![](https://secure.gravatar.com/avatar/2ae31eeb4905a377f371304724dc9acf.jpg?s=120&d=mm&r=g)
Joe,
I agree also. That is why I posted a message to the AMSAT-BB, back in September of last year,advocating the use of DSB modulation as a mode on the linear transponder satellites. Here, in part, is what I said:
What I propose, then, is the use of well-disciplined DSB (double sideband) modulation as a means of lowering the cost bar while providing interoperability with SSB voice stations that are working the satellites. What I mean by 'well-disciplined' DSB is as follows:
- Baseband audio bandwidth sharply limited to 2.5 KHz, resulting in RF
bandwidth or 5 KHz. This would realistically enable three to fifteen simultaneous 'channels' depending upon the linear bird being used. 2) Power output would be limited to just a couple of Watts. This is all that is really necessary to access the linear birds in most situations. It would reduce the possibility of signal interference. The cost of the PA would be relatively low. 3) The RF oscillator would be accurate and computer controlled (e.g. Silicon Labs Si570), which would enable active Doppler compensation via software with CAT control (e.g. gpredict).
Current SDR technologies already enable inexpensive, multi-band receiver solutions. The desired sensitivity and selectivity of the SDR receiver ultimately drives the receiver cost. The performance of the receiver, then depends upon the budget of the station builder. Solutions for every budget are now available, ranging from dirt cheap hardware derived from RTL-SDR dongles to more capable devices (e.g. SDRplay, AirSpy, FunCube Dongle).
At the sacrifice of some bandwidth, the following advantages can be had with using DSB modulation:
- DSB modulation is relatively easy to achieve. The band-limited audio
is fed into a double-balanced mixer, bandpass filtered for harmonics, and fed into a PA for transmission. The resulting hardware is comparatively inexpensive to construct and to tune. 2) Sideband inversion caused by some linear birds is no longer an issue. Having both sidebands present in DSB modulation means that the correct sideband will always be available for reception. 3) Interoperability with SSB stations would be maintained, as DSB modulation is a superset of SSB modulation.
This would require a homebrew solution, as there are no commercially-available DSB transmitters for VHF/UHF that I'm aware of. Such a rig, once again, would be relatively easy to construct and test. This is an experiment I would like to try.
Some may gripe that this approach wastes bandwidth on the linear transponder satellites. That may true but it is bandwidth that is currently underutilized. So what is the harm, if any, of using DSB when the potential end result could be increasing the number of users of the linear transponder satellites?
73,
Mac Cody / AE5PH
On 03/15/2018 06:42 PM, Joe N3XLS via AMSAT-BB wrote:
Its not too many satellites, not enough ops! -------- Original message --------From: Bob- W7LRD [email protected] Date: 3/15/18 6:23 PM (GMT-05:00) To: amsat-bb [email protected] Subject: [amsat-bb] idle comments Hello from Seattle
I read the bb almost thoroughly throughout the day. A small common denominator is subtly appearing. I read, "I was on the bird all alone", or something like, "no one to talk to". The unusual conclusion, we have too many satellites! I never thought this ham would even think of it. If I look at Satpc32 with "only" a dozen listed, in fast forward a bewildering barrage of circles floats across the screen. I am not saying this is a bad thing, it just spreads us out and at times, there is, "no one to talk to". I do testing like try different power levels, talk to myself til as close to AOS as I can get. You know the drill. From what I read there are more on the starting block. I'd like to see more L band time, maybe a bird with a S band DL a MEO, a HEO- I know, idle comments. We have the five & dime coming at us, which sounds like a whole other world, I'm looking forward to it. Then there is the massive off air time making all this stuff work. Currently testing between two L band antennas and between two different 70cm antennas. At this time I have my Satpc32 talking fine with the radio but not with the rotor. A com port issue which currently I can not figure out. Assistance solicited. On the ISS it would be fun to see one of the "hams" up there have that "burning in the belly" to yuck it up, get WAS, VUCC, DXCC or whatever. Again, just idle comments not a criticism of the ARISS system. Sunny day in Seattle, xyl says yard work.
73 Bob W7LRD
Seattle _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb