Working satellites with antennas under the roof!

This article was created in early 1996

The word "antenna ban" is expected for some OM's, as well as for me, not unknown. From this necessity, you're trying to be as much as possible QRV on the bands. Who then at least has the "happiness" to use the loft for himself, here are some suggestions.

First of all, here is the equipment I used during the tests:

2m: Yaesu FT225RD + 6ele. horiz. + MGF1302 ( ca.150W ERP)
70cm: Yaesu FT780R + 12ele. 10° Elev. (ca.100W ERP)
10m: Yaesu FRG7 + DV27 lang (1/4 lambda GP) + 25m RG58

All antennas under the roof (beton pans, no insulation)

With this station I could manage to work more than 300 QSO's over a period of about 3 months using the following satellites: AO-10, 13, 27, FO-20, RS-10, RS-15.
The possibility of using simple equipment to work over RS10 and RS15 should just only mentioned here (it was reported that QSO's out of the car has taken place!). The same applies to AO-27, it seems like almost a handy could work! AO-27 is only QRV during the day on weekends.

Satellite QSOs in November 1995

My main focus was on the two Phase 3 satellites and on Fuji Oscar-20. The AO-10 and AO-13 downlinks on 2m are below 30° elevation quite strong (at least ZRO-Level 6).So was my 12ele packet antenna was screwed to the rotor and the Yaesu FT780R (thanks to Dieter, DF6YG) has brought to operation.

AMSAT Oscar-10

Since more than 8 years, the satellite was not under control, because of the defective memory chips of his computer. Therefore it is not accurately predictable how, or whether it can be used. The publications in AMSAT-DL-Journal and the packet radio mailboxes should be pursued. In November 95 Oscar 10 was in a time of eclipses with a period of up to 2h. Entry and exit of the eclipse could be very well observed on the beacon signal at 145.809Mhz. (the program STSORBIT shows you whether the Satellite is in the sun or not).  However, the illumination of solar cells in this time seem quite good, because with the exception of the eclipse the signals from the satellite were very well. In addition, the current flight attitude must be near nominal (ALON/ALAT=180/0), because the signals are very well, despite the low uplink-power. Thus it was possible to get still good signals at apogee with the existing 80W erp. The most OM well-known strong QSB of AO-10 (caused through the damaged antenna?) was absent during a time of abt. 10days, which compared with several stations, could be due to the vertical polarization of the uplink antenna. Only a week later, this advantage was no longer visible. From all observations during this week suggests that at the operation of AO-10, the major advantage is the possibility to switch between all polarizations. Unfortunately, there are also times at AO-10 when no operation is possible. During this time the main axis of the satellite points towards the sun, witch means the illumination of the solar cells were close to zero. The result is a complete shutdown of all systems. Since about mid-January AO-10 is again in such a phase. At the moment (02.march.1996) the transponder and the beacon are back into operation. However, the beacon is still "FMing" due to a bad illumination of the solar cells. During such a period no operation on AO-10 should be made! So always watch the beacon, and then decide whether operation is possible or not! On AO-10, it is essential to constantly monitor and not simply "go for it." If we all go by this rules, then we maybe have quite a while to enjoy this satellite, which is not expected to be on duty so long.

ALON/ALAT of AO-10, (by James Miller, G3RUH)

Satellite operators frequently ask "what is the attitude of Oscar-10", or "can I have ALON/ALAT values for my computer program". Well, it looks like eleven year old AO-10 is coming in good again. Here's the analysis. When the computer failed on Oscar-10 in 1986 we knew approximately what its orientation was. Since then of course there has been no telemetry, and the only "measurements" we can take are subjective interpretations of transponder performance and beacon wobblies. At the time it finally failed, the spin axis/antenna direction lay exactly on the Sun's orbital arc (the Ecliptic). So because of the Sun's annual motion the solar panels were in turn fully lit then completely dark, twice a year. The Sun's angle to the panels just cycled up and down a sawtooth from -90 to 0 to +90 to 0 to -90. As you would expect, at zero illumination conditions the battery flattened, the beacon disappeared and there was no transponder. Exactly what we see to this day. Also at the time it failed it was spinning at some 30 rpm. Due to tiny frictional effects this spin was gradually falling at a rate of 0.0035 rpm/orbit, so the current (1994) spin rate is very low. Now a spinning satellite is just a gyroscope, and in the absence of any torques, should stay pointing in the same direction for all time. So one can extrapolate from the last known (1988) direction to the present day and beyond. The key phrase here is "absence of any torques"; if the spin rate is falling there must be some coaxial torque at least, and there is no reason not to expect some non-coaxial torques which would change the orientation a little. So with the forgoing caveats, the table below shows the predicted attitude of Oscar-10 based on the last known 1988 data. The pattern is likely to be more or less correct, but by now there is probably a few week's slippage. The only way to find out is to use the satellite and correlate experience with expectation. If users will take the trouble to let me have their observations we can together almost certainly refine this table. But I am not going to do it on my own. It looks to me as though we are in for some near "normal" times on AO-10 for a couple of years. Bear it in mind during those irksome periods when Oscar-13's attitude is so unsociable.

