John,

Nice to see you back on the group. Things have been a little rough here
lately but there's still hope. I often recommend your low noise antenna
with the balun located near the ground. It worked well for me. I can
listen to shortwave now without any interference from the computer,
television and other home appliances.

How are things in the X-ray universe?

John Doty wrote:

In article , "Dave"
wrote:

Is this Smith Chart stuff? (You must forgive me, I am a primitive.)

A Smith chart is a way of graphically relating impedances to reflection
coefficients. The code that made the plots on the web page did the same
sort of calculations numerically. The plots themselves are semilog
Cartesian coordinates, not Smith charts.


On Sun, 13 Jul 2003 12:21:23 +0400, "John Doty" wrote:

In article , "Dave"
wrote:

We are not concerned with the characteristic impedance of the wire
antenna. We are concerned with its RF impedance as an antenna, not a
piece of metal.

The characteristic impedance is where the center of the antenna's
impedance spiral is. That's a good choice for a matching impedance if
what you want is a broadband antenna.

See: http://www.anarc.org/naswa/badx/ante..._longwire.html


--
| John Doty "You can't confuse me, that's my job."
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Telamon wrote in message ..

Isn anyone going to comment on the transformer not showing a higher S
meter reading on the radio? This sure surprised me. Maybe the two
stations I picked happened to be in a good spot where it wasn needed.

Not too surprising.. Will depend on the freq. Being your antenna is
folded, I would have to model it to see the src data for each
shortwave band. I'm guessing it would be about as for a single wire
version, except the with appx 4 X transformation of the folded
antenna. Anyway, the feed impedance will vary all over the place from
band to band. You probably have about as good a chance getting a
usable match without the transformer, as you do with it. In some
cases, the transformer could actually make the match worse. Some will
be better. Some about the same. This is a common scenario when
running an antenna like a G5RV. Most use 4:1 baluns. But really a 1:1
balun makes about as much sense being you are already using a tuner.
Of course, I don't like the feeding of the average G5RV's. I'd dump
the coax and feed straight with ladder line. I don't like mixing
feedline types and then using a balun to try to assure a good match
between lines. Usually, the match is not very good, and you have more
loss. But this is mainly a transmit issue, not receiving at HF. MK

Telamon wrote in message

I only looked at a few frequencies but those were near the frequency for
which the antenna was cut. I¹m not worried about the other bands. I want
to know why I did not get a higher S meter reading on the band the
antenna was cut for. The transformer should have made for a better match
on 13 meters and it didn¹t.

I think mainly because the antenna is "folded". I tried modeling a
folded 40m dipole last night just to look at a few bands. At it's
design freq, the feed impedance is pretty low. You might need to
reverse the transformer to get a better match on that band if it was
set up to match mainly Hi-Z loads. If you want a good match to coax on
one particular band , I'd go to a straight dipole, not folded. I've
never used folded dipoles, so I'm not sure of any quirks they may have
as a multiband antenna. But really no matter...It sounds like you have
enough signal level no matter what route you take.
MK

Telamon wrote in message
I only looked at a few frequencies but those were near the frequency for
which the antenna was cut. I¹m not worried about the other bands. I want
to know why I did not get a higher S meter reading on the band the
antenna was cut for. The transformer should have made for a better match
on 13 meters and it didn¹t.

I mentioned in an earlier post that the folded dipole I modeled showed
a low Z. But after thinking about it, that didn't seem right. I had
always assumed most folded dipoles with two wires had about a 300 ohm
feedpoint. And double checking in a book, that seems to be the case. I
don't know why the antenna I modeled showed that, but I'll have to
look into it. But anyway, if you had a 300 ohm feedpoint, and used a
9:1 balun, you would end up quite low in Z to the radio.
A 4:1 would put you in the ballpark. But, I'd still prefer to use a
single wire dipole fed with coax for a single band dipole. No
transformer needed. Only a balun, and that can be a choke wound from
the coax. But again, as far as s/n ratio, not counting noise ingress
problems, any of them should work. MK

Mark Keith wrote:

Telamon wrote in message
I only looked at a few frequencies but those were near the frequency for
which the antenna was cut. I¹m not worried about the other bands. I want
to know why I did not get a higher S meter reading on the band the
antenna was cut for. The transformer should have made for a better match
on 13 meters and it didn¹t.

