jackho
Well-Known Member
Am I correct in assuming that most common radar reflectors do not return a response (because it's not a pulse/echo) from this latest technology radar.??
Radar reflectors and 3G Broadband Radar
- Thread starter jackho
- Start date
prv
Well-Known Member
It is an echo. It's not a pulse, but I can't see why that would matter.
Active RTEs don't respond to broadband radar, but AFAIK passive reflectors still work.
Pete
jerrytug
N/A
Yes as Pete says....and when will the RTE makers include the new type of radar in their grossly overpriced gadgets???
( I prefer to call it Frequency Modulated, or 'FM' radar, because:
a)That seems to be the main difference, and
b)The word 'broadband' is already in widespread use for something completely different.
Not starting an argument though.)
( I prefer to call it Frequency Modulated, or 'FM' radar, because:
a)That seems to be the main difference, and
b)The word 'broadband' is already in widespread use for something completely different.
Not starting an argument though.)
Skylark
Well-Known Member
We were asked by friends last weekend to take a look at their radar signature on my 4th Generation digital / broadband / FM (please chose the least offensive) Simrad. They had just fitted a new reflector. It was the type commonly clamped to the rigging.
Sea state was pretty clam, F2-3. I had an intermittent signal at about 3.5 miles but could not "aquire target" until about 2.5 miles.
Sea state was pretty clam, F2-3. I had an intermittent signal at about 3.5 miles but could not "aquire target" until about 2.5 miles.
jackho
Well-Known Member
FM Radar
Yes .. this was my experience - yachts with or without reflectors didn't appear any different. Also Seeme detectors have no effect either.
Interestingly seagulls rising up and flying across the boat show as targets which raises the pulse momentarily !!!
Yes .. this was my experience - yachts with or without reflectors didn't appear any different. Also Seeme detectors have no effect either.
Interestingly seagulls rising up and flying across the boat show as targets which raises the pulse momentarily !!!
rob2
Well-Known Member
If you are talking about the 2 inch diameter tube on the backstay, remember that when tested under laboratory conditions it was only just detectable. So much so that if it were out of phase with another echo propogated on the boat it could act to turn you into a stealth yacht. One of the things that came out of the general discussions following the Ouzo tragedy and subsequent testing of radar reflectors was a more general understanding that size matters with a reflector - both the physical size and the size of response! Definitely a shame that FM radar can't see an RTE, as these are the only way a small boat can offer a good, reliable radar return.
Rob.
jerrytug
N/A
That's right, and I would guess the best people to make an FM radar RTE would be...the FM radar makers!
I bet they could make one that plugged in to 12v for about a tenner, it would just need some little silicone-chip and a low power transmitter in a waterproof plastic box, surely?
I bet they could make one that plugged in to 12v for about a tenner, it would just need some little silicone-chip and a low power transmitter in a waterproof plastic box, surely?
prv
Well-Known Member
Arida
Well-Known Member
Must confess that I have not gthought about this previously, so perhaps there is a blimmin' obvious answer, but:
why should conventional RTEs (Echomax, See-Me etc) not wok with so-called "broadband" Radar? Some years ago, when I took one of these devices apart (an earlier X band only unit) it consisted simply of two vertically stacked antennas* with a high gain amplifier (as I recall three MMIC stages) in between them to produce a simple repeater, not too disimilar to those used in the past to bring broadcast TV coverage into valleys. The "I am being painted" output came simply from circuitry that detected an increase in current in the final amplifier stage. Really quite crude.
*actually each of these antennas was made using (I think) three PCB patches ant angles to one another in order to give omni coverage.
I can't see why an RTE like this would not be compatible with 3G radar, providing the RTE antenna and amplifers were broadband enough to be able to cover the entire FM radar transmission.
Or am I missing something more?
Regards,
Rob
why should conventional RTEs (Echomax, See-Me etc) not wok with so-called "broadband" Radar? Some years ago, when I took one of these devices apart (an earlier X band only unit) it consisted simply of two vertically stacked antennas* with a high gain amplifier (as I recall three MMIC stages) in between them to produce a simple repeater, not too disimilar to those used in the past to bring broadcast TV coverage into valleys. The "I am being painted" output came simply from circuitry that detected an increase in current in the final amplifier stage. Really quite crude.
