[Amps] VHF all-mode and DC-to-daylight rigs

[Manfred Mornhinweg]

Cathy,

> For weak-signal usage, you want low noise figure and high
> sensitivity, but you really don't care about dynamic range.  You are
> unlikely to have a strong signal next door to desense your rig.
> There is plenty of bandwidth and few signals.

The problem is just when you have nearby high power transmitters, on 
frequencies close enough to the ham bands to get through the front-end 
filters. Such as low UHF TV stations, and certain kinds of radar 
stations. Or perhaps a ham neighbor using significant power on the same 
band.

In my case none of that applies, so indeed I don't need much dynamic range.

> I do hope that with the launch of Phase 4 and geostationary
> communication on 5/10 GHz, we'll see a new era of ham satellite
> usage.  I know several local hams who are interested in building the
> 5/10 GHz ground station.

I would join in too. But I don't think that Phase 4 sats will be here 
very soon. Or at all. They are complex to build and expensive to launch. 
We have ever fewer technically capable people among us, and most of them 
are too engaged in the dollar hunt to devote lots of time to ham 
projects. So there is a severe shortage of committed, technically 
capable hams, to develop and build advanced satellites. And even when 
they build one, rising several million dollars for a launch of such a 
sat isn't easy either!

In the 1990s I was involved in building what we intended to be the first 
Chilean sat, CESAR-1. It would have been a Microsat with 9600 baud GMSK 
uplinks on 2m and downlinks on 70cm, and several added features and 
experiments. My own hands-on involvement ended when it was financially 
impossible to procure some essential test equipment, and I delivered the 
transmitters and one receiver without having been fully tested. Several 
other volunteers also had such trouble, or simply couldn't devote enough 
time to the sat. The project leader, CE2MH, ended up hiring people do to 
the remaining work, but those people had neither enough motivation nor 
expertise, and failed. The project was delayed ad infinitum, until CE2MH 
got ill and finally died, and that was it. Nobody stepped in to take his 
place. CESAR-1 will never fly.

And that was just a low orbit Microsat, largely based on a proven design 
by AMSAT-US. We just had to copy that, and add our own customizations. 
It's a far larger task to develop a new satellite from scratch, and a 
Phase 4 sat is enormously more complex than a low orbit Microsat.

>> Since there are no really usable sats, there is no demand for
>> VHF/UHF SSB operation
> 
> Your club doesn't do weak-signal tropo VHF?  That's too bad.

No, neither my club, nor anyone within my possible coverage. I'm not 
aware of anyone on South America regularly doing it! Maybe there are 
some, but I don't know about them. When I have tried casually listening, 
on those days when there are strong meteor showers, I haven't heard 
anything.

The closest we come to weak signal work on VHF in this part of the world 
is chasing distant repeaters, when there is some tropo ducting, mostly 
in summer. Oversea propagation between central Chile and Peru are fairly 
common, covering distances of 2500km or so. But that's of course all 
done in FM.

Manfred

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