[BC] Car Radio Antennas

[RichardBJohnson at comcast.net]

 >From this time on, we will just call this the April Submission.
That way, anybody reading it thinks we are just working
on a technical paper. In other words, we will hide in the open.
Anybody who wants to contribute should send me their
edits (off list) and I will merge them and put their name as
committee members submitting the proposal. Please do
not send "obvious junk," because I need to make this proposal
seem like a reasonable technical document. Technical proposals
do not require a filing fee.

So far, this is what I've started. I let the mailer deliberately wrap
so you can paste this into an editor with minimum work.




It is proposed to allow spread spectrum techniques to provide better 
spectrum utilization for Standard Broadcast (A3) facilities in the 
United States.

Current interference problems
Nighttime propagation effects cause interference between broadcast 
stations. In particular stations that are utilizing the new IBOC 
digital transmission standards produce significant sideband 
contamination of adjacent channel allocations. Furthermore, stations 
that are on the same frequency often produce low frequency beats 
which seriously affect the listen-ability of even the local station.

The proposed solution
Allow standard broadcast transmitters to frequency-modulate their 
carrier frequencies with a pseudo-random (noise) pattern. This 
spectrum-smearing will make beat frequencies impossible and move any 
IBOC sideband contamination outside the range of normal human hearing.

Technical specifications
It is proposed that the mean frequency of the carrier be maintained 
as at present within +/- 20 Hz of its assigned. However, the 
instantaneous frequency shall be smeared within a range of -127 to + 
128 Hz (8 bits, with 1 bit per Hz), using a pseudo-random sequence 
generator with a step-rate of 10 kHz. This will be a uniformly 
distributed pseudo-random number generated by the linear congruent 
method, resulting in direct sequence spread-spectrum modification of 
the amplitude modulation signal. The stepping rate is significantly 
higher than the bandwidth of most receivers and somewhat beyond the 
bandwidth available with current amplitude modulation transmitters. 
The result being that the separate steps of the transmitter's output 
frequency are not resolvable resulting in the appearance of a smooth 
rectangular spectrum about 512 Hz in width.

Reception
The frequency modulation of the transmitter carrier with a 
pseudo-random noise pattern does not put noise into the output of a 
linear envelope detector because it does not affect the amplitude. 
However, when either a receiver or the transmitters are tuned off 
frequency, FM to AM conversion can occur. This could result in noise 
being introduced into the demodulated audio. However, the selection 
of a stepping frequency of 10 kHz puts this noises component well 
outside of the bandwidth of current AM radios.




--
Cheers,
Richard B. Johnson