Antenna support question

[Detroit47]

   Well folks I am finally getting a 75 meter antenna in the air.The XYL has finally given her blessing after 900 honey doos. I am going to string it between a large tree and a wooden pole at the other end. There will be a slight slope from one end to the other. Will this slope cause me any problems with my match? I am going to be using a Johnson KW match box and a "W7FG 80-10m Doublet". I will be running the ladder line straight to match box no balun. There will probably be a 10 foot drop from one end to other. The antenna will be about 50 feet off the ground at the hi end. Also should I use rope around the tree branch or will wire and an insulator be a better choice. I have a pulley and a weight at the pole end for tree sway. I'm trying to do this right the first time I don't want to be in the mud. Also since I live in the city I am winding some chokes to go to ground where the feed line enters the house. Does anyone know how many turns on what diameter form will work well? I don't want to reinvent the wheel just copy a good one. And thanks to
Mike W8BAC.
73 N8QPC

[Ed/KB1HYS]

IMO the slope wont make much difference in the pattern (not so's you'd notice anyway). Keep the ladder line coming away at a right angle to the dipole proper for as long a distance as you can.

As far as the chokes to ground go, wind up a min of 2.5mH though i think you could buy some premade ones if you are not QRO.

[WA1GFZ]

If your match box has a problem tuning the antenna change the feedline or antenna length a few feet. A balun is useless in this case. Make sure you have a good ground on the match box. Put some common mode beads on the coax side if it is a long run to the rig. I found a dual antenna like a fan dipole is easier to tune all band. Make the second antenna slightly different length with the ends spaced apart a few feet.

[Detroit47]

Ed

I am going to be QRO. Like I said I don't want to be in the mud. I've been dying to get my desk on the air. As well as my John 5.

73 N8QPC

[kg8lb]

   .....And thanks to
Mike wb8ac.
73 N8QPC

   Perhaps a typo ?   Maybe that was Mike, W8BAC ? 

[Detroit47]

Yes that is a typo I don't know how though I copied and pasted it.
N8QPC

[K5UJ]

From what I've learned here from k1jj and huz it should work well.  Let's see...my experience with trees and wire antennas has been that it will go through a shake out time during which you'll have to tweek a few things like rope tensioning, adjustments to the weight of the counterweight and stuff like that, particularly after the first couple of windstorms.  Why not put the pulley and counterweight at the tree?  That way when it moves your feedpoint and feedline will stay more or less in one place if you have the rope at the pole end secured.   Sounds like the wood pole you have at the far end from the tree is a telephone pole?  Are you able to climb it?   If not, you might want to keep everything at that end fixed and simple and put the mechanical stuff like the pulley at the tree where if anything fails you can just shoot another rope with a pulley over it for a fix since that's a lot easier than trying to shoot a rope over a pole   

If you have to put the pulley at the pole and you can't get to it once it is erected, do some redundancy--put a second rope/pulley on it just in case you have a problem with the one you are trying to use (it's amazing how a rope can get hung up  once you can't get to it).   Use a marine pulley too; the $2 ones from the hardware store rust out and fall apart after a few years.  Routing the feedline can be fun (some find it frustrating but I kind of like it).  I use a bunch of 1 inch pvc water pipe sections for poles and Ts that the feedline spreaders fit through to support it over ground.   get a bunch of ten foot lengths and cut them to the height you need.  I have one every four or five feet.    If looks matter you can paint them some color (I just left mine as is because I'm aesthetically challenged). 

Last thing, I think you can try not using any ferrite chokes on the unbalanced feed between the matchbox and the rig because the matchbox is link coupled but having some on the coax certainly won't do any harm.

73

Rob
K5UJ

   

[k4kyv]

No need for a bal-un between Matchbox and open wire line, since the antenna is a balanced load and the link-coupled tuner is a balanced source.  I agree that since the tuner is link coupled, there should be no need for common mode choke between tuner and coax as long as the tuner contains no direct connection to ground on the secondary side (tuned circuit side) involving either the resonant coil or tuning capacitor.

The ideal spot for the static discharge choke would be inside the Matchbox (if it doesn't already have one), from a spot near the midtap of the tuned circuit coil which should always be cold, rf potential wise.  That way, the choke only has to handle a very small amount of direct current as it bleeds off static charge build-up, but no appreciable rf, and it would not affect the tuning.  But do not run a direct wire to ground from the midtap of the  coil or from the rotor of the main split stator capacitor, and disconnect one that might already be there, since this would almost assuredly generate common mode currents in the feedline to ground and result in unbalance.  The tuned circuit of a link coupled tuner should float free from ground except for the optional discharge choke.

A 2.5 mHy 500 MA rf choke like the one used with balanced transmitter tank circuits in rigs such as the BC-610 and homebrew push-pull rf finals, or any fair size transmitting type rf choke that will fit inside the box should do nicely for the choke (I am not talking about anything like a National R-175 or any other of those large chokes normally used as the main rf plate choke in the pi-network output of a KW transmitter).  Or if you don't mind drilling a hole in the rear of the matchbox enclosure and fitting it with a ceramic feed through insulator, the choke could be mounted outboard to the box.

This would be better than installing the choke(s) at the output side of the tuner.  In that case, the  choke's reactance will affect the tuning and possibly generate rf losses at any frequency in which the load, as seen by the matchbox, is anything but very low-Z with minimal reactance.

Don't count on that choke to provide any kind of lightning protection.  The only reliable way for that is to disconnect the feedline whenever there is potential T-storm danger, and preferably solidly ground both conductors of the disconnected feeders.  I used one of those jumbo military 2P2T rf knife switches for that purpose for years.

I am basing the above on my experience with homebrew link coupled tuners, since I have never owned or operated a Johnson KW Matchbox and, with the exception of the differential tuning capacitor they use in lieu of switchable taps on the coil, I would be unaware of any non-conventional quirks in the circuit design that Johnson might have incorporated.

[WQ9E]

Don states it perfectly as to choke placement and purpose.

The chokes will help get rid of annoying pops and prevent the static buildup flashovers resulting from wind or precipitation static but will vaporize on any significant induced surge.  When the station is not in operation the antennas are grounded and the shutoff switch to the panel for the station is thrown.

[K5UJ]

Hmm.  I have a question then (however I realize we have migrated from the topic so I apologize).  BTW Rodger, I got the 59 GDO, not cheap but the coils match.  Anyway, back to tuners.  I am currently getting a kw matchbox cleaned up to try using here.  After a few 10 minute 300 w. transmissions on 75 Saturday I discovered the bal. tuner I'm using had warm coils and the homebrew ferrite low Z common mode choke was getting even warmer.  I smoked the stock choke and made this one out of two feet of 213 and a bunch of big 1 inch long split beads but even it isn't up to AM 

Now, there is in fact a matchbox ground connection that is clearly intended to be used on it.   On the tuned side you have the variable caps between, or straddling, the ends of the tapped inductor, that go out to the balanced feed.  The sides of these caps  that meet at the symmetrical center between each side of the feed, are to be grounded.  I was going to do this but here is what I wish to clarify.  I always do this to a ground rod that is not tied in to the rest of the station ground.  I can certainly see the problems if this ground is common to the other ground potential i.e. the unbalanced feed shield, shack ground busbar etc.  When you guys talk about not grounding the link tuner is it the assumption that ground means the shack and unbalanced feed ground?  I planned to put the tuner at ground potential but not bonded to anything else as that would defeat the whole point I think of link coupling.  Yet obviously for some reason, Johnson engineers seemed to the sides of the tuner caps should be at ground potential else they would not have the lug on the back panel and the ground on the schematic.   

73

Rob
K5UJ