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cs
09-09-2007, 07:07 PM
The antenna book says that the wavelength is speed of light divided by the frequency (in hertz).

The Harris dude said to divide the frequancy (in mghz) by 2.34.

300,000,000 m/s / 300,000 htz

or

3mghz/2.34

I don't have a good calculator in front of me to check, but I think that both are correct.

JimD
09-09-2007, 07:11 PM

George Ray
09-09-2007, 07:13 PM
Velocity / Frequency = Wave_length

(meter/second) / (1/sec) = meter ..... (note the seconds cancel out)

It's always a good feeling when the units work out so you know your on the right track.

cs
09-09-2007, 07:13 PM
Huh? (Not to George but to Jim)

JimD
09-09-2007, 07:22 PM
Huh? (Not to George but to Jim)

A wavelength is the distance measured from one crest to the next crest. Or actually, from any point on a wave to the corresponding point on the next wave. If you're measuring wavelengths of EM radiation you would need a really small ruler and fast hands. :D

cs
09-09-2007, 07:27 PM
But if you need to find the wavelenght at freq 3 mghz so you can build your antenna.

The book answer is like listed above, but the Harris dude used the other formula to calculate and I don't know enough about rado freq's and building antennas to compare the 2 formulas.

BTW the wavelength at a freq of 3 mghz is 100 meters and being as a properly ground antenna will have half the antenna "mirrored" in the ground and use it as a reflector, your antenna needs to be 50 meter.

Mrleft8
09-09-2007, 07:30 PM
How many crumbs in your bed? How many hairs in a head? How many cuts in a knife? How many sighs in your life?

John B
09-09-2007, 07:33 PM
So lefty, you're saying the answer is " endless"?.

JimD
09-09-2007, 07:37 PM
Her love was like the waves on an ocean.

John B
09-09-2007, 07:41 PM
Don't rock the boat (baby).

JimD
09-09-2007, 07:43 PM
Skipping over the ocean like a stone.

Mrleft8
09-09-2007, 07:54 PM
So lefty, you're saying the answer is " endless"?.
Is "endless" a measurable quantity?

JimD
09-09-2007, 07:56 PM
Is "endless" a measurable quantity?

I think it referrs to the Bilge in general.

Mrleft8
09-09-2007, 07:59 PM
Ah................. So it's more a "Quality" thing, not so much a "Quantity" thing.....

Hwyl
09-09-2007, 08:12 PM
1 MHz is a million hertz (so I'm thinking your calcs are out by a factor of 10), speed of light is right, what's the frequency your working with

cs
09-09-2007, 08:13 PM
You know this was a serious question.

You probably didn't notice, but I've been gone a few days learning about HiFi Radio transmissions with our new radio and I was trying to get some help figuring out his way of wavelenght calculation compared to the book way.

BTW wavelength calculations is critical in long range radio shots (as well as frequancy selection in conjunction with the time of day).

cs
09-09-2007, 08:16 PM
Thanks. I had a feeling I had the hertz to meghertz wrong. I do know that at 3 meghertz the wavelegth is aproxt. 100 meters.

No paticular freq, just in general so that if needed I can calculate the wavelength in case I have to build something other than a NVIS antenna.

cs
09-09-2007, 08:38 PM

BTW I don't like using google as a calculator, nor do I like the calculator in the computer, even set to scientfic. I like my TI programable calculator which is at the office.

Joe (SoCal)
09-09-2007, 08:47 PM

cs
09-09-2007, 08:50 PM
For one thing my name isn't Bud.

Another thing, this is not about a freaking caluclator. I came here because there are some folks out there that have more pratical experiance with building HiFi Radio antennas and understand more about calculating wavelengths than I do.

Joe (SoCal)
09-09-2007, 09:13 PM
Ohhhh a Chad and Donn tiff ;)

What I find most fascinating is ya ever notice Donn never spell corrects Chad

frequancy

wavelenght

meghertz

paticular

scientfic

caluclator

pratical

experiance ?

Maybe now that they are arguing he will start being just as spelling obnoxious to Chad as he is to us select few :D :D

Bruce Hooke
09-09-2007, 09:13 PM

I know nothing about radio antennas, but by thinking it through it appears to me that George Ray has the math right, which means your antenna book does too.

The wavelength is, of course, the distance between two wave crests. The speed refers to how fast those wave crests move through space, and the frequency is the number of waves that pass a given point in a given span of time. So, the wavelength times the frequency equals the speed. (Say the waves are 10 meters long and 5 pass per second, that means the waves are moving at 50 meters/second.) So, we can rearrange that to be wavelength = speed of light/frequency.

