Coupling a T2FD to a S350DL
 

Hi

I am new to this forum and have a (most likely) dumb question

I recently aquired a S350DL receiver. I will be using this rig until I can buy a rela communications receiver. I will be using it to receive Shortwave only. I have constructed a T2FD (Tilted, terminated, folded dipole) with a design feed point impedance of 300 ohms. The S350 DL only has an unbalance high impedance external antenna point and a ground on it. How can I attach the T2Fd to the S350Dl and acheive a good impedance match.

1) Is the whip antenna on the S350DL a low impedance feed point (i.e. 50 or 75 ohms)? If so, could I use a 4:1 balun at the feedpoint of the T2FD to convert the feed line to 75 ohm coax (which would be unbalance line now) and just clip the center conductor to the whip and the sheild to a grounding rod?

2) I could use 300 ohm ladder line to connect to the T2FD but the problem is that the S350DL does not have a balanced esternal input point on it.

I guess what I am asking is what would be the best way to couple A 300 ohm T2FD antenna to a Crappy Radioshack S350DL receiver and achieve reasonable impedance matching.

I do not what to use an end fed long wire.

Any help would be appreciated.

Coupling a T2FD to a S350DL
 

On Tue, 26 Aug 2008 22:19:42 +0100, Bubblesdee wrote:

Hi

I am new to this forum and have a (most likely) dumb question

I recently aquired a S350DL receiver. I will be using this rig until I
can buy a rela communications receiver. I will be using it to receive
Shortwave only. I have constructed a T2FD (Tilted, terminated, folded
dipole) with a design feed point impedance of 300 ohms. The S350 DL
only has an unbalance high impedance external antenna point and a ground
on it. How can I attach the T2Fd to the S350Dl and acheive a good
impedance match.

1) Is the whip antenna on the S350DL a low impedance feed point (i.e. 50
or 75 ohms)? If so, could I use a 4:1 balun at the feedpoint of the
T2FD to convert the feed line to 75 ohm coax (which would be unbalance
line now) and just clip the center conductor to the whip and the sheild
to a grounding rod?

2) I could use 300 ohm ladder line to connect to the T2FD but the
problem is that the S350DL does not have a balanced esternal input point
on it.

I guess what I am asking is what would be the best way to couple A 300
ohm T2FD antenna to a Crappy Radioshack S350DL receiver and achieve
reasonable impedance matching.


On HF, matching imp for receiving should not make much difference give-or-
take a few 100%

I suspect whip antenna is high imp. ~2k and unbalanced. You would need
to make a one2one or four2one matching xformer placed near the radio with
ladder line coming from antenna. This will stop common mode noise from
entering your radio via feedline. Two 300-75 ohm TV xformers back to
back should work.

twinlead 300 xformer 75 short coax 75 - 300 twinlead

gator clip the xformer output to your collapsed whip
antenna and ear jack ground.

If you get allot of intermod from front end overload, place some
resistors between between whip and ear jack ground.

Thanks for your reply No Spam.

I was wondering if you might be able to clarify some points that you made.

1) Since I will be feeding the antenna via 300 ohm feedline, transforming it down to 75 ohms (coax) to eliminate noise and then transforming it back to 300 ohms, could I not just take one leg of the output of the transformer and connect it to the External antenna connector on the back of the radio instead of the whip? and then connect the other leg from the transformer to the ear jack ground. and then finally ground the radio via the GROUND connecter on the back of the set.

2) when you refer to to the ear jack ground, are you referring to the ground of the headphone jack. Is this the same point as the GROUND connector on the back of the radio or are the two points different?

Thanks again

Coupling a T2FD to a S350DL
 

Bubblesdee wrote:

Thanks for your reply No Spam.

I was wondering if you might be able to clarify some points that you
made.

