This week on the SignalsEverywhere YouTube channel host Corrosive explores why impedance matching matters when trying to obtain the best reception possible. To do this he reviews the NooElec 1:9 Balun, which is designed to convert the (roughly) 450 Ohm impedance of a long wire antenna or ladder line dipole back down to 50 Ohms, which is the standard impedance that an SDR expects. Small amounts of impedance mismatch are negligible for RX, but larger mismatches can result in poor reception.
An upconverter allows you to receive HF frequencies (0-30 MHz) with an RTL-SDR which has a lower frequency limit of 24 MHz. The ham-it-up upconverter was one of the first upconverters to go on the market that targeted users of the popular RTL-SDR dongle. Over the years the ham-it-up has slowly been revised and now it is up at version 1.3. The biggest changes in the latest version are a revised design that uses the ADE-1 in reverse (better VLF operation), a presoldered oscillator and it also now includes the previously optional noise source by default.
In his review Akos compares the ham-it-up v1.3 to the older v1.2 model. His results show that the revised design seems to have better immunity to noise and better FM broadcast filtering. He also tests out the new battery power via connection and shows that using battery power is less noisy.
Previously we posted a review comparing the ham-it-up v1.0, SpyVerter and Nobu’s Japanese upconverter. Although the ham-it-up v1.3 is much improved and we have not tested it, we still believe the SpyVerter is the better upconverter choice at the moment due to its better architectural design and included metal case, though Akos does point out that the ham-it-up is currently about $15 USD cheaper and has a passthrough switch.
In his second post Akos reviews the Balun 1:9 which is a $10 balun that is designed for attaching a long wire antenna to the ham-it-up. The goal of the balun 1:9 is to transform the high impedance long wire antenna down to around 50/75 Ohms for the receiver. In Akos’ results he writes that he mostly see’s identical or better performance with the balun connected.
To add to Akos’ review, we want to note that we think that there might be some confusion over baluns and ununs. We wonder if a 9:1 unun (instead of a balun) should be used for a long wire antenna, since a long wire is an unbalanced antenna. We think a balun should be used for a balanced antenna such as a dipole. In his review Akos also found that connecting two longwire antennas to the spring terminals improved reception. This may have possibly been because adding two longwires essentially created a balanced dipole antenna. To implement a longwire antenna unun with a balun, we think that the second terminal and coax shield should be connected to a good ground source like a cold water pipe. If you have knowledge on this topic please comment to confirm or expand on our theory.
The online store Nooelec has recently started selling two new RTL-SDR related products.
The first product is a lower cost RTL-SDR dongle with the E4000 tuner (ebay). The E4000 tuner was one of the original tuner chips used in RTL-SDR dongles when they were first discovered. Unfortunately Elonics, the company that owned the rights to the chip went under and the production of E4000 chips stopped, making them rare and expensive. The E4000 tuner has a tuning range of approximately 55 MHz – 2300 MHz, compared to the R820T tuner which has a range of around 24 – 1766 MHz. The cheaper R820T is better in most cases, but if you need the higher frequencies the E4000 may be an option. The new E4000 dongle is currently selling for around $50 USD, compared to the other E4000 models which went for around $100 USD.
They have also begun selling a low cost 9:1 balun for about $10 USD (ebay) which can be used with a long wire (or random wire) antenna when receiving HF on the RTL-SDR with an upconverter. The impedance of a long wire antenna is approximately 450 Ohms (very approximate, impedance varies with frequency and length). A 9:1 balun allows a match with a 50 Ohm receiver, which is close enough to the 75 Ohm input of the RTL-SDR.