Author Topic: What is the best HF RTL dongle. (Up-Converter or Direct conversion)  (Read 3003 times)

Anton Janovsky (ZR6AIC)

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What is the difference between a direct conversion and up-conversion HF RTL dongle?
1) Direct conversion is normally better than using up-convert for the following reasons.
There is now additional mixer and Local RF oscillator stage witch could add to phase noise and additional image rejection problems.
2) In a Direct conversion sdr the A/D converter needs to be faster than the selected receiving frequency for the SDR to work properly.
3) Up-converters is mostly used if the IQ Frequency is Mixed with a local oscillator and then down converted to the base band for DSP SDR decoding.
4) Because most cheaper RTL dongles only had there Mixer local oscillator IQ inputs exposed to the antenna it was the only way to have HF coverage by using an up-converters. ???
5) Only lately was it possible to configure the RTL dongles to be able to read there base band input pins for SDR use. The problem was that the base band input pins had a high input impedance and integration to 50 ohm antenna was not a good match from a direct connection point of view and there for sensitivity was not that good.
6) There is now a modification to the RTL dongle in a Kit or pre build format for the the RTL dongle that adds a impedance transformer for the Baseband input to the RTL dongles solving the sensitivity problem.
see details below. :) :)
Here is link to HF direct conversion RTL dongle Kit.

http://www.giga.co.za/ocart/index.php?route=product/product&path=59&product_id=183

Pre-build HF direct conversion RTL dongle.

http://www.giga.co.za/ocart/index.php?route=product/product&path=59&product_id=178
« Last Edit: December 11, 2015, 12:28:48 pm by Anton Janovsky (ZR6AIC) »