At 04:19 AM 5/30/2009, Bob Bruninga wrote:
For mobile work on AO27, SO50, AO51 a 2 metre quarter wave whip is all you need... to work the LEO's mobile and the satellite is 15 degrees or more above the horizon,
Absolutely, For a 19.5" whip in center of roof:
- Has 5 dBi gain above 20 deg on 2m
- Has 7+ dBi gain above 30 deg on 70cm
- Is an omni
- does not sacrifice 3 dB for circular
- Above 25 deg, satellite is 6 to 10 dB closer!
- works the birds solid for the center of high passes
- Simplicity at its best!
Read about it: www.aprs.org/rotator1.html
Disadvantage: The only disadvantage is TIME. On the above web page you can also see that satellites spend 70% of their daily pass times below 25 degrees. BUT! For those best passes in the morning and the evening (or whenever) you can make solid contacts while mobile for about 5 minutes.
Also note, that you do NOT need any tracking program to predict passes. AO51 schdule repeats evry 5 days for example. Just write down the CENTER pass of the morning and evening for each day for 5 days. Update those 10 times on a small 3/5" card on the dash about once a month or so will predict all passes whenever you are mobile. There will be a pass 100 minutes earlier and 100 minutes later each day too. So you can predict all 6 passes a day from those same 10 times.
See how: www.aprs.org/MobileLEOtracking.html
Bob, WB4APR
I've posted this before, but maybe it helps to repeat. When AO-51 launched, I used a 19-inch mag-mount mobile whip on a steel ground plane to copy telemetry on 435-MHz using a preamp. Signals were quite adequate. Probably low horizon AOS/LOS was limited (too long ago to remember). But very simple to implement and use as Bob states. I have two Lindenblad antennas under construction so will play with them (using my 435 preamp) when I get them up. I am preoccupied with finishing my 1296-eme station with 16-foot dish. In July, I should be able to re-assemble the old AO-40 tracking super-array of antenna as can be seen on my website.
*********************************************************** 73, Ed - KL7UW BP40iq, 6m - 3cm 144-EME: FT-847, mgf-1801, 4x-xp20, 8877-600w 1296-EME: DEMI-Xvtr, 0.30 dBNF, 4.9m dish, 60/300W (not QRV) http://www.kl7uw.com AK VHF-Up Group NA Rep. for DUBUS: dubususa@hotmail.com ***********************************************************