Monthly Archives: September 2015

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.

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Shortwave Radio Recordings: Radio Spaceshuttle International

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SWLing Post and SRAA contributor, Jim Clary (ND9M/VQ9JC), recorded the following final broadcast of Radio Spaceshuttle International while on board a US Navy ship off the coast of Rota, Spain. Jim notes:

I was packing up to leave my ship and return to the USA this week when the latest SWLing Post e-mail showed up with info about SSR’s final broadcast literally seven minutes before he was to come on the air. I’d already broken down the receiving gear, but it came back together in record time, and I was able to get the recorder going with a minute before the transmission started.

Click here to download Jim’s recording as an MP3, or simply listen via the embedded player below. Note that Jim’s recording starts a few minutes before the broadcast begins:

Jim, thanks so much for putting all of your receiver and recording kit back together to make this recording!

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Kim Elliott on shortwave radios & signal jamming in 2015

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(Source: USC Center on Public Diplomacy)

BBC Russian Wants to Expand, But It’s Not So Easy

The BBC, as part of its 2015 Charter Review document, announced proposals to “invest” in BBC World Service. This includes a desire for a “bigger digital presence in Russian through a new digital service on platforms such as YouTube and the Russian equivalent Rutube, together with TV bulletins for neighbouring states. We would also start a feasibility study for a satellite TV channel for Russia.”

[…]The feasibility of BBC satellite TV for Russia is problematic. Very few Russians have rotatable satellite dishes, surfing the Clarke Belt in search of outside news. About 25% of Russian homes have fixed Ku-band satellite dishes to receive proprietary domestic direct-to-home services such as TricolorTV and NTV+. Western Russian-language news channels are not included in these channel packages and are unlikely to be invited aboard. Content from Western Russian-language broadcasters, including Voice of America and Radio Liberty, is also legally not welcome on Russian domestic terrestrial television and radio stations.

[…]So far, Russia has not blocked the Internet content of Western international broadcasters, at least not on a continuous basis. The Kremlin’s repeated denials of any intent to block Internet content suggest that it has at least been thinking about it. And recent press accounts indicate that Russian authorities may even try to ban anonymizers and other methods used to work around online censorship. Circumvention tools would have to become even cleverer, and Russian users would have to be willing and able to use them. In an extreme scenario, Russia could physically cut off the landlines of Internet traffic into the country. Then no circumvention tool within the Internet Protocol would work.

This could bring BBC Russian full circle to the venerable but unfashionable medium of shortwave radio. To be sure, Russians are out of the habit of listening to shortwave. Shortwave is no longer used for domestic broadcasting in Russia. BBC Russian eliminated its shortwave broadcasts in 2011. But, if need be, Russians could dust off their Cold War era shortwave radios. Or they could purchase inexpensive Chinese-made portable radios with shortwave bands.

In addition to traditional voice broadcasts, text, images, and even formatted web pages can now be broadcast using existing shortwave transmitters, and received on any shortwave radio. The audio must be fed to a PC or mobile device equipped with appropriate (free) software. Such a method allows reception of content even in difficult reception conditions, and allows unattended reception. This new capability of existing shortwave broadcast technology has been demonstrated through the VOA Radiogram experiments.

If Russia blocks Internet content from abroad, it will also probably try to jam shortwave radio content from abroad. Most jamming transmitters of the Cold War era have been dismantled or have fallen into disrepair. Many of the jamming transmitters are outside of Russia, in former Soviet republics. Reviving a shortwave jamming apparatus would be a much more expensive proposition than blocking Internet content. Various Cold War anti-jamming tactics, using various tricks of ionospheric propagation, can be employed. Text via shortwave would be even more resistant to jamming than voice broadcasts.[…]

Read the full article by Kim Andrew Elliott at the USC Center on Public Diplomacy online.

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Radio Spaceshuttle International: another attempt at a final broadcast

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I just received word from Dick at Radio Spaceshuttle International. Last week, they had technical difficulties which prevented them from transmitting their final broadcast.

Fortunately, RSI is making a third(!) attempt to get the show on the air. Dick has informed me that Radio Spaceshuttle International will broadcast tomorrow (Sunday) September 20 from 19:00-20:00 UTC on 13,600 kHz.

