CCGS HENRY LARSEN, built in 1987 by Versatile Pacific, British Columbia, is the most modern icebreaker in the Canadian Coast Guard Fleet, and is named after RCMP Inspector Larsen who, aboard the compartively tiny ST. ROCH, completed the first Northwest passage between 1940 and 1942.
The most experienced Ďbreakerí skipper in the CCG Fleet, Captain Steve Gomes has been assigned to the LARSEN since her construction. Also assigned to the vessel since itís construction was Radio Officer Rick Falvey, VE1HA.
However, prior to the 1995 Arctic voyage, however, Rick took retirement, and I was lucky enough to be in the right place at the right time with a freshly renewed General Maritime ticket. Although I only had four days to say my goodbyes my family, I managed to assemble the gear to work the Low Earth Orbit (LEO) hamsats whilst onboard the LARSEN. I brought my IC251A 2-Metre rig, an 80 watt brick, a Hamtronics 70-to-10 rx converter, a copy of WinOrbit, a fresh set of keps, and a 70cm GaAsFET pre-amp that was featured in DUBUS.
Whilst transitting Davis Strait, my first attempt at building a 2 Metre "eggbeater" was unsuccessful; I couldnít seem to get a reasonable SWR. Keen to get on the Mode A birds (RS-10 and 15) ASAP, I abandonned the eggbeater plan for a horizontal loop. Using an Icom 781 with a 23 foot whip for receive, I had no problem receiving my downlink on 10 metres using just 10 watts into RS-10. RS-15 usually required that the 80 watt brick be switched inline, and signals were weaker than that of RS-10.
Reception with the 23 foot whip was fair although somewhat noisy, and a number of stations in the south were worked, both in North America and Europe. I discovered that the spectral display function on the Icom generated noticeable "birdies" on 10 metres which disappeared when the display was switched back to the main menu.
Next I tackled the 70cm side of the house for the FO-20 downlink. As I had no way of determining SWR on 70cm, I decided to build a simple half-wave inverted vee dipole for FO-20 downlink reception. My low noise pre-amp was mounted quite close to the antenna for best noise figure. Although FO-20 was near perigee while over the Canadian Arctic, I did not find the downlink nearly as readable as that of RS-10.
All connections were double-checked, but 70cm reception remained poor, especially when the satellite was below 20 degrees in elevation. I decided to take a mathematical approach to the problem. Knowing the distance to the satellite upon Acquisition Of Signal (AOS), the approximate Effective Radiated Power (ERP) of the satellite beacon, and the approximate noise temperature of my preamp, I thought I could predict the signal levels I could expect.
To determine path loss, I used :
d = distance
which with a maximum distance to the satellite at AOS of 4,500 KM, the path loss should be -158 dB. With a CW beacon output of -10dBW (100 mW), a 4 dB antenna gain for FO-20 and a -3dB loss because FO-20ís 70cm signal is circularly polarized, while my inverted vee was linear, I could expect a signal of approximately -167 dBW at the antenna.
With my preamp located practically at the antenna, the internally generated noise of the preamp sets the system noise figure. Although my GaAsFET preamp has a noise temperature better than 50° K, I used a much more conservative 200° K for my calculations, given that my (hopefully) omnidirectional inverted vee would be picking up much of the "warm" earth noise than an gain antenna trained on the bird.
Noise power in decibels referenced to Watts can be calculated using the formula
Preamp Noise Power (dBW) =kTB where:
k = Boltzmannís Constant
T = preamp Noise temp in Degree Kelvin
B = bandwidth in Hz.
x 200 x 2700 = -171 dBW
Therefore, I could expect -167 - (-171) a received signal strenth of 4 dB above the noise upon AOS and increasing as the satellite got closer.
However, this was not the case. So I returned to the bridgetop to re-check all connections. It was when I was inspecting the inverted vee for cold solder joints that I realized my mistake. The formula I used to cut my dipole was for a half-wave dipole; I had cut one half-wavelenth piece of wire for each leg of my inverted vee. In essence, I had a full wave dipole feeding a pre-amp that was tuned for 50 ohms input impedance. According to the RSGB VHF/UHF Manual, the performance of my low-noise GaAsFET under this condition was poor indeed!
Quickly trimming the inverted vee to what I hoped was closer to resonance, I awaiting the next pass of FO-20. Sure enough, upon AOS, the CW beacon came booming in and I worked Pat, EI4CL on SSB with good signals, switching to CW as FO-20ís elevation at Patís QTH approached zero.
These were the signals I expected from FO-20! Because of the low ambient noise level on 70 cms, all subsequent QSOs were almost "armchair copy" anytime that satellite was above 10 degrees in elevation and not shadowed by the shipís funnel. On occasion, odd fading and doppler scattering of my signal indicated that aurora, which I could not see because of the 24 hours of daylight, and sporadic E was having some effect on my 2 metre uplink and perhaps on the satelliteís 70cm downlink as well.
An interesting facet of using the 70cm-to-10metre receive converter was being able to plug it into the radio console. As a large icebreaker such as the LARSEN has numerous MF and HF receivers but real estate for antennas is limited, signals from the two receive whip antennas are split by wideband multicouplers to provide signals to various receivers. By plugging the output of the 70cm receive converter into the multicoupler, several HF receivers could be used to listen to different portions of the FO-20 100khz wide downlink. I could carry on a CW QSO while the 2nd mate could listen to an SSB QSO further up the band.
8 VEís were worked, as well as 18 U.S. and 10 European stations while in Lancaster Sound off of Resolute, Little Cornwallis Island and Bent Horn. Iíd like to thank the CCG installation and maintenance techs for supply the odds and sods to build the antennas, and of course, those patient hams I worked before I discovered the error in my ways.
Check the LARSEN's stats at the Coast Guard's Web Page.