Long before everyone was an expert on ferrites and grounding in the early
80's I had 100' of 25G with a 10 to 20M Christmas tree of PV-4 yagis plus a
220 vertical on top for simplex voice and another on 2M for the DX Packet
Cluster.
Each yagi was fed with 12 of the 1.25" long beads, over CATV RG-11, which
turned out to be 43 Mix and private labeled for Chromerics, which I picked
up a couple of cases as scrap at a local auction. Not knowing any better I
used them on the verticals also.
Grounding was thru the aluminum booms to galvanized steel mast and verticals
to mast as they were on a crossarm and I needed the height to connect to the
cluster and get a good signal about 60 miles on 220 with 10W FM. A length of
1" diameter tinned braid connected mast to the tower in a rotator loop.
The tower was shunt fed on 160 and there was no interference or damage even
using 2 bands simultaneously, talking on 220, sending on 160 and watching
the Cluster. 220 was a private DX net for just a few of us in NH, MA and RI.
with topbanders such as K1MM, K1MEM, K1IU, and a few others.
Only 160 was grounded at the tower base and all equipment went to a copper
water pipe ground in the basement which connected to the panel ground.
In the shack the rotator lead was wrapped thru a FT240-43 a few times (there
was no 31 Mix then) and the HF coaxes terminated in a set of switches that
had one coax to the 2 LPF's. Another 12 beads were between amp and LPF and
12 more smaller ones between rigs, another 1500W LPF and amps over RG-6 quad
shield. The idea was to force all RF thru the filters as I was in a fairly
dense residential area and was primarily concerned about TVI and RFI. The
digital age crud was still years away.
Im sure the 43 beads were far from perfect on 160 but they did the job
anyway. All cables ran about 20' on the ground and then about 8' high over
the lawn and then down and into the basement.
Carl
KM1H
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <topband@contesting.com>
Sent: Sunday, April 15, 2012 12:28 PM
Subject: Re: Topband: Topband Tower Antenna With Two meter Vertical
> On 4/15/2012 8:49 AM, Wayne Rogers wrote:
>> Also - on the antenna installation. Typically the two meter vertical's
>> outer conductor will be grounded to the tower at the base of the two
>> meter antenna. I could also keep the two meter antenna insulted from the
>> tower for its entire length up to the lightning protector just before it
>> enters the house. What's the recommended practice? Ideas?
>
> First, always run rotor cables and coax for antennas mounted to the
> tower INSIDE the tower. This allows skin effect to minimize 160M current
> on those cables. Second, proper bonding of the coax shield to the tower
> top and bottom is good practice for lightning. Third, coming away from
> the base of the tower, wind as many turns as you can of each cable
> through at least one #31 toroid. This prevents these cables from
> becoming part of the radial system.
>
> Ferrite beads clamped onto a cable are next to useless on the HF bands
> because they are inductive, not resistive, so all they do is TUNE the
> cable to which they are attached.
>
> If the tower is very close to the house, it should be bonded to the
> combination of all grounds in the house, which, MUST be bonded
> together. That includes power entry, telephone entrance, cable TV,
> satellite dish, ham shack, etc. If the tower is distant from the house,
> only the cables coming from the tower should be bonded, not the tower
> itself.
>
> 73, Jim Brown K9YC
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1424 / Virus Database: 2411/4938 - Release Date: 04/15/12
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|