Frequency affect on range

[rescuer]

Hello,
First off, I tried to search for and answer but couldn't find anything specific.

If all things where equal (make, power, antenna, terrain, interference, etc.), how much would frequency affect the range of radio operation? I would rather the answer be in lay-mans terms.

Example: A 50 watt radio on 30.000 MHz may talk simplex 10 miles. What would the range be at 150Mhz, 460Mhz, and 850Mhz? Again, all things equal except frequency.

Bonus question? If range decrease as frequency increases, why do thay make similar radios with lower power at higher frequencies?

Example: A lo-band Maxtrac can be 60 watt, a hi-band 45, a UHF 40, and an 800 35? Would one not want higher power at higher frequencies to offset the decrease in range?

[Al]

In layman's terms or any other terms, all other things being equal, frequency has *no* effect on range.

Bonus answer: FCC and the US Federal government set exposure limits for human soft tissue which depend on frequency(energy density) and distance from a transmitting antenna. As frequency increases, energy levels increase and the maximum exposure for a given distance increases....thus the lower power limits on transmitters(antennas).

[Wicho]

In layman's terms or any other terms, all other things being equal, frequency has *no* effect on range.

I'm going to have to disagree on this one.

Example: UHF works better in buildings, VHF better outdoors through vegetation. So, all things being equal, UHF will have better range than VHF in buildings, VHF will have better range than UHF outdoors in a forest.

Then there's lowband, etc.

[Bruce1807]

Normally, the major loss of energy is because of the spreading out of the wavefront as it travels from
the transmitter. As distance increases, the area of the wavefront spreads out, much like the beam of a
flashlight. This means the amount of energy contained within any unit of area on the wavefront
decreases as distance increases. By the time the energy arrives at the receiving antenna, the
wavefront is so spread out that the receiving antenna extends into only a small portion of the wavefront.
Now having said that low frequency has a large period and takes longer to spread out. 800 on the other hand has a short period and spreads out quicker.
Therefore the recieved signal is of greater level on low band than at 800.

[Al]

I should have been more clear in that I was referring to the simplest case where there are no path obstructions between the transmitting point and receiving point....in that case, the path loss is not frequency-dependent, it's only a spreading loss(the tx power divided by the area of a sphere[4*pi*r squared]. Everyone is aware that 800 Mhz, for example, "slips" through cracks and openings in buildings better than 35 Mhz because of the much shorter wavelength, but that is not the case I was alluding to. The original question asked only about range vs. transmit power, and I assumed [obstruction-free] range.

[Wicho]

I should have been more clear in that I was referring to the simplest case where there are no path obstructions between the transmitting point and receiving point....

Point taken.

[Bruce1807]

I should have been more clear in that I was referring to the simplest case where there are no path obstructions between the transmitting point and receiving point....in that case, the path loss is not frequency-dependent, it's only a spreading loss(the tx power divided by the area of a sphere[4*pi*r squared]

path loss is always freqency dependent.
It's called free space loss

30 Mhz at 10 miles is 86.1dB
160 Mhz at 10 miles is 100.7dB
460 Mhz at 10 miles is 109.9dB
820 Mhz at 10 miles is 114.9 dB

The free space loss can is calculated by the formula listed below which is the transmission loss between two antennas, separated by a distance. and the distance between the two attennas in miles under obnstruction free conditions.
20 * Log10 (frequency in MHz) + 20 * Log10 (Distance in Miles) + 36.6

The loses are overcome by ERP from the antenna and calculated into a total system loss.

[kf4sqb]

Sorry, but I just have to confuse the issue on this one. With the afore-mentioned information in mind, my experiences don't make much sense. A local 2m repeater is app. 40 miles from my house, with the antenna at app. 600' on the tower. I can almost get good coverage with an HT from inside my house, but I can't walk around with it. There is also a 440 repeater on the same tower, with it's antenna at app. 200' on the tower. I can reliably get excellent coverage with an HT from inside my house, while walking around, as well as outside, and even in the area while mobile with the HT and no external antenna. There's no way I can do all that with the 2m repeater. What gives? BTW, I'm in a mobile home, so I wouldn't think that "shielding" would be an issue at either frequency.

[Bruce1807]

Now your getting into total path loss.
Need to know the power of each repeater, the cable, connectors,lightning suppression and finally the type of antenna and the gain.

[W6JK]

Not to mention the size and shape of your windows.

[Jim2121]

Sorry, but I just have to confuse the issue on this one. With the afore-mentioned information in mind, my experiences don't make much sense. A local 2m repeater is app. 40 miles from my house, with the antenna at app. 600' on the tower. I can almost get good coverage with an HT from inside my house, but I can't walk around with it. There is also a 440 repeater on the same tower, with it's antenna at app. 200' on the tower. I can reliably get excellent coverage with an HT from inside my house, while walking around, as well as outside, and even in the area while mobile with the HT and no external antenna. There's no way I can do all that with the 2m repeater. What gives? BTW, I'm in a mobile home, so I wouldn't think that "shielding" would be an issue at either frequency.