*actually each of these antennas was made using (I think) three PCB patches ant angles to one another in order to give omni coverage.
I can't see why an RTE like this would not be compatible with 3G radar, providing the RTE antenna and amplifers were broadband enough to be able to cover the entire FM radar transmission.
Or am I missing something more?
Regards,
Rob
jerrytug
N/A
That's very interesting Rob, I was already sure the S and X band RTE's couldn't justify their prices, why can't the Chinese start knocking them out for a tenth of the price?
As for the FM RTE possibilities, let me try to explain my thoughts why it might be much less straightforward, and why the manufacturers might need to be involved, at least to give out some information.
X-band is just a timed echo, the frequency of the echo is the same as the pulse that was transmitted. (s-band the same). So it is a relatively simple job for the RTE to receive a pulse, and then transmit, just at the right instant, an amplified echo. The echo is of a suitable length to paint a blob on your screen, job done.
However, the pulse sent by FM radar changes is frequency, from the start of the pulse to the end.
Whatever exact instant the echo gets back to the radar, it will have a different frequency.
The initial frequency modulation of the pulse would need to be 'known' by the RTE, along with the way the radar deciphered the return.
That is much more complicated information than a timed echo, which is why I fear it is not an easy add-on for eg SeaMe to incorporate, but it would need cooperation with the radar makers.
However, I am sure radar makers, SART makers, etc must already cooperate, or at least share certain standards, so there is hope for the future...
I do not have the technical knowledge to discuss it in much more depth unfortunately,
my understanding of FM radar is transplanted from a brilliant explanation of FM bat sonar by Richard Dawkins, but the principle is identical, cheers Jerry
jerrytug
N/A
That's very interesting Rob, I was already sure the S and X band RTE's couldn't justify their prices, why can't the Chinese start knocking them out for a tenth of the price?
As for the FM RTE possibilities, let me try to explain my thoughts why it might be much less straightforward, and why the manufacturers might need to be involved, at least to give out some information.
X-band is just a timed echo, the frequency of the echo is the same as the pulse that was transmitted. (s-band the same). So it is a relatively simple job for the RTE to receive a pulse, and then transmit, just at the right instant, an amplified echo. The echo is of a suitable length to paint a blob on your screen, job done.
However, the pulse sent by FM radar changes its frequency, from the start of the pulse to the end.
Whatever exact instant the echo gets back to the radar, it will have a different frequency.
The initial frequency modulation of the pulse would need to be 'known' by the RTE, along with the way the radar deciphered the return.
That is much more complicated information than a timed echo, which is why I fear it is not an easy add-on for eg SeaMe to incorporate, but it would need cooperation with the radar makers.
However, I am sure radar makers, Racon and SART makers, etc must already cooperate, or at least share certain standards, so there is hope for the future...
I do not have the technical knowledge to discuss it in much more depth unfortunately,
my understanding of FM radar is transplanted from a brilliant explanation of FM bat sonar* by Richard Dawkins, but the principle is identical, cheers Jerry
* 'The Blind Watchmaker'
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Arida
Well-Known Member
Thanks Jerry. The RTE unit I took apart was essentially a broadband amplifier rather than anything more complicated involving a pluse detector and pulse generator, therefore it would work over a renge of input frequencies. Of course, whether the range of frequencies covered by the amplifier and antennas would be correct (and broad enough) to cover those used by the FM radar ssytem is a moot point - as yet I have not found any detaisl of the frequency range used by these "broadband radar" systems.
There is also anther possible issue - the FM radar systems operate at very low power, in contrast to conventional pluse radar, so will probably only be amplified by the RTE if it emplys completely linear amplification. If it uses (Say) a class C amplifuer in the final stage in order to reduce standing current, then this amplifier is unlikely to be turned on by the weaker signal from the broadband radar system. The "I am being painted" output is also very unlikely to work...
