Softrock Ensemble II vs the RTL-SDR + Upconverter on Shortwave
Over on YouTube user mutezone has posted a video comparing the RTL-SDR with upconverter against a Softrock Ensemble II software defined radio. The Softrock Ensemble II is an SDR dedicated to the HF frequencies and is thus expected to have better performance for that purpose. Mutezone writes
A performance between the Softrock Ensemble II vs the RTL-SDR (R820T) on shortwave. Here we are trying to see which one is best at receiving AM broadcasters. Both SDRs were using the same longwire antenna connected to an ATU (Antenna Tuning Unit).
Although I know this comparison is somewhat unfair, since the RTL-SDR is not meant for shortwave & the Softrock is, it is to show that there is a difference in performance, even though the RTL-SDR has a much wider frequency range & cannot be beaten when it comes to value for money. My opinion is that if you want an SDR that should deliver on HF / Shortwave performance, then go for a dedicated one like the Softrock, Afedri, SDR-IQ or any others that do the same job on the market. Even when using a decent HF Upconverter, the RTL-SDR will still not match the performance of more upmarket HF SDRs.
This guy using a very bad converter. Its look like hi connect few meters wire on direct sampling! Very very bad movie. Try usign TA7358 to build upconverter!!!
Let’s not forget that for more than a year I’ve been marketing my HF Upconverter through Easy-Kits that’s installed IN the RTL2832U dongles and successfully have 200+ placed out in the US and other continents. With an injection frequency of 120 MHz and with a 0.5 to 54 MHz lowpass filter, this HF SDR has performed excellent in view of the ‘outboard’ designs that are out there. If anyone wants to review that, just click on the ‘HF’ link on the Categories on this website to see what’s been out there. 200+ Hams can’t be wrong on it’s performance…I use my HF SDR more than my station rig (Yaesu 1000MP).
Since none of the upconverter designs I’ve looked at were suitable for this application, I designed my own.
The issues have to do with the RTL dongle being a wide-band tunable IF and how the mixing process works. The mixer output is not only the sum and difference, between the converter’s desired input and local oscillator , but includes numerous undesired higher order output products, that need to dealt with as well.
Specifically, the input on NooElec Ham-It-Up converter only has a low pass filter on the input. While this provides attenuation of FM broadcast stations above the desired HF frequencies, but no attenuation from strong signals from the AM broadcast stations below 1.8 MHz, which can overload the system and/or become part of the mixing process. Additionally, the 820T based dongles, do not provide true zero IF I/Q signal to the RTL 2832, but operate at an IF frequency, in the 4 MHz area.
As a result, the band-scope, between the Softrock Ensemble II, which uses octave band pass filtering vs. RTL-SDR, clearly shows the numerous spurious signals present when receiving with an up-converter and RTL device.
For an up-converter to work well, the input needs to be very well filtered to protect out of band signal overload and/or becoming unwanted mixer products. Additionally, the converter’s crystal clocks operate in overtone mode, so to prevent additional frequencies (e.g. fundamental and lower order frequencies) from entering the mixing process, the local oscillator needs to be band pass filtered as well.
Well, most of the statements are true but not all.
Not all crystal clocks operate in overtone mode and this makes some difference…
Regarding the design, most of the guys designing this gadgets understand the problems, but if you want to have a top notch upconverter, it will not cost 50$ but a several times more than that.
Who will spend let say 250 $ for the upconverter that wil be hooked to the dvb-t dongle?
So the design have to follow the basic receiver where the price is low 10-20 $ for the DVB-T dongle.
The gadgets should not be much more expensive than the dongle if not the same price.
Most sound cards, needed by the Softrock, are 16bit to 32bit vs a rtl-sdr at 8bits. The one thing that the RTL-SDR will win on in this comparison is greater Panoramic Display 2.4MHz vs 22.05 to 96KHz from a sound card. If the rtl-sdr sacrificed it’s 2.4MHz of bandwidth via to gain an extra 3 bits of resolution and suffered the corresponding drop in bandwidth to 37.5KHz, it would be a more fair comparison.