Community discussions

MikroTik App
 
mperdue
Member Candidate
Member Candidate
Topic Author
Posts: 288
Joined: Wed Jun 30, 2004 8:18 pm

Help me understand Antani and Bandwidth

Thu Nov 02, 2006 6:20 pm

On a FM Radio tower we have a 12.5db Omni antani with a 3db downtilt and at my home which I want to make into a relay I have tried several directional antani's.

The 14db Backfire directional signal shows recieve -74 transmit -79 and the other day I switched it for a vagi directional and shows a signal recieve of -69 transmit of -73.

The house antani is mounted to the chimney with the routerboard mounted directly under the antani.

I purchased and switched out all of my radios to the Sanyo 400mw a/b/g cards yesterday as well.

The link is 3 miles line of site from hill top to hilltop but my house chimney is on the back of the house and the peak of the house between the antani's. I have raised the antani and looks like it should clear the peak.

On 802.11b I am only able to get a 1m/1m connection and sometimes it will pop up to 5.5m but never stays.

What can I do to increase the bandwidth when I know that the singal to noise ratio is quite good?

There is no earth ground on the chimney antani. All of the cables are new and the right type.

I have other connections to the radio tower that are futher in distance through some trees that stay at 5.5M so I don't think there is a problem with the radio tower relay.

-Michael
 
jo2jo
Forum Veteran
Forum Veteran
Posts: 974
Joined: Fri May 26, 2006 1:25 am

Thu Nov 02, 2006 6:50 pm

can you switch it to 802.11 B/G or maybe move over to 5 GHZ but you would need new anteannas on both sides..
 
mperdue
Member Candidate
Member Candidate
Topic Author
Posts: 288
Joined: Wed Jun 30, 2004 8:18 pm

Fri Nov 03, 2006 2:56 am

I had thoughts of that too. but I have 20 802.11b clinets off that tower. When I tell the tower Mikrotik unit to use 802.11b/g all of the b clients drop.

5g isn't really an option at the moment because teh 5g antani on the fm tower is a directional that points back to the feed site. And my installer isn't around to be able to clime the tower for a few weeks.

Do you think G would really improve the speed? because I was told G was more for indore use and I was better off using B since at times I'm shooting through light trees.
 
mperdue
Member Candidate
Member Candidate
Topic Author
Posts: 288
Joined: Wed Jun 30, 2004 8:18 pm

Fri Nov 03, 2006 5:30 pm

Looking over the radio spec sheets thers normally a little charge that lists db and rate.

Am I readling it correctly that if your link says you have a signal strenth that matches or is lower than the specified number then you should be able to obtain the stated rate?

Example:

Output Power / Receve Sensity
19dbm/-95dBm @ 1 mbps
19dBm/-90dBm @ 11 Mbps

Does this mean that if my signal strenth is -79 i should be able to get 11 Mbps?

If there are any url's that explain all of this I'd be glad to read that first if you know of any.

Thanks,
Michael
 
0ldman
Forum Guru
Forum Guru
Posts: 1450
Joined: Thu Jul 27, 2006 5:01 am

Sun Nov 05, 2006 6:19 pm

You may have excellent signal strength but may have retransmits.

Ping across the link, see what your latency is. I almost guarantee it will vary wildly.
 
mperdue
Member Candidate
Member Candidate
Topic Author
Posts: 288
Joined: Wed Jun 30, 2004 8:18 pm

Mon Nov 06, 2006 1:22 am

Ok so if you have good signal quality but lots of re-transmits what do you do to improve or remove the interferance?
 
mperdue
Member Candidate
Member Candidate
Topic Author
Posts: 288
Joined: Wed Jun 30, 2004 8:18 pm

Tue Nov 07, 2006 3:51 pm

Ok thers been no more replays so let me post additional information.

What we have is a 15db omni on a fm tower. It is I'm guessing 500 feet in the air on top of a mountain. The omni is 1/2 the way up the tower and has 15 other clients attached. Most all are connected at 5.5mb. There a few at 1mb due to trees but they still have a reliable connection.

On the user end I normally use the 14db backfire directional (dish looking antani).

At my home I am setting up a relay (there is another post about this in the fourms and the relay does work).

I have tried several antani's but the current is a vagi highly directional 16db. It is on a 8 foot pole mounted on my chimmney.

The vagi is mounted about six feet up the pool with an relay omni antani on the very top.

The vagi points across the roof top and clears the roof by four feet. The antani is mounted about 6 feet from the roof line to the chiminey.

The line of site is complelty clear strait across the rooftop and is a hill top to a mountain. 3 or 4 air miles

Singal Srenth -73/-69
Noise -96
Signal to noise 27
tx/rx ccq 12/13
ack timeout 49
top rate: 1m both directions.
framing none
polling none
tx power default

Sanyo Wireless (Atheros AR5413)

Thanks!
 
muehlbauer
just joined
Posts: 10
Joined: Wed Nov 08, 2006 9:37 am

performance issue.

Wed Nov 08, 2006 9:48 am

There are many factors to consider and check.
First, I would recommend the 24dB directional directional grid antenna.
The extra dB helps cut through some noise on an already crowded range.
Might be a dumb thing, but make sure you have a vertical mast and have the antenna mounted for a vertical polarity (being your base is an omni.
Finally, hop around the channels a bit, see what kind of noise there is. Also with respect to noise, you mentioned you are on an FM tower. Depending on what is co-located you can have some noise injected directly into your cable which doesn't help. A line filter installed at the antenna might help this.
That's about all I can think of. Your install sounds good and your freznal zone from the roof shouldn't be a factor at all.

Who is online

Users browsing this forum: McSee and 31 guests