Moonbounce (EME) UHF TVDX

May 2002
Inspired by Ian Robert's detection of Kenya's low VHF TV carrier by moonbounce the previous month, I set out to try my luck
detecting 5 MegaWatt UHF TV carriers from the USA using simple equipment.  The task was made easier by the total lack of TV allocations below 526 MHz here in AustraliaInitial detection was of KWBT-19 at Muskogee, Oklahoma, illustrated in the spectrum analyser scans below.

spectrum analyser scansWith my Yagi pointed at the moon, a weak carrier with frequency drift of about -1.5 Hz/minute was noted at moonset on three consecutive dates, May 26-28.  The signal-to-noise ratio was several dB.  These scans were done every 40 seconds and the bandwidth (spectrum analyser bin width) is about 2 Hz. One could watch progress of signal in near real time. For example, the signal on 501.25 on 27 & 28 May fluctuated by at least 7 dB (in/out) several times and was strongest a few minutes before fade-out. The signals were present for several minutes before strengthening, then abruptly disappearing. KWBT has an unusually large offset (-2 kHz), much greater than the Doppler effect, which is typically only a few hundred Hz (for Perth to USA).

The antenna was a 22 director Yagi (in Australia, Jaycar's "91" element fringe antenna, model LT3182) with ~ 10dBd gain at 500 MHz. It was mounted (on a camera tripod) at 1.5 above ground level, with fixed horizontal polarisation and manual adjustment of the elevation and azimuth to track the moon (see photo). It was mostly elevated at about 22 degrees (optimum for the longitude of KWBT).  The USA is so far from Western Australia that the rotation of signal polarisation due to geometry (spatial polarisation) is generally less than 20 degrees. So, if the ionosphere is benign and causes negligible polarisation ("Faraday") rotation, the receiver polarisation is well matched to the transmitter and maximum signal is received.

The (1st) preamp was a 2 dB noise figure GaAs FET unit, with 20 dB gain, mounted at the antenna. It is a JIM model M-75, made in Japan (once sold in Australia by Dick Smith Electronics). It has a bandwidth of 225-1500 MHz.

The receiver was an Icom R7000, in usb mode, plus PC (Macintosh) based audio spectrum analyser sampling the receiver's audio through the sound card.

To measure frequency accurately I used harmonics (weak at UHF) of a frequency divider chain which provides combs every 10 kHz from a very stable 5 MHz crystal oscillator. The 5 MHz reference is a high performance Vectron ovenised quartz crystal (circa 1989 vintage), with a frequency drift of better than 0.001 ppm/day.

A simple calculation of the signal-to-noise ratio [= PG/LkTB, where P = tx erp, G = rx ant gain, L = path loss (264 dB at 500 MHz), k = 1.4 x 10E-23, T = noise temperature, B = bandwidth (Hz)] gives about 15 dB for a 3 Hz bandwidth and 300 K noise temperature, which is in the right ballpark.  If the tx uses "beam tilt" signals may be several dB less. On the hand "ground gain" at the tx end may add 6dB, momentarily. 

In the following month twenty UHF TV carriers were detected, including one from Australia, and their details can be found hereThe timing of their fade-out and the rate of Doppler shift (Hz/minute) is in excellent agreement with a moon scheduling program (such as GM4JJJ's) for moonset at the tx site. The frequency of the Australian station is in good agrrement with a terrestrial measurement made by Todd Emslie 200 miles from the tx and this confirms the accuracy of the Doppler correction. The most readily received US stations radiate the maximum power of  5000 kW erp (mostly hor. polarised) and have a favourable (preferably omni-directional) radiation pattern.  Info on these stations may be found at the FCC TV database and Doug Smith's databases, http://www.w9wi.com/articles/uhflow.html  


Dec 2002 I improved the signal-to-noise ratio by several dB,  This was brought about by employing a higher gain Yagi (~14dBd), an RF Industries narrowband Yagi (480-500 MHz, gain 14 dBd), and lower noise preamps (NF <1 dB):  