4cye is your brother?...... EOM

[Wowbagger]

BTW, I'm in a mobile home, so I wouldn't think that "shielding" would be an issue at either frequency.

You live in a big metal box, and you wonder about shielding?

To 2 meters, your windows don't exist (or just barely exist) - they are too small for a 2 meter long wave to "see" as an opening. To a 70cm wave, your windows are, well, windows - the wave can travel through them just fine, and then diffracts within your house.

There's penetration and there's propagation, and the two are VERY different things. Higher frequencies can slip through smaller holes, and thus can often get inside buildings better, but they don't carry as well.

[kf4sqb]

You live in a big metal box, and you wonder about shielding?

Um, no. Walls framed with wood 2X4s, with sheetrock on the inside, and vinyl siding backed by foam-board on the outside. Where, I ask you, is the metal? Perhaps you confused mobile home with motor home, or maybe you're thinking of mobile homes built 30 to 40 years ago.

4cye is your brother?

Jim, I wondered how long it would be before someone took the time to "translate" the code in my signature. KI4CYE is, indeed, my brother.

[Wowbagger]

You live in a big metal box, and you wonder about shielding?

Um, no. Walls framed with wood 2X4s, with sheetrock on the inside, and vinyl siding backed by foam-board on the outside. Where, I ask you, is the metal? Perhaps you confused mobile home with motor home, or maybe you're thinking of mobile homes built 30 to 40 years ago.

No, I understand the difference between a home that could move and doesn't and a home that does move frequently.

And as for "where is the metal" - I suggest you look more closely at that foam-board. Oft-times that stuff has an aluminized Mylar backing as a vapor barrier.

[Satelite]

Hello
Im no profesional on the qestion per freqs ect but this was my personal experience on VHF.
Canada fly in fishing trip.
wanted portable coms between boats.
Decided on a 5 watt GP300 with a marine freq in it.
Believe i was told it was ch#69 marine freq. ( 156 area ???? )
The lake was very rocky islands all over everywhere.
Found that VHf portable to portable range when having rocky islands in the path was somewhat scratchy with 1.5 miles maybe 2 at best.
If in the open if that was even possible maybe three miles.
I wasnt real impressed but it was usable so to speak.
Im now wondering whether 450 uhf or the low band 42 to 50 mhz would have done better.
Problem with these two choices is that i dopnt think theres a freq i as a USA citizen could legaly use for this situation.
But id like to know what others have had for experiences with this same type of situation as curiousity.
The canadian ontario hydro power division did at one time use 42/50 mhz 99ch special purpose maxtracs = Not sure if they still do but i wonder if it wasnt because range was better over the water on low band ?
Satelite

[RadioSouth]

Hello
Im no profesional on the qestion per freqs ect but this was my personal experience on VHF.
Canada fly in fishing trip.
wanted portable coms between boats.
Decided on a 5 watt GP300 with a marine freq in it.
Believe i was told it was ch#69 marine freq. ( 156 area ???? )
The lake was very rocky islands all over everywhere.
Found that VHf portable to portable range when having rocky islands in the path was somewhat scratchy with 1.5 miles maybe 2 at best.
If in the open if that was even possible maybe three miles.
I wasnt real impressed but it was usable so to speak.
Im now wondering whether 450 uhf or the low band 42 to 50 mhz would have done better.
Problem with these two choices is that i dopnt think theres a freq i as a USA citizen could legaly use for this situation.
But id like to know what others have had for experiences with this same type of situation as curiousity.
The canadian ontario hydro power division did at one time use 42/50 mhz 99ch special purpose maxtracs = Not sure if they still do but i wonder if it wasnt because range was better over the water on low band ?
Satelite

As far as portables in open terrain I think you'll find that a 5 watt VHF HT is as good as it gets. In flat FL in my neighboorhood of one and two story homes I get about 1.5 miles on 5 w VHF. 4w UHF only did
about 3/4 mile. I also had my hands on a pair of 46 MHz portables which I believe are 6 watts, just about a mile. Believe the limiting factor on a low band portable is the lack of adequate ground plane and why it didn't get a better result than VHF. Course there are many variables but I've gotten over twice the range on several occasions
on VHF over UHF. I also have a Motorola Radio Range calculator which is a pretty rudimentary cardboard
slide rule type thing, after doing several calculations for, flat, obstruction free areas VHF always trumped UHF. Calculations were for base to mobile applications.

[RKG]

My take (putting together a number of points that have been adverted to by others):

"Range" is the result of a number of factors, including frequency, but also including power, system efficiency, radio horizon, terrain, buildings (penetration) and multipath.

Confining our discussion to MUF (frequencies above those that can be bounced off ionspheric layers): in open space, the lower the frequency the greater the range.

In urban environments, particularly where free space range isn't an issue because ERP is more than sufficient to cover the service area, UHF often outperforms VHF because of building aperture penetration and multipath issues. Interestingly, 800 seems not to outperform UHF.