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RF Amplifiers on PtP Links

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WD6EBY
RF Amplifiers on PtP Links
Hello All,

I was looking as some of the proposed link paths in discussion.  We use the stock equipment and base our PtP links locations on the performance of a stock radio.  Has anyone in the group considered using an external RF bi-directional amplifier.  Now that we are able to go into our band segment, we could easy employ a 1 or 2 watt, or even a 5 watt amplifier to achieve a greater link distance.  Company's (note 1) make Bi-directional RF Amplifiers not quite legal for the commercial market but would be perfectly for Amateur use. 

Let me know your thoughts.

Paul...
WD6EBY

http://www.qsl.net/n9zia/wireless/appendixD.html

http://www.ebay.com/sch/i.html?_odkw=WiFi+802.11n+amplifier&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.X5.8ghz+WiFi+802.11n+amplifier.TRS0&_nkw=5.8ghz+WiFi+802.11n+amplifier&_sacat=0

http://www.l-com.com/wireless-booster-58-ghz-wifi-amplifiers

 
K5DLQ
K5DLQ's picture
I haven't.  We have some
I haven't.  We have some users with 98 MILE links using rocket+dish combos.   How much further do you want to go? 

 
AE6XE
AE6XE's picture
Paul, I bought one of these
Paul, I bought one of these Chinese made amps in the linksys days. When reviewing the specs the "optimal" max input power without distortion ended only putting out ~1W, even though it is advertised as 5W. I was using it with a ch 1 bandpass filter. I couldn't tell any appreciable difference using it. Buyer beware...
KE2N
KE2N's picture
caveat

Yeah - some of these are only suitable for 802.11b only - you need to be careful the one you get is suitable for OFDM "g" and "n" modes.  There will be quite a price difference between the two (b and g).  Speaking of two, if you are using a MIMO radio, then you will need two of these amplifiers to maintain the MIMO feature. Of course, in a PtP link you need the same signal at both ends, so in total you need 4 amplifiers.

Lastly - the LCOM units have an upper power limit of 20 dBm before letting the smoke out of the input side.  I would not trust my $80 wireless router not to accidentally make +26 dBm under some unforeseen circumstance.  For that reason, you need to make sure to have at least 6 dB of attenuation between the radio and the amplifier - either coax cable or a 50 ohm microwave attenuator in the line.

Good luck. 

kj6dzb
kj6dzb's picture
I think your aproching the
I think your aproching the legal limit? is there a ERP limit on 2.4ghz when operating under part 97? or is there just a PEP limit. is it still 1500w as in other bands? 

( transmitter dbm ) + ( Antenna dbi ) = total dBm  
 
dBm
Watts
 
dBm
Watts
 
dBm
Watts
0
1.0 mW
 
16
40 mW
 
32
1.6 W
1
1.3 mW
 
17
50 mW
 
33
2.0 W
2
1.6 mW
 
18
63 mW
 
34
2.5 W
3
2.0 mW
 
19
79 mW
 
35
3.2 W
4
2.5 mW
 
20
100 mW
 
36
4.0 W
5
3.2 mW
 
21
126 mW
 
37
5.0 W
6
4 mW
 
22
158 mW
 
38
6.3 W
7
5 mW
 
23
200 mW
 
39
8.0 W
8
6 mW
 
24
250 mW
 
40
10 W
9
8 mW
 
25
316 mW
 
41
13 W
10
10 mW
 
26
398 mW
 
42
16 W
11
13 mW
 
27
500 mW
 
43
20 W
12
16 mW
 
28
630 mW
 
44
25 W
13
20 mW
 
29
800 mW
 
45
32 W
14
25 mW
 
30
1.0 W
 
46
40 W
15
32 mW
 
31
1.3 W
 
47
50 W


http://www.air802.com/fcc-rules-and-regulations.html

http://www.qsl.net/kb9mwr/projects/wireless/pwr.html
KE2N
KE2N's picture
QRO

The KB9MWR link you supplied has the answer - as long as you are not running spread-spectrum (802.11g is OFDM not SS so OK) then you can put 1500 watts into the coax and no limit on the antenna gain either. Getting a T/R switch that can operate 50 times a second is probably out of the question so separate transmit and receive antennas (with receiver protection) would be required. Efficiency at 2.4 GHz might be 10% and at 5.8 GHz more like 5% so three-phase AC power is going to be required.  There are limits on out-of-band, or adjacent band, emissions so some filtering may be needed.

Figure the 2.4 GHz unit wll cost as much as a luxury car; the 5.8 GHz unit will cost as much as a good-sized house.
 

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