Re: VF Varies With Frequency
Posted by
Wes Stewart-2 on
Apr 01, 2020; 11:54pm
URL: http://elecraft.85.s1.nabble.com/75ohm-Impedance-question-K3S-and-Antenna-side-tp7659364p7659436.html
I would not be buying any cable from them.
Wes N7WS
On 4/1/2020 2:45 PM, Mpridesti via Elecraft wrote:
> Requested technical comment from a long established coaxial cable manufacturer on this topic.
>
> This was the response:
>
> The Vp is not measured at any frequency and is independent of frequency. The only variable in play is the dielectric constant. The Vp represents the speed at which a signal transmits along the cable as a % of the speed of air. Air/vacuum will be the fasted medium to use to transmit an RF signal. The thing is, air is usually not practical since there is nothing to support the center conductor, can be easily crushed and is susceptible to the ingress of moisture.
>
> We use foamed dielectrics and expanded tapes to get as close to air as possible. Vp will vary based on the specific dielectric used. The vast majority of our cables range in velocity of propagation from 76% to 86%. For a given cable, the Vp will likely not vary more that +/- 1% over it’s length but as I mentioned earlier, it would be best to use +/-2% for planning purposes.
>
> End response
>
> Regards,
>
> Mark, K1RX
>
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