Build your dipoles with 300 Ohm twinlead
David
Then you can use plain old RG-6 and F-Splitters. Not only is this
incredibly cheap, the entire antenna system is at DC ground*.
Caution, do not use Baluns with little capacitor inside.
*Use an F Grounding Block where the coax enters the house. And a
drip loop.
http://members.shaw.ca/weskyscan/images/TwinLeadFoldedDipole.gif
Dale Parfitt
"David" <ric...@knac.com> wrote in message
news:kum5615mdg4f31ig3...@4ax.com...
intended for CATV have very poor performance at HF- i.e. balance is poor,
insertion loss can be well above theV/U values. For the splitters, port to
port isolation can be very poor, loss higher than may be acceptable.
Finally, I have yet to see a CATV Balun that is acceptable for out door use.
I wouldn't count on the system being at DC potential either- there are
several methods for creating a 4:1 balun- and seeing as how the wire used in
these baluns is smaller than #36 gauge- it wouldn't take much to fry it
anyway.
Wouldn't it be much simpler to build a classic dipole from single conductor
wire, place several clamp on #43 cores at the dipole to feedline transition
and forget about the CATV stuff and fragile twinlead??
Dale W4OP
David
I have built these suckers resonant at 6 mHz and survived tropical
storms. The purpose of DC ground (easily verified with a DVM with a
buzzer) is to bleed static charges, not substitute for accepted
lightning amelioration SOP.
As far as the perfomance at lower frequencies, the little suckers work
just fine. Don't let the 5-900 mHz specs fool you. As long as there
are no serices caps inside, they work way lower than 5 mHz.
Co-ax Seal under Scotch 33+ makes anything weatherproof.
These are definitely workingman's antennas, quite modest but also very
capable. They are more wideband than their single wire equivalents
(though theoretically not usable on even harmonics.) Make 3, one for
6, one for 10, one for 15. use an A/B/C switch and you'll have a lot
of fun.
Michael A. Terrell
>
> I have built these suckers resonant at 6 mHz and survived tropical
> storms. The purpose of DC ground (easily verified with a DVM with a
> buzzer) is to bleed static charges, not substitute for accepted
> lightning amelioration SOP.
>
> As far as the perfomance at lower frequencies, the little suckers work
> just fine. Don't let the 5-900 mHz specs fool you. As long as there
> are no serices caps inside, they work way lower than 5 mHz.
>
> Co-ax Seal under Scotch 33+ makes anything weatherproof.
>
> These are definitely workingman's antennas, quite modest but also very
> capable. They are more wideband than their single wire equivalents
> (though theoretically not usable on even harmonics.) Make 3, one for
> 6, one for 10, one for 15. use an A/B/C switch and you'll have a lot
> of fun.
The losses are already bad at 5 MHz and get worse as you go lower.
You may get away with them, but you might not hear a really weak signal
you're looking for because of the added losses. Have you measured the
insertion losses for properly terminated two way splitters? I would
open the case, remove the directional coupler and install a couple
hybrid amps and protection circuits to help match the 50 Ohm impedance
and maybe give a dB or two of gain. Have you measured the return loss
of any of the splitters?
I built a 1 in, 32 out distribution amplifier for Microdyne to
distribute their 10 Mhz in house frequency standard. I used the LH0002
buffer amps, but there are newer parts with even better performance.
The advantage of individually buffered outputs is that any noise
generated by one load isn't reflected back into another load and you can
connect or disconnect equipment without affecting other loads.
--
Former professional electron wrangler.
Michael A. Terrell
Central Florida
dxAce
David wrote:
I'd be a bit sceptical of that 300-75 ohm TV type balun. But then again I'm
sceptical of anything that's 75 ohms.
dxAce
Michigan
USA
David
wrote:
It's a hobby experiment thing. Springtime. I tried it just for fun
and got surprisingly good results.
Dale Parfitt
"dxAce" <dx...@milestones.com> wrote in message
news:4263C1B7...@milestones.com...
splitters for marine use. Port to port isolation was abysmal below 5MHz,
insertion loss and return loss well below rated spec - Their need extended
down to MW, so I could not recommend any of the ones we tested.
If you have a field strength meter, here's a simple test to evaluate a
baluns actual balance.
