On 11/29/2010 7:07 PM, Paul Christensen wrote:
>> By far the most practical approach is the tuner in the shack. It's what I
>> have and I've never bothered with measuring
>> or calculating the loss from the tuner in the shack approach as it's not
>> going to change.
> That's practical if the shack is located against an exterior wall. Open
> transmission line easily cross couples with Ethernet cabling and household
> SMPS devices.
I use all coax, even to the 75 center fed dipoles and 160 half sloper.
It's LMR-600 all the way to the half sloper and to the remote antenna
switch for the 75 meter antennas with Davis BuryFlex(TM) (OR LMR-400)
from the switch to the dipoles.
I would prefer tower mounted tuners, but for 160 that would be at the
top and part way up for 75 and even 40. Were I 20 years younger I'd
certainly consider and probably tackle it as a project.
As it is I'll be happy to get the tribander up and the 160 half sloper
hooked back up.
> A balanced line easily keeps its balance on transmit so long
> as the conductors do not couple to nearby objects. But on receive, it's a
> different story. It's rare for a noise source to balance evenly onto the
> conductors. Invariably, the line will become perpendicular to a source at
> various points. So, multiple noise sources from within the home can make a
> balanced line seem rather unbalanced. The wider the line spacing, the lower
> the line loss -- but susceptibility to noise sources will increase. It does
> not take much imbalance to produce noisy results on receive.
>
> For me, the most practical approach was to locate the tuning function in a
> Wx-proof enclosure, located as close as possible to the load, yet still have
> access to it for maintenance purposes. About 60 ft. of 600-ohm line is used
> between the ATU and a 135 ft. dipole at 55 above ground. A 50 ft run of
> LMR-400 is used between the shack and ATU. Of course, that solution
> requires some means of remote-controlling the C and L components. Practical
> for some, but not for all.
>
In other times that would be my choice as well. OTOH the shack although
on an outside wall, favoring the tower(s) is inside my shop, the
interior of which is bonded 'barn metal'. Even the doors are metal
...although there are two casement windows. Tis not a great place for
using your cell phone. You have to stand in the proper place, take the
proper posture, and hope for the best. The cell tower is less than 2
miles and can be seen from any of the three doorways including the man door.
73
Roger (K8RI)
> Paul, W9A
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