On Sep 29, 8:48 pm, "Dave" wrote:
here in the states we call 13.56MHz an ISM frequency. Meaning Industrial,
Scientific, and Medical. near any populated area you are liable to run into
diathermy machines, plasma ovens, rfid tag readers, and a host of other
noise generators there. i would suspect your environment may be similar.

for ground wave the vertical would probably be best, especially for
omnidirectional covereage... though a low dipole would likely work almost as
well.

frequency stability with modern equipment shouldn't be a problem, just be
sure to build everything nice an solid so it doesn't 'bounce around' and it
shouldn't be a problem... not like bouncing around tubes with mechanical
elements that would vibrate and move in the distant past.

"Bob Bob" wrote in message

news


Hi all

I am gradually working up to a project to TX telemetry from the car at
very low QRSS type data rates. Because of the unattended nature of the
system I am going to start using the HiFER freq of 13.56Mhz rather than
a "real" amateur allocation.

This of course means very low output power and no doubt a number of
other limitations for the TX. I really only need the system to work
predominately 10 miles from the base.

Yes I am aware of the frequency stability issues for very narrow band
signals. No doubt the vehicle bouncing around wont help either! May end
up using a Picollo type system where the freq difference between two
states is used to send data.

I am after some feedback and ideas about antenna systems to use. I
suspect the car TX antenna will only be a wire draped across the rear
window or a loaded broadcast antenna. The RX base antenna was going to
be just a dipole but I reasoned that this would be great for DX but
terrible for groundwave. Then thought about a vertical dipole, but am
concerned about the higher noise level. I'll probably end up trying
both. Initial tests are only going to be looking for a CW signal on a
waterfall.

Would also consider experimenting at a MedFER freq around 1700KHz but
base antenna efficiency might be pretty bad. There is also a lot more
RFI there.

Ideas welcome. If however you want to say it "wont work" please back it
up with some maths/calcs or your own direct experiences.

Cheers

Bob VK2YQA- Hide quoted text -

- Show quoted text -

10 miles ground wave at 14 meg is going to be iffy....

denny / k8do