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Help understanding use of "Upconverter"

Posted: Mon Oct 12, 2020 10:23 am
by SeanL
Hi all,
I would be grateful if somebody could explain how to correctly use an upconverter. I am relatively new to SDR but I have a reasonable understanding of radio frequencies etc.

My setup is as follows:
Hardware: NooElec NESDR SMArTee v2 dongle + NooElec Ham It Up Plus HF Upconverter
Software: SDR#

According to the technical documentation, the SMArTee dongle works for frequencies in the range 25 MHz to 1750 MHz (so for frequencies outside that range, an upconverter is required).

The documentation for the upconverter states it has a frequency capability of 300 Hz - 65 MHz in “upconvert mode” and 300 Hz to 6 GHz in “passthrough mode”.

If my understanding is correct, passthrough mode effectively means bypassing the upconverter which means the SDR software is using the SDR dongle only (I could be wrong!).

I have tried to represent this graphically in the attachment. I do understand the need to use the “Shift” value in SDR# when using an upconverter but I don’t understand when I should and shouldn’t use upconvert vs. passthrough modes.
If my understanding of the technical documentation is correct, if I use the upconverter in passthrough mode, I should be able to receive signals between 300 Hz and 6 GHz but that doesn’t make sense to me – if I’m bypassing the upconverter by using passthrough mode then I should only be able to receive signals between 25 and 1750 MHz i.e. the frequency range of the dongle.

I hope I’ve described my question clearly. Any help would be greatly appreciated!
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Re: Help understanding use of "Upconverter"

Posted: Mon Oct 12, 2020 5:55 pm
by hotpaw2
In pass-thru mode, the upconverter acts like it isn't there. So use the pass-thru mode in situations where you wouldn't need an upconverter at all (e.g. the frequencies are within the range of your USB dongle).

Re: Help understanding use of "Upconverter"

Posted: Mon Oct 12, 2020 7:04 pm
by SeanL
Thanks for your reply hotpaw2, but I'm still confused!! I get what you are saying (sort of!) and that was my original understand for the need to have an upconverter however, going by the manufacturer's description, passthrough mode is for frequencies between 300 Hz and 6 GHz - that's well beyond the range achievable using the dongle on it's own.

Re: Help understanding use of "Upconverter"

Posted: Mon Oct 12, 2020 7:34 pm
by Stromeko
SeanL wrote:
Mon Oct 12, 2020 7:04 pm
going by the manufacturer's description, passthrough mode is for frequencies between 300 Hz and 6 GHz - that's well beyond the range achievable using the dongle on it's own.
Well, it says those frequencies make it through the upconverter in bypass mode (if they were present in the input to start with). It doesn't say that you can do anything useful with them using whatever happens to be connected to the output. In other words, to make use of the full range of passthrough bandwidth you would need something way more expensive than an RTL-SDR.

Re: Help understanding use of "Upconverter"

Posted: Mon Oct 12, 2020 10:48 pm
by hotpaw2
Yes. The manufacturers description is technically correct, but confusing and not useful. It can pass-thru signals that you can't use (with a basic RTL-SDR).

Re: Help understanding use of "Upconverter"

Posted: Tue Oct 13, 2020 8:36 pm
by SeanL
To Stromeko & hotpaw2: thanks for your replies. It makes sense now. I agree the manufacturers description could be better.