All my RX path questions

[mmckenna]

What dbi is considered as high, medium and low gain antennas

There isn't a standard. Decibels is a reference between two levels, so high, medium and low are subjective.

For radio/antennas, the reference is either a 1/4 wave antenna or a dipole in free space.

tldr; It depends entirely on what YOU are comparing it to.

 

[prcguy]

Zero dBi gain is 2.14dB less than a dipole which would make it -2.12dBd gain. I would consider an antenna with less than 0dBi gain up to about 5dBi gain a low gain antenna with 5dBi being less than 3dBd gain. From 5dBi to about 8dBi might be medium gain and maybe 9dBi and up might be considered high gain being over 7dBd.

 

[Bonkk083]

There isn't a standard. Decibels is a reference between two levels, so high, medium and low are subjective.

For radio/antennas, the reference is either a 1/4 wave antenna or a dipole in free space.

tldr; It depends entirely on what YOU are comparing it to.

What's the difference between 1/4 and 1/2 wave

 

[Bonkk083]

Zero dBi gain is 2.14dB less than a dipole which would make it -2.12dBd gain. I would consider an antenna with less than 0dBi gain up to about 5dBi gain a low gain antenna with 5dBi being less than 3dBd gain. From 5dBi to about 8dBi might be medium gain and maybe 9dBi and up might be considered high gain being over 7dBd.

I see some antennas 5, 6, 7, 8 dbi, but I might go with a 6 or 7 but I'm unsure about the 8

 

[ladn]

I see some antennas 5, 6, 7, 8 dbi, but I might go with a 6 or 7 but I'm unsure about the 8

Remember, there is no free lunch. All that antenna gain comes at a price which includes:

• Size
• Acquisition cost ($$$)
• Bandwidth
• Radiation/reception pattern

And, whatever "gain" the antenna provides can be easily mitigated by feedline losses.

Choose wisely!

 

[Bonkk083]

Remember, there is no free lunch. All that antenna gain comes at a price which includes:

• Size
• Acquisition cost ($$$)
• Bandwidth
• Radiation/reception pattern

And, whatever "gain" the antenna provides can be easily mitigated by feedline losses.

Choose wisely!

I'm planning on using 50 feet of Lmr-400, The 8 dbi Laird omni is $160 plus $30 for the mounting hardware

 

[prcguy]

I'm planning on using 50 feet of Lmr-400, The 8 dbi Laird omni is $160 plus $30 for the mounting hardware

What band?

 

[Bonkk083]

What band?

851-860

 

[prcguy]

851-860

There are a lot of good used antennas for much less than that new Laird. I recently picked up a pair of Antenna Specialists 15ft long 8.5dBd omnis with adjustable downtilt for $50 each. Check eBay and local Han swap meets, surplus 800 antennas are usually dumped cheap.

 

[Bonkk083]

There are a lot of good used antennas for much less than that new Laird. I recently picked up a pair of Antenna Specialists 15ft long 8.5dBd omnis with adjustable downtilt for $50 each. Check eBay and local Han swap meets, surplus 800 antennas are usually dumped cheap.

This is my results for line of sight

 

[wtp]

best to get buying and trying, that is the only way YOU will find out.

 

[Bonkk083]

best to get buying and trying, that is the only way YOU will find out.

I'm getting there

 

[Bonkk083]

What is the difference between a 1/4 and 1/2 wave

 

[Whiskey3JMC]

What is the difference between a 1/4 and 1/2 wave

Read here

 

[Bonkk083]

Read here

All the antennas I saw are 1/4 except for one is 1/2, how can the 1/2 avoid more obstacles with it more horizontal I don't quite understand

 

[jwt873]

A quarter wave at 850 MHz is about 3.3 inches long.. A half wave is twice that at 6.6 inches. I'm not sure what you mean about avoiding obstacles.

 

[Bonkk083]

A quarter wave at 850 MHz is about 3.3 inches long.. A half wave is twice that at 6.6 inches. I'm not sure what you mean about avoiding obstacles.

• 
  No Ground plane is required for 1/2 wave antenna while its required for 1/4 wave antenna.
• More energy will be transmitted horizontally in 1/2 wave antenna compared to 1/4 wave antenna.
• Half wave antenna will be taller is size and would therefore be able to avoid more obstacles than quarter wave antenna.

 

[jwt873]

OK, looking at the link Whiskey3JMC posted. Yes, all the above is correct.

On the obstacles.. Is your installation going to be that tight that an extra 3 inches in length is going to make a difference?

 

[Bonkk083]

OK, looking at the link Whiskey3JMC posted. Yes, all the above is correct.

On the obstacles.. Is your installation going to be that tight that an extra 3 inches in length is going to make a difference?

It's a outdoor base the 1/2 wave antenna I saw is 4.85 dbd 57" and a 1/4 was 6 dbd 65"

 

[jwt873]

At 57 and 65 inches, those aren't half and quarter wave antennas. What they do is stack several quarter and/or half wave antennas on top of each other. What that does is increase the gain by directing the energy towards the horizon. This is known as a collinear antenna.

Since the Decibel scale is logarithmic and not linear, the difference between 6 dBd and 4.8 dBd would be negligible.