Key:

ALON deg  Attitude longitude in orbit plane coordinates (BLON)
ALAT deg  Attitude  latitude in orbit plane coordinates (BLAT)
SA   deg  Sun Angle
ILL%      Percentage illumination = 100*COS(SA)
SEL  deg  Sun's elevation above orbit plane
SAZ  deg  Sun's azimuth in orbit plane coordinates

Orbit plane coordinates: longitude is measured clockwise from perigee;
latitude is measured up from the orbit plane

James Miller, G3RUH

AMSAT-Oscar-13

The operation on AO-13 is more predictability, so work is much easier than on AO-10. However, we are discovering that the receiver of AO-10 is significantly more sensitive than that of AO-13. This is probably due to the fact that the AGC of AO-13 very often makes the RX insensitive, always when, unfortunately, EME stations "join" the transponder. Through these strong signals AGC regulates the RX down and the QRP-stations were no longer heard from the satellite. Our own signal should never be stronger than the beacon! This of course also especially for the old Oscar-10. At the beginning of my tests beginning Nov 95, I used horizontal polarization on the uplink. However, SSB operation was possible only close to nearly ideal squint. A key improvement by switching to vertical polarization was not given. An a Squint <30° the signals were sufficient, the QSB low. However, since the antennas are not elevatable, I could only work on satellites at around 3-30° elevation. In the last hour before the switch to Mode-S (shortly before apogee) 10W were more than enough and the signals are often stronger than "normal" stations. 350W ERP provided excellent signals, often stronger than the beacon!. Principle the kind of polarization seems to be not as crucial  on  AO-13 than on AO-10. Since a lack of a circular antenna, the claim of lower QSB could not to be checked. Because of the rare place below roof, assembling a crossyagi is not possible. The horiz. polarization works on with good results AO-13 (at least in Nov 95, HI) and therefore requires no amendment.

Here we have a detailed view of AO-13 from the modell in the German Museum, Munich.

FUJI-OSCAR-20

About the Mode-JA (2m UP/DOWN 70cm) transponder new successes take place nearly every minute. Even intercontinental QSO's to Canada and the United States were not the exception! However, the using of a preamp for 70cm is strongly advised, because the signals were only slightly above the noise level. During the November 41 QSO's take place, 16 with North America. Due to the altitude of the satellite all eastern states of the USA and not only the coastal areas are reachable! Changing the polarization from horizontal to vertical on the receiving side, provides only a low signal improvement. On the 2m-side unfortunately only horizontal polarization was available.

Finally, a few logbook excerpts:

AO-10:

AO-13:

FO-20:

(and many Europeans)

Closing Remarks:

The experiment to work the various OSCAR's with a small equipment, requires a lot of patience, especially on AO-10 and AO-13. For best results you should experiment with the antenna-polarization. Switching between all polarizations is the best way and enables the direct comparison between them. It was common to observe that stations with 25W and long Kreuzyagis (about 400W ERP) signals delivered worse than my indoor antennas at <100W ERP! In my view, it can only be due to the handling of the Crossyagis. Often the feedlines were incorrectly laid through the radiation field, and/or the antennas are mounted on a metal tube. If transformation lines were used, the dimensions has to be as accurately as possible in order to ensure that the fewest possible linear polarization shares (horiz. or vert), and the radiation pattern is not distorted. A possible use of lossfree coaxcable goes without saying.

Finally, it only remains to say that it is in any case worth to test on the satellites with under-roof antennas without possibility of elevation satellites. The logbook extracts shows this impressive. If only once since P3D (God willing), then you have a good beginning equipment in order to continue when AO-10+13 are no longer available.

Have fun experimenting and QRP-DXing via satellite

73 de Michael