From: =?utf-8?B?VklHSUxBTlQgTHVpcyBGZXJuw6FuZGV6?= <luis@vigilant.es>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: LF: Ebnaut receiver frequency stability qustion
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Date: Wed, 19 Dec 2018 13:42:09 +0000
Message-ID: <6DB8451D7F3D3947A5918808A59621EA26397DBA@servigilant.vigilant.local>
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 <5C19FFCB.1060305@posteo.de> <16876196-3308-f722-dfca-5232150e7394@n1bug.com>
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Subject: RE: LF: Ebnaut receiver frequency stability qustion
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Hi EbNaut

My downconverter is based on NE602 and is crude simple. No filters, no gain stages. A bit deaf and birdie-rich
but wanted to test it that way for EbNaut and check if it works. It is based on K0LR article you can find here
https://www.qsl.net/k0lr/SW-RX/sw-rx.htm

The LO based in Xtal and 74HC4060 is REPLACED by a series 10K resistor and series 100nF connected to the GPS output
So, for the LO, a cheap uBlox GPS will provide both 120 or 125KHz for the LO and 1pps to discipline the soundcard
You only need to connect the GPS to USB and use the uCenter software to configure the GPS outputs and save
this cnfiguration as default for the GPS

No worth to use the same GPS for Tx. It is so chip you sure can afford another one for Tx at 2x the frequency if you
are using a D class PA


-----Mensaje original-----
De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de N1BUG
Enviado el: miércoles, 19 de diciembre de 2018 13:01
Para: rsgb_lf_group@blacksheep.org
Asunto: Re: LF: Ebnaut receiver frequency stability qustion

Hi Stefan, Luis, LF,

Yes, yes! Please grab some paper and start drawing those circuit diagrams! ;-)

The non-engineers have many questions...

If I understand this correctly... with the NEO-M8T then I just need one module... use one time pulse pin for LO and the other one for 1 PPM to discipline the sound card? Else with the NEO-6/7 or M8N I need two.

For the older modules U-blox says they use a 48 MHz NCO and that the time pulse output will have less jitter if configured to a frequency which divides evenly into 48 MHz. So I guess 120 kHz...

But I couldn't find any information about the oscillator frequency for the M8T. Does anybody know?

What kind of mixer?

Can filters help? Band pass filter on antenna input to mixer? LPF on LO to mixer?

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?

73,
Paul


On 12/19/18 3:22 AM, DK7FC wrote:
> Hi Luis, LF,
> 
> I agree, this is indeed the most reasonable design. Using the same 
> here
> ;-) but a 125 kHz LO, locked to GPS.
> Maybe we should provide easy converter crcuits. A compromise between 
> high end and easy to build up, for the 'EbNaut-newcomers'?
> 
> 73, Stefan
> 
> Am 19.12.2018 07:39, schrieb VIGILANT Luis Fernández:
>> Hi EbNaut
>>
>> I think that using expensive receivers is NOT the way to go. I'm 
>> using a simple mixer as downconverter. The LO is 120KHz generated 
>> from a uBlox GPS. So the 137KHz outputs as 17KHz and can be feeded to 
>> PC soundcard. The second channel of GPS provides 1pps to discipline 
>> the soundcard using Spectrum lab
>>
>> Not using filters at all and no amplifier stages. So there is room 
>> for improvement, but it works
>>
>> 73 de Luis
>> EA5DOM