By the way, I asked Dick why he was leaving the air. He told me that it’s simply a matter of time–something he has in short supply right now. Will RSI return to the air sometime in the future? Dick responds:

So, I shall not say final goodbyes…. Hopefully Radio Spaceshuttle will return “on some sunny weekend”

Very good. We’ll be listening! Speaking of which, I will make an effort to hear the RSI broadcast tomorrow, State side, if propagation is in my favor.

Let’s hope the third time is the charm!

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Hearing shortwave on the Sony SRF-59 AM/FM walkman

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The Sony SRF-59

SWLing Post reader, Steve, writes:

I check in on your blog frequently. I’ve been a casual SW and AM dxer since my childhood. I’m a mechanical engineer, and have some basic electronics knowledge, but I’m no RF expert, and half forgot most of what I used to know.

On 9-13-15, around 11am eastern time, I was playing with a Sony SRF-59 down low on the AM band. The lowest station I can hear at my location near Valley Forge PA is a Spanish language station on 540–WLIE, on Long Island I think. My dial is badly calibrated but I know I was below that station on 540, maybe even below 530 or 520, and heard some noise. It took some really careful back and forth tuning, but I could hear a voice. I put the radio against my AN200 passive loop and heard the clear unmistakable voice of “Brother Scare”, (Overcomer Ministry). I scanned the shortwave and found a simulcast on 9840, WHRI Cypress Creek SC. The info I have says it’s a 250 kW broadcast.

Grundig AN200 Loop Antenna

I scratched my head and thought there must be a pirate rebroadcasting it on the bottom of the AM band, but I couldn’t hear it on my CC 2E, or my Grundig G3 which tunes continuously from LW into MW. It is really touchy to tune on the SRF-59, but with work, I could hear him barefoot, and very cleanly with the loop. I checked in several times the next few hours and it was there until WHRI went off the air at 3pm I think. Unfortunately, I never got a station ID.

On the morning of Monday Sept 14, at 9pm local time, with the same radio and loop, I got a station ID for China Radio International, and then found the same broadcast on 9570 from Quivican Cuba–also a 250 kW signal. I could not hear it clearly barefoot, as with WHRI, (it is quite a bit more distant) but with the loop is was incredibly clear. Also it doesn’t seem to matter where the tuning dial on the loop is, or how it’s oriented (I was aimed east/west). The radio and loop both function normally higher up the AM band (you need to tune the loop, and the reception is amazing with it).

I know I was below 540, because I passed local stations on the way down–610(WIP), and 560 (WFIL)–and could hear Spanish voice just below that, which had to be 540. The shortwave was just below that. The only thing i get below that on any other AM radio is Cuba and Canada on 530, both of which I can obviously only get at night time. I don’t know how the tuning circuits could jump 9mHz so suddenly.

Call me mystified. I thought I could find something about this on the net; I can’t be the only one with this experience; but no. Have you ever heard of this?

Steve followed up later noting that he is actually able to tune in the whole 31 meter band, as long as a signal is strong enough to overload the SRF-59.

I’ve done a lot of MW DXing with the SRF-59 and had never noticed harmonics, but I’m not surprised they can be heard either. I might try to replicate what Steve did using my AN200 loop coupled to the SRF-59.

Has anyone else as heard 31 meter band signals on their SRF-59?

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The Mighty KBC test broadcast September 27

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DJ Eric van Willegen, “Uncle Eric” hosts The Giant Jukebox on the Mighty KBC.

(Source: The Mighty KBC)

For our listeners across the pond:

Uncle Eric is testing Saturday September 26th on 7395 kHz between 23:00 – 24:00 UTC.

Our normal broadcast on 7375 kHz is on Sunday September 27th 00:00 – 03:00 UTC.

Please spread the word and send your reports for 7395 kHz.

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Does the Tecsun PL-880 have a hidden ETM function?

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SWLing Post reader, Claudiu, writes:

I have a question regarding the ETM (Easy Tuning Mode) function on the Tecsun PL-880 model. Its indicator is visible on the LCD screen [see above], but I couldn’t find any mention of this function for this model. What should one do to enable that indicator and use the function? I’ve seen mention of this for earlier models (PL-380/PL-390), but not for PL-880, even after looking over the hidden features. Do you, or your followers, have any idea on this?

Very good question–it would be nice if the PL-880 had a hidden ETM function, but I suspect the PL-880 may simply use a stock Tecsun display; “ETM” may be standard print.

By chance, has anyone discovered a hidden ETM function on the Tecsun PL-880? If so, please comment.

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