Message-ID: <589042FBC49042C1BC9B6E9BC667F079@DELL4>
From: <jrusgrove@comcast.net>
To: <rsgb_lf_group@blacksheep.org>
References: <10f465fa-37f0-4ac6-b53d-793f955ea011@email.android.com> <5C19FFCB.1060305@posteo.de> <16876196-3308-f722-dfca-5232150e7394@n1bug.com> <5C1A3F32.9070604@posteo.de>
Date: Wed, 19 Dec 2018 11:05:34 -0500
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Subject: Re: LF: Ebnaut receiver frequency stability qustion
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>Yes, a band filter in front of the mixer and then an image rejection
>filter on the AF side. Thus it is better to use an LO frequency of 125
>or 120 kHz rather than 135 kHz because filtering will be easier then.

The image rejection filter needs to be ahead of the mixer ... otherwise noise (and possibly signals) 
at 113 kHz will appear as part of the i-f signal at 12 kHz.

Jay W1VD


----- Original Message ----- 
From: "DK7FC" <selberdenken@posteo.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, December 19, 2018 7:53 AM
Subject: Re: LF: Ebnaut receiver frequency stability qustion


> Hi Paul,
>
> Am 19.12.2018 13:00, schrieb N1BUG:
>> Hi Stefan, Luis, LF,
>>
>> Yes, yes! Please grab some paper and start drawing those circuit
>> diagrams! ;-)
>>
> No problem. I've drawn the circuit years ago. But the design (based on a
> G4JNT design) is a bit more complex. But there you don't need image
> rejection filters, which is an advantage. Image in the attachment.
> This is what i use for LF transmissions. The xtal is GPS locked by
> another circuit that is not shown in this schematic. But instead one can
> use the NEO GPS modules. Not only EbNaut, the converter is good for
> WSPR, QRSS, DFCW, OP32, JT9 and so on.
>
>> What kind of mixer?
>>
> For the RX i'm using an SBL-3 DBM. But a SA612AN will work too ( i use
> that one for the MF converter). There, you will need narrow band filters.
>
>> Can filters help? Band pass filter on antenna input to mixer? LPF on
>> LO to mixer?
>>
> Yes, a band filter in front of the mixer and then an image rejection
> filter on the AF side. Thus it is better to use an LO frequency of 125
> or 120 kHz rather than 135 kHz because filtering will be easier then.
>> Probably more questions but since I am not an engineer and have
>> never seen a diagram of this, I don't know what else to ask.
>>
>> Can the same LO and mixer be used for a tx up-converter?
>>
> I'm using the same LO for the RX and then TX converter.
>
> 73, Stefan
>