[Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston

[Al Klase]

Receiver impedance matching, especially at HF and below, is a lot like 
horseshoes and handgrenades;  All you have to do is come close!

My two cents,
Al

On 2/21/2019 2:20 PM, Jim Whartenby wrote:
> Blame Bell Labs for the coax impedance compromise.
> See: https://www.belden.com/blog/broadcast/50-Ohms-The-Forgotten-Impedance
>
> Best impedance for power transmission: 30 ohms
> Best impedance to withstand high voltage: 60 ohms
> Best impedance for lowest loss: 75 ohms
> The BTL compromise impedance considering all of the above: 50 ohms
>
> As already mentioned:
> Impedance of a vertical antenna is about 36 ohms
> Impedance of horizontal antenna is about 72 ohms
> Hum, a two to one difference in impedance between these two antennas.....
>
> Mismatch loss between 36 ohms and 50 ohms: 0.177 dB with a VSWR of 
> 1.389 : 1
> Mismatch loss between 36 ohms and 75 ohms: 0.572 dB with a VSWR of 
> 2.083 : 1
> Mismatch loss between 50 ohms and 75 ohms: 0.177 dB with a VSWR of 
> 1.50 : 1
> Mismatch loss between 72 ohms and 75 ohms: 0.002 dB with a VSWR of 
> 1.042 : 1
> So the compromise impedance holds for either a vertical or horizontal 
> antenna impedance and a 50 ohm transmission line. Depending on 
> frequency and cable length, RG-8 attenuation loss could easily mask 
> the mismatch losses of the above.
>
> Can't calculate the Mismatch Loss and VSWR for the UHF connector since 
> the impedance of the connector is not controlled; it could be 
> anything.  Which makes the initial mismatch loss concern between 75 
> and 50 ohm cables connecting to the CU-872A/U antenna coupler 
> meaningless if UHF connectors are used.
>
> BTW, the eBay price of UHF and N connectors is $2 v $4.44, not all 
> that much of a difference IMHO.
>
> Regards,
> Jim
>
>
>
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-- 
Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

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