RadioBanter - small shortwave antenna

RadioBanter (https://www.radiobanter.com/)

- Shortwave (https://www.radiobanter.com/shortwave/)

- - small shortwave antenna (https://www.radiobanter.com/shortwave/74829-small-shortwave-antenna.html)

small shortwave antenna

On 2005-07-18 20:38:50 -0400, squeege boy said:

I am livign in an apartment, so I cant transmit (no towers and what
not) so I am looking for what would suit my needs best for HF and
shortwave recption in general

I have googled a bit and havent found much in the way of easy to build
or easy to obtain parts to build antennas

any help would be really appreciated
cheers

You sure you googled?

http://www.google.com/search?hl=en&q... oogle+Search

--

PCs, like air-conditioners, are useless when you open Windows.

I am livign in an apartment, so I cant transmit (no towers and what
not) so I am looking for what would suit my needs best for HF and
shortwave recption in general

I have googled a bit and havent found much in the way of easy to build
or easy to obtain parts to build antennas

any help would be really appreciated
cheers

-------------------------------------------------------------------------

A metal slinky with a MLB on the end and feed your radio with
coax. Use inside or out. Collapses down to a very small package when
not using and works amazingly well. Use it vertically or horizontally.
About the most simple and most effective HF ant. you could use for
apartement life. Dont waste your money on an active antenna, they
are notorious for picking up all sorts of electrical noise, sometimes to
the point of the radio being unlistenable.

J

what is a MLB

On Tue, 19 Jul 2005 21:48:31 GMT, "Jeff"
wrote:

I am livign in an apartment, so I cant transmit (no towers and what
not) so I am looking for what would suit my needs best for HF and
shortwave recption in general

I have googled a bit and havent found much in the way of easy to build
or easy to obtain parts to build antennas

any help would be really appreciated
cheers

-------------------------------------------------------------------------

A metal slinky with a MLB on the end and feed your radio with
coax. Use inside or out. Collapses down to a very small package when
not using and works amazingly well. Use it vertically or horizontally.
About the most simple and most effective HF ant. you could use for
apartement life. Dont waste your money on an active antenna, they
are notorious for picking up all sorts of electrical noise, sometimes to
the point of the radio being unlistenable.

J

squeege boy wrote:

what is a MLB

Magnetic Longwire Balun...

dxAce
Michigan
USA

On Tue, 19 Jul 2005 21:48:31 GMT, "Jeff"
wrote:

I am livign in an apartment, so I cant transmit (no towers and what
not) so I am looking for what would suit my needs best for HF and
shortwave recption in general

I have googled a bit and havent found much in the way of easy to build
or easy to obtain parts to build antennas

any help would be really appreciated
cheers

-------------------------------------------------------------------------

A metal slinky with a MLB on the end and feed your radio with
coax. Use inside or out. Collapses down to a very small package when
not using and works amazingly well. Use it vertically or horizontally.
About the most simple and most effective HF ant. you could use for
apartement life. Dont waste your money on an active antenna, they
are notorious for picking up all sorts of electrical noise, sometimes to
the point of the radio being unlistenable.

J

"squeege boy" wrote in message
...
what is a MLB
----------------------------------------------------------------------------

It stands for Magnetic Longwire Balun. Its really not a balun ,
rather it is more of a transformer to match the impedance of the
antenna to that of the radio......... roughly 50-60ohms. Its usually
a torroidal magnet with 2 windings, a primary and a secondary.
They work very well for their intended purposes. They are 35-45$
but are worth it IMO. Do a google search for them and read all
about them.

J

screw $45-$60 for a MLB! you can wind it yourself for $5. the info is
out there. i am sure that someone here would help. CW has it on his
site, maybe he will check in with the address.

