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GSM Spring Magnetic Antenna comparison based on physical dimensions

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dineshreil

New Member
The left antenna (A) has:
1. Smaller in height.
2. More number of small radius turns
3. Small base (magnetic mount)

The right antenna (B) has:
1. More height
2. Less number of turns which larger radius comapared to A.
3. Large base (magnetic mount)
4. Extra Single turn above multiple turns.

Q1: How can i determine the dB gain of antenna?
Q2: If there is no relevant measuring instrument available, can i choose the best among two just on mere physical dimensions?
Q3: What is the purpose of helix/spring in both the antenna?
Q4: What is use of extra helix in Antenna-B?
 

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JimB

Super Moderator
Most Helpful Member
Q1: How can i determine the dB gain of antenna?
Measure it.
You will need:
a signal generator
a calibrated receiver or spectrum analyser
a suitable "antenna range"

Q2: If there is no relevant measuring instrument available, can i choose the best among two just on mere physical dimensions?
Not easily.

Q3: What is the purpose of helix/spring in both the antenna?
Difficult to say without knowing the dimensions of the antennas and the frequencies involved.
Basically loading and phasing.

Q4: What is use of extra helix in Antenna-B?
Who knows?
Looks good to the casual observer.
Adds another $5 to the price?

JimB
 

davenn

Active Member
Q1: How can i determine the dB gain of antenna?
Q2: If there is no relevant measuring instrument available, can i choose the best among two just on mere physical dimensions?
JimB answered those well :)

tho for #2 ... RF experience tells me B has more gain ( reason in answer #4)


Q3: What is the purpose of helix/spring in both the antenna?
just up from the base, loading, provides 3 common purposes
1) --- impedance matching to feedline
2) --- changes the radiation pattern of the antenna ... for base loading it aims the radiation pattern upwards
3) --- it can also be a phasing section between antenna sections


Q4: What is use of extra helix in Antenna-B?
this is purely a phasing section
so there are 3 sections
a 1/4 wave below the main coil and either 2 x 1/2 or 5/8 sections above the main coil with the phasing loop between

this arrangement is pretty common for phased arrays

Dave
 
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