It would be nice to figure out what the Harris dude is getting at, since that would provide another confirmation that you are on the right track.

cs
09-09-2007, 09:19 PM
I tried to question the instructor from Harris to get clairfication on this, after all he said that this was the best book on antennas out there, and he never really tried to clairify. He just told me to do it the way he said.

I'm sure his way gets you pretty close to the same answer but I'm not sure how he gets there.

cs
09-09-2007, 09:22 PM
I'll check back in the morning. Right now I'm going to bed. Today was a travel day and I've got to meet another Harris rep in the morning to start installing these new radios in some vehicles.

Bruce Hooke
09-09-2007, 09:32 PM
The antenna book says that the wavelength is speed of light divided by the frequency (in hertz).

The Harris dude said to divide the frequancy (in mghz) by 2.34.

300,000,000 m/s / 3,000,000 htz

or

3mghz/2.34

I quoted the original information above to keep it handy. Note that I corrected the hertz value on the presumption that we are talking about 3 Mghz.

Since it seems quite clear that the first calculation is correct ( 300,000,000 m/s / 3,000,000 htz = 100 meters) and since 3/2.34 does not equal anything like 100 meters (it equals 1.282), it seems like something screwy must be going on with the second calculation. Are you sure it is supposed to give you the wavelength in meters? It just does not seem to be getting even close to the kind of figure you should be looking for.

It should maybe be noted that if great precision is called for then you should be using the real speed of light (299,792,458 m/s) not the more approximate figure of 300,000,000 m/s.

dredbob
09-09-2007, 09:47 PM
Exactly what kind of antenna are you wanting to construct and what kind of equipment are you going to connect it to?

The equation for wavelength that you have is correct, but almost never is any practical real world antenna one wavelength long. They are usually one quarter wave against a ground, or two quarter waves arranged as a half wave dipole. The lengths of the quarter or half waves are not usually found from the "free space" wavelength formula (the one you have, ie.

wavelength in meters= 300/frequency in megahertz.)

Formula for practical, real world antennas, must take into account the material they are made from and their proximity to the earth and other structures, etc.

Antennas on boats, especially sailboats, are frequently a so called random wire (ie, not a multiple or fraction of any specific wavelength) worked through an antenna tuner so that it can be used on multiple frequency bands with out damage to the transmitter.

Bob

09-09-2007, 11:42 PM
For a long wire antenna you will want to make either a dipole or a quarter wavelength vertical antenna as a normal rule normalized to use a 50 ohm impedance coaxial line (cable) or with certain antenna tuners perhaps 300 ohm to match parallel lines or 450 ohm open ladder lines.
You can use the formula frequency in megahertz divided into 468 for wavelength in feet for a full wavelength, divided by four for an end fed vertical, and each half of the dipole will be one quarter wavelength each side....the formula works if you use frequency in megahertz divided into 300 for wavelength in meters. With a dipole antenna you will need a balun (balanced to unbalanced transformer to feed the dipole antenna with an unbalanced coaxial line)
If you are working with vertical antennas, a quarter wave vertical must have a counterpoise (sometimes referred to as a ground) but can be made by pulling the braid of the coax back over the outside of the cable an eqaul amount to the center conductor used as the radiating part of the antenna.
If it is a higher frequency antenna and you have the space, make the vertical antenna either 1/2 wavelength or 5/8ths wavelength high and you will not need a counterpoise for efficient radiation.
Another important step.....if you have excess coax do not coil it up somewhere but snake it randomly on the ground, as when you coil it the cable becomes the significant part of the radiator and increases the natural inductance, thereby lowering the natural / proper radiating impedance of the antenna. Make sure the cable is well grounded at both ends, or at certain frequencies you may achieve some unwanted resonance and the cable exterior will become "hot" at various points along it's length. To work properly, the antenna should also be at least 1/4 wavelength above ground...a full wavelength is much better.....VHF antennas should be 10 wavelengths above ground.
The ARRL publishes and excellent book on antennas for radio amateurs....it is the same book used in the field to teach special ops on how to build field expedient antenna systems...my former specialty code was T30450, instructor...amateur for 50+ years, commercial FCC 48 years....

and ...if you send me a private message with your snail mail address, I will send you a slide rule calculator for frequency/wavelength...I have a few left over from a class I was teaching....better yet, since I can't drive to the post office, send me a large self addressed envelope with 1\$ in postage on it to me and I'll drop it in the mail for you. send private e-mail for address...

