Ford,
Unless your system noise is limited by your receivers internal thermal
noise floor (usually not the case on 160 meters), the mismatch loss caused
by the 220 ohm termination will probably be inconsequential. You can check
for this by listening to the noise floor with and without your antenna
connected.
If on the quietest night of the year, your noise floor still drops when you
disconnect your most inefficient receive antenna, you have nothing to worry
about (this indicates that atmospheric noise dominates in your receive system).
Do you have a schematic of the front end circuit? That may give you some
clues as to whether 220 ohms is expected by design, or if perhaps something
is broken or mistuned.
73 de Mike, W4EF....................
----- Original Message -----
From: "Ford Peterson" <ford@cmgate.com>
To: <towertalk@contesting.com>
Sent: Thursday, January 18, 2001 10:14 PM
Subject: [TowerTalk] RX input impedance
> I just used the Autek VA-1 to measure the input impedance of the receiver
> port on my IC-746.
>
> Interesting!
>
> On most bands, the input impedance measured in the neighborhood of 50 ohms.
> On 160 meters, it was over 220 ohms. What's up with that? Do you suppose
> it makes a difference? My 160 antenna is almost a perfect 50 ohms at 1830
> at the shack.
>
> My question is, do I care? More important, should I care?
>
> Ford-N0FP
> ford@cmgate.com
>
>
>
>
>
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>
>
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