800 cell question

Status
Not open for further replies.

jhsands

Member
Feed Provider
Joined
Sep 6, 2006
Messages
355
Location
Texarkana, Arkansas
Hello all:

(see pic)

The antenna up top is an 800MHz 9dBi (6.9dBd) omni antenna located at 18ft from the ground. I use it to receive scanner info only. Works awesome for VHF, too...

I have a 6dBd 800MHz Motorola yagi I want to use for the ATT/Vz towers 8.3 crow miles away. I have verified through phone diagnostics I am only using 850MHz and not 1900. How far below the omni do I need it?

You may slap me for this, but is a 6dBd yagi any more efficient than a 6dBd omni when trying to acquire the signal from a direct point?

Thanks!!
 

Attachments

Last edited:

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
A 6dBd yagi would at least have some rejection off the sides and back that a 6dBd omni would not have, so in that regard, it could help.

BTW, I rather doubt that's a 6db gain antenna. It looks a bit short. I'd guess 3 dBd and some poetic license on the part of the manufacturer's marketing department.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
15,508
Location
SNCZCA01DS0
Since you will be transmitting on the Yagi, you do want a bit of separation, but you won't need much. I'd give it 6 inches from the elements of the Yagi to the base of the vertical. That should be sufficient. By the time your cell phone TX makes it to the antenna, it is going to be quite low power. Coaxial losses on both your yagi feed and your vertical feed should give you plenty of isolation.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
15,508
Location
SNCZCA01DS0
I've got a base 800MHz vertical antenna on the roof of my office with both a transmitting VHF Yagi and a Nextel Bi-directional amplifier donor antenna within a foot of the vertical, and no issues on any of the systems. VHF is running 50 watts on 1/2 inch hardline, BDA is a short run of 1/2 inch also. Probably less than a watt on the BDA.
 

Confuzzled

Member
Joined
Aug 16, 2008
Messages
704
What are you trying to do? Use a cell phone repeater? Or connect direct to your phone somehow? If you're using a repeater/booster, how much of a signal do you get inside the house now? Instead of a Yagi, can you raise your antenna higher?

I use one of these:

Wi-Ex Factory Refurbished - Wi-Ex zBoost Cell Phone Signal Booster (800 MHz Only) YX500-CEL (Wireless Extenders) from Solid Signal

The included outdoor antenna is mounted about 40' up and my closest cell towers are about 5 miles. I get a full 5 bars inside.
 

jhsands

Member
Feed Provider
Joined
Sep 6, 2006
Messages
355
Location
Texarkana, Arkansas
@zz0468 - It is a Cellphone-Mate CM100-L. It is 25".

@Confuzzled - I have a cyfre BDA with indoor 5dBi omni I want to move outside. The inside omni is as-high-as it can go and is a mobile magnet mount attached to a 12" metal pizza pan. ;-)

I get -97 on Vz BB and a -101 on ATT iPhone without the amp. Also, I'm using a yagi to make use of specific towers, because they are the microwave hosts and have the main bandwidth.

The Vz tower used to be the only tower in the county and I was able to get signal here, so I'm sure a yagi with BDA will work wonderful.

@mmckenna so I'm thinking 4 feet should be more than enough :)
 

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
@zz0468 - It is a Cellphone-Mate CM100-L. It is 25".
The typical 3dBd gain 800 antenna is about 2' long. The typical 6dBd gain antenna is 5-6 feet long.

So, yours is about 3 dBd. The marketers of consumer grade antennas usually exaggerate gain. If you upgrade to a yagi, anything over 3-4 elements will be an improvement
 
Last edited:

jhsands

Member
Feed Provider
Joined
Sep 6, 2006
Messages
355
Location
Texarkana, Arkansas
@zz0468 I need to keep that omni for my scanner and it is working quite well, so I'll just accept it for what it is.

The yagi I am going to transmit using a cyfre DBA, which will be a separate antenna and feedline, thus needing separation space.
 

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
@zz0468 I need to keep that omni for my scanner and it is working quite well, so I'll just accept it for what it is.
Yeah, 3db is plenty for a scanner. Much more and it would overload. I just thought you'd want to be aware that that 6db is delusionally optimistic for an 800 MHz antenna that size.

