[RFI] Choke questions

[donovanf at starpower.net]

We're not discussing a choke operating at very high frequencies, 
we discussing its performance at 1.8 or 3.5 MHz. At these frequencies, 
a few feet of 50 ohm transmission line such as RG-142 or RG-400 
connected to the end of a 75 ohm line has a tiny -- nearly immeasurable -- 
effect. 



Using this on-line transmission line calculator: 
www.iz2uuf.net/wp/index.php/transmission-lines-calculator 


Two feet of RG-142 connected to a 75 ohm load has an input impedance 
of 75 -2j ohms at 1.8 MHz and 74.8 - 4J at 3.5 MHz. It would be very 
difficult to measure such a tiny impedance transformation, much less 
trying to measure its insignificant affect on the performance of a 
4-square array. 


Even a four foot length of RG-142 transforms the impedance to only 
74.8 - 4j ohms at 1.8 MHz and 73.9 -7.5j at 3.5 MHz 


73 
Frank 
W3LPL 



----- Original Message -----

From: "Gedas" <w8bya at mchsi.com> 
To: rfi at contesting.com 
Sent: Wednesday, January 22, 2020 2:59:21 PM 
Subject: Re: [RFI] Choke questions 

Another Teflon based coax similar to 50-ohm RG-142 and 75-ohm RG-179 is 
75-ohm RG-187. 

Gedas, W8BYA EN70 

Gallery at http://w8bya.com 
Light travels faster than sound.... 
This is why some people appear bright until you hear them speak. 

On 1/22/2020 1:35 AM, Jim Brown wrote: 
> On 1/21/2020 8:02 PM, John K9UWA wrote: 
>> Is there a 75 ohm equivalent to RG400 coax? 
> 
> Not that I know of, although are there's at least one sort of like 
> RG142. KZ1W sent me several miniature coaxes to evaluate for chokes 
> for TX 4-squares, the most useful of which seems to be RG179. It's 
> addressed in the Cookbook. 
> 
> 73, Jim K9YC 
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