Connect the 75 Ohm end the the FSM input. Connect a short wire to one lead
of the 300 Ohm end; tune in a loud SW station near the freq of interest and
note its level in dB. Being careful not to move the wire, short both sides
of the 300 Ohm and note the new level. At V/U the change is typically >30dB
indicating acceptable balance and pretty much guaranteeing the outer shield
of the coax will not be a significant part of your antenna. At HF, its
anybody's guess.
I seem to recall that the wider bandwidth of the folded dipole configuration
is attributable to the effective larger diameter conductor- probably easily
offset by using a larger wire diameter in a classic wire dipole.
Dale W4OP
David
>is attributable to the effective larger diameter conductor- probably easily
>offset by using a larger wire diameter in a classic wire dipole.
>
>Dale W4OP
TV Twinlead. A T2FD is an example of a widebanded folded dipole.
http://www.bwantennas.com/pro/fdipole.pro.htm
RHF
.
Shortwave Listener's (SWL) Dipole Antenna
that is built with 300 Ohm Twin Lead
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/2955
.
Looks like 'i' am in-agreement with you that this simple
TV 'type' Parts Shortwave Listener's (SWL) Antenna can be
a reasonably good performer for use with Shortwave Radios;
for those SWL's who are mainly Program Listeners who wish
to hear the major International Shortwave Broadcasters.
.
1. They offer several Do-It-Yourself and How-To "Advantages"
(Build Your Own SWL Antenna) for the Shortwave Listener (SWL) :
.
* Low Cost TV 'type' Parts
.
* Readily Available TV 'type' Parts
.
* Ready Made TV 'type' Parts
.
* Ease of Assembly using common TV 'type' Parts
.
.
2. The Issue of 5 MHz Frequency Limiting Factor :
.
* Yes there is an Attenuation of RF Signals below 5 MHz.
So for the Shortwave Listener (SWL) this means that they
may not be able to hear some Shortwave Bands like the :
120 Meters (2.3-2.5 MHz); 90 Meters (3.2-3.4 MHz) and
75 Meter (3.9-4.0 MHz).
.
* ALL the Shortwave Bands "Above" 5 MHz are available to
be heard : 60 Meters (4.7-5.1 MHz); 49 Meters (5.9-6.2 MHz);
41 Meters (7.1-7.6 MHz); 31 Meters (9.3-9.9 MHz);
25 Meters (11.6-12.2 MHz); 22 Meters (13.5-13.9 MHz);
19 Meters (15.1-15.8 MHz); 16 Meters (17.4-17.9 MHz);
13 Meters (21.4-21.9 MHz) and 11 Meters (25.6-26.1 MHz).
.
* Plus the Attenuation of RF Signals and External Antenna
'overload' from the AM/MW Broadcast Band 530-1710 kHz.
.
.
3. The Folded Dipole Design (Configuration) and the use
of a Matching Transformer (Balun) for a reasonably Broad
Banded Shortwave Listener (SWL) Antenna.
.
* The Folded Dipole Reading List :
- Folded Dipole - by W4SAT
http://www.qsl.net/w4sat/fdipole.htm
- The Hairpin Monopole Antenna - by Wilfred Caron
http://www.antennex.com/preview/monopole.htm
- Unfolding the Story of the Folded Dipole - L.B. Cebik [W4RNL]
http://www.cebik.com/wire/fdpl.html
- The Half Wave Dipole (Hertz) Antenna
http://www.ycars.org/EFRA/Module%20C/AntDip.htm
.
* Cutting the Folded Dipole for the Lowest Shortwave Band
60 Meter (5 MHz) or 49 Meter (6 MHz) 'usable' Frequency :
- 60 Meter (5 MHz) = 468 / 5 = 93.6 Feet
- 49 Meter (6 MHz) = 468 / 6 = 78.0 Feet
.
.
4. The Tilting Terminated Folded Dipole Antenna :
Note the above basic Folded Dipole Antenna can be
'modified' to become a so called Tilting Terminated
Folded Dipole Antenna (TTFD or T2FD)
.
* First - The 'addition' of a "450 Ohm Resistor" at the
Center of the upper Dipole Element to make the Folded
Dipole a Terminated Folded Dipole Antenna (TFD).
.
