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Retrofit SDR Transceiver
for the Price‑Conscious Crowd

Serge Y. Stroobandt, ON4AA

Copyright 2015–2016, licensed under Creative Commons BY-NC-SA

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Introduction

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.

WebSDRWebSDR
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!

Hardware

Yaesu FT-990 HF transceiver

Yaesu FT-990 HF transceiver

IF1 tap

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).

Block diagram

Block diagram of the Yaesu FT-990 receiver front-end; The 47.210 MHz SDR signal is tapped at the output of the Q1013 IF1 amplifier (between the first and second block from the left).

Block diagram of the Yaesu FT-990 receiver front-end; The 47.210 MHz SDR signal is tapped at the output of the Q1013 IF1 amplifier (between the first and second block from the left).

RF unit

Schematic detail of the Yaesu FT-990’s RF unit, showing jumper J1002, RF transformer T1013 and transistor Q1013

Schematic detail of the Yaesu FT-990’s RF unit, showing jumper J1002, RF transformer T1013 and transistor Q1013

p.61 RF UNIT
T1013

RF unit header J1002 tap connections
pin № label description
1 RXIFOUT IF1 RX output at 47.210 MHz
2 GND transceiver ground
12 R12 12V on receive

The receiver of the FT‑990 resembles the second receiver of the FT‑1000.

Buffer amplifier

Yaesu FT-990 RF unit tapped at IF1 with the Z10000B‑U buffer amplifier (red printed circuit board).

Yaesu FT-990 RF unit tapped at IF1 with the Z10000B‑U buffer amplifier (red printed circuit board).

The RF unit board retrofitted with the IF1 tap fits snugly within the innards of the Yaesu FT-990 HF transceiver.

The RF unit board retrofitted with the IF1 tap fits snugly within the innards of the Yaesu FT-990 HF transceiver.

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

The FUNcube Dongle Pro+ and its specifications.

The FUNcube Dongle Pro+ with and without its plastic housing.

The FUNcube Dongle Pro+ with and without its plastic housing.

The FCD Pro+ received a new shielded housing. Spinning the USB cable ten times over a FT-140-43 ferrite core results in an effective sheath current choke, keeping PC noise out.

The FCD Pro+ received a new shielded housing. Spinning the USB cable ten times over a FT-140-43 ferrite core results in an effective sheath current choke, keeping PC noise out.

The shielded FUNcube Dongle Pro+ mounted on the modified Yaesu FT‑990 with a strip of 3M™ Dual Lock™ hook & loop fastener.

The shielded FUNcube Dongle Pro+ mounted on the modified Yaesu FT‑990 with a strip of 3M™ Dual Lock™ hook & loop fastener.

Firmware upgrade

Upgrade the FUNcube Pro+ firmware with Qthid, available as qthid-fcd-controller in Debian derived GNU/Linux distributions.

Computer

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.

SDR software

By now, you should know that I am picky about OS

gqrx employs GNU Radio components.

About 16 kHz of low-noise pass band at 47 MHz is available for demodulation by gqrx. The dial of the FT-990 transceiver is used to tune through the HF spectrum. Razor-sharp bandpass filtering by gqrx keeps nearby interference at bay.

About 16 kHz of low-noise pass band at 47 MHz is available for demodulation by gqrx. The dial of the FT-990 transceiver is used to tune through the HF spectrum. Razor-sharp bandpass filtering by gqrx keeps nearby interference at bay.

Best results are obtained by setting the RF gain of both the transceiver and the various FUNCube Dongle Pro+ stages (LNA, MIX & BB) to an absolute minimum. FCD Pro+ gain settings can be configured through the gqrx software.

Best results are obtained by setting the RF gain of both the transceiver and the various FUNCube Dongle Pro+ stages (LNA, MIX & BB) to an absolute minimum. FCD Pro+ gain settings can be configured through the gqrx software.

First impressions

Here are my first impressions for SSB signals:

Other FT-990 modifications

TX 1.8–30MHz

Close with a solder blob JP5002 on the control unit.

References

1. Pieter-Tjerk de Boer, PA3FWM. WebSDR. Available at: http://websdr.org/.

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Last update: Wednesday, March 29, 2017.