BrianW
09-10-2007, 12:08 AM
You probably didn't notice, but I've been gone a few days learning about HiFi Radio transmissions with our new radio...

Just for clarification, are we talking about HiFi, as in High Fidelity. Or, HF as in High Frequency?

Tylerdurden
09-10-2007, 05:36 AM
Thank god you jumped in Paladin, I was about to start banging my head for this poor bastard.

cs
09-10-2007, 05:51 AM
You're right Brian HF not HiFi. I must have been thinking about when we were talking about my stereo the other week.

I just got back from an operator's class on the PRC-150 Falcon II radio made by the Harris Corp.

http://www.rfcomm.harris.com/testimonials/images/150c.jpg

We will use this radio to talk AM between 1.4 mghz and 29.9999 mghz on the Upper Side Band. Above that we would use FM comms.

Chuck I appreciate the offer of the slide rule, but it would probably be wasted on me being as I'm not the one the would typically sit this up, just trying to get more info for my own needs.

The main type of antenna that we would be using is the NVIS (Near Vertical Incidence Skywave). This would be using an antenna in the "broadside) so send a signal up at a high angle so that it can bounce off of the ionsphere and blanket the area (300 mile radius) with a signal.

But if we had to make long range shots we would need different configurations. We talked about different ways to make an antenna directional including reflectors and directors and crows feet. The book mentions a quarter wave vertical atenna, but we talked more about a half-wave dipole antenna (or doublet), inverted vee (or drooping antenna) and we actually set up a sloping vee. We touched on others like the half-rhombic and field expidiate antennas. Did you know that this radio can tunes itself to transmit on a paper clip antenna?

Some of the things that we didn't get into to much was the height of these antennas, but rather we talked more about the size. I imagine that the height changes the take off angle which is critical in long range shots. We did talk about the vertical height enough to know that and to also know that you need to lower it to get it into the NVIS configuration (at least for a half-wave dipole).

Bruce the formula he gave is messing with my head. He says that is the one to use and I wonder if I wrote something down wrong. I beleive his answer came out in feet as opposed to meters, but he went over that so fast I must have missed something. We spent the majority of our time actually working the radio.

P.I. Stazzer-Newt
09-10-2007, 05:51 AM
The antenna book says that the wavelength is speed of light divided by the frequency (in hertz).

The Harris dude said to divide the frequancy (in mghz) by 2.34.

300,000,000 m/s / 300,000 htz

or

3mghz/2.34

I don't have a good calculator in front of me to check, but I think that both are correct.

300,000,000 (3E8) divided by the frequency in hertz will give the wavelength (in vacuo)..

Wavelength = (Harris dude divide the frequancy (in mghz) by 2.34.)

This is either twaddle or really badly misunderstood - if you double the frequency, you halve the wavelength and vice versa - the "Harris Dude Equation" does not do that, it does exactly the opposite.

cs
09-10-2007, 06:01 AM
I know I have to have something wrong with his formula, because he makes it work and has been doing this way longer than me. I'm getting ready to leave and meet some other Harris reps to start the installation of these radios so maybe I can get some clairfication or at if I have to I can call Harris Dude.

Tylerdurden
09-10-2007, 06:04 AM
If you want simple effective long range and broadbanded try a G5RV
or a Carolina Windom wire antenna. With an Autotuner they will both do the trick. I have both and can do every HF band with My cheapo LDG autotuner.
If you have trees where you are going buy a slingshot and some lead fishing weights to launch them or a bow. If no trees look for fiberglass masts on ebay

09-10-2007, 08:53 AM
Chad...an antenna tuner does not tune an antenna.....The radio is designed to transmit into a 50 ohm load...if the antenna is "improper", a large percentage of the energy is reflected back into the radio as heat and contributes to the destruction of the power amplifiers. The "tuner" is a device to fool the radio into thinking that it has a near perfect load and the tuner absorbs the heat energy, and only a very small part of the radio transmitter energy is effectively radiated as intelligence.... (and Harris is one of the worse)(in my opinion).
Forget all the weird "possible antenna confihurations.....a \$5-10K radio is a piece of crap if you can't transmit, and a good \$10 antenna can transmit around the world with a \$5 radio if you do it right......if you really want to be able to use the radio, get a MUF chart for the time of year and the approx lat. and long......memorize them, and you can pick the time of day and frequency for maximum range....and forget the BS about bouncing the signal off the atmosphere and back down, you need signals in the 2 giogahertz range for that, it's called tropo scatter, and again...the absolute worse equipment ever designed was Harris....so bad the only place they could sell it was Idi Amin.

