Tnx all !!!
got a lot answers, mni tnx !
summary:
My earlier Omega-match:
yes, I know that corona effects. Picture was only an example for my last winter
fight.
Later I solved that, but got other probs. Burned a lot....
That days I used my lower shunt-feed, tap-point 11m (35ft) which is fine for
80m with
210pF gamma Cap, SWR 2 BW +/- 80kHz.
But I had to much trouble with that omega match for 160m; high voltage and
current,
even VacuumCaps 15kV ones makes trouble. Connections were getting unsold !
So that one was to lossy ! (tnx WX7G David !)
Thats why I decided to make a better match, and hoped for a gamma one.
Situation now:
Due to the construction of my vertical ( 2003 I used what I have...) I am a bit
fixed to
some points, like tap-point, distance etc....
Tnx Tree N6TR: will play a bit with that "against the wind" possibilities.
Well, in my
not "normal" vertical there could be some surprisings, for sure ! And hope to
work u,
also on 80m !
But, I have no chance for an easy gamma-match;
Earl K6SE brought it to the points (like others):
---------------------------------------------------------------------------------------------------
On a shunt-fed tower with a gamma (single capacitor) match, there are only
three ways (to my knowledge) of raising the frequency of the best SWR:
1) Move the shunt wire tap point down the tower, closer to ground.
2) Decrease the spacing of the shunt wire to the tower.
3) Use a larger diameter shunt wire or use a multiple shunt wire "cage".
Andy says that options 1 and 2 are not possible, so option 3 is his only
possibility unless he decides to change his single-capacitor "gamma" match
to some other method of tuning.
----------------------------------------------------------------------------------------------------
Tnx Earl !
1) not possible
2) not this year
3) also not that easy, not this season
So, better looking for "some other method of tuning" !
And thats the new Question:
How can I bring that resonance QRG up ? With not that losses like the
omega-match
last season ? Some Fixed VacuumCaps and Variable AirCaps (12mm / 1/2" plates
distance) are in stock. Winding coils is not a problem.... Copper-pipe up to
8mm /
1/3" diameter is also in stock...
- I got a hint, to use a serial L at the bottom of the shunt arm.
- On Toms (W8JI) page I found, that I only can realize it in my setup with a
PI-filter.
Any hints are very welcome...
vy 73 de André (Andy) DF9OX
Old quest:
Topbanders,
I spent some time to change my lossy and critcal shunt feed omega match
against a better one. Maybe someone remember my endless burning
experiences last winter/spring. Burned 7/8" Coax-dynamite-bundle as a cap,
example:
http://www.df9ox.de/pics/20051101_78_burned.jpg
Now I am feeding my 26.5m (88ft) vert with 2 wires, tap point around 19.5m
(65ft). Its a kind of not normal solution, I had to do. Due to mechanics
of my tower, the tap point can not be lower than now, also some other
points like spacing apart tower are given, because of vertical design.
Btw, radials are 120 times abt 20m long.
http://www.df9ox.de/pics/20051101_vert.jpg
Vertical is straight, artefacts are from stitching software. 160m
Tap-point is that flying-T up in the air. For relations, tower part is 11m
(35ft), tower-face is 0.7m (3ft).
Problem is: Now I have a fine AM medium-wave gamma-matched tower.
Resonance frequency is below 1700 kHz, Variabel-cap says abt 130 pF.
Bandwith +/- 15kHz (border SWR 2).... Could be rented by AM-Pirates....
:-)...
Question: How can I bring the QRG up to 1830kHz?
I know the basics, but:
- lower tap point = not possible
- decrease distance of wire = not possible in upper part (detailed: I have
tried that in the lower part, but it gives me only some 10kHz, SWR 1 was
at 1750kHz, at best) - tnx W8JI-site, PI-filter would work, but 2 more
parts than a gamma-cap are needed, so lossy ?
For easy matching:
Is the only solution to raise the feed-point ? Would not be that easy, it
is a kind of crank- up tower. Think, if it is only solution, I need
"some"meter... For up/down I can not use the tower as box support.
I hope I am missing a simple basic, which gives me a red face, saying
"...ohhh....excuse my question, Sir..."
vy 73 de André (Andy) DF9OX
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