Hello all

I've made a first attempt at installing an antenna. It's a 2 Slinky dipole
strung across my roof. I chose the Slinky dipole because it promised to give
good (if not excellent) results in a relatively short antenna. I strung it
between two 2' wood standards at the top of the roof. The roof is about
25-30' from the ground. I used the twin feedline, which is about 18', and
the insulators from a GSRV Mini antenna I bought. The twinline is connected
with a balun to a 50' RG-8X cable that runs across the roof and down to my
window. I've temporarily led it in through the window. The excess cable,
probably about 20 feet or so, is loosely coiled between the inner and outer
window.

The reception is great. I was picking up DX from Europe. However, I got no
answers to any attempt to call out. I wasn't expecting DX for my very first
QSO, but I was hoping for someone.

I think it may be because the feedline runs along the roof rather than
hanging in free space. Could this be the case? The SWR was terrible; it took
my automatic tuner a lot of work to get a match, but I was getting 1.5 or
less on 80 and 40.

Thank you for any advice you can offer.

73
Basil Burgess, VE3JEB

My email is basilb which is through hotmail

Basil Burgess wrote:

Hello all

I've made a first attempt at installing an antenna. It's a 2 Slinky dipole
strung across my roof. I chose the Slinky dipole because it promised to give
good (if not excellent) results in a relatively short antenna. I strung it
between two 2' wood standards at the top of the roof. The roof is about
25-30' from the ground. I used the twin feedline, which is about 18', and
the insulators from a GSRV Mini antenna I bought. The twinline is connected
with a balun to a 50' RG-8X cable that runs across the roof and down to my
window. I've temporarily led it in through the window. The excess cable,
probably about 20 feet or so, is loosely coiled between the inner and outer
window.
I think it may be because the feedline runs along the roof rather than
hanging in free space. Could this be the case? The SWR was terrible; it took
my automatic tuner a lot of work to get a match, but I was getting 1.5 or
less on 80 and 40.

Actually, the entire antenna design is terrible. What is the SWR
on the coax at the balun? Steel is not a good conductor to use in
an antenna at RF frequencies.
--
73, Cecil http://www.qsl.net/w5dxp

Thank you for your response

I'm afraid I don't have a way of measuring the SWR at the coax.

Should I consider connecting the balun directly to the slinkys rather than
at the end of the twinline? Should the twinline be supported so that it is
not lying on the roof?

Or should I just dismantle it and go back to positioning the GSRV Mini.
That, at least, is a copper dipole.

Thanks again

Basil, VE3JEB

"Cecil Moore" wrote in message
. com...

Actually, the entire antenna design is terrible. What is the SWR
on the coax at the balun? Steel is not a good conductor to use in
an antenna at RF frequencies.
--
73, Cecil http://www.qsl.net/w5dxp

Basil Burgess wrote:
Or should I just dismantle it and go back to positioning the GSRV Mini.
That, at least, is a copper dipole.

I won't presume to tell you what you "should" do. There are
too many unknowns in your system. You may need to spring for
an antenna analyzer, like the MFJ-259B. If it were me, I
would junk the slinky antenna. At least the half-sized
G5RV is known to work relatively well on 40m, 20m, 10m,
and 6m.
--
73, Cecil http://www.qsl.net/w5dxp

"Basil Burgess" wrote in message
...
Thank you for your response

I'm afraid I don't have a way of measuring the SWR at the coax.

Should I consider connecting the balun directly to the slinkys rather than
at the end of the twinline? Should the twinline be supported so that it is
not lying on the roof?

Or should I just dismantle it and go back to positioning the GSRV Mini.
That, at least, is a copper dipole.


As Cecil said , it is hard to tell you what to do with the limiated
information you have given. Nothing simple beats the good old dipole
antenna. Problem is it is mostly a one band antenna. I have up an off
center fed antenna and it seems to work fair for all the harmonic bands.
The swr is a bit high on the WARC bands. It is about 130 feet long with a
4:1 balun in the center and fed with rg-8x coax.

Even with the antenna you have up you should be able to work something if
the rig will load it. It may be that the internal tuner to the rig is not
able to match the antenna and most of the power is not getting out of the
rig. The inernal tuners are only good for about a 3:1 or less swr to the
antenna on most rigs.
Cecil mentioned an expensive MFJ device. It is probably way too much over
kill for most hams. One of the least expensive SWR meters will tell you if
the antenna is anywhere in the ball park and which way you need to trim the
antenna if you take several readings across the band.

