[TowerTalk] 75 ohm - v - 50 ohm coax

[K8RI]

On 2/19/2013 2:38 PM, Jim Brown wrote:
> On 2/19/2013 9:28 AM, Roger D Johnson wrote:
>> s not the loss on receive determined by the RX input impedance? IOW
>> It's the LOAD on
>> the transmission line.
>
> Yes, BUT -- signal to noise on receive on the MF and HF bands is nearly
> always determined by band noise (that is, noise picked up on the
> antenna), not circuit noise in the RX.  VHF/UHF is a very different
> story -- circuit noise CAN be the limiting factor for hams living in
> quiet locations, and in those situations, line loss on RX does matter.
>
> Also, the input impedance of most receivers is not well controlled, and
> often differs significantly from its nominal value.
>
> A good rule of thumb is that if the band noise increases by 3dB or more
> when you connect the antenna, your RX system is mostly limited by noise
> picked up on the antenna, and for a 6dB increase is entirely limited by
> external noise.  in those quiet locations where circuit noise is the
> limiting factor, we usually want an RX preamp up on the tower.
>

Does such a place exist on 160, 75, and 40?..Except when the bands are dead.

73

Roger  (K8RI)


> 73, Jim K9YC
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