I've been playing with radios since I was 10 years old, and I have been a licenced amateur radio operator since 1983.
My current callsign is VE6VQ (actually VE6VQ/W7),
I've also been known as VE4TCP and VE7UDP,
and my first callsign was VE6BOA.
Here's a picture of me at Mt. St. Helens, WA in 2004, listening to Ken, N7IPB,
on the 224.78 Mhz repeater in Mt. Vernon, some 200 miles to the north!
Packet Radio
In 1989, a friend and colleague of mine, Mr. Stephen Mead,
VE6UF, and I installed one of the first amateur packet radio
satellite "wormholes" between Calgary and Ottawa, Canada in August
of 1988 (the Calgary node had the callsign VE6PAK). The satellite
link was provided by
Telesat Canada
, and provided an asynchronous 9600 baud link between the
two cities. We attached the standard 1200 baud AX.25 modems and
radios at the Calgary end and voila, we had a (relatively) fast,
reliable link between Calgary and Ottawa. Many many megabytes of
e-mail and message traffic were carried on this link, and I believe
that it is still operational today. One key thing to remember about
this link is that no one has ever paid a cent for any use of it,
which differentiates it from the IPARN network and is more in
keeping with the amateur radio spirit, in my humble opinion.
Confessions of a High-end Receiver Addict
After spending many years and many dollars on receivers, I must confess that the receiver is only one leg of the triad of successful radio reception. The other two legs are antennae and location . Unfortunately these two can be much more inconvenient and vastly more expensive than receivers are (unless you get into the habit of "paying retail" for military radios).
Many years ago, I started thinking about the ultimate receiver, and what it would be like. I began collecting references and articles about receiver design and associated topics. I call this my homebrew receiver project, and although it hasn't gone far yet, recent technological advances, such as DDS synthesizers and DMOS FETs are making it more and more feasible.
In 1994, I wrote an (incomplete) series of articles outlining modern receiver design for the Canadian International DX Club (CIDX) newsletter "The Messenger". I'll update and finish the rest of this series one day when I feel sufficiently guilty and idle. I've put links to them here:
My most used radio at the moment is an AR7030 (warning - 460 kb PNG file) HF receiver from AOR . This little box from England is a jewel. It makes heavy use of state-of-the-art components and computer control techniques to create a modestly priced receiver that can give the military/government vendors a run for a quarter of the money. The first mixer uses DMOS FETs, and is fed by an ultra low noise DDS synthesizer. This, plus judicious use of roofing filters and IF filter cascading gives this set an incredible +32 dBm third-order intercept.
Recent rumors indicate that the AR7030 is no longer in production and that only existing stocks remain available for purchase. The successor is alleged to be designated the AR7070, but my opinion is that it is going to be very difficult to reproduce the "bang for the buck" that the AR7030 created when it arrived.
Ialso purchased (and subsequently sold) a Collins HF-2050 HF receiver which was used by the Canadian Military. What is unique about this radio is that the first IF is 99 Mhz, the second IF is 3 Mhz, and everything after the 2nd IF is done digitally. All of the filtering, detection, bandpass tuning, etc. is done in the digital domain. I consider it to be a mark of high distinction indeed to have such a modern receiver compared quite favorably to the venerable Collins R-390 boatanchor by none other than Chuck Rippel, Mr. R-390 himself.
My Receiver Gallery
These are receivers I have (or still do, or hope to) own. As time goes on, I will add a few notes regarding my own impressions of these sets. My favourites would have to be (thus far) the Drake R-7 and SPR-4, although my AOR AR7030 is definitely starting to spoil me!
Heathkit GR-78
(picture by Bryce, KI0LE)
Yaesu FRG-7700
Drake SSR-1
Racal RA-17
Sony CRF-1
AOR AR7030
Software Defined Radio Era
There has been a lot of discussion on the Premium-RX mailing list about the relative merits of DSP-based receivers, which are fairly recent arrivals in the world of communications receivers.
There are three main components to receiver performance:
- Front-end, mixers, RF/IF stages to the detector
- The detector
- The audio stages and speaker/headphone following the detector
I would suggest that perhaps one of the reasons that DSP-based receivers seem to have an edge over others is that a DSP implementation of a detector is likely quite perfect as compared to an analog circuit.
I think the state of audio amplifier design is quite good, and due to the proliferation of "hi-fi" and stereo consumer electronic equipment the quality of the audio stages is generally quite good, and technical specifications for these audio stages are quite well evolved. e.g.:
- output power: 2.5 watts into 4-16 ohms
- frequency response: 20-20,000 Hz +/- 3 dB
- distortion: 0.01% total harmonic distortion
- hum and noise: 70 dB down
RF specifications are also fairly well evolved. However, very rarely do you see any specifications for distortion or sensitivity for an AM detector. I would submit that this is the real weak spot in many receivers, and perhaps even one that is often neglected in favour of a focus on the "sexier" RF parameters like IP3 and MDS. The Collins HF-2050 has exceptional detectors because it's likely that the Collins engineers had to design them from scratch, in the DSP. In a receiver with an analog detector implementation, the tendency would be to throw in a diode for an AM detector and call it a day. Rarely, people do pay exceptional attention to detector design; For example, the Drake SPR-4 design for the AM detector took into account the defects of real-world semiconductor diodes. To overcome the forward bias gap of the diode, a small DC offset voltage was applied to the AM detector diode.
So, does anyone have any good ideas for quantitative specifications for detector stages?
FlexRadio SDR-1000 Transceiver
Software Radio Era
The simultaneous emergence of:- High performance integrated analog-to-digital converters (ADCs)
- Fast, inexpensive programmable gate arrays (FPGAs)
- Low cost, low jitter/phase noise clock sources
- Commodity priced PCs with high speed USB interfaces, large memories and fast CPUs
have combined to make it possible to develop radio systems that used to cost many orders of magnitude more, and were exclusively in the realm of exotic government and military users.
These are differentiated from earlier, software defined radio systems by the fact that the entire radio is implemented by a combination of high speed digital logic and software. There are no significant analog components in the signal path of such a radio, other than the ADC.
Of the items listed above, the most critical to SDR performance is the ADC. The receiver frequency range is determined primarily by the sampling frequency of the ADC, and the dynamic range and noise figure are determined mostly by the resolution of the ADC (i.e. the number of bits per sample) and the quality of the ADC clock signal.
Although earlier ADC generations have been successfully used in amateur/hobbist SDR receivers, the most recent 14 and 16 bit ADCs from Analog Devices have enabled the development of receivers (e.g Ettus Research USRP, Rfspace, Perseus) that are both inexpensive in comparison to conventional receiver designs and very competitive in terms of performance.
My main interest in HF radio listening is stations which are called "Utility" stations, because they are neither broadcasters, nor amateur radio operators. This domain takes in ships at sea, aircraft, military, governments and embassies, and mysterious "spy numbers" stations.
I especially enjoy listening to the long-distance operational control (LDOC) of commercial aircraft. The communications are worldwide, and the bands used are uncrowded. I provide an audio feed to the LiveATC website for the NAT-D region.
I remain hopeful that newer technologies like ACARS and HFDL don't arrive too soon and that we will have a few more years of enjoyment listening to voice traffic on the HF aeronautical bands.
