Driver and Amp help!

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OldskoolPirate
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Driver and Amp help!

Post by OldskoolPirate » Mon Jun 04, 2018 1:24 pm

Hi, I have this rig iv had for years that I’m looking to fix. I can’t work out how it’s setup. Somehow, the driver has no DC connection, only a coax cable to the amp and coax to the rca. I don’t understand how it’s being powered. Only way I can think is through the coax. There’s a 15v connection on the amplifier. Has anyone seen this setup before ?

s2000
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Re: Driver and Amp help!

Post by s2000 » Mon Jun 04, 2018 1:48 pm

I believe so yes, on the old broadcast warehouse 150w pa there appeared to be some similar feature where it could put 15v down the coax. There was a jumper setting to either enable or disable the voltage. Personally I never used it but wondered what driver board needed it, never seen one? I would imagine the driver would have some kind of dc blocking capacitor on the output so the voltage can be taken off and sent to the dc input.

There are lots of items that work like this with power over a coax, for instance satcan and lnb etc...

Got any pics of the box, would be interesting to see it? :tup

nrgkits.nz
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Re: Driver and Amp help!

Post by nrgkits.nz » Mon Jun 04, 2018 8:43 pm

Setting it up this way could allow the PA to be placed closer to the antenna, especially where there's a very long run of coax involved and no power source near the antenna. It's far easier to boost the driver by a few dBm to compensate losses in the cable than it is to boost the output of the PA by the same. You could get away with using a long run of RG58 (as long as you have sufficient drive) and have the PA right next to the antenna saving the expense of a long run of more expensive low loss coax like LMR400.

Albert H
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Re: Driver and Amp help!

Post by Albert H » Wed Jun 06, 2018 2:46 am

I built several rigs back in the 80s with concealed PAs - the PAs were housed inside the antenna support pole! The coax to the pair of dipoles also ran inside the mast. The exciter was housed in a separate diecast box with the power supply in the same box. The transformer, rectifier and smoothing capacitors were relatively cheap - as was the exciter - and when Gotts raided, he took the box containing the PSU and exciter which was cheap to replace. When he disconnected this box, it went off the air - job done as far as he was concerned. The link receivers were also concealed elsewhere, and Gotts would take away a dummy link receiver - the real ones were quite expensive!
"Why is my rig humming?"
"Because it doesn't know the words!"
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teckniqs
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Re: Driver and Amp help!

Post by teckniqs » Wed Jun 06, 2018 6:37 pm

Yes the DC is usually fed through a cap to separate it from the RF. If it's the same one then the board you're probably referring to is in a very small metal box. Built by G**g.

OldskoolPirate
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Re: Driver and Amp help!

Post by OldskoolPirate » Thu Jun 07, 2018 1:21 pm

Yes Iv heard through the grape vine that it’s a G rig. Black amplifier, tin box around the driver. It came in a big box of radio shit I got off a mate.

Effemm
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Re: Driver and Amp help!

Post by Effemm » Fri Jun 08, 2018 1:32 pm

:lol: still to this day story's of gotts makes me laugh.the geezer certainly got about.

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