Reception of an Experimental 40m QRPp Beacon

Peter VK3YE has built an experimental very low power (QRPp) double-sideband beacon for 40m which has been heard 500 km away!  This page describes the beacon and how it has been received.

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Beacon Characteristics

Operator: Peter VK3YE
QTH: Chelsea, VIC
DSB suppressed carrier frequency: 7160 kHz
Output power: 20 mW
Antenna: G5RV
Modulation: DSB-SC *
Identification signal: Continuous loop consisting of 8 seconds of 1 kHz tone, 8 seconds of CW ("VK3YE"), and 14 seconds of voice - see diagram below.

The figure below shows the identification signal timeline.

VK3YE beacon ident

With a transmitter output power of only 20 mW, the beacon can be classed as QRPp, or "very low power QRP".  Peter VK3YE has produced this very interesting video which provides a guided tour of the beacon transmitter.

Signal reception on Sunday 20 March 2011

The beacon first transmitted with this power level, but using only a DSB voice identification signal (the "ident"), on Sunday, 20 March 2011.  It was received by VK2IG outside Gundaroo, NSW, at  0059Z.  Receiving equipment used included a Yaesu FT-817 transceiver, a Kenwood TS-180S transceiver, and an inverted vee cut for half-wavelength on the 80m amateur radio band.  The signal did not register on the S-meter of either transceiver (for what that report is worth), but the readability was assessed as 4. There was some background noise which could possibly be integrated electronic hash radiating from Canberra or another of the nearby population centres. The biggest impediment to readability was the signal fading (QSB).  Because the voice ident message repeated, readability was assessed as 4, but if it had've been a one-off message then readability would've been assessed as 3.

Shown below is the ionogram at the time of reception as recorded by the Canberra Ionosonde operated by the Ionospheric Prediction Service.  Although Canberra is very close to the receiver location, and strictly speaking is not at the mid-point of the ionospheric propagation path between VK2IG and VK3YE, the relatively short path length (500 km) means the ionospheric conditions prevailing at the path mid-point would not be vastly different from those measured at Canberra.  This ionogram shows that the foF2, or F2 critical frequency (the maximum frequency at which F2 layer refraction returns the "ordinary" wave of the transmitted signal to the ground), is slightly higher than the transmitted frequency of 7160 kHz.  The Maximum Usable Frequency (MUF) for the path would be higher than the foF2 due to the "obliquity factor" applying when using oblique incidence angles (ie, not vertical incidence).  The MUF being only slightly higher than the transmitted frequency means ionospheric refraction of the signal still occurs while signal attenuation due to ionospheric absorption is minimum.

Canberra ionogram - 0103 UTC, 20 March 2011

As stated above, the calculated great circle path distance between VK3YE and VK2IG is very close to 500 km.  This distance is outstanding for 20 mW DSB-SC, considering that SSB-SC * receivers were used - which meant the effective transmitter power was 10 mW due to the receiver processing the information in only one of the two identical sidebands in the DSB-SC transmission.

* SSB-SC means "Single Sideband - Suppressed Carrier", and DSB-SC means "Double Sideband - Suppressed Carrier"; which are the proper terms for the modulation schemes commonly known as "SSB" and "DSB" in amateur radio circles.

Later that day the beacon was modified to transmit the continuously looping ident described in the beacon characteristics table above.  The CW ident was easily identified throughout the day, especially when using the 500 Hz bandwidth "CW Narrow" filter in the TS-180S transceiver.  The advantage of using a keyed audio tone as the input to a double-balanced modulator to generate the CW ident became readily apparent from mid-afternoon to late evening when the interference (QRM) on the 40m band increased markedly in strength.  Depending on the frequency of the interfering station(s), most times either one sideband or the other could be selected at the receiver for recovering the CW ident.  (The worst case interference occurred when, for example, a station operating on lower sideband (LSB) used a suppressed carrier frequency between 7161 kHz and 7162 kHz; because this would cause interference to both sidebands if the interfering signal's modulated bandwidth was 3 kHz or more.)  Later in the evening, the interference decreased markedly; and although the voice ident could not be copied with any degree of reliability, the CW ident was almost always present.  The beacon signal level eventually increased slightly and then faded completely at 1047Z when the propagation path between transmitter and receiver failed.

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Signal reception on Saturday 26 March 2011

Peter put the beacon to air again on Saturday, 26 March 2011.  At 0220Z I was able to obtain a video recording of the signal reception using the TS-180S as the receiver.  The antenna was the same 80m half-wavelength inverted vee described above.  The signal level is quite low; and while the CW ident is weak but readable, the voice ident is not readable. Anyone viewing the video will need to listen closely to copy the CW ident - note the "12 o'clock" position of the Audio Frequency (AF) gain control on the far right of the transceiver front panel. Even so, this is not a bad result for 20mW (actually 10 mW effectively) over a 500 km path!

Shown below is an ionogram at the time of reception as recorded by the Canberra Ionosonde operated by the Ionospheric Prediction Service, which shows (from the viewpoint of the observed foF2, at least) that propagation conditions were similar to those prevailing at 0103Z on Saturday 20 March 2011.

Canberra ionogram - 0223 UTC, 26 March 2011

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Signal reception on Sunday 27 March 2011

The beacon was on-the-air again on Sunday, 27 March 2011.  Conditions were similar to those noted during reception on Sunday, 20 March 2011.  On this occasion, I was able to obtain another video recording at 0220Z - this time, the audio identification signal is easier to understand.

This map shows the distance traversed by this QRPp beacon signal.

VK2IG & VK3YE location map

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This page was created by Mike Dower VK2IG: 11 Jun 2011.  Material may be copied for personal or non-profit use only.