[RFI] Radar Engineers Model 251 Parabolic dimensions?

[Dave Cole]

Be very careful pointing lasers upwards...

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 5/13/21 4:06 AM, Mike Martin wrote:
> Charlie considered using a mounted green laser sight. During the winter months when the Sun goes down it makes it very difficult to see where you're pointing.  If I remember correctly, green seems to produce the most noticeable color for day and nighttime spotting.
> 
> ⁣Be safe,
> Mike
> 
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> On May 13, 2021, 6:12 AM, at 6:12 AM, Charlie Delta via RFI <rfi at contesting.com> wrote:
>> Hi Mike
>> I have studied the various datasheets for Ultrasonic receivers. Most
>> have a broad beam width that is something like more than 60 degrees.
>> This includes the widely used Kobitone transducer. I have check many
>> datasheets including those from Murata, Monacor, Kobitone and those
>>from many expensive USA made sonar transducers. All seem to have
>> similar sensitivity figures all the Kobitone transducer appears to be
>> 6db more sensitive. I just assumed that the perfect FD ratio with the
>> perfect parabolic shape  when combined with the broad beam-width would
>> be sufficient to flood the transducer.
>> I will be using a laser beam and LED endoscope light source and I will
>> test  all of the variables as I have some  time.
>> I have also been informed that the Radar Engineers unit uses the 25khz
>> frequency rather than the 40khz frequency. This apparently makes a big
>> different in the usable   detection range. So the assumption that 40khz
>> would produce similar results to the RE unit is clearly incorrect since
>> the lower detection frequency would have a propagation distance
>> advantage.
>> 73CraigVK3OD
>> "One aspect of the design that may be
>> overlooked is the beamwidth of the
>> ultrasound transducer itself.  Even
>> with a proper F/D ratio, the transducer
>> may not fully illuminate the reflector
>> or instead spill over the edge, both reducing
>> gain.  The transducer's sensitivity is
>> another obvious factor.  Getting the perfect
>> reflector geometry won't mean much if
>> it's not matched to the transducer beamwidth.
>>
>> Mike, K8CN
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