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[email protected] · September 22nd 06, 01:37 AM posted to rec.radio.shortwave

After 35 years I recently bought a Realistic DX-160 - the same model I
had as a kid. I quickly hooked up to an antenna in the attic I used
about 20 years ago on a 1937 RCA 8K console.
The reception was nil. I recalled many more stations as a kid so
tonight I rigged up a 35' each side dipole in the attic. I think it
means that the antenna is a balanced dipole. Please correct me if I am
wrong. I used coax to run from the center to the radio, one side
attached to the center lead and the othe attached to the shield.
So far this setup is working much better and the HAMs and more stations
are coming in.

My questions are
1. Is this the proper way to hook up this antenna? It runs to the A1
and A2 connection points on the back of the receiver and the jumper
from gnd to A2 has been removed.
2. With this setup I lose the shielded lead - should I look for a 2
lead shielded cable?

I will have more questions - I hope not to pester.

Thanks
Brian

Telamon · September 22nd 06, 04:57 AM posted to rec.radio.shortwave

In article . com,
wrote:

After 35 years I recently bought a Realistic DX-160 - the same model I
had as a kid. I quickly hooked up to an antenna in the attic I used
about 20 years ago on a 1937 RCA 8K console.
The reception was nil. I recalled many more stations as a kid so
tonight I rigged up a 35' each side dipole in the attic. I think it
means that the antenna is a balanced dipole. Please correct me if I am
wrong. I used coax to run from the center to the radio, one side
attached to the center lead and the othe attached to the shield.
So far this setup is working much better and the HAMs and more stations
are coming in.

My questions are
1. Is this the proper way to hook up this antenna? It runs to the A1
and A2 connection points on the back of the receiver and the jumper
from gnd to A2 has been removed.

The antenna and coax connections sound OK.

My best guess on the jumper is to not connect it since you have a
balanced antenna connected to the radio. I would expect that you would
connect the jumper for a single wire antenna.

2. With this setup I lose the shielded lead - should I look for a 2
lead shielded cable?

No. You have a good setup.

--
Telamon
Ventura, California

RHF · September 22nd 06, 08:57 AM posted to rec.radio.shortwave

[email protected] · September 22nd 06, 11:59 AM posted to rec.radio.shortwave

* Use a Balun with a Dipole Antenna
Another 'improved' Shortwave Listening (SWL) Antenna
design would use a Balun {Matching Transformer} between
the Dipole Antennaand the Coax Cable feed-in-line. This
is most often a 4:1 {Four-to-One} Matching Transformer.
Using the Balun will better 'match' the Dipole Antenna to
the Coax Cable feed-in-line and the Receiver across a
wide frequency range then simply using a Dipole Antenna
that is directly connected to the Coax Cable.
- - - The direct conneted Dipole Antenna is great for Hams
working on a single Shortwave (HF) Frequency Band.

It's this balun similar to the ones used to connect 75ohm coax to the
screw connects on the back of a TV?

Brian

[email protected] · September 22nd 06, 02:55 PM posted to rec.radio.shortwave

* Use a Balun with a Dipole Antenna
Another 'improved' Shortwave Listening (SWL) Antenna
design would use a Balun {Matching Transformer} between
the Dipole Antennaand the Coax Cable feed-in-line. This
is most often a 4:1 {Four-to-One} Matching Transformer.
Using the Balun will better 'match' the Dipole Antenna to
the Coax Cable feed-in-line and the Receiver across a
wide frequency range then simply using a Dipole Antenna
that is directly connected to the Coax Cable.
- - - The direct conneted Dipole Antenna is great for Hams
working on a single Shortwave (HF) Frequency Band.
+ + + The Dipole Antenna using a 4:1 Balun is better for
Shortwave Listeners (SWLs) who are Listening to a
variety of Frequencies across the Shortwave Band.

Please correct me if I am wrong...

I thought the simple dipole had a 75 ohm feed where a folded dipole had
a 300 ohm feed and would need a 4:1 balun.

