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Reviews > Environmental Monitoring Gear > Weather Recorder > Kestrel 3500 > Brian Tannehill > Test Report by Brian Tannehill

June 25, 2007



NAME: Brian Tannehill
EMAIL: tannehillclan (at) gmail (dot) com
AGE: 32
LOCATION: Colorado Springs, Co
HEIGHT: 5' 7" (1.70 m)
WEIGHT: 185 lbs (83.90 kg)

I am fairly new to backpacking, but I have hunted/fished/camped all my life in East Texas, Colorado, and California. My young kids (4, 10, 12) limit me to weekend overnight camping trips, or day hikes Geocaching. I am also an avid mountain biker. Currently I live in Colorado Springs, Co at the base of the Rocky Mountains. Pike National Forest surrounds me at 9000 - 14,110 feet (2743 m - 4301 m). Snow can happen 10 months out of the year and summer is the hottest reaching 65 F + (18 C +), the other months average 45 F (7 C).



IMAGE 4  logo

Manufacturer: Neilsen-Kellerman
Year of Manufacture: 2007
Manufacturer's Website:
MSRP: US$ 249.00
Listed Weight: 2.3 ounces (65grams)
Measured Weight:
Without cover 2 1/4 ounces (66 grams)
With Cover: 3 5/8 ounces (102 grams)
Fig 1 courtesy Neilsen-Kellerman


Fig 2 courtesy Neilsen-Kellerman

Fig 3
My first thought when looking at the Kestrel 3500 on the web site is this may be hard to operate. Once it arrived though I was pleasantly surprised. It's very easy to use. There is a power button along with a left and right arrow (Fig 3). It can't get much simpler than that. It is very easy to scroll through the main menus. All of the measurements are abbreviated. In the second column of Fig 2 labeled "Hint", it shows what the measurements are abbreviated as along with the icons in column three. The hardest thing to do so far, and I still haven't gotten that resolved correctly is to set the barometer and altimeter.

When I first opened the unit, I noticed something odd. The impeller that measures wind speed is very sensitive to any air movement. However once it slows down to a stop it appears to be imbalanced and teeter totters back and forth coming to rest. This really freaked me out until I read in the directions that it is meant to do this. From the instructions "Why does the Impeller Appear Imbalanced? It is NORMAL for the impeller to oscillate as it comes to a stop. It is NOT improperly balanced. Rather, it contains a very small magnet which responds to the earth’s magnetic fields. This does not affect the accuracy of the wind speed readings because the magnetic field applies both a braking and an accelerating force which cancel each other. The impeller has been calibrated to provide wind speed readings accurate to within at least
± 3%."


I don't need any stinking Instructions. I'm a man hear me roar! OK well I did need them to figure out how to set the altimeter and barometer which I still have not totally figured out. The full instructions can be downloaded from Kestrel's homepage. Operating the unit though is very simple.

Quoting from the instructions:
1) Slide off cover.
2) Turn on. Press the center button to turn on the unit.
3) Select measurement. Press the right arrow to scroll through the measurements
listed below. Press the left arrow to scroll through the measurements in reverse order.
The instantaneous measurements will be displayed. Each measurement screen is
preceded by a brief hint to clarify which measurement is being displayed. (See
Understanding the Measurements section for more information.)

Barometer and Altimeter Operations
Obviously this does not have a GPS device in it. So it must be basing the altitude off the barometric pressure. I can adjust both refernce points for the barometer and altimeter. From the directions it appears I can only monitor one or the other while out hiking/camping.


impeller removal
Fig 4
Like I noted it is pretty simple to use. I like to show my wife the relative humidity, or lack there of in our house due to the heater being set so high. One thing I am really interested in is how the impeller works. The impeller can be changed out by the user. There are no wires to unplug, all I have to do is gently push the impeller out of the housing (Fig 4). So how does it send the information to the display? I'm not really sure. My guess is it involves magnets and voodoo. I've used it a few times outside sticking it in snow to measure the temp of the snow. Guess what? It is cold. I've measured the water temp of my tap water. The impeller is really quit, but I do notice when the wind is up around 7 mph (11 km/h), that it becomes noisy. The instructions say "High Speed Use After several hours of sustained operation over 25 M/S (~49 KT, 90 KM/H, 56 MPH or 4,923 FPM), the Kestrel will lose some accuracy due to wear of the sapphire bearings in the impeller."


Some questions I want to answer from this test series include:

How quickly can I get an accurate temperature reading? Wind Reading? Barometric reading? Altitude reading?

The documentation says I'll get 300 hours of use out of the batteries, is this accurate?

How bright is the backlight? Will it ruin my night vision? Is it bulky?

Is there a certain hand position I need to hold this thing so my body heat does not influence the temp reading?

How many different data points can I store on this unit?

How easy is this thing to use?

