Mile also uses a band pass filter and notch filter to improve the dynamic range of the RTL-SDR. Additionally, in the video he shows a comparison between a large delta loop antenna and the mini-whip active antenna which shows better performance by the mini-whip.
RTL-SDR on VLF (ALPHA Russian Long Range Navigation System receiving in Macedonia with MiniWhip)
Over on YouTube user Alex swl has uploaded a video showing his reception of a Very Low Frequency (VLF) radio signal using a laptop running SDRSharp and a Chirio Mini Whip antenna connected directly to the laptop’s sound card input.
Every year on Alexanderson Day (this year on 29/06/2014) and some other days the Varberg VLF Radio Station in Sweden transmits a morse code message using a 1.9 km (1.2 mile) horizontal wire antenna at 17.2 kHz with callsign SAQ. Because the transmission frequency is so low, a standard PC soundcard can be used to directly receive the signal.
Alex swl was able to receive this signal in Italy.
In previous posts we have featuredMartyKN0CK’spopularmodified RTL-SDR dongles which have either a miniature built in high quality HF upconverter with amplifier and filter, or an amplified and filtered direct sampling modification applied to them. With these modified dongles you can receive the HF frequencies from 0.5 MHz to 54 MHz. These kits were previously available for sale on a webstore, however that store has since closed down.
Fortunately, Marty’s modified RTL-SDR dongles are still available at http://www.kn0ck.com/HF_SDR/. The HF upconverting dongle can be bought for $75 and the direct sampling dongle at $60. The store page also shows example videos of the performance you can expect.
KN0CK HF Upconverting RTL-SDR ModificationKN0CK HF DIrect Sampling RTL-SDR Modification
The DX Patrol 100 kHz to 2 GHz SDR receiver appears to be a custom built RTL-SDR with upconverter built in. It is made by CT1FFU who is also known to be a good manufacturer of upconverters for the RTL-SDR. The DX Patrol SDR can be bought for 79 Euros at CT1FFU’s website. It’s features are as follows:
Ultra Wide-band Coverage SDR Receiver
Full coverage reception form 100KHz to 2GHz SDR
Independent antenna inputs for Shortwave and VHF
USB computer connection ( mini usb)
Very High dynamic range receiver
Low noise pin-diode band switch
Accurate and efficient band filters
Very clean audio reception
SMA golden antenna connectors
LED power and band indication
40MHz local oscillator for HF conversion
DBM balance diode ring mixer
Small size board
Freeware software
Up to 3.2 M Sample rate.
Ultra Wide band DX Patrol SDR Receiver 100KHz to 2GHz
We aren’t sure how this compares to a standard RTL-SDR with conventional upconverter, or direct sampling mode and we also aren’t sure about the truthfulness to their very high dynamic range claims as the RTL-SDR is known to have dynamic range that isn’t what could be called very high (8 bits ~ 50 dB).
Over on YouTube user OfficialSWLchannel has uploaded a video review. OfficialSWLchannel gives a generally positive review of the hardware.
The SoftRock Lite II is a (now fairly old) soundcard based software defined radio kitset that is capable of receiving on the HF bands. Over on YouTube user w2aew has uploaded a video showing the entire kitset build process for the SoftRock Lite II SDR radio. He also goes over the circuit blocks explaining their function and how they work.
This is an excellent video if you are interested in learning more about the components and circuits used in some SDRs.
#148: Software Defined Radio kit | Tutorial | Build | Test | Softrock Lite II
Over on this Japanese language blog, ttrftech has been experimenting on a type of direct sampling front end board (Use Google Translate) for a direct sampled RTL-SDR dongle. More info about his direct sampling front end can be found on this post. Translated, it appears his board has the following feautres.
Filter x2 up to fifth order
RF switch
Amplifier
Power regulator
Input transformer (optional)
The RJ-45 (optional) or the SMA input connector
Power supply to the antenna
Output to U-FL or SMA (ipex) connector
The results seem to show his board does improve reception. Note that the RJ-45 appears to be the antenna. There also appears to be review of the board by “pup” here and a video showing the board filtering out a broadcast FM image in the video below. On Pups blog there are also more posts about the board under this tag.
A new super budget HF upconverter has appeared over on cosycave.co.uk, a UK based trading site. It is currently priced at £9.99. The budget HF upconverter uses a 50 MHz oscillator and an NE602AN double balanced mixer and oscillator integrated circuit. It is only suitable for use on the R820T and is incompatible with the E4000.
This circuit appears to have no preselection or filtering circuits.
Over on YouTube user Theo Faber has uploaded a video showing his adjustable multiband HF preselector project for his RTL-SDR dongle. The preselector covers the entire HF band. Theo designed and built his own homemade upconverter for this project as well.
Preselectors on the RTL-SDR can vastly improve reception quality. Without preselection, noise and strong images of other nearby stations can cause strong interference.
My project ‘pre selector’ for wideband radios and in particular the popular tv-sticks than can be used for SDR reception. The sticks are very cheap and the software free available on the internet. SDR Sharp in this case, is operating stable under XP and W7. Sticks are sensitive, however the input level can only vary +- 20dB. The sticks are easely overloaded and will produce cross and intermediation. So you need in front of the stick / converter band pass or tunable filters. Hopefully this inspired you to build your own set of filters, to fully benefit from the perfect performing of this affordable SDR.
for more info contact me on: t.faber87__AT__upcmail.nl
kind regards and 73’s