and commenting on the picture that you posted...that's gotta be the absolutely worst possible scenario for operating that radio...keep the antenna as vertical as possible, and get away from those motor vehicles unless you are in the bed or standing in the doorway with the radio on the cabin overhead......any angle reflection is pure bull****.....at frequencies below 60 megahertz...the signal starts corkscrewing in the atmosphere...after 200-300 wavelengths from the transmitter site you cannot predetermine what the phase rotation of the signal will be. If you want geood HF training, hire someone from Collins.

htom
09-10-2007, 09:50 AM
Pet peeves:

The unit is named after Heinrich Rudolf Hertz, so when it's abbreviated the H is capitalized, like the B in decibel, dB.

megahertz = MHz
gigahertz = GHz
millihertz = mHz (very, very, very long wavelengths.)

mghz = MG hurts. ;)

09-10-2007, 09:57 AM
unless you measure in Nepers, based on the Neparian logarithmic scale.:p

P.I. Stazzer-Newt
09-10-2007, 09:59 AM
Napier? - now there's a man who "made his bones" in a most unusual fashion.

09-10-2007, 02:23 PM
neper (Np)
neper (Np): A unit used to express ratios, such as gain, loss, and relative values. Note 1: The neper is analogous to the decibel, except that the Naperian base 2.718281828. . . is used in computing the ratio in nepers. Note 2: The value in nepers, Np, is given by Np = ln(x 1/x 2), where x 1 and x 2 are the values of interest, and ln is the natural logarithm, i.e., logarithm to the base e. Note 3: One neper (Np) = 8.686 dB, where 8.686 = 20/(ln 10). Note 4: The neper is often used to express voltage and current ratios, whereas the decibel is usually used to express power ratios. Note 5: Like the dB, the Np is a dimensionless unit. Note 6: The ITU recognizes both units.

cs
09-10-2007, 08:47 PM
Chuck I guess in a perfect world you would set the radio up with a perfectly matched antenna, but you of all people should know that hardly ever in the military are you in a perfect world. You have to make do with what you have and so the equipment has to be able to make adjustments.

That is what this tuner does, it makes adjustments so that you can use the radio in any situation.

And about the MUF, you as a soldier don't get to choice what freq you use. You have to send up a freq request to whomever your freq manager is and he (or she) will tell you what freqs you will be using. Hopefully you will get a good range of freqs so that you will find one that works best for your area and time of day.

Another thing will your \$5 radio do freq hop or can you load crypto keys into it? Can it generate crypto keys? Can it do Automatic Link Estableshment (ALE) and actually 3G+? Can it talk CyperText or send data? Can it send Instant Messages? Does it have a "Last Ditch Voice" capability?

You should know that a \$5 dollar radio that you buy at Radio Shack can't do the things that one designed for secure millitary transmissions can do. You may not like Harris, but this is what the Army has issued us and who better to train on us on the Harris PRC-150 Falcon II radio than Harris?

And about that photo. That was the only photo on the web that I found that I could link here. And about how and where he is transmitting, he is in the Army and we can't always find the perfect spot to transmit from.

But none of this is what I'm after, I'm trying to figure out how his formula works when I know that the wavelength forumla is different.

Don't mean to come across cross here, but it seems like every time I post something almost everyone here is trying to bust my chops over one thing or another.

09-10-2007, 09:05 PM
Chad...I was merely trying to explain about antennas and the question you asked....and point out in the particular photo that you posted was not a good position BETWEEN TWO VEHICLES with the radio on the ground....
and my thoughts on Harris comes with long experience....
And yes my radio shack radio will frequency hop...faster than the Harris unit by a large margin...and yes, I can load in a 256 bit crypto key....and yes it will outperforn the Harris unit and yes...my radio is used by all the major three letter agencies in the greater washington DC area and no it's not as cheap as a Harris but it's a helluva lot more secure and the antenna tuner works faster than the Harris with better resolution and after going through a complete tune cycle remembers all the pre set settings, and no my radio isn't built in France like the Harris and No I didn't sell it to the Bulgarians either....like Harris....and as a side note...I designed (me alone, not a staff) the predecessor to the Harris radio in 1979.

cs
09-10-2007, 09:15 PM
Chuck I know you are trying to help and I appreciate it.

