Actually the transition to top mounted radios had nothing to do with TX
loss, nor RX dB loss. TMA's (tower mounted amplifiers for RX) had been
around forever, and TX power is cheap at the 20-60 W levels.
It was all about PIM (passive inter-modulation) which reared it's ugly
head during the transition to 4G LTE (which requires VERY low noise
floors). The typical coaxial TX path from ground to antenna had a
zillion connectors. It rapidly became clear that maintaining a zillion
paths, each with up to 20 connectors, to the low PIM levels demanded by
LTE (and knowing that 5G was coming down the road), was going to be
impossible.
The main decision now is between RRU + RF jumpers + antenna, which has
some flexibility for maintenance (but you still get flaky connectors),
or AIR antennas which have the radio built in, but any fault in either
the radio or antenna requires an expensive replacement of the whole unit.
-Steve K8LX
On 5/17/2022 2:56 PM, Gene Smar via TowerTalk wrote:
In commercial (cellular, LMR) services, the decision of where to put the power
stage (in the equipment hut or on the top of the tower) depends on the cost to
generate enough power to compensate for dB loss in the coax. At today's
mm-wave freqs for 5G operation, e.g., Freq Range 2 from 24-52 GHz, it would be
costlier to put a PA of sufficient power in the hut at the tower base to yield the
necessary ERP at the antenna than it would to put a smaller PA stage at the tower
top and run a fiber/copper cable assembly to it from the hut.
It's a different story at HF and even V/UHF. The coax losses are significantly less
in this freq range than at mm-wave so the advantage (coax loss reduction) of remoting the
RF components is not as great. For us Hams it becomes a matter of personal taste -
how loud do I want to be? - vs how loud MUST I be?
On another hand, running fiber vs coax to the tower could eliminate much of the
danger from lightning strikes. The problem then becomes (a simpler?) one of
protecting the power feed(s) going to the electronics from inside the Ham shack.
73 deGene Smar AD3F
-----Original Message-----
From: Chuck Dietz <w5prchuck@gmail.com>
To: Kelly Taylor <ve4xt@mymts.net>
Cc: Steve Maki <lists@oakcom.org>; TowerTalk@contesting.com
Sent: Tue, May 17, 2022 12:34 pm
Subject: Re: [TowerTalk] Fw: Feeding single band HF yagis 500+ ft from the shack
I was wondering the same thing. I’m surprised that no amp company makes an
amp to go at the tower. Maybe remote a rig and amp close to the towers?
Chuck W5PR
On Tue, May 17, 2022 at 11:23 AM Kelly Taylor <ve4xt@mymts.net> wrote:
Curious… at what point, given the cost of hardline, does one consider
running code-compliant power out to the towers, putting the RF components
there and using either ethernet or fibre between the control heads in the
shack and the rf components?
Just a question. Flames will be ignored.
73, kelly, ve4xt
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