[TowerTalk] Coax Loss -- RG-Numbers Don't Tell us Much

[Roger (K8RI)]

jimlux wrote:
> Roger (K8RI) wrote:
>   
>> Jim Brown wrote:
>>     
>>> On Thu, 4 Feb 2010 10:38:19 -0800, Rick Karlquist wrote:
>>>
>>>   
>>>       
>>>> This is *generally* true, if comparing all copper cables.
>>>> But even in that case, the HF loss is not proportional to
>>>> DC resistance when comparing different sizes of cable.
>>>> And all bets are off when copper plating is involved.
>>>> It is also worth noting that Al has something like 1.6 times
>>>> the DC resistance of Cu but only 1.3 times the RF resistance.
>>>> Finally, 75 ohm cable has considerably more DC resistance than
>>>> 50 ohm cable with the same RF loss.
>>>>     
>>>>         
>>> Rick,
>>>
>>> My point is that virtually all transmission line losses at HF are I squared R 
>>> losses. 
>>>       
>> That's why you want to install the largest coax you can afford.
>>
>>     
>
>
> So, are we going to see articles in QST about "How to fabricate coax air 
> line from thinwall 6" aluminum irrigation tubing" or " How I learned to 
> stop worrying about rain on my openwire line and to love my TIG welder"
>   
Nope! How to use your plumbing skills to get that RF to the antenna!

Unfortunately have you seen the price of copper lately? The size 
calculations are in "The Handbook".
Air core, using copper pipe isn't all that difficult to build, but it 
takes the rigid refrigeration tubing to get a nice straight center 
connector.  Then there is the problem of making all joints not only 
water proof, but air tight, and then creating a fitting to allow using 
dry N2 to purge the whole line.  Time you get done it'd cost a small 
fortune.

Hence purchasing the largest you can afford is the best answer I can see.

73

Roger (K8RI)
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>