Recent content by bmnet

I would think the small fluctuations are a result of induced voltages. The conduit should be acting as a wave guide and thus the variations of voltages at various points.

From the schematics, I think your antennas are the four interlocking traces on the reverse side of the pcb. Looking at the modifications that you made, you shorted out two of them and that would explain the range reduction. The terminations resulting from the above would also act as a source of...

If you're dealing with multiple receivers, try moving one of them and hopefully you'll move it away from the 'null'. Most likely the tx antenna's pointing in a different direction to cause acute reflection angle (the change in water level too could necessitate an adjustment of the tx antenna)

Try changing the feed point as well... Most of the time they do have a significant influence on your operating frequency...

Looks like a VLF antenna... Seen a few of them used in WW1 to receive and tx with submarines... That was before sky waves were used... Got a similar structure in Canberra, Australia and I think Sweden... Could operate at powers of up to 140MW! I think... They're no longer used commonly now days...

Hey, I think the metal box will block all your signals, or make your antenna receive from a certain direction only... As for the LNA, would be better placing it behind the ground plane of the antenna...

why not try using a sonar? But then you'll need a detector, not sure how much those cost but should be cheap... Bmnet

Higgler, the dielectric constant in air makes the difference... I did start again but made L:W ratio about 1:1.5.. Not bad now. Just got 50MHz off target. Thanks guys for all the help. Bmnet

I think you'll get a frequency reading that's slightly higher than 30MHz but less than 60MHz if you switch between 30MHZ and 60MHz. As VE1BL mentioned above, detecting the frequency normaly uses the zero point crossing, thus a small bit of the cycle will be going slowly (low freq) while the...

Got up this morning and had a crazy idea... Before going on the trimming idea, I decided to shift the feed point... After about 15 holes of trial and error, I got the frequency down from 1.5GHz to 1GHz!! Think I should be happy with that (considering I didn't even callibrate the network...

Thanks Higgelr... Your last point's looking interesting by the minute (even though its crude)...

Thanks Higgler. Sorry about the bandwidth, needed it to be as wide as possible ( about 200MHz at the least). I guess what puzzles me the most is the failure of the antenna to operate at its design frequency... As for the simulation Savedadogs, it did agree with theoretical design calculations I...

A company called Alien have got some RFID readers, wouldn't it be better to use an already built one than trying to reinvent the wheel.. Ps. Instead of using two antennas, just try a circularly polarized one... Then tx using H-polarized and rx a V-polarized ID...

Yes, Higgler, its 1/2 wave resonant antenna. I used the simulator to find the 50Ohm point in the patch for the coax probe, lacated about 15% off the center.. Got a BJC (gold coated) connector at the bottom, then even checked for shorts... The ground plane dimensions are 300x300mm. The substrate...

I thought we didn't help students do their assignments here? I don't really get what your doing... Mind giving more details?