RF Amplifiers on PtP Links

6 posts / 0 new

Sat, 02/13/2016 - 18:26

WD6EBY

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

Sat, 02/13/2016 - 19:31

K5DLQ

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?

Sat, 02/13/2016 - 20:39

AE6XE

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...

Sat, 02/13/2016 - 21:41

(Reply to #3) #4

KE2N

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.

Sun, 02/14/2016 - 02:41

kj6dzb

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

Mon, 02/15/2016 - 21:41

KE2N

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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