Gettuing quite interested in this. If anyone has proper technical info (rather than marketing blurb) on the broadband radar systems and their frequency ranges then I would be very interested to know...
Regards,
Rob
There is also anther possible issue - the FM radar systems operate at very low power, in contrast to conventional pluse radar, so will probably only be amplified by the RTE if it emplys completely linear amplification. If it uses (Say) a class C amplifuer in the final stage in order to reduce standing current, then this amplifier is unlikely to be turned on by the weaker signal from the broadband radar system. The "I am being painted" output is also very unlikely to work...
Gettuing quite interested in this. If anyone has proper technical info (rather than marketing blurb) on the broadband radar systems and their frequency ranges then I would be very interested to know...
Regards,
Rob
RAI
Well-Known Member
I think the proper term for these new radars (in old speak) is FM-CW radars. Continuous Wave that is. See
https://en.wikipedia.org/wiki/FMCW#Modulated_continuous-wave
I think the RTE should work with them, but maybe their power is too low to trigger the RTE threshold.
https://en.wikipedia.org/wiki/FMCW#Modulated_continuous-wave
I think the RTE should work with them, but maybe their power is too low to trigger the RTE threshold.
jackho
Well-Known Member
I guess ... back to the start. My friends was surprised when his dual Echomax Seeme didn't show on my radar 200mt from my boat.
jackho
Well-Known Member
No the debate is about the new 3G Radar advertised as Broadband?? and not visible to Echomax and standard type radar reflectors.
Mistroma
Well-Known Member
Rob was referring to post #4 and making the point that the type of reflector used might have a very poor return anyway in that particular test with new type radar.
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BelleSerene
Well-Known Member
Echomax claim that with a minor mod their active reflector WILL respond to so-called broadband radar. On their FAQ at
http://www.echomax.co.uk/faq.html as below.
The idea of making this happen by 'reversing the polarity' (of what?!) of the radome seems very strange to me - I'm going to ask them. Can anyone shine any light on this?
[h=4]Question: Could you please advise whether your X band RTE is effective when interrogated by the new generation of FMCW (surprisingly called broadband) small craft radars?[/h]Answer: If you discard the control box and reverse the polarity of the radome wiring the RTE will respond to broad band radar but will take 220 mA on standby. Your Active-X will continue to receive signals from both broad band and conventional radar.
The power used on broadband radar is very low and can only be used on pleasure craft.
SOLAS radars must remain on X band as it is a requirement that they respond to both Racons and SARTs neither of which will respond to CW non pulsed radar.
http://www.echomax.co.uk/faq.html as below.
The idea of making this happen by 'reversing the polarity' (of what?!) of the radome seems very strange to me - I'm going to ask them. Can anyone shine any light on this?
[h=4]Question: Could you please advise whether your X band RTE is effective when interrogated by the new generation of FMCW (surprisingly called broadband) small craft radars?[/h]Answer: If you discard the control box and reverse the polarity of the radome wiring the RTE will respond to broad band radar but will take 220 mA on standby. Your Active-X will continue to receive signals from both broad band and conventional radar.
The power used on broadband radar is very low and can only be used on pleasure craft.
SOLAS radars must remain on X band as it is a requirement that they respond to both Racons and SARTs neither of which will respond to CW non pulsed radar.
jerrytug
N/A
Very interesting, thanks for investigating. Not that I really understand his response..
lw395
Well-Known Member
Really quite crude?
Or really a bit more subtle?
I can see lots of difficulty in making an FMCW repeater.
For a start, as the pulse is much broader in time, with a lower peak, it's harder to sort the threshold of when the transponder should transmit.
And the radar's receiver is much more selective of what it will regard as a valid return.
Which might be quite handy if you want to ignore decoys on a missile radar....
lw395
Well-Known Member
Drawing 220mA continuosly sounds to me like it will amplify anything it sees, instead of only responding above a threshold.
Best not put two of them in sight of each other, they might continuously amplify each other's response is my first reaction?