What would the Balun do with the dipole I rigged up?

Brian

Telamon · September 23rd 06, 12:16 AM posted to rec.radio.shortwave

In article om,
wrote:

* Use a Balun with a Dipole Antenna Another 'improved' Shortwave
Listening (SWL) Antenna design would use a Balun {Matching
Transformer} between the Dipole Antennaand the Coax Cable
feed-in-line. This is most often a 4:1 {Four-to-One} Matching
Transformer. Using the Balun will better 'match' the Dipole Antenna
to the Coax Cable feed-in-line and the Receiver across a wide
frequency range then simply using a Dipole Antenna that is directly
connected to the Coax Cable.
- - - The direct conneted Dipole Antenna is great for Hams
working on a single Shortwave (HF) Frequency Band.

This BALUN information is incorrect.

It's this balun similar to the ones used to connect 75ohm coax to the
screw connects on the back of a TV?

The dipole antenna is around the 72 ohm mark, which will vary with
height but is close enough that the BALUN is not needed. If you want to
improve the match with a BALUN you will need a fractional two core unit
to achieve this transform.

A better antenna in the same space would be a folded dipole, which would
use the common and cheap 4:1 transform used with FM and over the air TV
antennas.

If you are going to used a made for TV unit some do not work well at 3
to 30 MHz. Generally look for a unit with more heft due to the more
massive core inside. The units that do not work well from 3 to 30 MHz
use a capacitive matching circuit with a smaller core.

--
Telamon
Ventura, California

Telamon · September 23rd 06, 12:17 AM posted to rec.radio.shortwave

In article . com,
wrote:

* Use a Balun with a Dipole Antenna
Another 'improved' Shortwave Listening (SWL) Antenna
design would use a Balun {Matching Transformer} between
the Dipole Antennaand the Coax Cable feed-in-line. This
is most often a 4:1 {Four-to-One} Matching Transformer.
Using the Balun will better 'match' the Dipole Antenna to
the Coax Cable feed-in-line and the Receiver across a
wide frequency range then simply using a Dipole Antenna
that is directly connected to the Coax Cable.
- - - The direct conneted Dipole Antenna is great for Hams
working on a single Shortwave (HF) Frequency Band.
+ + + The Dipole Antenna using a 4:1 Balun is better for
Shortwave Listeners (SWLs) who are Listening to a
variety of Frequencies across the Shortwave Band.

Please correct me if I am wrong...

I thought the simple dipole had a 75 ohm feed where a folded dipole had
a 300 ohm feed and would need a 4:1 balun.

Yes.

What would the Balun do with the dipole I rigged up?

A fractional two core. You might find a ham unit that has this transform.

--
Telamon
Ventura, California

Mark Zenier · September 23rd 06, 06:16 PM posted to rec.radio.shortwave

In article ,
Telamon wrote:

A better antenna in the same space would be a folded dipole, which would
use the common and cheap 4:1 transform used with FM and over the air TV
antennas.

The set is nowhere near a 50-75 ohm input. Especially if the RF gain
isn't fully on.

Looking at the schematic of the DX-160, the antenna inputs feed a 2k
ohm potentiometer, (the RF gain control), (with a back to back pair of
protection diodes from the wiper to ground), and then are switched to
the input windings of the first tuned circuit.

Next, there's a cascode FET RF amplifier and another tuned circuit feeding
the mixer. Both tuned circuits are tuned with the main and bandspread
variable capacitors. And the input coil is tuned with an antenna trim
control, too. (There's plenty of places to mis-tune this RF amp, if the
unit seems a little deaf). Then to a mixer and a 455(?) kHz ceramic
IF filter.

I would try a folded dipole direct to the balanced A1-A2 inputs. The set
doesn't need a balun.

