[Antennas] Advice pse--Shunt Fed Tower on 80m (or 160m)

Thu, 1 Aug 2002 14:17:04 +0200

Hi Mike

Do all your other coax cables and rotator control cables exit the tower at
ground level?  Things will not be happy if these cables exit the tower
higher up.

Deon ZR1DQ
.
----- Original Message -----
From: Mike & Coreen Smith <[email protected]>
To: Bob Garrett <[email protected]>; <[email protected]>;
<[email protected]>; <[email protected]>
Sent: Thursday, August 01, 2002 1:33 AM
Subject: [Antennas] Advice pse--Shunt Fed Tower on 80m (or 160m)

| Hi Bob/K3UL !! (and groups)
| Long time no hear Bob(on 6 or 160, hi hi!!)
|
| Hope your shunt-fed tower is working out for you.  Your country totals are
| amazing !
| =========
| To everyone: (you too Bob ;-)
|
| I just shunt-fed my tower on 80m, but it's not working "right".
| I think my tower is resonant somewhere around 2.6MHz (give or take), but
| I'll be daRned if I can
| get it to load with a nice low/sharp SWR curve on 80m or 160m.  I'd prefer
| to get it on 80m as my Inverted L on 160m works nicely.
| <<80m -*and*- 160m would be a bonus>>
| Someone mentioned that they thought you guys could give me some advice as
to
| how to do it correctly. (yes I have searched the web and TT archives, but
| I'm not finding exactly what I need (not yet anyway).
|
| I am in the process of kinda temporarily (for 1-2 yrs) rebuilding a lot my
| antennas as most of the whole farm was dismantled earlier this year (long
| story).
|
| I can get the towers' SWR FLAT @ 2.6Mhz (MFJ ant. analyzer) @ various cap
| settings, gamma tap points, spacings and even pulling the gamma wire out
| like a delta feed.  I can 'also', (using diff settings) get a very broad
SWR
| curve which is lowest and around 2.1:1 centered on 3.5MHz which is what I
am
| using now, but I really don't think the tower is working "well" as some
80m
| signals are louder on my 160m inverted L. (especially as I go up the band
| towards the SSB portion)
|
| For info, it's a 48' Delhi self supporting tower in 3.5 cu yds of
concrete,
| VG moist to wet soil,
| The tower has a TH6DXX on top, right @ the thrust bearing.  Up the mast
~12'
| there is a CC D40 Dipole, ~4' above that there is a
| ~23' boom 5el 6m yagi and on the VERY top there is a Ringo Ranger 2m
| Vertical. There is a picture of it at:
| http://ve9aa.tripod.com/th6_and_k6sti.jpg
| The wires and dipoles you see in the photo are no longer there. The 3el 6m
| side mounted beam is also no longer there.
| The 2 small vertical ropes that are about 1' away from the mast ARE still
| there but are non conductive and do not affect
| any of the antennas.  I was going to add inverted vees or dipoles for the
| WARC bands but never got around to it.
|
| I've tried tap points @ 12', 20', 30' and currently around 35'. Tried
| spacings @ 1', 2' and 3' away from the tower.
| Gamma wire is #14 AWG stranded/insulated. R90 or TWU I think.
| Little difference (believe it or not) no matter what combination of
| "settings" I used.  It just seemed to make the SWR curve
| broader the less capacitance in line, however the broader the curve got,
the
| higher the SWR was too.
| My only cap is an ~800pF air variable.  Shield of coax connected to lots
of
| 127' radials. (field common to my 160m inverted L -  30' away)
| I don't (currently) have another cap for an Omega Match.
| ***
| *******Q U E S T I O N S************
| Do I need to go to the top of the tower with my gamma wire? (I hate
climbing
| btw)
| Will grounding the shield of the coax at the tower base make ANY
difference?
| (just conn to radials now)
| Do I need to go further than 3' or closer than 1' to my tower for the
gamma
| wire?
| What band(s) will this brute load on?
| Do I need to scrap the whole idea and just toss my 60-70' of wire over the
| nearest fir tree and be done with it? ;-)
|
| 50 or 60 trips either up the tower or outside to tweak the cap or move the
| angle of gamma wire and I
| and just about ready to fling the 80m inverted L wire over the nearest
tree,
| like I had before.....
|
| Lastly,
| THANKS!! :-)
|
| 73 de Mike
|
| - - -
|
| Your moderator for this list is:
| Larry Wilson KE1HZ [email protected]
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