1) Since I will be feeding the antenna via 300 ohm feedline,
transforming it down to 75 ohms (coax) to eliminate noise and then
transforming it back to 300 ohms, could I not just take one leg of the
output of the transformer and connect it to the External antenna
connector on the back of the radio instead of the whip? and then
connect the other leg from the transformer to the ear jack ground. and
then finally ground the radio via the GROUND connecter on the back of
the set.

2) when you refer to to the ear jack ground, are you referring to the
ground of the headphone jack. Is this the same point as the GROUND
connector on the back of the radio or are the two points different?

Thanks again

My S350DL has unbalanced, 500 ohm antenna terminals on the back; I
would imagine yours to be the same.

A 1:1 balun (balanced-to-unbalanced) at the dipole and coax (75 ohm) and
a 6.666:1 UNUN (unbalaced-to-unbalanced) between the coax and the S350DL
would be the ideal setup.

Regards,
JS


Half-a-Brain-McCain'n Insane; So Lawdy Mama, It Looks Like Obama!

Coupling a T2FD to a S350DL
 

John Smith wrote:


My S350DL has unbalanced, 500 ohm antenna terminals on the back; I
would imagine yours to be the same.

A 1:1 balun (balanced-to-unbalanced) at the dipole and coax (75 ohm) and
a 6.666:1 UNUN (unbalaced-to-unbalanced) between the coax and the S350DL
would be the ideal setup.

Regards,
JS


Half-a-Brain-McCain'n Insane; So Lawdy Mama, It Looks Like Obama!

Oh chit, it is folded dipole, duh!

A 1:1 current choke and forget the slight mismatch!

Regards,
JS
Half-a-Brain-McCain'n Insane; So Lawdy Mama, It Looks Like Obama!

Coupling a T2FD to a S350DL
 

John Smith wrote:
John Smith wrote:


My S350DL has unbalanced, 500 ohm antenna terminals on the back; I
would imagine yours to be the same.

A 1:1 balun (balanced-to-unbalanced) at the dipole and coax (75 ohm)
and a 6.666:1 UNUN (unbalaced-to-unbalanced) between the coax and the
S350DL would be the ideal setup.

Regards,
JS


Half-a-Brain-McCain'n Insane; So Lawdy Mama, It Looks Like Obama!

Oh chit, it is folded dipole, duh!

A 1:1 current choke and forget the slight mismatch!

Regards,
JS
Half-a-Brain-McCain'n Insane; So Lawdy Mama, It Looks Like Obama!

Actually, that is in error. Since the folded dipole is balanced and the
500 ohm terminals on the receiver show they are unbalanced, the 1:1
balun should suffice. It seems you will be going from 300 twinlead
(balanced) to the 500 ohm terminals.

450 ohm feedline with a 1:1 balun is yet another option ...

Regards,
JS

Half-a-Brain-McCain'n Insane; So Lawdy Mama, It Looks Like Obama!

Coupling a T2FD to a S350DL
 

On Wed, 27 Aug 2008 22:05:35 +0100, Bubblesdee
wrote:


No Spam;643798 Wrote:
On Tue, 26 Aug 2008 22:19:42 +0100, Bubblesdee wrote:
-
Hi

I am new to this forum and have a (most likely) dumb question

I recently aquired a S350DL receiver. I will be using this rig until
I
can buy a rela communications receiver. I will be using it to
receive
Shortwave only. I have constructed a T2FD (Tilted, terminated,
folded
dipole) with a design feed point impedance of 300 ohms.

We can only presume this 300 Ohms comes from a resistor, otherwise an
antenna does NOT present one impedance across all frequencies; and not
even across the bandwidth around 10% of 1 frequency.

The S350 DL
only has an unbalance high impedance external antenna point and a
ground
on it. How can I attach the T2Fd to the S350Dl and acheive a good
impedance match.

This begs the question: "Why do you want a match, when you have
already inserted a resistor that absorbs the power?" Another
question: "A match to what?"

1) Is the whip antenna on the S350DL a low impedance feed point (i.e.
50
or 75 ohms)? If so, could I use a 4:1 balun at the feedpoint of the
T2FD to convert the feed line to 75 ohm coax (which would be
unbalance
line now) and just clip the center conductor to the whip and the
sheild
to a grounding rod?

