Category Archives: Guest Posts

Guest Post: Joris’ home brew Si4835-based receiver

Many thanks to Joris van Scheindelen (PE1KTH)–an SWLing Post contributor from the Netherlands–for the following guest post:

High Tech AM-FM DSP Receiver From

The old mode AM is still an interesting mode for amateur radio communication, also in amplitude CW.

Building your receiver is not difficult and quite fun. The semiconductor industry makes interesting integrated receiver chips today that will be useful for an AM receiver. Not only for broadcast reception but also for amateur AM reception or as part of an AM transceiver.

Silicon Labs also makes Si4734/35 receivers; these need a CPU to control the receiver, but are of interest for amateur use because the frequency can be tuned in 1 KHz steps and the audio channel bandwidth in 7 steps. There is no need for the transmitter to be on the receiving channel…

Si4835 AM-FM receiver

Looking for a small SW broadcast receiver design, and pocket size, I came to the excellent range of modern DSP receivers in a single chip from Slicon Labs.

I made a test bed set up has been made for the Si4835 AM-FM receiver.

The target specification was:

minimal components,
no micro-controller,
low power,
backlash free mechanical tuning,
good sensitivity,
earphone,
robust housing,
a short and small antenna system for outdoor use,
and minimal controls.

The Si4835 makes miniature design possible on a PCB (see photo Figure 1).

The red Dip (band) switch was replaced by a rotary switch in the final receiver design (Figure 4).

The receiver power is minimal 2 x 1.2 = 2.4 volts or a one cell LI-ION accu.
5 volts is the maximum for the Si4835 chip; current consumption is 30 mA.

Fig 1. Testbed setup for the Si4835.

The receiver has an RF pre-amplifier transistor and the LF amplifier is the TDA7050T.
All receiver functions are in the chip; the schematic is very simple and can be built with minimal components (see schematic appnote AN555 Fig 2. below).

Only an LF amplifier has to be added to complete the receiver.

Fig 2. Receiver schematic Si4835 in the AN555 application note.

The Si4835 receiver has the following frequency bands–they are divided in sub bands 800 or 900 KHz wide (See Figure 3). The frequency step tuning is 10 kHz on AM, following the international broadcast raster standard.

Fig 3. Si4835 receiver sub bands.

This means there are 80 or 90 receive channels in the sub bands and make finding the BC stations on the scale more easy. The 10 KHz scale steps are linear. The frequency stability is locked to the 32 kHz X-tal via the synthesizer so there is no frequency drift. The AM LF audio channel is 5 kHz wide set by the DSP filter. Volume control can be done width 2 up-down push switches or by a LF potentiometer..

Fig 4. The experimental pocket aluminium receiver housing on PCB2.

Receiving results

I have been testing many hours and I am surprised about this little receiver.

The receiving results are excellent on FM and AM and signals of 2 -3 uV are well received.

Also the audio quality is good–especially on FM. As can be seen in the frequency table the 40 and 20 meter band are in the range. Clear AM phone amateur transmission has been received when the transmitter was tuned on the 10 kHz raster in 40 meter band on AM.

Also AM modulated CW signals can be received bud not un-modulated carrier CW–they sound “plop…plop”.

The 5 kHz wide LF channel is a bid too wide so many CW signals pass through the audio at the time, but if AM modulated that should not be a serious problem.

The broadcast stations in the SW bands (when the daytime conditions are good) up to 20 MHz are good and strong.

Conclusions

The Si4835 receiver can be a fine broadcast receiver for outdoor work and if an AM transmitter is tuned in the 10 kHz raster this receiver can also used for amateur phone reception.

Addendum: The Si4734/35 is a better amateur AM Receiver

The Si4734 and Si4735 are a better receiver choice for amateur AM purpose because the frequency tuning can be done in 1 kHz steps. Also the BW of the LF channel can be adjusted to 1 kHz wide.

In Fig 5. from the programming APP note you see the code 0X3102 AM CHANNEL_FILTER it is possible to adjust the audio width by sending this code to the Si4734/35.

Fig 5. From the programming APP note

The LF bandwidth can be set on 1, 1.8, 2.5, 2, 3, 4 and 6 kHz wide.

This is excellent for modulated CW and AM phone discrimination in the audio channel.

The disadvantage is the need of an CPU and LCD display, “away from a minimalistic design”.

See also the note 1 and 2 improved 100 Hz rejection. See data sheet of the Si4734/35.