Jeff wrote:
I am livign in an apartment, so I cant transmit (no towers and what
not) so I am looking for what would suit my needs best for HF and
shortwave recption in general

I have googled a bit and havent found much in the way of easy to build
or easy to obtain parts to build antennas

any help would be really appreciated
cheers

-------------------------------------------------------------------------

A metal slinky with a MLB on the end and feed your radio with
coax. Use inside or out. Collapses down to a very small package when
not using and works amazingly well. Use it vertically or horizontally.
About the most simple and most effective HF ant. you could use for
apartement life. Dont waste your money on an active antenna, they
are notorious for picking up all sorts of electrical noise, sometimes to
the point of the radio being unlistenable.

J

I have done that and my SLINKY (vertical) drops off severely on
wavelength shorter than 40M...Study of SLINKY antenna resources indicate
it is resonant around 7.2 Mhz

Yodar

See:
http://www.hard-core-dx.com/nordicdx/antenna/feed/feed1.html
and
http://www.webex.net/~skywaves/ANTENNA/antsys.htm#4:1%20Balun
and
http://members.aol.com/WA1ION/nrants.pdf
the last one uses a MiniCircuits 9:1 tranformer that caosts about ~$5.
It has been several years since I bought one.

John Doty is very correct about the advantage of "TV" mathcing
cores over the more common 1" feritte cores. Pluse the TV cores
are cheap and still fairly pentifull.

Terry

Great antenna performers and bargains from DWM Communications:

http://qth.com/dwm

73, Bill - WA8MEA
Host, DX Radio School

Telamon wrote:

That depends on the core. Some are no good for 3 to 30 MHz.
TV operates at 50MHz.

--
Telamon
Ventura, California
-----------------------
So people keeep telling me.
I have built many, around 30,of these little gems and they all
worked down to below MW with minimal losses. Read Mr Doty's
comments. They have all worked great from .5MHz to above
20MHz with every scalvaged TV core I have used. Perhaps I
have just been lucky, or maybe, just maybe for cores so small
loss are not as high as many people think.
I will include an observation from Mr Doty himself:"
------------------
"John Doty Sep 6 2000, 1:48 pm show options
Newsgroups: rec.radio.shortwave
From: "John Doty"
Date: Wed, 06 Sep 2000 08:47:12 -0500
Subject: "Improved" matching transformer

In article (Who Did you Expect?) wrote:
I use the same core that I do for the matching transformer, but with 10
turns for both primary and secondary. And while we are on the subject of
cores, I still can not find a lot of difference in ANY [ferritte not
powdered iron!] core that I have tried. Anyone have any thoughts on
that?

The biggest difference in performance due to different ferrites will be
at
longwave, not shortwave. At the highest shortwave frequencies, size
will
matter: 10 turns on a big core will have too much capacitance and
leakage
inductance at 30 MHz. At 10 MHz, 10 turns at 50 ohms looks good with
almost any ferrite.
--
| John Doty "You can't confuse me, that's my job."
--------------------------
and
--------------------------
John Doty Sep 8 2000, 2:57 pm
Newsgroups: rec.radio.shortwave
From: "John Doty"
Date: Fri, 08 Sep 2000 09:56:55 -0500
Subject: "Improved" matching transformer

In article (Who Did you Expect?) wrote:
By "large", what do you mean? I am using the 1.2" OD type 43 Amidon
ferritte core.

That's about the size where the problem becomes interesting. The rule
of
thumb I use is that if the total amount of wire in the transformer is
less
than 5% of a wavelength, the parasitics are likely to be negligible no
matter how you wind it, but if you have more wire, the winding details
will matter in complex ways. 5% of the wavelength at 30 MHz (10 m) is
50
cm, or 20". One turn on your core is about an inch, so a 10:10 is at
the
edge, and a 30:10 violates the rule by a factor of 2 (but it's only a
rule
of thumb).

10 turns was a conservative estimate based on the minimum inductance
expected from a small TV core. With detailed specs, you can compute the
turns required more accurately. If you want a lower 3 dB cutoff of 500
kHz
(this is likely to suffice even for LW DX), you want the magnetizing
inductance on the 50 ohm side to have a reactance of 50 ohms at 500
kHz:

Z = 2*Pi*f*L, so L = Z/(2 Pi f ) = 50/( 2*3.14*500000) = ~16 uH

This calculation is only valid if the lower cutoff is below the knee in
the permeability versus frequency curve. For 43 material, this is at 5
Mhz, so we're fine.