The yagi I am going to transmit using a cyfre DBA, which will be a separate antenna and feedline, thus needing separation space.
Try it with a few feet of separation, and don't be surprised if you end up needing to put it on the other side of the house to avoid interference to the scanner.

BTW, you might want to read up on the legalities of BDA's. If you use one, you should at least be aware of what you're up against if don't work quite right.
 

jhsands

Member
Feed Provider
Joined
Sep 6, 2006
Messages
355
Location
Texarkana, Arkansas
I took down an Alltel tower for two days because I was parked 1/4 mile from the tower. Talk about oscillation!!! Alltel techs were definitely not happy...
 

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
I took down an Alltel tower for two days because I was parked 1/4 mile from the tower. Talk about oscillation!!! Alltel techs were definitely not happy...
I believe it. And I've had home BDA's take down public safety systems that were over a mile away from the site. I don't like the damned things at all.
 

jhsands

Member
Feed Provider
Joined
Sep 6, 2006
Messages
355
Location
Texarkana, Arkansas
Do you think I will still get great scanner signal if I lower it 4' to where it is 1' over the roof? I don't want to put up guy wires.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
15,508
Location
SNCZCA01DS0
Should be just fine. as long as there is (more or less) line of site from your antenna to the cell site, it's going to work the same no matter if it's a foot above your roof or 20 feet above your roof. Of course feed line losses and possible affects on the patter from your roof top might affect this, but I doubt given the situation you need to be concerned about this.

Also, while self oscillation may be a big concern, and a good one at that, being in a metal sided trailer is going to help. Just keep your indoor antenna far away from the outside antenna. Ideally you don't want the two antennas to be anywhere near each other, and to have as much metal in-between them as you can.

I've also had problems with BDA's oscillating and taking out one channel of my 800 trunked system. Not a fun thing to track down.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
15,508
Location
SNCZCA01DS0
OK, Then you don't want to have your Yagi pointed in the direction of your indoor antenna. Ideally it would be in the opposite direction. If the Yagi can "hear" the indoor antenna, the amp will start oscillating and it will not function for you, but as others pointed out, it can affect the cell site. Some of the Wilson units have a LED that will let you know if it is oscillating. Usually adjusting the separation between the two antennas can fix this. Not a hard thing to do, just be aware that it can happen, and how to deal with it.

Gonna be a nice set up when you are done. I had a Wilson docking station for my phone in my old truck, and it really made a big difference. There were places where my phone would not work at all, and with the amp, I had no issues making calls.
 

jhsands

Member
Feed Provider
Joined
Sep 6, 2006
Messages
355
Location
Texarkana, Arkansas
Well I at least have the inside antenna in a dungeon :)
(see pic)

The rear and sides are foil encased, so the antenna is stuck in a sleeve.
 

Attachments

Last edited:

krokus

Member
Premium Subscriber
Joined
Jun 9, 2006
Messages
4,826
Location
Southeastern Michigan
Wirelessly posted (BlackBerry8530/5.0.0.973 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/105)

jhsands said:
I took down an Alltel tower for two days because I was parked 1/4 mile from the tower. Talk about oscillation!!! Alltel techs were definitely not happy...
My old ship did that, to an entire waterfront area. Nobody told the techs that the (analog) Battle Group Cellular needed to be turned off, prior to entering port. :)
 

krokus

Member
Premium Subscriber
Joined
Jun 9, 2006
Messages
4,826
Location
Southeastern Michigan
Wirelessly posted (BlackBerry8530/5.0.0.973 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/105)

jhsands said:
Hello all:

(see pic)

The antenna up top is an 800MHz 9dBi (6.9dBd) omni antenna located at 18ft from the ground. I use it to receive scanner info only. Works awesome for VHF, too...

I have a 6dBd 800MHz Motorola yagi I want to use for the ATT/Vz towers 8.3 crow miles away. I have verified through phone diagnostics I am only using 850MHz and not 1900. How far below the omni do I need it?

You may slap me for this, but is a 6dBd yagi any more efficient than a 6dBd omni when trying to acquire the signal from a direct point?

Thanks!!
What phone system are you using? (I would guess Nextel.)
 
Status
Not open for further replies.
Top