Radar

tcijoe

Thanks to advertising, we ( as a group ) seem to have lost sight of what exactly takes place in modern devices. In this case ( rec. marine radar ) the catch is "time". Or rather using the correct unit of measurement. That 4kw radar certainly does produce a microwave signal "at the rate of 4000 watts per second". The "catch" is that it does not run continuously, but that it pulses ( I'm not going to check the manual, so what follows is approximate ) about 180 times per full revolution, with each pulse only a few nanoseconds long. Ah, but what is a nanosecond? It is one one billionth of a second. So it becomes obvious that even a prolonged exposure to a rec marine radar will produce far, far less than 4kw ( watts, total, not watt-seconds ) of energy transfer. SO, the truth is that, over a period of time, very little energy is radiated. So little that it won't heat much of anything ( the basis of the risk ). In contrast, the microwave oven that you warm you Starbucks in radiates continuously and that 1600 watt micro will dump more energy into that poor unsuspecting cup of coffee in a few seconds than your marine radar produces in total over a period of a year.

---

The use of microwaves as a heating device was noticed when the chocolate bar in the engineers pocket melted during a test...
 
Getting back to VHF antenna radiation......I've never heard/read of this and would like more information. Does it radiate continuously [like a microwave] or ?????? My antenna has been installed at waist level, standing, or chest level sitting, for 15 yrs. I always have my radio on when I am underway; per my hour meter, that is almost 1000 hrs. Is this a serious concern? Let me know please.
 
A VHF antenna radiates only when you are "key down", that is Xmit key pressed and you are talking. It does not radiate when recieving, listening.

I have seen many VHF installations where the antenna is mounted on the gunwale, and the operator stands ( sits ) right next to the radiating element. This is never recommended. The "fix" is to get the base of the antenna ( where it mounts at the bottom; where the antenna lead is attached ) above the head of all aboard. This serves two purposes: a) it raises the antenna height, giving greater range, and b) gets the humans out of the strongest portion of the radiated signal.

Though there is no sharp pattern, you can think of those pictures you have seen of an old lighthouse, with its rotating spotlight. The VHF antenna "shines" perpendicular to the antenna shaft, and radiates little or no energy out of the ends. While it is unlikely that you have "cooked" anything, standing in the path of the signal is not something to do intentionally, on a regular basis. Placing the base higher than your head, serves the purpose of reducing the exposure by several magnitudes.

--

In short, don't worry, but next convenient opportunity, mount the antenna higher.

-edit-

One quick, easy, and not too expensive method of raising the antenna is to use an "extension shaft" Shaksphere sells them, as do others ( Here is one from Digital at Boatfix ). they come in lengths of 2', 4' 6' and 8' ( I think ). Just put the extension between the current base mount and the bottom of the antenna. I'd have to research further to know how the antenna feed line is handled. In any event, this is usually the way this gets fixed.
 
Bill thanks for the very good information!

Yikes, I guess I need to get one of those extensions, cause the only part of my boat above my head is the top of the window frame. Right now it is mounted outside on the gunnel aft of the my helm seat.

Fortunately I do not "chat" on the vhf. I mainly listen. If I want to chat with someone, I use my cellphone.

I always get useful info on this site, even when it is "incidental" to the topic!
 
The use of microwaves as a heating device was noticed when the chocolate bar in the engineers pocket melted during a test...

so something did get cooked/melted. kind of interesting in itself.

learn something new everyday!
 
quote:
Originally posted by giolic

I don't want my insides cooking.

Click to expand...


uuhhmmmmm....

back when i was in the navy (for a country that shall remain unnamed) we use to shot birds outta the sky with the radar......

there were very defined spots where NOT to be when up on the superstructure....and a standing rule that if you were anywhere up there and started feeling warm on the inside, to GET AWAY !

if youve ever seen a polish sausage in a microwave....well, you get the idea...

recreational radar is not nearly as strong as military units, but why risk it ?....
 
Look on the bright side, stand in front of the radar long enough and you probably won't need to use the courtesy lights to see around you at night...
 
Thanks for the vhf info, Bill.

I was going to post a quesiotn on this topic, I just purchased a new VHF and notice the mounting instructions for the antenna stating it should be mounted above your head or atleast 1 meter from where anyone would be (not an exact quote, just what I recall).

My antenna is mounted almost as close to my head as you can get. It is mounted on the side of radar arch.

I assumed that it would only be bad during transmit, but good to get confirmation. I would also assume that using the 1 watt transmit would be much less harmful then the full wattage. Like the other poster i don't transmit often and mostly listen.

what about a hand held unit?

Thanks,
 
quote:
Originally posted by ChezBippy

what about a hand held unit? Thanks,

Click to expand...