This would presume a match to the resistor on the T2FD. However, is
the receiver a 75(50)Ohm input? 50 Ohms source Z is a convention of
transmitters, and specified as so; but it is not always a given for
receivers' input Z. Some literally supply the 50 Ohm resistor
internally and at the gate or base of the input transistor. The gate
or base is functionally a much higher Z, but the necessity of bias and
other considerations sets this characteristic to something lower (but
may still be quite high).

Hence, without knowing this characteristic, you maybe discarding your
effort.


2) I could use 300 ohm ladder line to connect to the T2FD but the
problem is that the S350DL does not have a balanced esternal input
point
on it.

Being a "tilted" antenna, it will NEVER be balanced either!

I guess what I am asking is what would be the best way to couple A
300
ohm T2FD antenna to a Crappy Radioshack S350DL receiver and achieve
reasonable impedance matching.

I think what you are asking is can you improve performance - matching
be damned. A receiver demands much less attention to this as there is
usually excess capacity in gain within it.

On HF, matching imp for receiving should not make much difference
give-or-
take a few 100%

I suspect whip antenna is high imp. ~2k and unbalanced. You would need

to make a one2one or four2one matching xformer placed near the radio
with
ladder line coming from antenna. This will stop common mode noise from

entering your radio via feedline.

A matching transformer is not always a choke. A choke is not always a
matching transformer. A choke reduces common mode currents, but it
has to present an impedance that is in excess of the impedance of your
input (still little understood). Chokes and transformers do not
reduce noise without also reducing signal - UNLESS that noise arrives
from your home, and travels into your receiver through the inherent
imbalance of the system. A choke WILL aid you here, but it won't cut
down on the crackle of tropical storms.

73's
Richard Clark, KB7QHC

Hi

Thanks to everyone that responded.

I am a little confused but this is most likely my fault.

So i will simplify the question.

How could I transform from 300 ohm balanced antenna to 300 ohm unbalanced line without using coax. I will do the transformation right before the balanced (one antenna and one ground connector) on the S350DL.

I think that all I need to do is come off the T2FD with 300 ohm Twin lead and then into a 1:1 balun that does not use coax inside it but a ferrite choke. Does this sound right? If so, then my next question is DOES anyone know how to build a 1:1 balun not using coax to transform 300 ohm balanced to 300 ohm unbalanced?

Thanks again

Coupling a T2FD to a S350DL
 

On Thu, 28 Aug 2008 22:35:32 +0100, Bubblesdee
wrote:

I think that all I need to do is come off the T2FD with 300 ohm Twin
lead

Fine enough.

and then into a 1:1 balun that does not use coax inside it but a
ferrite choke. Does this sound right?

Not as stated. Ferrite is a material, the line running through it
becomes choked because of that material.

my next question is
DOES anyone know how to build a 1:1 balun not using coax to transform
300 ohm balanced to 300 ohm unbalanced?

Stuff the (insulated paired) wires through the ferrite bead/torus/tube
just like you would a coaxial line. Total length of ferrite (a
combination of about 40-60 beads or equivalent) on the order of a
foot. A large torus can support several wraps through it to the same
effect.

73's
Richard Clark, KB7QHC

Coupling a T2FD to a S350DL
 

Richard Clark wrote:
. . .
Stuff the (insulated paired) wires through the ferrite bead/torus/tube
just like you would a coaxial line. Total length of ferrite (a
combination of about 40-60 beads or equivalent) on the order of a
foot. A large torus can support several wraps through it to the same
effect.

Bear in mind that the impedance of multiple turns is proportional to the
square of the number of turns. So 5 turns, for example, through a single
core gives you the same impedance as 25 cores strung along the line.

Roy Lewallen, W7EL

Coupling a T2FD to a S350DL
 

Bubblesdee wrote:

Hi

Thanks to everyone that responded.

