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Re: [TowerTalk] Using Stubs to Reject Harmonics

Subject: Re: [TowerTalk] Using Stubs to Reject Harmonics
Reply-to: "Tower and HF antenna construction topics." <>
Date: Thu, 4 Feb 2010 06:32:47 EST
List-post: <">>
Jim, you are right, it was a 200 ft length for 432 MHz and 100 ft for  
higher frequencies. This is a great application for old RG8 coax that has gone  
200ft of new RG213 measures right at 4.5 dB/100ft at 432 MHz so 200ft is  
almost 9 dB and a return loss of 18 db with short or open at the far end. I 
have  a couple of calibrated for loss 100 ft cables that I use for 
attenuators for  these higher frequencies. They allow power measurements using 
power Bird  slugs which seem to be more accurate than the 2500 watt slugs I 
have used,  especially at 1296 MHz.
Of coarse the Bird meter is terminated with a smaller 200w load when used  
this way and the return loss looking into the "attenuator" cable becomes  
more like 30 to 40 dB.
Gerald K5GW
In a message dated 2/4/2010 2:50:49 A.M. Central Standard Time, writes:

On Wed,  3 Feb 2010 20:24:47 EST, wrote:

> For example, a  100ft length of RG213 has about 10 dB loss at 432 MHz

That would be  some pretty awful coax -- Belden's RG8X (9258) is only 
6.6dB/100 ft at 400  MHz, and a decent RG8-sized coax is on the order of 
3dB/100 ft.  

Yes, an infinitely long line looks like a resistor equal to its own  Zo, 
even with an open circuit as a load but it takes more like 1,000 ft to  
approach that at 432 MHz. 


Jim  K9YC


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