CDMA aerials

For your CDMA phone, the best antenna on the market would be the CD1795 from RFI - ph 1800 773 511 for you nearest dealer.

Expect to pay anywhere from $140 - $160

This antenna is a true 6.5dbi gain antenna, and is used by QLD Emergency Services and telstra.

This antenna will work on both GSM & CDMA

To get more details on this Phone go to
http://www.rfi.com.au/rfiproducts/mobileAntennas/CD1795.pdf

There is also a matching UHF Antenna - CD5000

Thanks cruiser

I notice there are some 4db, 6db and a guy tried to sell me a 9db today.

Have you made inquiries into this side of things and if so what made you go with your choice?

cheers

Andrew

I assume this is with a CDMA phone?

Yes, Nokia CDMA 3105

Got my aerial from Telstsat in Seaford.

On GSM there is a signal timer system, which means that the signal will not go past 34 to 35km.

This means that you can have full service in one spot, move over that 35k line without another tower to pick up then you will have no service, regardless of your antenna.

This, however is not true on cdma. The CDMA signal wil just gradually fade as it gets further from the cell.

Essentially, this means that if you are using a GSM phone, then you really need no more than a 3db gain antenna, simply because you just get no benefit from anything else.

On CDMA, howvever, you will get a great benefit from a higher gain antenna providing that it is being used on good flat ground.

Antenna Guru

So, the higher the number i.e. 9db, the better??

If so, whay doesn't everyone just get the highest when it comes to CDMA?

After all, we are all after phone reception for as long as possible. It seems silly to get a lower gain aerial when a higher one will operate further.

What's the story?

cheers

Andrew,
Unfortunately the higher the gain, does not necessarily mean the best reception.

Probably the easiest way to explain antenna gain is to picture a Balloon.

When the balloon is blown up in a nice round shape, that is what we call unity gain or 0dbd. This would be a nice high signal that saturates, so if your antenna signal would get into the dips and around hills. If in the city it will get in and around the high rise buildings providing good saturation.

If you then take your balloon and squeeze it from the top and bottom, that would be the equivalent to your antenna gain getting higher. A 3 or 4 db gain antenna is going to give you a best of both worlds between distance and saturation. If you go to a 6db gain antenna you are going to have more distance on good flat ground but start to loose your saturation as you radiation pattern gets flattened out.

So a 6 db Antenna is going to give you optimum performance on good flat ground where you can see for miles and miles, but is going to be pretty much useless in hilly country.

As a side bar to that. I have never seen a true mobile 9db cellular antenna. Reason being is to get gain, you need height in your antenna (in 99.9% of cases).

In all fibreglass bull bar mount antennas on the market (GME AT6AN and the like) except for the RFI CD1795 the antennas are built phasing together tuned lengths of coaxial cable. To get 3db of gain, you essentially need to double the length of your antenna.

If we look at the AT6AN Antenna from GME which stands at approx 750mm high. This antenna is rated at 4dbd of gain, which equates there about to 6dbi of gain. To make that antenna 9dbi of gain GME (orZCG Scala who manufacture it) would have to double it's length.

That would make it about 1.5m in length. I have never seen one that long. So all 9DB rated antennas on the market, just simply are not a true 9db rated antenna.

I hope that answers your question

Guru

Thanks for that Guru, a lot of good info there.

Crowie mentions (In a thread below) not to mount your phone aerial next to your UHF.

I had intended on doing just that and have seen many who do.

What is your opinion on the issue.

cheers

Andrew

Andrew,
There is a school of thought that you should not mount your Mobile Phone Antenna next to your UHF Antenna.

The reasoning behind that is the two frequency would interfere with each other. By mounting yuur antennas futher apart then you would get greater isolation between the antennas.

I do not subscribe to that school of thought for two main reasons.

Your UHF Antenna is going to be Transmitting and Receiving at 476 - 477 Mhz and your CDMA Antenna (Lowest Cellular Frequency) is transmitting and receiving at 820 - 890 Mhz. The frequency isolation between the two frequencies is well over 120db (minimum isolation required to not get interference between the frequencies).

The other is that Horizontal Isolation between frequencies is very poor because the amtennas are omni directional in radiation pattern. The difference between 5cm and 2 metres (Well over the distance between two antennas mounted on the front two corners of your buulbar) is very minimal.

These two points mean that you are not going to get any benefit by mounting your antennas on either side of your bullbar to mounting them right next to each other.

My advise is to mount your antennas in a spot where you will be happy with the look and in a spot where it will provide the least amount of disruption to the driver.

Thanks Guru

You info is much appreciated. Now i'm in the picture I can make an informed decision.

Many thanks

Andrew

crowie

My electronics bloke in town tells me he has a 9db CDMA/GSM aerial for $105.

Excellent according to him. And the only one he stocks because of quality/price/performance.

How does that sound to you?

cheers

Andrew

There is a posting further up the thread which talks about so called 9db gain antenna. I still suggest that you stick to the RFI,(excellent quality) and a genuine 6.5db gain. Keep it away from UHF antenna and don't cut the cable. Andrew in the end the decision is yours. A 9db antenna sounds great but at $105 I just wonder. Go to the RFI website and check them out.