I am a little confused but this is most likely my fault.

So i will simplify the question.

How could I transform from 300 ohm balanced antenna to 300 ohm
unbalanced line without using coax. I will do the transformation right
before the balanced (one antenna and one ground connector) on the
S350DL.

I think that all I need to do is come off the T2FD with 300 ohm Twin
lead and then into a 1:1 balun that does not use coax inside it but a
ferrite choke. Does this sound right? If so, then my next question is
DOES anyone know how to build a 1:1 balun not using coax to transform
300 ohm balanced to 300 ohm unbalanced?

Thanks again

This should get you started ...

Here are diagrams of one type of balun which will serve you well:

http://assemblywizard.fr33webhost.com/balun1.jpg

http://assemblywizard.fr33webhost.com/balun2.jpg

You will need to pick the proper material you need for the core, and
compute the turns necessary for the freqs in question (lowest freq will
determine these), there are abundant design pages on the web ... google
is your friend.

Regards,
JS

Coupling a T2FD to a S350DL
 

Roy Lewallen wrote:
Bear in mind that the impedance of multiple turns is proportional to the
square of the number of turns. So 5 turns, for example, through a single
core gives you the same impedance as 25 cores strung along the line.

Something that fooled me is the way Amidon specifies
"one-turn" impedance for beads in their brochure. Their
"one-turn" for beads is a wire running through the center
hole, wrapped around the outside, and back through the
center hole. (I would count that as two turns and
would say one-turn is just a wire running straight
through the core.)

As a result, for their FB-77-5621 bead, for instance,
they specify 270 ohms per turn. If one simply threads
these beads over RG-58, the impedance is about 1/4
of that amount, i.e. about 67 ohms per bead, requiring
about 15 of them to get to 1000 ohms.

As Roy says, ten turns of coax on an FT-240-77 core
is roughly equivalent to 100 FB-77-5621 beads strung
over coax.

Interestingly enough, Amidon specifies "one-turn" on
an FT-240-77 core to be 76 ohms, obviously a different
kind of "one-turn" than that of the 270 ohms for an
FB-77-5621.
--
73, Cecil http://www.w5dxp.com

Coupling a T2FD to a S350DL
 

In message , Cecil Moore
writes
Roy Lewallen wrote:
Bear in mind that the impedance of multiple turns is proportional to
the square of the number of turns. So 5 turns, for example, through a
single core gives you the same impedance as 25 cores strung along the


Something that fooled me is the way Amidon specifies
"one-turn" impedance for beads in their brochure. Their
"one-turn" for beads is a wire running through the center
hole, wrapped around the outside, and back through the
center hole. (I would count that as two turns and
would say one-turn is just a wire running straight
through the core.)

As a result, for their FB-77-5621 bead, for instance,
they specify 270 ohms per turn. If one simply threads
these beads over RG-58, the impedance is about 1/4
of that amount, i.e. about 67 ohms per bead, requiring
about 15 of them to get to 1000 ohms.

As Roy says, ten turns of coax on an FT-240-77 core
is roughly equivalent to 100 FB-77-5621 beads strung
over coax.

Interestingly enough, Amidon specifies "one-turn" on
an FT-240-77 core to be 76 ohms, obviously a different
kind of "one-turn" than that of the 270 ohms for an
FB-77-5621.

Yes, '1 turn' on a torroid is 'once through the centre'. For any coil to
work as an inductor, there must be a return path somewhere. For a
torroid, this has to be 'around the outside'. As the permeability of the
core is generally much greater than that of air, it doesn't matter much
whether the wire is close to the surface of the ferrite, or very slack
indeed. With a single turn, the return path could be quite circuitous
(literally).
--
Ian

Coupling a T2FD to a S350DL
 

Bubblesdee wrote:
Hi

...
I recently aquired a S350DL receiver. ...