An FT-114-43 has a core constant of about 0.6uH/turn^2, so 5 turns
yields
25*0.6 = 15 uH, which is close enough. A 5:5 is comfortably within the
rule of thumb, while a 15:5 is at the edge (but is probably better than
a 30:10).

I have also used a BLN-73-202 with 7 turns triflar wound, both worked
about the same.

This is a really good core for this kind of transformer. Just *two*
turns
on the 50 ohm side yields 34 uH, for a lower cutoff below 250 kHz.
Since a turn is less than 4 cm, a transformer like this should have
good performance well into the VHF region. This appears to be the
core ICE uses in their transformer (if it isn't this one, it's
something
with very similar specs).

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

-------------------------------

I have found his 5% of a wavelength "rule" to be very true.
And by using it Ihave never had a "TV" core, either the
binoculer or the small "O" , fail.

Before getting lost in theory, why not wind one and
see how it works.

Terry

Telamon wrote:

That depends on the core. Some are no good for 3 to 30 MHz. TV operates
at 50MHz.
--------------------------
And this post by Mr. Doty should put this argument to rest.
----------------
John Doty Feb 18 1999, 9:00 am
Newsgroups: rec.radio.shortwave
From: John Doty
Date: 1999/02/18
Subject: Buiding Matching Transformer

J W Schermerhorn wrote:

2/18/99

The TV torroid is probably not suitable for winding a balun transformer
for shortwave (HF) frequencies. It's formulated for VHF/UHF and doesn't
work well below about 10-Mhz.

Works fine if you use enough turns. For a 30:10 turn version, I've
measured a lower 3 dB cutoff of 330 kHz. A higher permeability material
optimized for HF would let you use fewer turns, but otherwise doesn't
perform better at HF, assuming the core is small.

The ICE model 180 transformer uses an HF core with only one turn on the
low impedance side. At HF its performance is nearly identical to 30:10
transformer on the TV core, but its lower 3 dB cutoff is 1 MHz, so it
isn't as good at MF and LF (needs more turns).

--
John Doty
--------------------------------------------------

To sum it up, the "correct" ferrite core will require fewer turns.
But, a VHF material will work fine, if you can get anough turns
without exceeding the "5% of wavelength" rule.

Terry

This might be a little larger than you had in mind, but it's
interesting:'

http://cgi.ebay.com/ws/eBayISAPI.dll...ayphotohosting

Telamon wrote:
-------------------------------
In article .com,
wrote:
Telamon wrote:

That depends on the core. Some are no good for 3 to 30 MHz.
TV operates at 50MHz.

--
Telamon
Ventura, California
-----------------------
So people keeep telling me.
I have built many, around 30,of these little gems and they all
worked down to below MW with minimal losses. Read Mr Doty's
comments. They have all worked great from .5MHz to above
20MHz with every scalvaged TV core I have used. Perhaps I
have just been lucky, or maybe, just maybe for cores so small
loss are not as high as many people think.
I will include an observation from Mr Doty himself:"

Snip

Well then how many times am I going to have to tell you then is the
only question left.

All cores have a frequency response range. You have to pick an
appropriate one depending on where you intend it to operate. I have
come across ferrite cores that are worthless 10 MHz so it may work
well on the upper bands and poorly on the lower. You may not notice
this right off because evening and nigh time signals on the lower bands
generally have more signal power.

I believe you have some basic equipment so you can check it out.

I think you may have better luck in the power supply section of
equipment you are tearing apart for components. Specifically the EMI
section will likely have some common mode chokes that are designed to
operate over the short wave spectrum to suppress conductive noise.

TV RF ferrites are designed for 50MHz to 500MHz or something along
those
lines and their response of some falls off on the low end so I don't
recommend using them unless you can test them.