Is it suitable for backpacking? Hiking? Throwing in my pocket for a quick hike?

How easy would the impeller be to replace if need be? Is one provided or do I need to buy an extra one?

How accurate are the readings?

How easy is the wet bulb test to perform?

My test plan will consist of using the kestrel 3500 on any and all my hikes/campouts. I mainly would like to use it when I test out my winter hammock set up to see at what point I start to get cold in my sleeping bags if I get cold at all. I'll test the outside temperature and the inside temp of my sleeping bags. I'd also like to know if I could get a surface reading off my sleeping pad, both above where I would lay and below where the air would affect it the most.

Please check back in two months for the Field Report, at which time I should have answered most of these questions.




I've taken the Kestrel 3500 on three different hiking trips, and two different fly fishing trips and numerous times just out in the yard trying to impress my weather man neighbor. Temperature has ranged anywhere from the low 20's F (-6 C) to the normal temp of 75 F (24 C) in my house. Wind speed has been anywhere from nothing to 20 mph (32 km/h). It's been mostly sunny, with a few snow banks left around the trails. One fishing trip the water temperature was 35 F (2 C) with chunks of ice floating down the river.



I used this device to measure all kinds of temperatures. I've measured anything from snow banks, to river streams, to air temp, temps off my grill, and temps in the house. I found it really neat to watch the water temperature of the Arkansas River warm up through out the day as I stood in it. When I got in the river, it was hovering around 32 F (0 C) with chunks of ice floating down the river. Through the day it warmed up ever so slightly to 35 F (2 C). This will be helpful to know when certain bugs are about to hatch, as they need a certain sustained water temperature to be able to hatch. I also found that I could measure stream flows in miles per hour. However I could not find a conversion from cubic feet per second to miles per hour. Cubic feet per second is the standard unit of measurement for the stream flows around here. The Arkansas River runs anywhere from 300 -3000 cubic feet per second. So I'm not really sure what good it did me to measure the flow in miles per hour, but it was cool to do none the less and impressed my fly fishing partner when I "guesstimated" the stream flow.

I have also stuck this device in some snow banks to get the temperature of the snow. Snow is cold, that's all I really need to now, but there again the cool factor was high, and I could impress all the teenagers around and make a few bucks guessing the snow temp! Ok not really, but I did find it was difficult to clean all the snow from the impeller afterwards.

When I hike with this thing I turn it on and hang it from my neck and leave it on. I've found that I like to take the protective cover off while I hike because it clanks and makes noise. I usually acquire a good reading with about 30 seconds of starting the unit, and I've found no affects on temperature readings from letting it bounce off my stomach while hiking. I would have thought letting it hang so close to my body would affect the temperature reading but I have yet to see it.

One thing that does get affected by carrying it this way is the average wind speed. It's kind of useless to get an average windspeed, unless you hold it in the wind for the duration of the measurement. The average wind speed is calculated from the time you turn it on. So if I turn it on, and then measure the wind speed, then let it hang in front of me while I hike, it doesn't pick up the wind at all. The unit does not give an accurate average wind speed at this point. I would need to turn it off and back on again.

I've also found if there was no wind, I could get a close estimate to how fast I was walking by holding the unit up while I walked. This was fairly close when compared to the speed of my GPS. If there was wind, I could take a wind reading, then walk, and subtract the difference. However with the gust and crosswinds this method was not very accurate.

I'm still trying to figure out the barometer, and altimeter. I can use one or the other during hiking but not both. I have to set a reference point for each one, and that affects the other since the altimeter is based off the barometer. One thing about the barometer I do not like is the sensitivity to pressure changes. I think it is too sensitive for me. It constantly changes pressure, which in turns constantly changes the altitude. Sitting still holding the Kestrel in one spot, I've noticed the altitude change as much as 10-15 feet (3-5 m) at a time. Another barometer I have used the pressure only changes every 5 inhg at a time, which is better for a steady reading. This Kestrel changes every 1 inhg at a time as the air pressure is constantly changing, which in turn affects the altitude reading.


So far I like this unit. I like being able to tell wind speed and temperature any time I want to, especially while out hiking. The unit is small enough it packs just fine for any hiking that I do. I usually just hang it from my neck and go. One of the things I will be monitoring for the next few months is the face of this device has very small scratches in it from sliding in and out of the case. See fig 3 in my IR above.

Check back in two months around the end of June for my long term report.



I've continued to use this tool as described in the previous two reports. I'm still measuring the temperature on anything I can find. I've even used it to measure the inside temperature of my computer case. Temperatures have ranged anywhere from the low 30's F (~ 1 C) to 85 F (29 C). Wind speed has been anywhere from nothing to 20 mph (32 km/h).

Below are multiple images within minutes of each other on one of the hikes I went on. Starting from left to right is temp, then the temp again a few minutes later, temperature with the wind chill, and then just the wind speed.