Thank you, Ralph

I'm sorry if I am giving inadequate information. Besides the basic
description of the antenna, I'm not sure what else to offer. I doubt it took
anyone long to realize that I am a novice and have as much info on antennas
as one learns for the Canadian basic exam, and and can glean from a borrowed
copy of the ARRL Antenna Book.

The only additions I have are that on closer inspection, the balun is Van
Gorden's (the manufacturer of the original antenna) Hi-Q Center Insulator.
Also, I am using an external automatic tuner, a Z-11 Pro by LDG. It
apparently tunes the antenna down to an SWR of 1.5, but doesn't have the
means to give a more accurate figure. My FT-875 displays SWR, as a bar
display, but when the tuner has done its job, the rig seems to display no
SWR bars, which I take to mean the rig sees a 1:1 or close to it. Still, I
guess that's no guarantee that the power is being used efficiently.

Anyway, thanks again for your help

73
Basil Burgess, VE3JEB

The best, all round, all band, antenna is a high centre-fed dipole of
no particular length, fed with an open-wire feedline of no particular
length or impedance, all the way to the shack, used with a choke-balun
and an unbalanced tuner.

It is good down to the frequency at which the dipole is about
1/3-wavelength long.

Simplicity = efficiency.

Once tried you will never return to anything else.
----
Reg.

Basil Burgess wrote:
It apparently tunes the antenna down to an SWR of 1.5, ...

An antenna tuner doesn't change the SWR between the tuner
and the antenna. If it's 100:1 before the tuner does its
thing, it is still 100:1 after the tuner does its thing.
The extra feedline losses are caused by that unchanging SWR.
--
73, Cecil http://www.qsl.net/w5dxp

On Sat, 18 Mar 2006 14:54:25 -0500, "Basil Burgess"
wrote:

Thank you, Ralph

I'm sorry if I am giving inadequate information. Besides the basic
description of the antenna, I'm not sure what else to offer. I doubt it took
anyone long to realize that I am a novice and have as much info on antennas
as one learns for the Canadian basic exam, and and can glean from a borrowed
copy of the ARRL Antenna Book.

The only additions I have are that on closer inspection, the balun is Van
Gorden's (the manufacturer of the original antenna) Hi-Q Center Insulator.
Also, I am using an external automatic tuner, a Z-11 Pro by LDG. It
apparently tunes the antenna down to an SWR of 1.5, but doesn't have the
means to give a more accurate figure. My FT-875 displays SWR, as a bar
display, but when the tuner has done its job, the rig seems to display no
SWR bars, which I take to mean the rig sees a 1:1 or close to it. Still, I
guess that's no guarantee that the power is being used efficiently.

Anyway, thanks again for your help

73
Basil Burgess, VE3JEB

For a first attempt, it sounds like you've built a complicated affair:
slinkies, twinlead, balun, coax, tuner, etc. You might try the other
extreme, simple. A dipole of two straight wires cut to frequency, and
a length of coax to the rig. Make the antenna a little long, and use
your rig's swr meter to adjust the length down to resonance.

bob
k5qwg

On Sat, 18 Mar 2006 10:21:27 -0500, "Basil Burgess"
wrote:

Hello all

I've made a first attempt at installing an antenna. It's a 2 Slinky dipole
strung across my roof. I chose the Slinky dipole because it promised to give
good (if not excellent) results in a relatively short antenna. I strung it

There is nothing in your post to indicate how long or short your
antenna is. Perhaps it is a well known design and I just haven't heard
of it in my limited experience.

You say how difficult the coax was to match with an ATU, that is a big
hint that the coax is operating at high VSWR. You say the SWR was
terrible, what does that mean, do you have the numbers? Coax operated
at high VSWR for significant length is quite lossy.

If the impedance presented to the tuner is extreme, you can expect
excessive losses there too.

The ambient noise on low HF bands is very high compared to the noise
floor in your receiver. An antenna system could be seriously lossy,
and yet still allow you to hear all signals above the noise (though at
reduced S meter deflection). Beware of depending on a simplified
receiver test to infer transmit performance.

Owen
--