You either need to know that the material is of a certain type or be
able to test it.

--
Telamon
Ventura, California
-----------------------------------------
OK I am trying to be polite.
There is already enough anger in the world.
But, this is getting silly, back in Nov 2001
this same thread came up and John Doty explained why,
for this application, with small TV cores, the ferrite type
didn't mater that much. He gave actual loss values.
Your response was:
---------------------------
Newsgroups: rec.radio.shortwave
From: Telamon
Date: Tue, 13 Nov 2001 05:05:09 GMT
Subject: 4.1 Balun

In article ,
"John Doty" wrote:

In article om,
"Telamon" wrote:

I've kept my mouth shut about magnetic core material for a long while
now. At some point people in this group need to understand that if the
wrong material is chosen these RF transformers will not work right.

Most do not realize this due to the fact that they generally wind them
bi-filar.

I generally wind mine with separate windings, not bifilar.

In addition (at the frequencies of interest) they are not getting the
inductance they think they are achieving.

Since I measure the characteristics of my transformers, I'm sure that I
do.

snip

My post was directed at discussions about this topic in general in this
group and was not directed at you.

--
Telamon
--------------------------------
At the risk of repeating the obvious:
---------------------------------
John Doty Nov 13 2001, 12:14 am show options
Newsgroups: rec.radio.shortwave
From: "John Doty" - Find messages by this author
Date: Mon, 12 Nov 2001 18:14:17 +0500
Local: Mon,Nov 12 2001 2:14 pm
Subject: 4.1 Balun

In article om,

"Telamon" wrote:
I've kept my mouth shut about magnetic core material for a long while
now. At some point people in this group need to understand that if the
wrong material is chosen these RF transformers will not work right.

Most do not realize this due to the fact that they generally wind them
bi-filar.

I generally wind mine with separate windings, not bifilar.

In addition (at the frequencies of interest) they are not getting the
inductance they think they are achieving.

Since I measure the characteristics of my transformers, I'm sure that I
do.

Go here http://www.amidoncorp.com/f_mf g.htm

"Material #06, red/gray color (=B5 A Carbonyl 'E' iron powder material
having high volume resistivity. Offers high 'Q' for the 2 MHz to 30
MHz. frequency range. "

High Q is of little use in a broadband transformer. Q refers to the
efficiency with which stored energy may be recovered, but you don't
want a
broadband transformer to *store* energy, you want it to transfer the
energy without storing it.

The virtue you want in a broadband transformer core is a high
permeability-frequency product f*mu. This maximizes the magnetizing
impedance for a given core size, minimizing the stored energy for a
given
applied voltage.

The classic material choice for broadband transformers at HF and above
is
type 43 ferrite, whose f*mu is about 2700 at 3 MHz, rising to 10000 at
30
MHz. Above 30 MHz, f*mu is approximately constant with this material.
The
TV transformers I've tested use a material similar to this. Materials
with
high f*mu are generally pretty lossy, but in a well designed broadband
transformer little energy actually enters the core material, so little
is
lost.

On the other hand, your #6 iron material has a permeability of only 8.
While its permeability probably doesn't decrease much with frequency
(unlike ferrite), this stuff still has a f*mu of only 24 at 3 MHz, and
240
at 30 MHz. This is a very poor choice for a broadband transformer core.
A
broadband transformer using a #6 core will need 6-10 times as much wire
as
a similar transformer using a #43 core. Wire length is directly related
to
leakage inductance and parasitic capacitance, the main factors limiting
high frequency performance of this sort of transformer.

There is a price to be paid by separating the windings and that will be
a reduced transfer of desired signal energy. You can of course wind the
transformer bi-filar and still get the benefit of using the right core
material.

Bifilar windings are mainly an antidote to leakage inductance. For a
small
amount of wire on a high mu core, leakage inductance is negligible
anyway,
so bifilar windings have little advantage.

There is no "right" amount of turns for a broad band transformer
because the frequency range of short wave is so large. You would pick a
center frequency of a range of frequencies you want the transformer to
operate over and use that in your calculations for inductive reactance.

