Hi Guys
I have never used a filter before but i’ve heard a thing or two about them
How do they work / What do they do?
Am I correct in assuming that I pick a channel, say 5800, and then get a filter to block out all other channels?
I don’t know what your application is so I can’t acess why and if you need them. But you buy filters with a center frequency and then a range around them. Say a filter with a 5.8GHz center with a 200MHz range would mean the filter would “pass” 5.6GHz to 6.0GHz. Anything outside of that gets attenuated like 30dB.
In my application, filters are essential. I share a waveguide with high power 6GHz equipment and if I don’t use them my radios get crushed by the other radios. But for regular WISP applications filters aren’t always necessary. I guess it just depends on the situation.
Are there filters for 2.4 Ghz. and do they help in area of high interference.
thanks mahnet
Does the radio still get interference from say 5500 even if it is set to 5800?
I thought that only channels within 40mhz interfere? or am I horrible wrong?
I am running VOIP backhauls and things are going pear shaped on some links…I don’t want to spend $$$ on motorola or Radwin so i’m looking for an alternative. Filters are not that expensive compared to replaceing radios i should imagine?
The specs on some rf filters can be found on each datasheet here:
http://www.l-com.com/category.aspx?id=3016
They have a center frequency with a small attenuation (approx 2db) and attenuate any off-frequency signal by 45db to 60db, depending on the number of poles.
ADD: They work best for reducing nearby high-power interference.
What is the distance of links?
I found Voice to work good for me for a 6 km link with 2 set RB 411, parabolic antennna, compex cards. Throughput was approx. 27 mbps. Freq. 2.4 ghz. Throughput changed to 35 mbps with 5.8 ghz.
Do I place the filters between LMR400 and antenna or LMR400 and pgtail?
They look like the could help quite a bit
I think closer to the radio is best. It is basically a receiver aid. That would also reduce any transmission line noise. You are sacrificing 30-40% of your signal strength mid-frequency, so if you have no high power interference nearby, you will lose performance.
really 30-40%, wow thats alot, why is that? thought it was only 2db for the centre channel?
-3db is half so -2db would be 2/3rds of 50% which is 33%
Sorry, I missed this part.
No, that’s not how it works. Channels are totally arbitrary distinctions. Filters don’t know anything about channels, just frequencies. If you get a 5.8Ghz filter with a center of 5800MHz and a 400Mhz range then that filter is going to allow anything (noise, your signal, your competitor’s signal, etc) in that range to pass through mostly unmolested. It sounds like you’re trying to really micromanage what gets through within the band. I’m not sure you’ll be able to get something like that.
Oh yes ofcourse, sorry I forgot that 3dB = double output.
I suppose it would be good to use on a sector that with a max EIRP of 1w, coz then you can just increase the TX power by 2db to get back to where you were.
You say that it only really increases the receive sensitivity, would it be overkill to use on an XR5 that has really good receive sensitivity anyway? EDIT, I missed the boat here. It will only help if there is above 6mhz highpowered interference or below 5600mhz. So it would help on an XR5 if there was such interference
Ah yes I understand now, thanks…Yes i was hoping to basically block everything except the channel I pick, but I suppose 200mhz each way is a good start.
Is there a way to detect if there is >6ghz highpowered radios nearby?
If you are running 4.3 or above, choose superchannel then set your scan channels to 5800-6200 or whatever, then hit freq usage.
it will give you an idea of what is going on out there.
If you want to see what is going on in your location, you might want to invest the $600 to get one of these:
http://www.metageek.net/products/wi-spy-dbx
ADD: You will see a visual similarity to the spectrum analyzer used by U.C. Berkeley on the SETI project.
Can R52’s etc go above 6000mhz?
Do the metageeks support 5.8ghz? I had a look but it looks like it only works with 2.4ghz
The link I posted above is for the 2.4GHz/5.8GHz unit.