--- Bruce Robertson broberts@mta.ca wrote:
In your previous letter, you describe the antennas as "turnstile on 2m and a turnstiled moxon on 70cm"; are these fixed, like the moxon Cebik recommends, or are they rotating beams?
Actually, the 70cm is just like Cebik published in QST. But, for some reason, I don't get as good performance on the 2m version, so I switched that to a regular turnstile 3/8 wavelength above a layer of Reynold's Wrap. I've also managed to work a number of 2M SSB stations on that antenna. I don't have any rotators; they're just pointed straight up.
As you probably know, depending on the roofing material, you are suffering a not inconsiderable loss on 70cm from the signal passing through the roof. Last time I looked into it, I figured on about 2dB for my shingled wood roof.
I didn't know how to figure this, but I figured it would be 1 or 2 db. Winter snow is going to be unworkable, of course, so the plan is to move them outside.
One of the biggest negative impacts I've had is when I added the 70cM brick. It has about a 6db loss on receive and it took me awhile to figure that out.
If you are certain you don't want to try mode B, you could even get a receive-only 70cm preamp,
Actually, I have made a handful of mode B contacts on both AO-7 and VO-52. I've just gotten kinda sidetracked with this 70cm polarization thing and I figured anything I did that improved reception (other than using a preamp of course) would improve my mode B uplink. I've listened to a few contacts on AO-7 mode A recently, but for some reason, neither of my 2M antennas has enough oomph to get me an SSB signal that I can hear - even with the 80 watt brick turned on. I'll get that worked out, eventually. I really want to have some mode A QSOs using my KWM-2A on downlink.
On 70cm CW you can also try LO-19, which has a booming signal. I find it easier to use these to assess the effectiveness of an antenna than to use the FM birds.)
I'll give that a try. One of the problems I have is that I don't have anything to use as a baseline. I recently found a very strong digital repeater on 433.7xx and I used the signal from that every 20 seconds to discover the amount of loss in my 70cm brick on receive. Normally, for alignments, I use the IF bleedthrough from my VX-5R in WFM mode.
Yep. I just worry that you're not getting enough out of the antennas you've already built. Quite honestly, I'd rather spend an evening doodling on the birds with my indoor 1/4w whip and a preamp on 70cm than with my outdoor beam and no preamp!
I'll squeeze everything out of the antenna I can and then I'll add preamps. But, I really want to build them myself if I can get over the engineering/ parts list issues.
However you proceed, *please* keep reporting your results to the list. I think the best thing we can do as a group is support each other in antenna-building and -experimentation. If you can demonstrate a reliable station with attic antennas, I think you'll be breaking some ground for all of us.
Will do. I've made a lot of contacts on the FM birds with my setup. Of course that's just a callsign and a grid-square. But, the thing about doing this is that I've had to optimize everything, including squeezing the last bit of S/N out of this old FT-726R that I could tune for. For that, I resorted to the IF bleedthrough mentioned above and tuned for lowest noise. But, I have to admit that the difference from that to max signal might have been only wishful thinking. ;)
Bob - AE6RV