MikroTik

I'm using v2.9.6 with a CM9 and i'd like to test an amplifier.
I found 1 watt amplifier, but i have some problems.
After 20 - 50 minutes of perfect operation, RX signal on the
Registration screen of winbox falls 20-23 dbm.
Tx signal remains stable.

Before the problem i have TX -50 dbm, RX -40dbm
After the problem TX - 50 dbm, RX -60dbm

This amplifier has 20db! (real) gain on RX.

When :
1. disable wireless interface,
2. unplug amplifier
3. enable wireless
4. Plug the amp again
Rx signal is perfect again.

Where do you think is the problem ???

P.S. Please don't tell me that the amp is the problem, because
is working very stable with a cheap WRT54g.

I made the test with an Sr2 400mw, but the problem the same.

Thank you in advance

do never use amplifiers. always upgrade to latest 2.9 version before asking questions. upgrade to 2.9.23. amplifier will only make things worse unless you have zero interference, no noise and perfect signal.

I want to make a 25 km link. The interference is zero and signals are
perfect too. Two antennas are on mountains (1200m-1400m).
I have the same link with 2 wrts with a stable ping (5-12ms).

we have a customer who has a 95KM link with no amplifiers and he has a stabile ping of 2ms.

check this presentation:
http://wiki.mikrotik.com/wiki/MUM_2006_USA/Long_range

Very, Very good link, but i'd like to use an amp. Is that a problem ???
I'm a radio amateur and i have all the essential licenses.
Do you have any other argument why not to use an amp ???



What kind of problems do you mean ?

Sorry for bother you

well use it if it works for you. but i'm just saying that if you have little noise, the amp will make it into big noise and you will have more problems.

In the early days, I used amplifiers quite often. But I've found, that they add quite a bit more adjusting factors to your link. For one thing, there are some decent amps and some really poor amps out there. Even if you get a decent amp, you won't get the best throughput. Amps tend to increase noise and retransmits on the link. Also they can be a big extra point of failure; there are only a few amps out there that will still pass RF even when they fail (lightning, etc). I've been generally happy with PtP links where the signal is between -55 and -69.

If you really need the power, then I would recommend the 400mw cards. Also, there are some reasonably priced higher gain dish antennae.

Anyway, if you want maximum throughput for whatever setting you use on your radio, you cannot do it with amps.

Eric

Use higher gain antennas. Amplifiers cut into your available bandwidth, elevate noise floors, increase latency, and is just another point to troubleshoot when the link has problems. You want your physical layer to be as simple as possible. Adding an amplifier just introduces more variables...

As a radio amatuer, (at least in the US), you are obligated to use no more power than is required. Many people think this applies to just HF, but I was under the impression it applied to all amatuer communications.

damn, why do you need 1W amplifier for 25km link ?!?!?!? This is what you call proper RF design? Damn, your RF license is WASTED !!

Do you use 10kW power plant for your RF needs when you want to do 2500km? I guess no.


25km link on 2.4GHz band has around 128dB loss. Calculate with me:

+14dB (=25mW output from CM9 that nobody wants because it's "underpowered", everybody seem to need 23489324987mW at least)
-128dB free space loss
-4dB connectors/cable/pigtail loss
+30dB antenna on first side (around 100cm diameter)
+30dB antenna on second side
-------------------
result : -58dB = ABSOLUTELY EXCELLENT SIGNAL WITH FULL THROUGHPUT and SUPER MARGIN.

WHY THE HECK YOU NEED AMPLIFIER ?!?!?!?!??!?!?!?!?!?!??!?!?!?!?!?!

People stop using those stupid amplifiers, they do nothing good. NOTHING. When you properly design links, you NEVER need to use amplifier with distances lower than 50km !!!!!!!!!!!!!

And yes, I'm still speaking about CM9 and not SR2 !!!!

I hooked a CM9 up to a Hyperlink 1W amplifier not too long ago, we found that it worked very well under 1km range, but beyond that got very slow (20-30kbit throughput) instead of the 4-5mbit from under 1km.

While there are many good points to not use amlifiers, there are many points where they are quite useful - mostly with point-to-multipoint AP's. Generally, you'll never need one on a point to point where you can solve the problem with higher gain antennas.

Our solution was to use a 2511MP radio with the output power turned down low enough to not overdrive the amplifier.

I agree totally with abc123 above.

My "rules" for building links
- use as few parts as possible

- use GOOD antennas, it's better to listen well then to scream loudly!

- make sure you have short high quality cables (NOT the kind that most people call lowloss! Use real low-loss, 1/2" or 7/8". )

- if you have to use them, use as few and as good bulkhead connectors that money can buy

- make sure all connectors are properly done, a bad connector can cause grey hairs!

- check that you spectrum REALLY is clear of interference, microwave owens and bluetooth equipment normally doesn't show up on the test tools but they wreac havoc on your system! We had an installation that at times failed completely; indoors, good coverage, no interference etc... turns out that one of the sales guys had a bluetooth headset that did continous broadband "pings" on ALL 2.4GHZ channels when it lost contact with it's phone We found out that one when we took one 2.4GHz device at a time out of the office... lots of work to find all gear with bluetooth in them! Not to mention separating a sales guy from his headset / phone

- understand LOS.... just because you can see the destination doesn't mean you have LOS, radio needs a wide path!

- stay legal! If you have an output limit make sure you are following it. OK I understand, you might feel that you need to squeeze just a few more dB to make the link.... but be sure, someone will find out and then FCC (or you version of them) will come down on you and force you to reduce the power... leaving you with a non-working link and a very mad customer! A 30dB antenna is not legal in most countries if you feed anything above 0dB to it

- that said... use the SR-cards, not for the added output power but for the increased sensitivity! They listen VERY well!

All in all, I am VERY satisfied with the integrated antenna that MT has. Decent antenna gain, no cable loss, no extra connectors (just a pig-tail), mount neatly (no dish to collect snow) and with SR-cards.. but for 25km their ears aren't quite big enough (not enough antenna gain to hear the signal)

/Jörgen

!!!!!!! !!!!!

Your argumentation is excellent. You prevail me !!!.



I just use 2MTs with 24db antennas and the link is excellent. !!!

Thank you All.