Stumbled across this on the net (article describes an rf
transformer/antenna he uses--pay attention to the direction of the
windings on the toroid):

http://www.qrp.pops.net/swl-ant.asp

and thought about your S350Dl and thought I would let you give it a read ...

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

Thanks John and everyone for your responses.

It looks like I am going to have to learn how to wind some baluns up.

I will keep you posted on progress

Thanks again

Coupling a T2FD to a S350DL
 

In message , John Smith
writes
Bubblesdee wrote:
Hi

...
I recently aquired a S350DL receiver. ...

Stumbled across this on the net (article describes an rf
transformer/antenna he uses--pay attention to the direction of the
windings on the toroid):

http://www.qrp.pops.net/swl-ant.asp

and thought about your S350Dl and thought I would let you give it a read ...

Regards,
JS

This is an example of the 'traditional' 9:1 impedance transformer which,
on most MW and SW frequencies, gives a better match between the antenna
impedance and a 50 or 75 ohm receiver input impedance. On relatively
narrow bands of frequencies where the antenna impedance is naturally
lowish (where it is near odd multiples of a quarterwave), the match will
actually be made worse than if the transformer were not used. This
obviously depends on the physical length of the antenna. In the diagram,
the antenna length shown is 33m (say 100'), which is not far short of a
quarterwave on 160m. However, on the MW band, and on various parts of
the SW band, the transformer should improve reception.

I note that the writer correctly stresses that that the transformer is
an 'UNUN' (an accurate - but ugly - word). Many similar articles about -
and adverts for - these devices WILL insist on calling them baluns
(which, of course, they are certainly not).

The direction of either winding on the torroid should not matter one
bit.
--
Ian.

Coupling a T2FD to a S350DL
 

Ian Jackson wrote:

This is an example of the 'traditional' 9:1 impedance transformer which,
on most MW and SW frequencies, gives a better match between the antenna
impedance and a 50 or 75 ohm receiver input impedance. On relatively
narrow bands of frequencies where the antenna impedance is naturally
lowish (where it is near odd multiples of a quarterwave), the match will
actually be made worse than if the transformer were not used. This
obviously depends on the physical length of the antenna. In the diagram,
the antenna length shown is 33m (say 100'), which is not far short of a
quarterwave on 160m. However, on the MW band, and on various parts of
the SW band, the transformer should improve reception.


Actually, the antenna terminals for the HF bands is marked "500 Ohm" on
my S350DL, 9 X 500 = 4,500 Ohms (the transformation I would expect from
a 9:1.) However, the author did claim an improvement of a number of
S-Units on his S350DL. This made me wonder, since I didn't want to
build it to see what was up, I just passed it along. I would not call
the author a "liar" without absolute confirmation ... who knows, perhaps
his "antenna arrangement" has resulted, somehow, in the end of that
(actually off center feed point) being 4,500 Ohms--perhaps Grundig lied
and the antenna terminals do exhibit a 50 Ohm impedance--I am lazy ...
some youngster can figure it out ... ;-)

I note that the writer correctly stresses that that the transformer is
an 'UNUN' (an accurate - but ugly - word).

Actually, I would not refer to it as an UNUN. A balun is a TLT device,
in following, and since UNUN was coined from balun, I would expect UNUN
to only apply to TLT devices. The device in the article is a simple RF
Transformer ... I like UN-UN, and the logic of following the naming
convention of the Bal-Un is followed, making it "intuitive."

Many similar articles about -
and adverts for - these devices WILL insist on calling them baluns
(which, of course, they are certainly not).

The direction of either winding on the torroid should not matter one bit.

The device here is not, IMHO, an UNUN, it is an RF Transformer, my first
post referred to it as such ... The winding direction, in regards to the
relationship of the direction of one winding to the other, matters a
great deal--indeed, since a 180 degree phase relationship is at stake,
the direction causes one to be an "opposite" of the other ... I have
always found the phase reversal winding direction(s) to exhibit superior
behaviors ...