Or Google up RHF's posts from a year or three ago about using a room
sized loop on a ceiling or wall with the DX-160.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)

Bob Miller · September 24th 06, 03:11 AM posted to rec.radio.shortwave

On 22 Sep 2006 05:55:06 -0700, wrote:

* Use a Balun with a Dipole Antenna
Another 'improved' Shortwave Listening (SWL) Antenna
design would use a Balun {Matching Transformer} between
the Dipole Antennaand the Coax Cable feed-in-line. This
is most often a 4:1 {Four-to-One} Matching Transformer.
Using the Balun will better 'match' the Dipole Antenna to
the Coax Cable feed-in-line and the Receiver across a
wide frequency range then simply using a Dipole Antenna
that is directly connected to the Coax Cable.
- - - The direct conneted Dipole Antenna is great for Hams
working on a single Shortwave (HF) Frequency Band.
+ + + The Dipole Antenna using a 4:1 Balun is better for
Shortwave Listeners (SWLs) who are Listening to a
variety of Frequencies across the Shortwave Band.

Please correct me if I am wrong...

I thought the simple dipole had a 75 ohm feed where a folded dipole had
a 300 ohm feed and would need a 4:1 balun.

What would the Balun do with the dipole I rigged up?

Brian

If your antenna is fed with coax you don't need a balun. The 50 ohm
coax is close enough to the 70-or-so ohms of a plain dipole.

bob
k5qwg

Telamon · September 25th 06, 12:46 AM posted to rec.radio.shortwave

In article ,
(Mark Zenier) wrote:

In article

, Telamon wrote:

A better antenna in the same space would be a folded dipole, which
would use the common and cheap 4:1 transform used with FM and over
the air TV antennas.

The set is nowhere near a 50-75 ohm input. Especially if the RF gain
isn't fully on.

Looking at the schematic of the DX-160, the antenna inputs feed a 2k
ohm potentiometer, (the RF gain control), (with a back to back pair
of protection diodes from the wiper to ground), and then are switched
to the input windings of the first tuned circuit.

Next, there's a cascode FET RF amplifier and another tuned circuit
feeding the mixer. Both tuned circuits are tuned with the main and
bandspread variable capacitors. And the input coil is tuned with an
antenna trim control, too. (There's plenty of places to mis-tune
this RF amp, if the unit seems a little deaf). Then to a mixer and a
455(?) kHz ceramic IF filter.

I would try a folded dipole direct to the balanced A1-A2 inputs. The
set doesn't need a balun.

Or Google up RHF's posts from a year or three ago about using a room
sized loop on a ceiling or wall with the DX-160.

The radio input impedance is a separate issue.

Re-quoting RHF post I specifically object to the following.

* Use a Balun with a Dipole Antenna Another 'improved' Shortwave
Listening (SWL) Antenna design would use a Balun {Matching
Transformer} between the Dipole Antennaand the Coax Cable
feed-in-line. This is most often a 4:1 {Four-to-One} Matching
Transformer. Using the Balun will better 'match' the Dipole Antenna
to the Coax Cable feed-in-line and the Receiver across a wide
frequency range then simply using a Dipole Antenna that is directly
connected to the Coax Cable.
- - - The direct conneted Dipole Antenna is great for Hams
working on a single Shortwave (HF) Frequency Band.

RHF wrote about matching a dipole.
I wrote about matching a folded dipole in a follow up to his post.
A dipole is around 72 ohms and a folded dipole is around 300 ohms.

********

There are three items involved, antenna, transmission line, and radio
input impedance. They all have to match. The 4:1 BALUN is incorrect to
match a dipole to 50 ohm coax what is happening on the other end of the
coax does not change this relationship. The closest easily attainable
would be a 1:1 BALUN. All impedances need to match or you have
reflections and the signal that the antenna picks up will only
partially be used by the radio input.

If the 50 ohm coax to radio input is an issue then you need another
transform between the coax and radio input. Most radios have a 50 ohm
input. Generally, you can figure this out by the connector used. On
most radios the radio input may not be right at 50 ohms but will be
somewhere in that area over the 3 to 30 MHz input range.

--
Telamon
Ventura, California

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