[600MRG] Pracitical Discussion...

[Edward R Cole]

Ken,

At 12:43 PM 1/24/2018, Kenneth G. Gordon wrote:
>What I am hoping folks will discuss here are the practical 
>applications of info such as
>Rudy's most excellent site offers.
>
>Like, what did you do to weather-proof your system?

Southcentral AK climate could be called maritime, so we are more 
moderate in temp compared with interior or northern arctic 
regions.  We get enough rainfall so that one does not need to water 
the lawn after May which is the driest month.  Aug-Oct. is very 
rainy.  I seal my cables with heat-shrink covered with two layer of 
high quality electric tape (Scotch-33+).  I leave outdoor enclosures 
open to air on the bottom side vs trying to achieve 
water-tight.  Temp extremes pull moisture into interior which needs a 
way to dissipate (free breathing air exchange permits this).  I run 
cable thru bottom openings as a rule to avoid making water-tight entrances,

In Fall humidity can be close to 99% (its raining) yet temps run from 
35-40F to below freezing overnight.  Moisture trapped inside freezes 
then melts causing corrosion if trapped.


>What troubles did you run into when you built your system?

I ran my inverted-L radials on ground surface which required rolling 
them up in summer in order to mow grass.  I used three ground planes 
of 2-foot chicken wire fencing 70-foot long tied to a ten foot copper 
ground rod located at base of vertical section of the tower.  Someday 
we will remove the rough wild grass and landscape for a real lawn 
upon which I intend to trench and bury ground wires (at least 30) a 
couple inches below surface.  My VHF 1-5/8 inch Heliax coax line 
shield becomes part of the radial system since it is grounded at both 
the tower and at the house entrance.


>How do you keep the random kids from getting across the RF HV?

No problem with kids in the area. Neighbors dogs and occasional moose 
walk across the ground but do not seem interested in the vertical 
wires of the antenna (the only RF current exposure).  Base coil is 
inside a plywood box.


>What did you do to prevent damage from storms?

Towers are guyed and wires of inverted-L are supported by nylon rope 
run over tower-top pulleys.  Winds do not exceed 50mph.


>How did you implement measurement of, say, RF current?

I am using a surplus NDB which has a built-in RF ammeter.


>How did you manage remote control of tuning?

do not have any.  Base coil tap needs to be changed about two turns 
between summer and winter (ground frozen).  I have the taps prewired 
and just move the antenna wire between the two tap terminals (1/4-20 
brass bolts).  Coil is approx 10-inch diam by 11-inch long with No. 
12 solid copper wire with turns spaced 1/4 inch (roughly 680uH for 
entire coil which I use about 75% of the coil.  Coax connects to a 
tap about 2-1/2 turns above ground for 50-ohm match.


>What did you do for lightning protection?

Nothing.  We experience virtually no lightening (there is no summer 
lightening crash noise on 600m).  Thunder is only heard about once 
every four years or so.


>Etc?
>
>For instance, in my case, I am going to have to use some heavy-duty 
>relays at low-RF
>voltage points to switch my loading coil for 160 meters and that for 
>630 meters into and out
>of the circuit.
>
>According to my calculations, I'll need a 680 uH inductance at the 
>bottom of my vertical to
>resonate it on 630 meters. I need about 38 uH to resonate it on 160 
>meters now, where it
>gives me, presently, about a 3:1 50 ohm SWR (approximately 150 ohms or so).
>
>I have severely modified an old satellite TV dish-mover to adjust 
>the rather large roller-coil
>(95 uH) which I got out of an old WWII military BC-939 antenna 
>tuner, and will control that
>with an old satellite TV dish-mover controller, which has a 
>numerical digital readout.
>
>The modified dish-mover has built in adjustable limit switches, and 
>runs from 12 VDC. The
>mover itself outputs a square wave as the motor runs and this 
>square-wave causes the
>controller to readout counts-per-turn of the roller-inductor.

Good ideas as I would like to eventually be able to use the antenna 
on 160m or even 80m.  I could see inserting a roller coil in series 
with the fixed coil.  Would have to find that point 
experimentally.  Extra taps needed for those bands to make antenna 
resonant.  I modified a MFJ-269B antenna analyzer by adding a ferrite 
in series with lowest freq coil in the LO.  Very simple and effective 
if not too close to BC broadcast stations.  Meter measures the 
antenna Z with coil as Z = 20+j0 at 503 KHz.


>Anyway, those are some of the sorts of things I hope we discuss here.
>
>Ken W7EKB

My 600m webpage was hacked a few years ago and I never restored 
it.  I have a new webpage started but not much content at this point:
http://www.kl7uw.com/630m.htm


73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com