lost watts through duplexer?

bayfire300 · Post by **bayfire300** » Mon May 15, 2006 6:11 am

hey gang i have a question reguarding watts lost through a duplexer.

the duplexer i have is a bp/br decibel product 3 can(1 for rx and 2 on tx)
and i am losing 20 watts through it........if i got a 4 can would that be better?
the duplexer was tuned professionally i was losing 30 watts.

why such a big loss? or is that sound right...........to me 20 watts seems like alot
oh one more thing ......its uhf 462/467
thank you

otto

RKG · Post by **RKG** » Mon May 15, 2006 7:25 am

Insertion loss of a duplexer can run from 1 dB for expensive ones to as much as 3-4 dB for others.

In order to calculate the loss through a duplexer, you have to measure the power input to the Tx side of the duplexer and the power out of the common (antenna) side. Make a fraction of which the numerator is power out and the denominator is power in (the fraction will be less than 1). Take the common (base 10) log of the fraction (result will be a negative number). Multiply that number by 10 and you have the insertion loss in dB.

If the insertion loss is significantly greater than expected, the duplexer may be not properly tuned for your frequencies.

Bruce1807 · Post by **Bruce1807** » Mon May 15, 2006 8:34 am

What power are you putting in

bayfire300 · Post by **bayfire300** » Mon May 15, 2006 8:43 am

i was told the transmitter is putting out 80 watts to the duplexer and a loss of 20 watts out of it

otto

Vercomm · Post by **Vercomm** » Mon May 15, 2006 9:29 am

After calculating your tx power loss that sounds about right, you seem to be loosing about 1dB, which with 80watts of Tx power would drop you close to 63watts, so 20watts of power loss would seem very close. So I would say your duplexer is alright cause it's got 1dB of insertion loss. If you are interested in seeing the calculations let me know and I'll email them to you.

Jamie

k2hz · Post by **k2hz** » Mon May 15, 2006 9:40 am

If you only have a loss of 20W for 80W in, that is only 25% which works out to a little over 1 db. It does not get much better than that and it is certainly nothing to worry about.

bayfire300 · Post by **bayfire300** » Mon May 15, 2006 9:42 am

oh ok cool............what about a 4 can would that help or is that a waste of money

otto

HLA · Post by **HLA** » Mon May 15, 2006 9:49 am

just use a high gain antennae to make up for the difference or even do better than your original 80 watts. use a 3db gain antennae and you will be around the equivalent of 150 watts.

k2hz · Post by **k2hz** » Mon May 15, 2006 9:51 am

More cans usually means better isolation but more loss. It a waste of money to worry about an insignificant power loss like that.

SZ$DEF · Post by **SZ$DEF** » Mon May 15, 2006 6:50 pm

Additionally, you should be making up for the loss through the cans via your antenna (EIRP).

440roadrunner · Post by **440roadrunner** » Mon May 15, 2006 8:26 pm

Don't get all jacked up about so many (huge) watts here, and there, etc.

A dB is a dB is a dB. It matters not. 3 dB at the transmitter is still "half an S unit" at the other end, and THAT is half your power!!

You MUST suffer losses in the system, that's just the deal.

k2hz · Post by **k2hz** » Tue May 16, 2006 4:27 am

The important thing to remember is that 1 db has such a slight efffect on actual system performance, it is not apparent to the users in terms of signal quality, it can only barely be detected on test equipment.

A loss of about 3 db produces a slightly audible change in signal to noise and you need 6-10 db to really notice a difference.

In other words, 1 db is nothing to be concerned with. If you had a cheap duplexer with 3-4 db loss, then it might be something worth spending money to fix.

Base TX power is normally not an issue in most systems. The real concern is the ability of the base RX to hear the lower powered portables. Base station antenna gain, low loss coax and minimal duplexer loss in the receive path should be the primary concern, not a few watts more or less of TX ERP.