"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

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

Cecil Moore wrote in news:cIZSf.57484$Jd.33257
@newssvr25.news.prodigy.net:

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.

Yep, though feedline losses are not usually so large as to preclude at
least SOME QSO's on 80 and 40 unless that SWR is AT LEAST 50 (especially on
80m). Of course poor quality coax and twinlead that is touching metal can
really increase those losses, even though they actually REDUCE the SWR that
the tuner is seeing.

A slinky is such a poor antenna to begin with (basically a coil of iron),
it's probably best to just feed it in the center with good quality 450 ohm
line (which you then dress properly all the way to the tuner's balanced
output--if the tuner has one or a balun located AT the tuner if it
doesn't). Next best would be to feed it with decent COAX like LMR400 or
better.

For example, my balcony whip gives an SWR of almost 6 on CW at 3652. I
could lower this by adding a capacity rig at the stinger end of the
hamstick, but I'm a bit too lazy to keep going out and taking it off and
the thing is resonant on 3729 where our phone net meets. But it's still 88
percent as efficient as it is at resonance when tuned up on 3652 with my
tuner, which can tune that SWR flat. (We won't talk about how inefficient
an 8ft antenna actually is on these frequencies, but you get the point).

And that's using RG8X (Belden 9258). Better coax would improve that some.
If the slinky actually has an SWR of 100, then 450 ohm ladder line would
introduce additional loss, due to SWR of 2.04 db per 100 feet.

Moral of the story, when using inefficient antennas with weird impedances,
then make sure you use good, low-loss feedline and keep it short as you
can.


--
Dave Oldridge+
ICQ 1800667

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