That would be a major change to the loop amplifier, but nothing else. It also moves the scope of the project beyond that of the RCTech forum. But it's still a very good question!

Increasing the transponder power requires a new output circuit, but the only technically challenging part of that is emissions compliance. This would, of course, require a new PC board.

@notch johnson:
I have experienced in the Cano-design almost similar things: After sundown, the loop picks up a lot of environmental RF-signals. This is known from shortwave communications were sgnals travel much further during the night. Worldwide communications advantage from this fact. Normally you will not notice additional HF signals (around 5MHz) captured in the loop because the preamble-word needed to decode a valid transponder-ID is not met. The noise received from the sky after sundown has a random character. However I have added from the start of my experiments a monostabil multivibrator (1/2 74123 TTL) that is set to 100mS and controls a green LED by a transistor. The input is connected to the Valid-signal of the decoder. The LED blinks every time a car passes the loop. But also when environmental HF noise matches the set preamble word. To my surprice, after sundown the green LED is much more active compared to the situation during the day. Most passes of a car are still detected (they are send average every 3mS), but I still wonder whether others notice some degredation of sensitivity.

@notch: Could you try to start a test where the 11 - 12 hours of usage ends well before sundown to prevent the above explained to decrease the receiver sensitivty?
Thank you!

Hey guys, I hope this isn't too off topic but I'm looking for some help and you'll seem like you might have my answers :-) (I hope!)

I just installed an indoor carpet track in my shop with an RC4 decoder. The coaxial run is approximately 30 ft long (copper shielded wire). The detection loop is 1 ft x 5 ft.

The noise level on the coaxial by itself is around 9 to 10. The noise level on the whole system with the detection loop connected is around 70 during the day and as it gets later in the evening sky rockets to about 150.

I have mounted the detection loop on a piece of cardboard and moved it around the room and up and down with no real difference in the noise floor.

During the day, the noise is not a big deal because the signal from the cars is close to 100 points over the noise. But by 7 to 8pm, I'm concerned that the signal to noise ratio will not be great enough to ensure accurate readings 100% of the time.

Is there any way to shield the loop, or anything else to minimize the noise introduced to the system?

Thanks a bunch for your help!

Shannon

I don't have any technical advice for you, since I have no experience using the Mylaps (or AMB) decoders.

Don't be afraid to start a new thread to get help! There are many knowledgeable people here on RCTech, and I'm sure many will have good advice. But you may not reach those people on this particular thread.

Forgive me for pointing out the obvious, but have you asked MyLaps for advice? I'm curious to hear their response.

Thanks Howard,

MyLaps response was basically to get the loop away from metal and devices conducting electricity. Given that I have moved it all around the confines of the room that it is in, I'm kinda stuck.

I asked them about any kind of gain settings (not squelch) and they weren't of much help there. One of the guys was going to their headquarters in Europe this weekend and he was going to ask the tech guys over there about it and let me know.

Thanks again,
Shannon

Thanks Howard!
Here is my decoder smd components, made ​​by the scheme Howard.
_h ttp://rc-auto.ru/forum/index.php?act=Attach&type=post&id=31599

Loop Amplifier
h ttp://rc-auto.ru/forum/index.php?act=Attach&type=post&id=31600
I can not spread links, posts a little.

They look great! Here are the photos:

I was looking at the BSPK signal to figure out the encryption. Is this information available ?

I finished the decryption protocol coding AMB

Fantastic! Can you share the details with us?

convolutional codes and the Viterbi algorithm

How do you apply the Viterbi algorithm on binaries data ?

I was thinking about an RPi this before reading this thread. Great minds think alike. Im not a coder, but I would think a SDR receiver like the USB dongles found on ebay could work for decoding. I know some of them work for digital radio receiving on the ham bands for PSK31, etc.

The difficulty isn't in decoding, which is a problem Howard's excellent circuits handle fine. For accurate timing the problem is having a real time, low latency device capable of measuring the 'events' as they happen.

There are circuits in this thread which use a microcontroller to timestamp the data, these get good enough precision. Moving all decoding and timing to an FPGA (with averaging of multiple hits) gets both accuracy and precision even closer. Then there's the fancy analogue magic that AMB use (probably patented) that will get you the last bit of accuracy.

The Raspberry Pi is a great device but a normal operating system isn't going to get you accuracy or precision. You'll still need all of the decoding and timestamping to happen in a dedicated circuit.

Lastly many of the RTL SDR devices are designed as TV tuners (for DVB-T). These generally wont be able to tune low enough to get to 5Mhz-10Mhz. Even the HackRF (designed from the ground up as an SDR) isn't rated below 30Mhz.