[UK-CONTEST] OT: Aerial installation advice

[David G3YYD]

Keith

I suggest you look at the difference in loss between Ecoflex 15 and 
Westlake 103. On a 20m run for 2m the loss difference is very small but 
Ecoflex 15 costs a lot more especially if you use the bespoke 
connectors. You can use ordinary RG213 connectors with W103, but need to 
file down the inner conductor to fit the plug used. Takes a few minutes. 
By the way fill the mating part of the connector/socket and the threads 
with Petroleum Jelly ( XYL's Vaseline) to assist in moisture rejection. 
I also use a sacrificial small length of RG213 with in line connectors 
to the W103. The RG213 also takes the rotation motion as the W103  has a 
copper tape covered by a copper braid and although the braid will help 
with cracks in the tape, I prefer to avoid the potential problem. If it 
leaks at the antenna end or I need to unwrap the antenna connector I 
only need to cut back a bit of the RG213 and put the connector back on 
rather than loose the whole W103 length. Ecoflex is better if water gets 
into a connector as it is a foam dielectric while W103 has tubes of air 
running down its length so it fills with water. So ensure well sealed 
connectors.

Incidentally it is not the dielectric that reduces the loss per se but 
the larger diameter inner conductor that reduces the loss that is 
enabled by the lower capacitance of the air filled dielectrics over 
solid. QED fatter cables with the same dielectric have lower loss 
because the inner conductor is larger, but copper costs. Very large 
diameter coax uses a tube for the  inner conductor to save cost and weight.

Do you really need a mast head pre-amp? It will reduce the dynamic range 
of the RX and if it is say a FT897 or a TS2000 then you are already in a 
poor dynamic range position without the pre-amp. On the other hand if it 
is an excellent transverter into a K3 or similar you should not need the 
pre-amp either as the transverter noise will be well below band noise 
even with 30m of W103. Also it is something else to go wrong and is 
possibly a right pain to fix when it goes wrong. 70cm and above is 
different with band noise very much lower than 2m plus increased coax 
loss. On 70cm if you have a Tetra mast near by then excellent bandpass 
filtering will be required to stop overload of the RX system.

73 David G3YYD

On 14/03/2010 11:12, Keith Maton wrote:
> There's a lot of knowledge on here so I hope you'll excuse me this slightly OT post although it does have a contesting connection :)
>
> We did some aerial work at the club contest station a couple of weeks ago and it's made me realise that I need to improve my home station.  I have a 9 element Vargarda fed with some "RG-213".  I'm going to upgrade this to EcoFlex 15, replace the old rotator and fit a masthead pre-amp.
>
> Is it worth me taking the effort to replace the entire coax run right to the aerial or simply trim back the current stuff to the stub mast where the pre-amp will be located and run the new cable from there down to the shack?  That will leave me with 2-3 metres of the existing cable.
>
> I know it will make a slight difference replacing that tail but will it be too negligible to even notice?
>
> 73
> Keith, G6NHU
> Martello Tower Group, G0PKT
>
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