What's the "center frequency" of a 100 kHz-30 MHz transformer? For a
conventional inductive transformer, a more workable approach is to
choose
a core that gives you adequate magnetizing inductance at your low
frequencies while using less than 5% of a wavelength of wire at your
high
frequencies (rule of thumb for controlling leakage inductance and stray
capacitance). An example:

A BN-73-202 core needs about 4 cm/turn. 9:3 turns thus requires 48 cm
of
wire, or 4.8% of a wavelength at 30 MHz. The 3 turn secondary has about
75
uH magnetizing inductance, exceeding the impedance of 50 ohm coax above
100 kHz.

Running through the same procedure with your favorite #6 material, a
9:3
T-130-6 uses as much wire as the design above, but has a lower
frequency
limit of 90 MHz (*above* its upper limit of 30 MHz). Not an effective
design. You could improve it by using controlled impedance bifilar
turns
(but that's a much trickier way to go).
John Doty
--------------------
Please read the above repost as many times as you need
to understand the topic.
They work.

Every TV balun that I have tried has worked.

I have every reasond to expect every TV balun
core in the world to work. Theory is nice, but should
bow in the face of reality. I don't sell these things, I get
nothing out of these silly fights.

Have you ever built one?

If not, give it a try, and if it doesn't work flame away.

Do you remember the pointless flame war over "power dividers",
hybrids, or "passive multi set couplers? In your area of RF specialty
I am quite sure you know what you are toaling about, but as you
demonstrated in that thread you didn't ahve a friging clue what you
were talking about.
--------------------------
I will close this by reposting your comments from 20050427.
I am not claiming to be much of an expert in anything. I have
learned a few things over the years and based on my real world
experiences I will stand firm. Today I use Mini Circuit 9:! and 1:1
not because the TV cores didn't work, but because I can no longer
wind the damn things. Between my bad vision and stumbling
fingers it makes more sense for me to buy them. But the TV core
based units that I built still work, except for those destroyed by
lightning.

------------------------
Telamon Apr 27, 5:41 am
Newsgroups: rec.radio.shortwave
From: Telamon
Date: Wed, 27 Apr 2005 04:41:35 GMT
Subject: Telamon please email me

In article ,
"Tom Holden" wrote:
I think you are both in violent agreement - 6dB loss means the output
over the input is 1/2 for voltage (constant impedance), 1/4 for
power. A resistive 2-way minimum loss splitter has 6dB loss; a
transformer 2-way splitter is 3dB.

I just calculated it and you are right Tom. I have been a real dufus
and
giving Terry a headache for nothing. I generally don't think in terms
of
power since I work with small signals.

The resistive splitter is burning half the power as the T types three
16.7 ohm resistors in series are 50 ohms.

Sorry about that Terry. Looks like your transformer type is more
efficient in its bandwidth than the resistive type. Since you measured
3=2E2 dB on the transformer type you are very close to the ideal splitter
and your measurement on the resistive is also correct at 6 dB so you
can
stop scratching you head now.

--
Telamon
Ventura, California
----------------------------------------------------------
Sorry for being rude, but I am sick and tired of you offereing
expert advice that is so clearly wrong, and that is clearly refuted
by people like John Doty who have a real knowledge of how
small cored ferrites behave at HF. Remember you can only
get away with this cheating by using very small cores. Anything
much over 38" and the magic quits and you must use the correct
core.

Terry

I just calculated it a
nd you are right Tom. I have been a real dufus and
giving Terry a headache for nothing. I generally don't think in terms
of
power since I work with small signals.

The resistive splitter is burning half the power as the T types three
16.7 ohm resistors in series are 50 ohms.

Sorry about that Terry. Looks like your transformer type is more
efficient in its bandwidth than the resistive type. Since you measured
3=2E2 dB on the transformer type you are very close to the ideal splitter
and your measurement on the resistive is also correct at 6 dB so you
can
stop scratching you head now.

--=20
Telamon
-----------------------