinlead, conductors
connected at the far end to make a 100' loop.
No loop. Connect both wires in each end of the twinlead together so it
effectively becomes one wire. This is the horizontal section of your
antenna.
Connect one side of the near
end to the pigtail of a 300/75 ohm matching transformer that goes to the
center conductor (if I'm using TV matching transformers).
Not quite. Connect the near end of the twinlead (both wires) to one of
the 300-ohm pigtails. The other 'remaining' pigtail goes to the shield
of the coax on the 75-ohm side of the balun, which is the threads.
That's why you need the required grounding adapter 'block' for that
connection. This means that adapter will be located up at the end of the
coax where it connects to the threaded connector on the balun, not near
the ground.
Connect the other
side to the pigtail that goes to the coax shield on the other side of the
transformer. Connect the female F side of the 300/75 ohm matching
transformer to the male F connector on the coax. Coax goes down side of
house where it uses a male connector to connect to a F/F adapter mounted in
a grounding block, which is mounted on the grounding stake. On the other
side of the grounding block, male F connector on other side of the same F/F
adapter attaches to coax which goes underground around the corner of the
house (and past the A/C compressor) to my window and the radio. Is this
basicaly it, or have I gone totally off-center?
Now you're talking about a second grounding adapter or block near the
ground rod. That's fine but don't confuse it with the first adapter that
has to be located up at the coax end at the balun in order to have some
way of connecting one of the 300-ohm pigtails of the balun to the coax
shield and threads of the 75-ohm connector.
Sorry if I am making this complicated. I easily get lost in all the
male/female F connector to balun business. Main question I *think* I have
is- should I use the twinlead as a 100' loop, or a 100' random wire? And if
it is a loop, do I ground one side of it?
The twinlead should be used as if it was a single random wire (no loop)
running along your roof ridge. That's why you need to connect the wires
in both ends of the twinlead together. It becomes a single antenna wire
that happens to be made of two wires inside the twinlead.
Maybe it's time for a diagram but I think you're close to understanding
how to do it.
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