1. Winegard PA-4975 (NF~1 dB, gain 24 dB, nearly 20 years old)
2. 
Research Communications model 9247 (NF~0.5 dB, gain 20 dB)
3. 
homemade 1 stage GaAsFET LNA, 480-510 MHz (NF< 1 dB, gain 14 dB)

Below 520 MHz I used the narrowband Yagi, whose polarisation could be set to any desired value. Above 520 MHz I used the Jaycar  (with hor or vert pol). Normally I use horizontal antenna polarisation, which matches North America all of the time and Europe most of the time, except when there's Faraday rotation. However for locations 5000-6000 miles away, such as the Middle East (and north Asia), I always have to use vertical polarisation. The Research Communications unit with a nominal noise figure of 0.5 dB seems to give results not noticeably better than the others, perhaps because my antennas do not have a high enough front-to-back ratio (~30 dB) to reject ground radiation. It also cannot yet be used on the narrowband Yagi as it is unstable with that input - very strange.

With this improved set-up KBWT-19 gave a peak signal-to-noise ratio of about 18 dB using a 1 dB noise figure LNA and 14dBd gain narrowband Yagi made by RF Industries in Australia (see photo).  This is sufficiently strong to just be able to hear it in bfo mode on the R7000 rx. On 18 Jan 2003 I made an audio recording of KBWT-19. The last 5 minutes, displayed as a in the spectrogram below.
KWBT spectrogramIt's the broken white line at 1.5 kHz. The signal fades out completely at times. You can just hear it, on peaks above the noise in a bandwidth ~300Hz (the brown region), here.


KBWT-19 Muskogee, OK is one of the strongest (and longest duration) signals I've found from the USA.  Another good one is  This may not be true from other parts of the world. At my location the south-eastern horizon is partially blocked.  That seems to affect my ability to receive many US east coast txs, which peak when the moon is only several degrees above the horizon.
 

In early 2003 with a system that could see down to 500 kW I was able to detect known 0.5-1 MW txs from Finland, France, Germany, Poland, Spain,
Sweden, UK.  One megawatt txs from Sutton Coldfield, UK and Sweden (600-700 MHz) could be detected with up to several dB signal-to-noise ratio on the spectrum analyser (bandwidth ~2 Hz and ~16-32 averages). Kuwait City gives a strong and reliable signal for about 20 minutes on chE24 (and chE39) - it was there every time I looked, unlike some European and North American txs. I conjecture this is because the Kuwait City tx has an unobstructed view of the horizon at moonrise over the Persian Gulf.  Dubai's >1MW tx on chE33 has been found, but not the one on chE41. All these stations west of my longitude were detected with moonrise at the tx, and therefore my Yagi facing the setting moon. More Australian stations were detected: details of the txs are to be found here.

March & April 2003 Todd Emslie and I undertook successful simultaneous moonbounce observations, on KWBT-19, KUVS-19 and Kuwait chE24.  By this time I was using a better wideband antenna, the Televes Pro-75 (470-860 MHz; gain 13dBd at 470 MHz) with fixed, horizontal polarisation (see photo).

Oct & Nov 2003 On 4 nights around 2300-0200 local time I managed to detect Tokyo's 400 kW erp tx on 171.25 MHz using an 11 element Yagi (gain ~10 dBd, see photo).  The signal was only 3 dB and would pop above the noise monentarily a couple of times. But the frequency, after correcting for Doppler, consistently came out to 171.250003 MHz give or take 1 Hz.

Dec 2003 Jakarta's 3 MW tx on chE45 (663.25 MHz) was detected via moonbounce on 5 dates. The EME frequency measurements confirmed that I received this tx also via tropo! See the section on UHF tropo DX.  The Australian tx VTV35 has also been received via both modes.

The details of the eme loggings from Dec 2002 to Dec 2003 may be found here.


home