Propagation simulation in HamSphere
2010-09-24 14:14
Hi all !!!

I've just started to use Hamsphere transceiver application and I was just wondering how do you simulate the propagation conditions in HamSphere. What kind of conditions influence received signal strength? Distance between location of logged "transmitter" and "receiver" users? Band? Time of the day? Does received QRN/QRM signal strength also depends on similar conditions?

Re: Propagation simulation in HamSphere
2011-01-14 07:25
I'm also interested to know this information.
Re: Propagation simulation in HamSphere
2011-01-14 08:16
Re: Propagation simulation in HamSphere
2011-01-14 08:21

I use real radio principles with local oscillators, balanced mixers, filters etc. The modulation is true Double Sideband Modulation with carrier suppression hence the "donald duck" sound when you swirl the knob. The receiver is a direct LO-mixer detector where I just add the carrier (Beat oscillator) to detect the audio. Filters are made from 17-pole FIR filters producing effective 3.8, 2.8 and 0.7 kHz filters.

CW Keyer and CW operation is true Contineous wave operation. I simply inject a carrier wave in the Sphere and key that. You will notice that the built in keyer has a clean Sine wave on both side bands whereas if you modulate CW with a side tone oscillator it will produce two interfering tones.
In future releases operators will be able to key the transmitter on/off with a CW key producing a 100% clean sine wave.

There are however limitations in the HamSphere sampling process. Operation from 90 kHz offset and up (such as 50.190) might produce distorted audio. Due to the Sphere sampling frequency of 192 kHz the following frequency offsets should be avoided:

90-96 kHz (Some audio sampling artifacts)
96 kHz (Dead lock = Sample rate / 2, will not produce any audio)
96-100 kHz (Out of band operation, audio will be distorted by bit quantization noise)
0-1 kHz (Near Local Oscillator Deadlock. Out of band operation, audio will be distorted by bit quantization noise)

Tuning HamSphere outside the specs is not prohibited, but please observe the audio limitations.

Operating HamSphere within 20-30 kHz (such as 7020 kHz) offset would theoretically produce the best audio.

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