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

John

You hit the nail right on the head about the S350DL having a 500 ohm input but no 50 ohm input. I had the exact same questions that you brought up so I E-mailed the author to clarify some of the questions. I have a feeling that he is not using a S350 but an actual comm receiver with a 50 ohm input.

Still waiting for a reply..

I have not experience winding baluns so I will ask one more question, making it as general as possible, So here goes.

How do I wind/build a "Current Balun" (I state a current balun because all I am try to do is reduce RFI noise and change from a balanced antenna to an unbalance input) That has a ratio of 1:1, and preserves the impedance on either side of it. I would preferr not to use bead but a Torrid instead

example :

450 ohm antenna input impedance (balanced)---- balun-----450 ohm external antenna jack on my radio.

Now, on another note, my problem might be that I do not fully understand that the input impedance of a T2FD antenna changes depending on what frequencies I am trying to receive. Would this be a correct statement?

If so, I will most likely need an atenna Tuner correct??

Once again, I appreciate everyones help. This continues to be a great learing experience.

Coupling a T2FD to a S350DL
 

Bubblesdee wrote:

...
Once again, I appreciate everyones help. This continues to be a great
learing experience.

Oh, Bubblesdee, do not think "I know something." I have watched far
stranger "hook-ups" than what we debate, work!

If you have the core, if you have the wire, you can attempt multiple
configurations, hook them up to your receiver, and "KNOW FOR CERTAIN!"
Wind 'em one way, then the other. If you do as "he" did, on a PCB, they
a tough with a soldering iron, a few turns in the opposite
direction--you have learned something new (self-education!)--the world
it yours, quit asking these "dummies" and KNOW!

I am "caustic" to some of the "know it alls'" here, just because they
are stupid and I have done the homework to know it ...

I honestly would expect the author in question noted an improvement,
recorded it in his text--and let it stand. I would not be so surprised
if you duplicated his instructions and met with an improvement(s) in the
direction you are headed--indeed, this is the major reason I "passed
them along to you."

Too often, you only find "idiots" here ... :-)

Good luck, "wind 'em a few ways", experiment, you have data close enough
to achieve you ends easily, with only a few tweaks!

Warmest regards
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

Coupling a T2FD to a S350DL
 

Bubblesdee wrote:
How do I wind/build a "Current Balun"

Ten turns of RG-400 on an FT-240-77 or
FT-240-43 toroid. That's what I did.
--
73, Cecil http://www.w5dxp.com

Coupling a T2FD to a S350DL
 

Cecil Moore wrote:

...
Ten turns of RG-400 on an FT-240-77 or
FT-240-43 toroid. That's what I did.

.... you have a way of making it sound too easy ...

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

Coupling a T2FD to a S350DL
 

John Smith wrote:
Cecil Moore wrote:
Ten turns of RG-400 on an FT-240-77 or
FT-240-43 toroid. That's what I did.

... you have a way of making it sound too easy ...

If you want more difficulty, stack the two toroids
together and wind ten turns of RG-400 on them. :-)
--
73, Cecil http://www.w5dxp.com

Coupling a T2FD to a S350DL
 

Cecil Moore wrote:

...
If you want more difficulty, stack the two toroids
together and wind ten turns of RG-400 on them. :-)

Well, I was wondering about that, you at least did the crossover and
wound half the turns in the opposing clockwise direction, I HOPE! ;-)

Even though this guy:

http://www.w8ji.com/toroid_balun_winding.htm

poses an argument against it!

And, this guy:

http://www.arising.com.au/people/Hol...ph/CMBalun.htm

implies, "What the heck, wind 30T on a junk-box ferrite rod and do 160m!"

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

Coupling a T2FD to a S350DL
 

John Smith wrote:
Well, I was wondering about that, you at least did the crossover and
wound half the turns in the opposing clockwise direction, I HOPE! ;-)

Even though this guy:
poses an argument against it!

The main advantage I see for the crossover is that the output
is on the opposite side of the toroid from the input. :-)
--
73, Cecil http://www.w5dxp.com