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Old 01 April 2012, 14:07   #1
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VHF connections

Time to connect up the vhf on the Pac.....

The rear floor section is removable to access the jet unit /rear bilge and the cable run enters through a sealed box (via a cable gland).....it would be ideal (as per the electrics) to have a way of plugging /unplugging the vhf leads which track through the Aframe at this point (Transom)..... I would use pl259 male and female connectors but inside a waterproof box transom mounted....

I understand that every connection reduces power, but in real terms will this be noticeable /this apporach cause a problem? Alternative is to leave draw chords in the under deck conduit and draw through continuous cable when the floor is down, but tbh is a a bit of a phaff....

The run down the A frame is about 1.5m, and from the proposed connector the run would be about 3 / 3.5m to the Radio unit..... so 5m total with one conection.....

Any thoughts apprecitated
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Old 01 April 2012, 15:31   #2
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My uderstanding is that all connections on an aerial cable will reduce the signal strength, although I'm not sure by how much, and personally I wouldn't be too worried as we're not talking really high frequencies. You have the choice as you suggest of using pl259 and so259 for the joint or alternatively BNC plug and socket. BNC are smaller and therefore easier to feed through and around corners. They are also 50 ohm impedance so should be fine on standard RG58 cable.
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Old 01 April 2012, 15:42   #3
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Every Joint in and Antenna feed will reduce the signal strength by 3db !!!
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Old 01 April 2012, 16:10   #4
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The loss could be offset by using half-decent cable like RG8X instead of that crappy RG58
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Old 01 April 2012, 16:21   #5
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Agreed, however over the distance in a pac 22 hardly noticable

RG8x 3.6 db per 100ft
RG58 4.6 db per 100ft
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Old 02 April 2012, 12:08   #6
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Actually, insertion losses for connectors are typically in the 0.1 to 0.5 db range. It's quite difficult to get accurate data but the weight of evidence suggests that a PL259/SO239 insertion loss is around 0.2db, an N type is negligible, a BNC about 0.1db.
I'd use PL259s because I like their mechanical integrity.
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Old 02 April 2012, 13:03   #7
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Quote:
Originally Posted by Salty John View Post
Actually, insertion losses for connectors are typically in the 0.1 to 0.5 db range. It's quite difficult to get accurate data but the weight of evidence suggests that a PL259/SO239 insertion loss is around 0.2db, an N type is negligible, a BNC about 0.1db.
I'd use PL259s because I like their mechanical integrity.
That is not my understanding. I was always taught that a coax connector (as Ashbypower says) can drop the signal by 3db. Which by the way is half the power loss. But it also depends on the quality and workmanship of the connector.

They are much better out of the equation.

Gary
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Old 02 April 2012, 13:26   #8
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That is not my understanding. I was always taught that a coax connector (as Ashbypower says) can drop the signal by 3db. Which by the way is half the power loss. But it also depends on the quality and workmanship of the connector.

They are much better out of the equation.

Gary
Well, you have to have one at the antenna and one at the radio. If you think about it the idea of halving the signal output for every connector is rather far fetched.
Amphenol make high quality connectors, they say this:

"What is Insertion Loss and how is it specified?

Insertion Loss, expressed in dB is defined as 10*log (Po/Pi) where Po= Power Out and Pi=Power In. There are 3 main causes of Insertion Loss: Reflected losses, Dielectric losses and Copper losses. Reflected losses are those losses caused by the VSWR of the connector. Dielectric losses are those losses caused by the power dissipated in the dielectric materials (Teflon, rexolite, delrin, etc.). Copper losses are those losses caused by the power dissipated due to the conducting surfaces of the connector. It is a function of the material and plating used.

In general, the insertion loss of a connector is on the order of a few hundredths to a few tenths of a dB. As with VSWR, it can be specified as a “flat line limit” or as a function of frequency. Using the same examples as the VSWR, a BNC is specified at .2 dB maximum when tested at 3 Ghz. For the SMA, the requirement is .06*SQRRT Frequency in GHz when tested at 6 Ghz. For example, at 4 Ghz, the requirement would be .06*2 or .12 dB max. Although the connectors are specified to operate over a wide frequency range, they are only specified for testing at particular frequency because the test procedure required to obtain accurate measurements of such small losses is a very precise, and time consuming process."

Note that we are operating at frequencies of only 150 MHz or so, not the levels they talk about here.
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