Re: LF: Do I need an attenuator on LF RX??

To:	[email protected]
Subject:	Re: LF: Do I need an attenuator on LF RX??
From:	Markus Vester <[email protected]>
Date:	Mon, 12 Feb 2018 17:10:44 -0500
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Hi Chris,

the broad "noise hump" between 135 and 142 kHz seems to be just the band noise from the antenna, filtered by the IDC bandpass. The bandpass centering seems to be somewhat high, but that's not necessarily a disadvantage and may improve image rejection. In another IDC receiver which was operated outdoors in Tasmania, we have observed a significant temperature dependence from ceramic capacitors.

At lower frequencies, we can identify an Image and two IM products, but none of these appear to be a problem either:

2x138.83 - 147.3 = 130.36 kHz DCF39 / DDH47 (twin lines from FSK)
2x130.0 - 128.93 = 131.07 kHz DCF49 image with 130 kHz IDC-LO
2x138.83 - 145.0 = 132.66 kHz DCF39 / REN (Spain?, with MSK spread)

So all in all, your RX seems to be fine as it is.

Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Chris Wilson <[email protected]>
An: rsgb_lf_group <[email protected]>
Cc: dead.fets <[email protected]>
Verschickt: Mo, 12. Feb 2018 15:12
Betreff: LF: Do I need an attenuator on LF RX??

Hello LF'ers,

I would like to know if the experts here think I need an antenna
attenuator on 136kHz? I am using in this capture a little IDC
receiver:

http://icas.to/lineup/idc-136-kit-eng.htm

but see the same with a Softrock LF. I am unsure if the antenna is
overloading the RX, it's a big file at around 14 megs, but I guess
most people, unlike me in the sticks, have broadband :)

Thanks.

http://www.gatesgarth.com/Untitled26.mp4

--
Best regards,
Chris mailto:[email protected]

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