Took the words right out of my mouth. I think my icom high power is around 5 watts.
 
...there is a -reason- why a HH is limited to 5 watts, and offers mw power settings. If you want full power ( limited by FCC type acceptance to 25 watts ) you need a "fixed station" or "dash mount".

There is a whole body of research on the subject, and way too much to discuss ( hey, I ain't gonna type all that! ), but the human body reacts to different frequencies differently. The FCC generally sets limits that are reasonable ( like all such reports, some people think the limits should be higher or some lower... ) but in practice, these limits have served the public well. And while having a long-winded discussion while standing next to a 25W emiting VHF antenna is not going to drop you in place, it cannot be said to be completely healthful over the long term.

Before anyone gets all warm and paranoid, remember that recreational radios and radar are pretty darn safe, esp when compared to military equipment. A malfunctioning recreational unit is almost certainly not going to cause immediate, fatal injuries. And a properly functioning unit should cause no injuries, immediate or long term. Simply, use the tool as intended, and it will serve you well.
 
There is a common misconception of the dangers associated with various forms of eletromagnetic "radiation". This is due entirely to the unfortunate connotation of the word radiation. Electromagnetic radiation is nothing like nuclear radiation and has entirely different risks.

Electromagnetic energy ranges from low frequency radio waves up to x-rays and gamma rays. The higher energy forms (UV, x-ray, gamma ray) can cause direct biological damage. This direct damage can only occur at frequencies of UV light and above. This is why you need sunscreen to block UV rays, why you should avoid exposure to x-rays and why life would not exist on earth without the ozone layer.

Electromagnetic energy of lower frequencies (visible light, infrared, microwave and radio waves) CANNOT cause direct biological damage. They can only inflict damage by raising the temperature of your body. Massively powerful radars are in fact dangerous due to their ability to cause a fever or produce localized and undetected heating. They are not going to "make you glow" or effect your reproductive ability (unless you cook an important body part).

Modern radars work due to the fantastic sensitivity of their receivers, not by transmitting huge amounts of energy. The power deposited onto your body by a typical radar is of a lower frequency (hence lower energy) and of a lower power level than your spotlight or a powerful flashlight. You are in no danger from your radar unless it falls on you.

Unfortunately the common use of the word "radiation" gives people the impression that all forms of energy have insidious dangers. This is simply not the case.

Mike
 
quote:
Originally posted by SlowButFast

quote:
Originally posted by giolic

I don't want my insides cooking.

Click to expand...


uuhhmmmmm....

back when i was in the navy (for a country that shall remain unnamed) we use to shot birds outta the sky with the radar......

there were very defined spots where NOT to be when up on the superstructure....and a standing rule that if you were anywhere up there and started feeling warm on the inside, to GET AWAY !

if youve ever seen a polish sausage in a microwave....well, you get the idea...

recreational radar is not nearly as strong as military units, but why risk it ?....

Click to expand...


Back in the cold war days we would fly along the East German border and target their radar instillations with a focused microwave beam tuned to their frequency. In an F-111 Raven (ECM version) we could put our 175 kw (yes kilowatts) right on their receiver from 10,000' and fry their receivers as we flew along the border. It usually too them a week or more to get the parts to repair equipment, we were just having fun with them.

SeaQuest OE
 
quote:
Originally posted by TigerPaws

quote:
Originally posted by SlowButFast

quote:
Originally posted by giolic

I don't want my insides cooking.

Click to expand...


uuhhmmmmm....

back when i was in the navy (for a country that shall remain unnamed) we use to shot birds outta the sky with the radar......

there were very defined spots where NOT to be when up on the superstructure....and a standing rule that if you were anywhere up there and started feeling warm on the inside, to GET AWAY !

if youve ever seen a polish sausage in a microwave....well, you get the idea...

recreational radar is not nearly as strong as military units, but why risk it ?....

Click to expand...


Back in the cold war days we would fly along the East German border and target their radar instillations with a focused microwave beam tuned to their frequency. In an F-111 Raven (ECM version) we could put out 175 kw (yes kilowatts) right on their receiver from 10,000' and fry their receivers as we flew along the border. It usually took them a week or more to get the parts to repair equipment, we were just having fun with them.

SeaQuest OE

Click to expand...
 
I love this site. Where else can you get great reading like this?!
 
quote:
Originally posted by meide

They can only inflict damage by raising the temperature of your body. Mike
Click to expand...


Is that what gave me those hot flashes??? [:-boggled]

Seriously, Mike, thank you for taking your time to give this very good information on the subject. I appreciate the enlightenment! I don't think I'm going to yank my VHF out of the boat this weekend after all.[:-eyebrows]
 
You must log in or register to reply here.
Back
Top