I mentioned in an earlier post that the folded dipole I modeled showed
a low Z. But after thinking about it, that didn't seem right. I had
always assumed most folded dipoles with two wires had about a 300 ohm
feedpoint. And double checking in a book, that seems to be the case. I
don't know why the antenna I modeled showed that, but I'll have to
look into it. But anyway, if you had a 300 ohm feedpoint, and used a
9:1 balun, you would end up quite low in Z to the radio.
A 4:1 would put you in the ballpark. But, I'd still prefer to use a
single wire dipole fed with coax for a single band dipole. No
transformer needed. Only a balun, and that can be a choke wound from
the coax. But again, as far as s/n ratio, not counting noise ingress
problems, any of them should work. MK

Hi Mark,
What software are you using for modeling? NEC engines do not like close wires
(perhaps NEC4 has dealt with this).
EZNEC or AO should handle the problem better.

Dale W4OP
for PAR Electronics, Inc.

Michalkun wrote:
Is it true that if you feed a dipole in the middle you don't need a balun?

Depends on how you feed it, and what with.

--
The function of an asshole is to emit quantities of crap. Spammers do
a very good job of that. However, I do object to my inbox being a
spammer's toilet bowl. -- Walter Dnes

Michalkun,

If you are going to 'use' a "Balanced FeedLine" (300 Ohm Twin Lead or
450 Ohm Ladder Line) and connect this FeedLine directly into the
radio/receivers HI-Z Terminals then you do not need a BalUn.

However, if you wish to use Coax Cable as a 'feedline' from the
antenna to the radio's LO-Z Antenna Connector; then some form of
matching transformer should be used to get the best results from your
dipole antenna.


~ RHF
..
..
= = = Michalkun
= = = wrote in message 2.251...
Is it true that if you feed a dipole in the middle you don't need a balun?

RHF wrote:

Michalkun,

If you are going to 'use' a "Balanced FeedLine" (300 Ohm Twin Lead or
450 Ohm Ladder Line) and connect this FeedLine directly into the
radio/receivers HI-Z Terminals then you do not need a BalUn.

However, if you wish to use Coax Cable as a 'feedline' from the
antenna to the radio's LO-Z Antenna Connector; then some form of
matching transformer should be used to get the best results from your
dipole antenna.

A typical half-wave dipole fed with 50 ohm, or even say 75 ohm coax should feed nicely
right into the Lo-Z input on a receiver without a balun of any kind.

Purists may wish to put a 1:1 balun at the feedpoint though.

Steve
Holland, MI

Drake R7, R8 and R8B

LC,

I guess what you are inferring is that there are two approaches to
buying or building a Bal-Un (Un-Un) for an Antenna.

#1. MOST OF THE TIME: We buy or built a certain kind of antenna that
has a known XXX 'impedance' an installed it the best we can.
- - - Therefore We "ASSUME" that XXX is the antennas 'impedance' and
buy or build a Bal-Un (Un-Un) to match the antenna to the feed-line
and antenna input of the receiver.

2. SOME OF THE TIME: We buy or built a specific kind of antenna an
installed it correctly.
- - - Then We 'test' the antenna with an impedance bridge or antenna
tester and 'know' for a "Fact" the YYY 'impedance' of the antenna.
+ + + Next, knowing that YYY is the antennas 'impedance': We buy or
build a Bal-Un (Un-Un) to match the antenna to the feed-line and
antenna input of the receiver.
= = = Finally, We Re-Test the Antenna with the Bal-Un Installed to
confirm our results.


~ RHF
..
..
= = = "Lionel Carter"
= = = wrote in message ...
I would also be interested in the answer.
My impression is that particular balums are used purely on a custom and
practice basis and 'suck it and see'. I have not seen any guide to measuring
the rf resistance/impedance of a throw out or long wire antenna.
If someone doesn't answer your question the chances are they don't know
either.

Lionel Carter

"Michalkun" wrote in message
.251...
How does one can determine the impendance of a wire to get the right balun
for it, so it can be hooked up to the coaxial cable?

Dale Parfitt wrote in message

Hi Mark,
What software are you using for modeling? NEC engines do not like close wires
(perhaps NEC4 has dealt with this).
EZNEC or AO should handle the problem better.

Dale W4OP
for PAR Electronics, Inc.

It was MMANA "freeware" which uses the mininec engine. I finally got
it to work.
I wanted to try some other programs also. The first version I made
placed the wires at only .3m apart. "40m antenna" When I tried .5m, it
clicked in and started showing believable results. Around 300 ohms,
plus or minus depending if high or low from the design point. When I
tuned that particular antenna so I had nearly no reactance, I got
284.617-j0.444 . Thats probably fairly close. MK