DAB reception

Watch out for Rabbits.

You are quite correct! I can relax:-)

DAB is OK here. Use it in the house and car. More stations available, Talksport 2 or 5Livex for continuous cricket commentary.

Phew. So can I since he is off in the Caribbean now as the fields are too wet and there is sod all else to do

Oh, indeed. But the audible results are similar. And the same sort of problems with an inside aerial in VHF TV days.

Each transmission medium has its own individual problems.

??

So is my Humax HD FOXT2 PVR but I don't need to interact with it directly.

For a bedroom radio you want something that is easy to use even with the lights off !!

I haven't heard of this and I'm very interested. Please tell us more.

Bill

For VHF FM, a standing wave causing complete or near-complete signal cancellation obviously results in what is effectively weak or zero signal at the receiver. You'd expect degradation into noise pure and simple but there's usually another weak signal path from a reflection external to the room. With the direct path almost or completely cancelled out that signal becomes more significant so the audible result is often the high frequency audio distortion (lisping) that is also caused by simple signal reflections. In the case of analogue TV, standing waves within the room (or loft)can, by the same mechanism, cause ghosting rather than simple weak signal.

Bill

Edge diffraction there is a good article on it somewhere, can't think of it right now tho..

back in the days of 35MHz NBFM it was well known that flying at reasonable range over rusty fences would cause momentary loss of or corruption of signal. Generally seen as a massive twitch on all flight surfaces and a loss of throttle.

Whether it was multipath, or diodic mixing causing intermodulation I cannot say - or both.

For more information, the signal modulation on FM RC is/was a series of frequency excursions marking the edges of a series of channel frames about 1ms long with the lengh of a frame being the position of the associated servo - in the range of 0.5ms to 1.5ms. A very long frame -

This form of modulation has only one benefit. A simple CMOS shift regsiter could decode the pulse train to the servos.

But as an interference rejecting schema it was pants. Loss of a frame edge meant one channel got two channels worth of info and the subsequent channels got te wrong info.

Hence the massive glitch/twitch.

Interesting!

Time for OFDM perhaps;?..

Edge diffraction! Six miles from a high powered TV tx. Rounded and bare heap of colliery waste in way. Move the rx aerial vertically up and down and there will be distinct peaks and nulls. Bill

Thank you.

Bill

we have now gone 2.4GHz. Essentailly the wifi band. This uses a collision detection algorithm and spread spectrum. Also some frequency hopping. Since the frame rate is low - a complete model only needs 64 bits every 20 ms - a massive data rate of 3200 bits per second - the way the systems work is to transmit a frame with error correction and a transmitter ID, and back off if there is collision. The comms is bi directional so the receivers request retransmits if a frame is corrupt.

Loss of a frame simply means that the model carries on doing whatever it was doing - the actual perception is that it's sluggish and unresponsive. Ther is usally a watchdog tomer that will move the controls to user configurable preset positions - usully cut throttle and mild level turn - in the event of total signal loss.

Since every transitter has a unique MAC code, operation of dozens of models simultaneously is possible - all too many transmitters does, is slow the data rate down a bit. Its like having a shared wifi network.

I used to get some issues flying through a tight beam from the local radio mast that you know of all too well. Lets hope te 2.4GHz stuff is more resilient