It look like that this receiver is a good receiver for building a modern AM-(AM)CW receiver or in a transceiver application. Tuning can be done digitally.

Think about this receiver [and the Si4835 chipset] when you intent to build a high tech AM – T/RX.

73 ‘ Joris van Scheindelen PE1KTH

What a fantastic home-brew receiver, Joris! I love the simple design of your receiver and the fact that it’s quite portable. Thanks so much for sharing your notes and documentation.

Frank shares 1991 recordings and original notes of station IDs and interval signals

1 Reply

SWLing Post reader, Frank, writes from Germany:

First let me say that I enjoy your blog a lot.

After a 2005-13 hiatus, I have rediscovered a childhood hobby and your reviews have helped me find my way to the post-Sony portable shortwave radio markets.

First, I obtained my “childhood dream” radio (Sony ICF 2001D), because at the time I made these recordings I was still in school and 1300 DM would have equaled over 1 year of pocket money, so a Supertech SR16HN had to do. I thought I got some fine results with this Sangean-Siemens re-branded receiver then, using a CB half-length antenna, a random wire, and much endurance.

The Supertech SR16HN (photo: Radiomuseum.com)

I kept regular logs throughout the years, wrote to 50 international and pirate stations for QSL and compiled this cassette.

A few years before I got that trusty SR16HN, however, I recorded a few number stations (such as G3, Four Note Rising Scale etc) with an ordinary radio cassette recorder, and in 1991 I put them onto this tape as well. The other recordings are done with the same radio placed right in front of the SR 16HN.

Feel free to make use of these recordings. Most of it are the well-known international state-owned shortwave stations of the past; plus European pirates; plus number stations; and at the end, a few (off-topic) local Am and FM stations interval signals.

As I said, this collection I made shortly after the Wende/reunification period, when all former-GDR state broadcasters changed their names, sometimes more than once.

Please continue your good work on the blogs! Weather permitting I am often outside cycling and always have the tiny Sony ICF 100 with me (which I call my then-student’s dream radio of the later 90ies).

Cassette Side 1

Frank’s original hand-written notes. Click to enlarge.

Click here to download Side 1, or listen via the embedded player below:

Cassette Side 2

Click to enlage.

Click here to download Side 2, or listen via the embedded player below:

Wow! Frank, what a treat to listen to all these station IDs!

I had forgotten how many interval signals have changed over time and how many, of course, have disappeared. This tape represents a flood of nostalgia for me.

I should add, too, that I’ve enjoyed hearing so many IDs in German. It’s funny, but we all get hooked on listening to language programming from our native or second languages. It makes me realize just how many broadcasters used to have German language services.

Again, many thanks, Frank, for taking the time to digitize these recordings and scan your original hand-written notes. This stuff is invaluable, in my book!

Ken’s low-profile, low-cost vertical antenna

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Ken’s antenna “deployed” in his back yard.

SWLing Post reader, Ken Hansen (N2VIP), writes:

A few months ago I purchased a couple S9V18 18′ vertical antennas for $65 at cheapham.com, with the intention of deploying a quick HF aerial at my HOA-laden home for ham radio use. I found they work great for SWL.

The S9V18 antenna is made to slip over a 1″ o.d. pipe driven into the ground at least a foot, with 12″ of the pipe rising off the ground. You can pound a two foot pipe half-way into the ground, or do as I did and fill a bucket with cement and stick the pipe in that half-way.

This is a ‘close-up’ of the bucket. Note the plate the ground radials are attached to–it’s from Home Depot, it’s a bus bar designed to bond the ground wire for each circuit in a breaker box.

After adding a reasonable ground plane of 8x 14 ga wire cut about 15′ long I hooked up a 4:1 balun and ran it to my Kenwood TS-570D.

What I found was the aerial not only worked well on 20 meters, it also made a great shortwave aerial! Stations were booming in here in Texas at night.

The antenna slides over the pipe sticking out of the concrete in the bucket. Here is a picture of the bucket before the antenna base is slipped over it.

My ‘discovery’ was that a nice, modest vertical antenna can really improve reception on SW bands…

Cheapham.com sells the S9V18 antenna on close out for $35/each, the 2′ pipe is a few dollars more, add in a bit of coax and a modest ground plane and you can really up your SWL ‘game’.

