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Seeking 5G amplifier recommendations; chain polarity q

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Seeking 5G amplifier recommendations; chain polarity q


I am putting together a few nodes using Rocket M5s. I am seeking recommendations for good bidirectional amplifiers to pair with them. Ideally, so that a bit of pre-amplification can be done, in addition to the TX amplification. If the datasheet is accurate, the maximum TX power from the Rocket M5 is 27dBm.

As they have two chains, I am pairing them with antennas that have vertical and horizontal connectors. I'm connecting them with short RP-SMA to N pigtails. I'd like to place the amps as close to the antenna input as possible.  

On an unrelated note, does AREDN currently use both chains on the rocket M5 XM/XW nodes? If so, which chain is generally considered the 'vertical' chain?


K6AH's picture
Don't use amplifiers

I highly recommend against using outboard amplifiers with AREDN nodes.  Most amplifiers are not high enough quality to T/R switch fast enough... and you won't want to pay for those that do.  You will also generate a lot of noise on the band making it harder for the rest of us to communicate.

The vertical and horizontal chains are interchangeable.  They are both used, but for MIMO (802.11n) and path redundancy.  They get used when communicating with another MIMO device.

Andre, K6AH


I'll second the advise against amplifiers...

Tell us what kind of distance are you seeking to connect. Terrain? Obstructions?

Do you already have the antennas? Like most of ham radio, the antenna makes all the difference.


I do. I have a 120 degree

I do. I have a 120 degree 16dbi MIMO antenna.

This node is going to be in the hills above Milpitas, in the hills near east San Jose. I'm hoping to cover the city, maybe up into south Fremont. ~ 10 miles.

10 miles no problem

With your sector on one end, in a clear location, users will be able to easily connect with any high gain antenna. PowerBeam M5 400, Mikrotik LHG, QRT, or a Basebox or Rocket with an external panel or dish most of which are over 20dBi. Users nearby the sector might even hit it with a Nanostation (11~13dB). Most here would agree 10 miles is no problem with our "stock" equipment.


KE2N's picture

Its amazing how far 1/2 watt will go when you have a clear line-of-sight and good antennas.  So I would try it with low power first.  If the signal does not get through due so some obstruction, it's unlikely that an amplifier would help.  In that case what you really need is a taller antenna support or different location.

I think the L-Com amplifiers are good ones.  You want at least 10 dB signal improvement to make a difference so that's the 3-watt output unit (Ubiquity is 27 dBm or 1/2 watt meaning 1/4 watt per chain.  0.25 watts -> 3 watts is about 10.8 dB)

Amplifying an OFDM signal is a tough task.  All those individual carriers have to be amplified simultaneously without creating intermodulation distortion and the amplifier needs to handle a peak-to-average signal of something like 10:1 without flat-topping. It has to TR switch in a microsecond and the power supply needs to switch as well, because it would overheat if you left the power on continuously (and not just during packet transmission).  The receive preamp needs to switch really quickly too and have a very fast recovery time.

The Ubiquity final amplifier stages are not real clean at max power output, so you sure don't want to amplify signal level. For this reason the L-Com amplifiers have an input signal  range of 7-20 dBm.  That let's you run the Ubiquity at, say, +17 dBm output (10 dB below rated max) where is reasonably clean  (17 dBm total power output is 14 dBm per chain). 

You need to be careful not to send more than 20 dBm to the external amplifier (accidentally) or you may fry its input - so probably want an attenuator between the units (or an equivalent coax loss).  I found that the 2 GHz L-com produces rated power at about +12 dBm input level (roughly).

List price for the 3-watt amp is $1510 and you will need 4 per link, so figure 6K$ per installation  (and compare that to the cost of some tower sections)



K9CQB's picture
Wanna double your power? Use a 30dBm BaseBox 5.

To add to the wise advice of Andre and Ken, I would avoid external amplifiers and just buy a Basebox 5, which I think is 3dBm more than the Rocket M5 - that's twice the power at 30dBm.
I've used bi-directional amplifiers before, but to bring very low power devices (18dBm) up to 1 Watt. I also had to disassemble the amp and reduce the RX amplifier (LNA) because it causes too much noise on your front end  - they all do. That noise will make your node a lot more deaf. I only used in-line attenuators for testing RX LNA network while modifying it, otherwise you're also reducing the TX gain of your modem, but even worse, adding some noise. Unless you have decent soldering and EE skills to modify the LNA network on the bi-directional amp, I would avoid this altogether.
Just get a BaseBox.
I stopped buying Rockets and most other Ubiquiti gear because the MikroTik gear is so much better. I still have to buy 900MHz and 3.4GHz stuff all from Ubiquiti though; MikroTik doesn't have that stuff. I also buy Ubiquiti NanoStations (XW models) for the dual Ethernet capability and they're just awesome, and I also buy the PowerBeam PBE-M2-400 because it's the best PtP dish on 2.4GHz - at least until we get the MikroTik LHG-2 and LDF-2 series devices up on AREDN firmware.

-Damon K9CQB

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