I'm like really tired and have had a long day and it just seems like every time I post here somebody has a snide remark or they just go out of their way to make my day worse or they just say thing to discount anything I say.

And its not a matter of being overly sensative, just sick and tired of some of this crap.

And BTW I'm not really sold on the Harris radio, although it can do some pretty amazing things if worked right. I still prefer the Singards, but it doesn't have the range capabilty of the HF radios.

09-10-2007, 09:40 PM
Chad...my apologies...I did not mean to make a snide remard to or about you or your work....but a little background....
The South Africans built the first frequency hopping HF radio system in 1977-78 time frame....it was a rather large, mostly tube based system with some digital crypt capabilities using an 8 bit key...the U.S. Navy had the experimental WSC-3 radio that would also hop 5 times persecond that operated in the VHF range and was used aboard ship....the U.S. govt was looking for better equipment and sent out RFP's through DARPA.....
In 1979 I had returned to the U.S. to take on a contract for DIA so was working from early morning til late at night and living in an apartment in Alexandria Va. so started taking advanced engineering classes at GWU under Bob Dixon of Spread Spectrum fame. I took it upon myself to start the design of a frequency hopping radio as part of the Masters program....I built it of radio shack parts, and subsequently demonstrated it at GWU, and before the CIA and NSA...it ran 20+ times faster than anything the government had, sounded like a standard FM radio with no semblance of hopping, had integrated a voice/data encryption system at 64 kb.....and some other unique features......Some agencies wanted the radio immediately......and I arranged to have a limited number built professionally and each and everyone was purchased by NSA or the other local agencies....then they wanted a few thousand, so I set out to subcontract the design......the givment didn't like that...they insisted that I turn over the design to a major manufacturer like ITT, HarrisRF Communications or Collins....I refused......the givment then dropped me...and gave1-2 mil to each of the large companies to develop a similar product...two years later they still didn't have anything that worked, so they purchased more of my units......I tripled the price and sell about 30-40 a month for special operations needs...and the other companies sell cheap imitations.....
I don't care..I'd rather sell 10 units a month at \$15 K each than 200 at 3K each...and my units work better....in 25 years they are constantly updated, improved, use newer parts etc......and they will work after repeated submerging to 120 feet, work 4 times as long as the harris on the same battery, and go into direct sequence mode in the upper frequency ranges......and compare......the case around the harris unit costs less than 30 dollars finished...I use the same case as they do, but I add extra seals, I use the same auto tuner, the guy that designed it lives down the road from me, and he stole the design from Stonar Goral who stole it from someone else.....I designed my own frequency hopping controller and audio crypto and it still works better than Harris.......Harris is one of the companies that purchased two of my units in an attempt to reverse engineer the work.....Collins is the other....they didn't get them from me, they were given to them by Fort Meade after they purchased them from me.

Caleb Chia
09-11-2007, 03:23 AM
Woh! :eek::eek:
Do you still make them? Do you have a company or do you make them all by hand yourself?
Good on ya!

Iceboy
09-11-2007, 08:18 AM
Chad, here is a simple formula for antenna length. Formulas assume velocity of propagation equal to 95% of the velocity of light.
Length in feet = 234/fMHz for a quarter wave
Length in feet = 468/fMHz for a half wave

Jim...

09-11-2007, 09:25 AM
Caleb...the individual subassemblies are made under contract, and assembled under contract....The givment is my only client.

Iceboy...that's the same numbers that I gave him...

Iceboy
09-11-2007, 10:54 AM
I know Chuck. Just separating it out for him. Jim...

cs
09-11-2007, 07:56 PM
Chad, here is a simple formula for antenna length. Formulas assume velocity of propagation equal to 95% of the velocity of light.
Length in feet = 234/fMHz for a quarter wave
Length in feet = 468/fMHz for a half wave

Jim...

The Harris dude said to divide the frequancy (in mghz) by 2.34.

This is the answer I was looking for. Sorry Chuck if I didn't see it in your post, but this was it.

The Harris dude was giving us the formula to determine the quarter wave length which is half of what is need to build the dipole or inverted v or sloping v antenna. This is also the distance that the reflector and the director would be on a vertical antenna.

Harris dude's formular works for calculating the quarter wave, I just had remember it slightly wrong and I knew that I had, but I couldn't figure it out. All I really needed was some help. Now that I see the actual numbers laid out I can see where I made my mistake. Easy enough to see where the mistake was made.