DX-60B and Low Pass filter

[Bill Coleman AA4LR]

On 5/31/99 3:41, Yew Hoo at yew_hoo at YAHOO.COM wrote:

>I was seeing some TVI on the home TV so I put a low
>pass filter inline with the DX-60B, and it went away
>as expected(the tvi, not the tv).

Hmm. That's potentially bad.

>However, it seems to
>tune strange with the transmatch.

Adding a low-pass filter should not affect your transmatch.

>I have them in this
>order -- XMTR, LoPass Filter, Transmatch(Murch
>UT-2000), 40m dipole.

This is the correct order to place the equipment.

>Should the filter go where I
>have it or after the transmatch?

Do not put it after the transmatch. Low-pass filters require 50 ohm
impedances. Putting it after the transmatch would cause the filter to
have to deal with complex impedances, which may lead the improper
opreation of the filter, or perhaps component destruction within the
filter.

>The DX-60B specs say
>it has a built-in low pass if that makes any
>difference.

The DX-60 DOES have a low-pass filter built-in, which makes me wonder
what the heck is happening that that an additional filter is reducing or
eliminating TVI.

Perhaps you merely have excessive currents on the outside of your coax,
and the low-pass filter is modifying these currents. Does the dipole have
a balun?



Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at radio.org
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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