Hi AMSATs,

I am supprized to see that my mode-uv work for the P3e is still remembered :o) I wonder what happened with the mode-uv transponders designed by the other (New ealand, Russian, German and ??) groups ? Lately I only read about the SDX work of NA, UK and DL, but what about the other parts made by other (none NA,UK,DL) hams ?

From the messages I feel that the SDX seems to be the

best radio at all, with a larger dynamic range, better aligator killer, better HELAPS etc... SDR technology is very interresting and it should be explored, but somehow I feel that only its advantages are named. So I like to "flip the count" to its other side to have "the pair of scales in balance".

About the dynamic range, I wonder how it can be better than an analog receiver. I suppose the RX side (UHF) will not directly be digitalized (it would need an high speed and high power ADC) so there is still an analogue amplifier and down-mixer needed in front. Then there is only the IF part where it can be dynamically be better. I guess with analogue electronics this can also be done :o)

I also seen someone mentioned about 1970 electronics, as if todays electronics is only better in IC form. Todays 2007 transistors are much better than in 1970, they are much smaller, and have a better performance. Even analogue style transponders can be made better and smaller size than those in Ao-10, with todays transistors. Have a look at my modern analogue transponder system at: http://www.observations.biz When talking about old technology then HELAPS (or officially called EE&R) is even more older, from 1952 ;o)

That the HELAPS works better only due to the "modern" SDR system is not compairing in a fair way. Then you compair 2007 SDR electronics with 1975 transistor electronics. I believe with todays modern discrete electronics the HELAPS system will work equally or even better.

The SDR system with zero-IF is a nice system which is very flexible. However zero-IF can have problems with DC-drift over time what gives unefficient ADC use or even ADC clipping. It is also more sensitive for low frequency 1/f noise, and the high frequency digital processing signals are a serious threat on sensitive receiver inputs... (also a problems in modern cell-phone systems)

A Near-Zero-IF system might be a solution but is more complex to integrate. The filters at such low frequencies (zero-IF) can be made very sharp, but the same trick can be done in analogue way, with an RC low pass filter :o) Several years ago I present such a bread-bord system as "Quadrature transponder" where I could easily change the transponders bandwidth and change from inverted to none-inverted :o) The difference is that it takes far less power than a DSP does, and it was extreemly KISS...

I agree that digital DSPs are more flexible which is good when you like to use the same radio for other modes also.

This was my vote for the analog transponder systems :o) I hope the digital SDX works well and hope that its analog sister will also have a chance to do its work and gets its technical respect...

73 de William ---

____________________________________________________________________________________ Be a PS3 game guru. Get your game face on with the latest PS3 news and previews at Yahoo! Games. http://videogames.yahoo.com/platform?platform=120121