Antenna on closeout:

http://www.cheapham.com/s9-v18-18-vertical-antenna-closeout/

I suggest anyone buying this antenna seriously consider buying additional clamps at the same time, they are just a few dollars and will help extend the life of the antenna:

http://www.cheapham.com/products/S9V18-Replacement-Clamps.html

For shortwave broadcast listening a direct connection without balun would probably suffice, but I used an LDG 4:1 balun to support multi-band ham transmitting:

http://www.cheapham.com/rba-4-1-voltage-balun/

Just thought I’d share my ‘discovery’…

And we thank you for sharing your discovery, Ken! This is a great, simple solution for those who cannot erect a permanent “high-profile” antenna. I’m especially impressed with how budget-friendly your solution is, Ken.

Post Readers: If you have other suggestions for inexpensive low-profile antennas, please contact me or comment below!

Guest Post: Brian’s 1974 mix tape of off-air shortwave radio recordings

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Many thanks to SWLing Post and Shortwave Radio Audio Archive contributor, Brian Smith, for the following guest post and vintage recording:

Shortwave Radio 1974: Canada, Argentina, Spain, West Germany, Albania, utility stations

-Brian Smith (W9IND)

Want to know what shortwave radio sounded like in 1974? This 55-minute recording, recovered from a cassette, was never intended to be anything but “audio notes”: I was an 18-year-old shortwave listener who collected QSL cards from international stations, and I was tired of using a pen and a notepad to copy down details of the broadcasts. I wanted an easier way to record what I heard, and my cassette tape recorder seemed like the perfect means to accomplish that goal.

But it wasn’t. I soon discovered that it was simpler to just edit my notes as I was jotting them down — not spend time on endless searches for specific information located all over on the tape. To make a long story shorter, I abandoned my “audio notes” plan after a single shortwave recording: This one.

Hallicrafters S-108 (Image source: DXing.com)

Still, for those who want to experience the feel of sitting at a shortwave radio in the mid-1970s and slowly spinning the dial, this tape delivers. Nothing great in terms of sound quality; I was using a Hallicrafters S-108 that was outdated even at the time. And my recording “technique” involved placing the cassette microphone next to the radio speaker.

Thus, what you’ll hear is a grab bag of randomness: Major shortwave broadcasting stations from Canada, Argentina, Spain, Germany and Albania; maritime CW and other utility stations; and even a one-sided conversation involving a mobile phone, apparently located at sea. There are lengthy (even boring) programs, theme songs and interval signals, and brief IDs, one in Morse code from an Italian Navy station and another from a Department of Energy station used to track shipments of nuclear materials. And I can’t even identify the station behind every recording, including several Spanish broadcasts (I don’t speak the language) and an interview in English with a UFO book author.

The following is a guide, with approximate Windows Media Player starting times, of the signals on this recording. (Incidentally, the CBC recording was from July 11, 1974 — a date I deduced by researching the Major League Baseball scores of the previous day.)

Guide To The Recording

00:00 — CBC (Radio Canada) Northern and Armed Forces Service: News and sports.
07:51 — RAE (Radio Argentina): Sign-off with closing theme
09:14 — Department of Energy station in Belton, Missouri: “This is KRF-265 clear.”
09:17 — Interval signal: Radio Spain.
09:40 — New York Radio, WSY-70 (aviation weather broadcast)
10:22 — Unidentified station (Spanish?): Music.
10:51— Unidentified station (English): Historic drama with mention of Vice President John Adams, plus bell-heavy closing theme.
14:12 — Unidentified station (Spanish?): Male announcer, poor signal strength.
14:20 — Unidentified station (Spanish): Theme music and apparent ID, good signal strength.
15:16 — Unidentified station (foreign-speaking, possibly Spanish): Song, “Chirpy Chirpy Cheep Cheep.”
17:00 — Deutsche Welle (The Voice of West Germany): Announcement of frequencies, theme song.
17:39 — Unidentified station (English): Interview with the Rev. Barry Downing, author of “The Bible and Flying Saucers.”
24:36 — One side of mobile telephone conversation in SSB, possibly from maritime location.
30:37 — Radio Tirana (Albania): Lengthy economic and geopolitical talk (female announcer); bad audio. Theme and ID at 36:23, sign-off at 55:03.
55:11 — Italian Navy, Rome: “VVV IDR3 (and long tone)” in Morse code.

Click here to download the recording as an MP3, or simply listen via the embedded audio player below:

Brian, this is a brilliant recording–regardless of audio quality–and we’re very thankful you took the time to share it. Propagation has left something to be desired as of late, so time traveling back to 1974 has been incredibly fun.

Post Readers: If, like Brian, you have off-air recordings on tape that you’d like to share, please contact me! Even if you don’t have the means to transfer your tapes to a digital format, I’m a part of a small community of shortwave radio archivists who would be quite willing to help.

Guest Post: Richard tests the frequency stability of the Tecsun PL-880

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Many thanks to SWLing Post contributor, Richard Langley, for the following guest post:

Frequency Stability of My Tecsun PL-880

Recently, while recording the audio on a particular SW frequency unattended over night, I decided to set my Tecsun PL-880 in USB mode with the 3.5 kHz RF bandwidth setting as I had previously noticed splatter QRM from a station 10 kHz below my frequency of interest. I adjusted the frequency to the nearest 10 Hz for natural-sounding voice. On playing the recording, I was disappointed to find that the signal had drifted in frequency and although speech was still recognizable, music was distorted.

I decided to try to measure the stability of the receiver by recording the Canadian time signal station CHU on 7850.00 kHz in USB mode (CHU has no LSB component) over night for over nine hours. The receiver was operated with just its telescopic whip antenna indoors and the audio was recorded with a Tecsun ICR-100 radio recorder / digital audio player. I wrote a Python script to compute the audio spectrum of each one-minute segment of the recorded files using a fast Fourier transform (after removing a DC component). The script then looks for the largest peaks in the spectra centred on a specified frequency and prints out the frequency (to the nearest Hz) and amplitude of the peak. In case the signal has dropped below audibility, a threshold is set and if the detected peak is below the threshold (likely just detecting the random noise background), it is skipped. The specific centre frequency I was looking for was 1000 Hz, the frequency of the tone used to mark each second of the CHU broadcast except when the voice announcement and digital signal are transmitted. In AM mode, the spectrum would consistently show a peak at 1000 Hz but in SSB mode, the peak will vary depending on the receiver frequency setting and the actual frequency of the receiver’s oscillator.

The plot below shows the received CHU one-second tone frequency as a function of time (UTC) from when the receiver was first switched on.

StabilityPlot-CHU1000hz

It shows the tone frequency started out at about 1046 Hz slowly dropping in the first half hour to about 1012 Hz and after about an hour stabilized to 1011 Hz ± 1 Hz for the better part of an hour. (This shows that you may have to allow a receiver to “warm up” for perhaps up to an hour before attempting anything close to accurate frequency reading at the order of 10 Hz.) But then, over the course of the next seven hours when the signal was audible, the frequency slowly rose ending up at about 1034 Hz. The variation might be affected by the ambient air temperature (but this should have been nearly constant), air flow around the receiver, and perhaps the charge level of the receiver’s battery. On several occasions, I have turned the receiver on (after being off for many hours) and seen a CHU frequency offset of only 10 or 20 Hz. So, I intend to repeat this experiment sometime to check on the day-to-day frequency stability. This frequency stability measurement technique could also be used with WWV/WWVH by recording the 440, 500, or 600 Hz tones broadcast at different times during the broadcast hour.

Of course, it’s also possible to check the receiver’s frequency offset in real time by switching between AM and SSB modes while adjusting the receiver frequency in 10 Hz steps until the signal sounds the same in both modes. There is also freely available computer software for various operating systems that can display a real-time spectrum of audio passed to it through a microphone or line input. So, a CHU or WWV/WWVH test using such software could also be performed in real time. And alternatively, by tuning say exactly 1 kHz away from the transmitted carrier frequency in SSB mode, the software can be used to measure the audible heterodyne frequency to better than 10 Hz — even 1 Hz. This frequency can then be added or subtracted as appropriate to the dial reading (assumed accurate or with a noted offset) to get the exact transmitted carrier frequency.

By the way, it is possible to calibrate and reset the PL-880 using the procedure documented on the SWLing Post (click here to view).

As a side benefit of the analysis I carried out, we can also look at the quality of the received signal over the recorded interval. In this case, it is a measure of the level of a particular audio frequency rather than the RF signal+noise level we usually get from the receiver S-meter or other signal strength display. This is illustrated in the plot below for the CHU recording. As you can see, reception was mostly quite good between about 02:00 and 04:00 UTC and then became fair but above threshold level until about 05:30 UTC.

The signal was then essentially inaudible up to about 08:00 UTC when with bouts of fading it became audible again for an hour or two with sunrise approaching.

