Retrofit SDR Transceiver
for the Price‑Conscious Crowd
Serge Y. Stroobandt, ON4AA
Copyright 2015–2016, licensed under Creative Commons BY-NC-SA
- Retrofit SDR
This page is still under construction.
Over the last ten years, access to vast computing power has become a relatively cheap common good. This has lead to software defined radio (SDR) getting within reach of most radio amateurs. The personal computer (PC) in your shack is, after all, capable of many more things than just contact logging.
- If you have not played yet with an SDR receiver on HF, you should do so right now. One way to experience SDR first hand is on the Internet where many WebSDR receivers are open to the general public.1 Without any doubt, it will leave you convinced about the great potential of software defined radio, not the least as a new weapon in waging the uphill battle against ubiquitous man-made noise.
A couple of new ham gear brands (Flex Radio, Anan) have pioneered their way in this emerging market of 100 watt HF SDR transceivers. However, at the time of writing (2015 AD), the traditional brands (Yaesu, Icom, TenTec, Kenwood) still have to come with a first baseband SDR offering. Even if you are in the market for a new HF transceiver, it is not an easy calling. In a sense, it is still early days for SDR. On one hand, you have an offer of well-designed analog superheterodyne transceivers (like the Elecraft K3S) with all the buttons and knobs and some DSP at IF and/or AF. On the other hand, you have innovative SDR transceivers which directly sample the entire HF band without any prior frequency conversion. Leaving the Expert Electronics MB1 out of consideration —since it is really an SDR and an ordinary PC sharing the same box,— most of these SDR transceivers are lacking control buttons and dials. Edit: The first game changer might well be the Icom IC‑7300, introduced in the second quarter of 2016.
Some SDR transceivers employ your PC for the digital signal processing (DSP), while other have their own dedicated DSP processors. Irrespective of this, a number SDR transceivers will only work with proprietary software on a single proprietary operating system (Microsoft Windows™). SDR transceiver firmware, SDR software and the underlying PC operating system may all be closed source and subject to recurring maintenance and licensing fees.
Personally, I have severe reservations with a proprietary approach to SDR. Yes, high price certainly plays a role, but there are more profound reasons as well. One is that I have grown to rely exclusively on GNU/Linux as an operating system. This happened since that spring day in 2006 when a factory installed Windows™ XP turned a brand new, antivirus protected computer into a spam spewing botnet machine. Secondly, only open-source SDR software will allow twenty-first century ham operators to continue to experiment with wireless technology the way they used to do. Anyhow, experimenting is what amateur radio is all about in the first place!
A 1992 Yaesu FT-990, ROM v1.30. It is important to note that the purpose of this modification is improved receiver performance. weak signal and in-band interference not a band scope This is why the first intermediate frequency (IF1) of 47.210 MHz is tapped after the 40 kHz wide roofing filter and the corresponding IF1 amplifier (Q1013).
p.61 RF UNIT
|1||RXIFOUT||IF1 RX output at 47.210 MHz|
|12||R12||12V on receive|
The receiver of the FT‑990 resembles the second receiver of the FT‑1000.
Clifton Laboratories Z10000B‑U transimpedance buffer amplifier Since IF1 with 47.210 MHz is relatively high, the Z10000B‑U buffer amplifier is built to deliver more bandwidth at the cost of a lower nett nominal gain of only +6.7 dB. This implies that the Z10000B‑U is assembled with a value for R7 = 150R. R5 is kept at the default value of 4K7.
Down‑converter and sampler
A 2008 Intel Core 2 Duo E8500 on a GIGABYTE GA EP45T‑UD3R motherboard with 2× 2GB 1600MHz 7‑7‑7‑20 DDR3 RAM; all bought second-hand on eBay. I added a nice new case, a hard disk and a NVIDIA GeForce® 9500GT graphics card.
By now, you should know that I am picky about OS
Here are my first impressions for SSB signals:
- The FT-990’s RF gain in front of its first mixer can be reduced to a level where the FT-990 will no longer produce any sound whereas the FUNcube Pro+ will still demodulate. Third order IMD is largely attributed to unlinearity in the RF gain stage and the first mixer, so this certainly will have a very positive impact on 3rd order IMD.
- I can hear weak signals with the FUNcube Pro+ which I cannot hear with the FT-990, even if I increase the RF gain back up again.
- Depending on the employed SDR software, one now will be able to use DSP bandpass and notch filters, much sharper than those of the FT-990.
- With reduced RF-gain, the S-meter on the FT-990 no longer produces any useful information.
Other FT-990 modifications
Close with a solder blob JP5002 on the control unit.
1. Pieter-Tjerk de Boer, PA3FWM. WebSDR. Available at: http://websdr.org/.
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Unless otherwise stated, all originally authored software on this site is licensed under the GNU GPL version 3.