Re: LF: IDC-136-BLT 136kHz receivers

[Andy Talbot <andy.g4jnt@gmail.com>]

AH, thanks for finding that - must have missed it on first looking.

Yes I agree, the NE612 is a poor mixer to use for those purposes.   A diode ring, or bus switch would do a muxch better job

But why not an I/Q conversion and make use of all the decent SDR software out there?   

Andy  G4JNT

On 4 June 2015 at 14:05, Rik Strobbe <Rik.Strobbe@fys.kuleuven.be> wrote:

Hello Andy, Chris,

 

the circuit diagram can be found in this PDF: http://icas.to/idc-136ii/idc-136ii-kit-manual-eng.pdf

In contradiction to the block diagram at http://icas.to/lineup/idc-136ii-kit-eng.htm the circuit diagram show a J310 wideband preamp before the BPF.

I have played with SA612 chip in the past and found that it had rather poor IMD behaviour compared to a 74HC4053 mixer.

 

73, Rik  ON7YD - OR7T

 

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Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Andy Talbot [andy.g4jnt@gmail.com]
Verzonden: donderdag 4 juni 2015 14:44
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: IDC-136-BLT 136kHz receivers

Haven't seen / played / even heard of them, but we can get a rough idea of its possible performance just by looking at the picture of the PCB on  the web page.  Image filterign is teh biggest problem with this single conversion route.   Assuming all the image filtering is done by those three coils in cans that are visible on the photograph:.

An AADE design for a suitable third order bandpass filter, with 8kHz bandwidth and allowing a compromise 1dB ripple  suggests image rejection at 125kHz will only be around 30dB.   (Top coupled capacitor  design, so low side rejectino is better than high side)   Not sure what signals are down there to get through, and a highly resonant antenna will help a lot more with image rejection - but if its for a grabber, you're probably going to use a broadband active antenna.

Can't make out much else from the web page photos, and it give no specification.  But  such a simple converter concept can't go hopelessly wrong, if you accept the limited image filter that would be achieved with three tuned circuits

If I were to try that approach, I'd got for an IF of  15 - 19kHz, at the top end of  normal soundcard coverage, so bringing the image down to 105kHz and making it easier to filter - although there you would just be creeping into LORAN area.

Andy  G4JNT

On 4 June 2015 at 13:17, Chris Wilson <chris@chriswilson.tv> wrote:

04 June 2015


I  ordered one of these yesterday as I am getting tired of tying up my
TS-590 just listening on LF. I think a few people here may have used these,
what are your opinions of them please?

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



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Best regards,
 Chris                            mailto:chris@chriswilson.tv