Temps, Wind Chill, Speed


Here are some questions left unanswered from the first two reports:

How quickly can I get an accurate temperature reading? Wind Reading? Barometric reading? Altitude reading? Within seconds. For temperature readings, I can wave the unit back and forth or in a circle for about 4-5 seconds and it is spot on with the temperature.

The documentation says I'll get 300 hours of use out of the batteries, is this accurate? They last a long time. I've turned this thing on for every hike I've been on, along with every time I've used it, and just left it on. It has an internal timer that cuts the unit off after 45 minutes if no buttons have been pushed.

How bright is the backlight? Not the brightest I've seen but its close. I know that doesn't help, but I have no real way to measure the lumens of the light.

Will it ruin my night vision? Yes, it will ruin my night vision. I just turned it on to see if it would blind me at night. I can use it as a small night light to find my way around.

Is it bulky? Not at all. It's the perfect size to throw in a pants or jacket pocket or to hang around my neck.

Is there a certain hand position I need to hold this thing so my body heat does not influence the temp reading? Yes, if I smother the temperature sensor with my hand, it will affect the readings. For the most part, I hold it like shown in the above pictures.

How many different data points can I store on this unit? It doesn't really store any data points like I thought. Instead it has a hold feature that lets you take a snapshot of all the current readings, whether or not they are displayed. For example, if I use the hold function while viewing the temperature on the display, and then change over to relative humidity, it will show the relative humidity at the time I hit the hold function. It appears to read all the functions at once, but only displays whichever one is on the screen at that time.

How easy is this thing to use? Very easy. As I've described in the IR, it has simple buttons and simple menus.

Is it suitable for backpacking? Hiking? Throwing in my pocket for a quick hike? VERY! I like to throw it around my neck, and take off. That way I have quick access to the readings, and it is already acclimated to the outside environment versus pulling it out of my pocket where it may be a bit warmer than the outside air.

How easy would the impeller be to replace if need be? Is one provided or do I need to buy an extra one? No impeller is provided, I have to buy my own. It is very easy to replace, just push the old one out, and slide a new one in. There is no data though stating how long the impeller should last.

How accurate are the readings? As far as I can tell by comparing it to other environmental monitoring devices, the readings are spot on.

How easy is the wet bulb test to perform? I thought there would be some kind of voodoo magic formula for this, alas there is not. It is as easy as pushing a button. All I have to do is scroll to the "bulb" setting in the menu, and there it is. Easy as pie.

The last thing I was worried about is the calibration of the different readings. Browsing the web site I ran across a section on calibrations and they say, "Kestrel Meters can be quickly recalibrated in the field, giving users confidence to rely on their Kestrel. To field calibrate the wind or air flow readings, simply replace the impeller with a new one. For relative humidity readings, use the RH Field Calibration Kit. For pressure sensor calibration, check out the Knowledge Center, or contact our Customer Service Department for instructions.

The only sensor that cannot be field calibrated is the temperature sensor. The Kestrel’s accurate temperature readings are due to NK’s patented external thermistor, and over the 10+ years that we’ve been building Kestrels, we’ve never identified one that needed recalibration. "

After four months, I see no reason to have to recalibrate this unit at this time. There is also no data on expected time frame to recalibrate this unit, so I'm not real sure how long it will last.

A few more things about this unit. I don't really use the outer case a whole lot for two reasons. One, it makes the unit a little bit heavier and it clangs around against everything while hiking. Secondly, it has left 4 spots on the face of the unit from the inside of the case rubbing against the face of the unit while it opens and closes. Two of the marks are visible below the bird on either side of the number eight. These are the worst two. Another mark is visible above the three in 3500.

Marks on the face

As far as the altimeter and baraometric pressure, I don't really like them. Yes they give me immediate and real time weather updates, but I think they update too much. When reading the altimeter, standing still, it will jump all around because it is based on the barometric pressure reading that is constantly changing. I think it needs to change at like every five feet or so. I think a small trend graph for the barometric pressure covering the last 8-10 hours would be helpful, and maybe it is incorporated in another model.

This unit works best when facing directly into the wind. How I determine if I'm facing directly into the wind is to keep the protective cover on the lanyard. Hold the unit about arms length away letting the cover hang at the end of the lanyard. The protective cover will then act as a small sail. I just point the unit in the direction of the wind until the lanyard blows straight behind the unit. It is not 100% accurate, but if I see it blowing at a right angle to my Kestrel then I know I am in a crosswind.


Overall I really like this unit. It is not cumbersome around my neck and is very easy to use and understand. I will continue to use this tool for my hikes and weather spotting duties.

Thanks to BGT and Kestrel for allowing me to participate in this test series.

This report was created with the BGT Report Generator. Copyright 2007. All rights reserved.

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