* Second - The "Tilting" of the Terminated Folded Dipole
Antenna, making the Antenna a Tilted Terminated Folded
Dipole Antenna (TTFD or T2FD).
.
* Reading List - Tilted Terminated Folded Dipole Antenna :
- T2FD -- The Forgotten Antenna - by Guy Atkins
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fd.html
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2design.html
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fdfeed.html
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fdcomp.html
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fd_1.html
- Terminated Tilted Folded Dipole Shortwave Antenna - by John Conover
http://www.johncon.com/john/T2fd/
- How To Build the TTFD : A Broadband Antenna for
Shortwave Reception - by Arnie Coro [RHC] Dxers Unlimited
http://www.radiohc.org/Distributions/Dxers/ttfd2.html
- Modeling the T2FD - by L.B. Cebik [W4RNL]
http://www.cebik.com/wire/t2fd.html
.
.
5. Matching Transformer and Coax Cable Feed-in-Line :
* The use of a TV 'type' 300 Ohm to 75 Ohm Matching Transformer
facilitating the use of 75 Ohm TV 'type' Coax Cable as an Antenna
Feed-in-Line for improved signal levels and reduced noise levels.
.
.
6. Improved "Windom" Antenna - Off-Center-Fed Dipole :
Modify the basic Center Fed Dipole configuration to an
Off-Center-Fed 'improved' "Windom" Antenna with :
.
* Larger with a Total Length Tip-to-Tip of 71.2 Feet
- Longer-Side Cut for 60 Meters = 46.8 Feet (66%)
- Shorter-Side 'cut' for 31 Meters = 24.4 Feet (34%)
.
* Smaller with a Total Length Tip-to-Tip of 58.7 Feet
- Longer-Side Cut for 49 Meters = 39.0 Feet (66%)
- Shorter-Side 'cut' for 31 Meters = 19.7 Feet (34%)
.
.
7. Smaller Available Space {Random Wire} Dipole Antenna :
.
* Instead of "Cutting" the Dipole to SIZE. Simple 'measure'
the "Space" that is Available to Hang an Antenna and Dividing
that Number of Feet (Meters) by Two to determine the Length
of the Horizontal-Arms of what will become a "Random' {Size}
Dipole Antenna. After all this is 'intended' to be a Broad
Banded Shortwave Listener's (SWL) Antenna.
.
* Note - This same Smaller "Available Space" {Random Wire}
Idea applied to an Off-Center-Fed Improved "Windom" Antenna
with two un-equal sides:
- Longer-Side 'cut' to 62% of the Available Space.
- Shorter-Side 'cut' to 38% of the Available Space.
- With the Total Length Tip-to-Tip being the Available Space.
.
.
iane ~ RHF
.
All are WELCOME and "Invited to Join" the
Shortwave Listener (SWL) Antenna eGroup on YAHOO !
<http://groups.yahoo.com/group/Shortwave-SWL-Antenna/>
.
Some Say: On A Clear Day You Can See Forever.
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/502
.
I BELIEVE: On A Clear Night . . .
You Can Hear Forever and Beyond, The BEYOND !
With a Shortwave Listener SWL Antenna of your own making.
"If You Build It {SWL Antenna} You Will Hear Them !"
. . . . .
Telamon
Yes, the active devices will provide good output to output isolation.
One drawback of any passive splitter is poor isolation.
--
Telamon
Ventura, California
Telamon
"Dale Parfitt" <p...@parelectronics.com> wrote:
I have checked the insertion loss on some and found them not very good
with high loss 10MHz and down. The units with bigger cores generally
seemed to be better. I have some that are good down to 1 or 2 MHz. The
smaller higher permanence cores perform poorly below 10MHz.
--
Telamon
Ventura, California
Dale Parfitt
> On Mon, 18 Apr 2005 16:36:24 GMT, "Dale Parfitt"
> >I seem to recall that the wider bandwidth of the folded dipole
configuration
> >is attributable to the effective larger diameter conductor- probably
easily
> >offset by using a larger wire diameter in a classic wire dipole.
> >
> >Dale W4OP
> The dipole wire would have to be a half-inch in diameter for plain old
> TV Twinlead. A T2FD is an example of a widebanded folded dipole.
>
mark- about a 6% increase in BW which is not trivial.
Dale W4OP
David
I read it in an old QST or the ARRL Antenna book, decades ago.