— Richard Langley

Mike’s thrift store find: a Panasonic RF-888

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Mike's Panasonic RF-888 (left) and his GE Super Radio II (right)

Mike’s thrift store Panasonic RF-888 (left) and his GE Super Radio II (right)

SWLing Post contributor Mike (K8RAT) writes:

I happened upon a good find of a vintage radio recently when I visited my local Goodwill store in a small city in Ohio.

Among the electronic equipment on a shelf I discovered a Panasonic RF-888. I was not familiar with this radio. The large speaker along with switches and knobs for features found on the better radios impressed me.

The price on the sticker read $3.50. I paid at the counter and motored away not knowing what a bargain I had received.

The RF-888 audio is very good on FM and good on AM. Sensitivity and selectivity are very good on both bands. The tuning meter is useful.

I recommend visits to local second-hand stores. You never know what you might find.

Mike, K8RAT

Many thanks for sharing this story, Mike, as it provides a good lesson for us all: never pass by a thrift store! I’ve never had the good fortune of finding a gem like the RF-888–or a Sony ICF-2010 like Vlado–but I shall keep searching.

Panasonic RF-888s sell on eBay for $100 US and higher–at $3.50, I’d say Mike snagged a deal.

Radio Cook Islands: Guy’s 1993 recordings

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Many thanks to SWLing Post contributor, Guy Atkins, for the following guest post:

Radio Cook Islands

by Guy Atkins

A view from the driveway entrance to the Radio Cook Islands studio in 1993. Insulators on an antenna (T2FD or multiband dipole) can be seen as dark spots against the cloudy sky. A feedline is also seen rising above the left side of the building. (Photo: Guy Atkins)

(Photo: Universal Radio)

In 1993 I was fortunate to have the opportunity to visit Rarotonga with my wife, courtesy of a nice award through my company which afforded me an all-expenses-paid trip anywhere we’d like to go.

I chose the South Pacific island of Rarotonga, partly because I wanted to visit Radio Cook Islands after listening to their “island music” on 11760 and 15170 kHz through my teenage years.

During our visit to the island I recorded 90+ minutes of RCI on 630 kHz with a local quality signal using a Grundig Satellit 500 and a Marantz PMD-221 recorder.

Recordings

The programming of Radio Cook Islands is bilingual, and announcers are fluent in both English and Cook Islands Maori. Music selections on RCI encompass all styles, to appeal to many age groups. These recordings was scheduled to include as much local music as possible.

RCI programming includes all the hallmarks of a small, non-professional station: stuck records & tape carts, dead air, poor modulation, and other miscues.

However, that’s part of the flavor of local radio, and these errors are heard throughout this recording. Particularly noticeable is the bassy, over-modulation of the studio announcer during sign-on announcements.

Recording 1

Notes: National anthem & hymn; sign-on announcements & music.
Music; weather; sign-off announcements & national anthem.
Local & regional news; weather; ads; music.

Recording 2

Notes: “Party Time” music request show; weather; local ads; more music.

Two engineers from Radio Cook Islands, photographed during my visit in April, 1993. (Photo: Guy Atkins)

Sadly, RCI will likely never be on shortwave again; a fire in the local tele-comm building a few months before my 1993 visit destroyed RCI’s transmitter. I had an amusing exchange with the secretary when I visited; she insisted that their station was still on shortwave. Of COURSE we’re on the air she said, because “the frequencies are published right here in the newspaper!” The engineer and announcer confirmed, though, that the silence on their former frequencies was for real. They indicated they were covering the outer islands just fine with FM translators and had no intention of restarting shortwave.

Radio Cook Islands 630 kHz antenna on the school ground of Takitumu Primary School.

RCI’s headquarters is in downtown Avarua, and their 5 kw transmitter (reported at half power, 2.5 kw in Dec. 2012) and modern quarter-wavelength vertical antenna is located in the town of Matavera (northeast side of Rarotonga).

Bing.com maps view of Radio Cook Islands antenna, 630 kHz at Takitumu Primary School, Matavera.

The antenna is in the yard of Takitumu primary school; see photos from Bing Maps and Panaromio [above].

It sure brings back a flood of good memories when I listen to these MP3s! I’d love to visit the Cooks again sometime.

Many thanks for this wonderful stroll down memory lane, Guy–radio nostalgia at its best!

I, too, would love to visit the Cook Islands someday–it is on my bucket list. In the meantime, I’ll enjoy your recordings. Again, many thanks for your guest post!