Just looking at this board is enough to set it leaps and bounds above another board being discussed in this section. Obviously we have real RF transistors that are still in production being used. But have a look at the PC board itself and notice all of that intact copper ground plane surface it has around the transistors. Something completely absent on the larger "1000" board, where it's required even more.
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Skywave AMPS
- Thread starter lrz50
- Start date
Just looking at this board is enough to set it leaps and bounds above another board being discussed in this section. Obviously we have real RF transistors that are still in production being used. But have a look at the PC board itself and notice all of that intact copper ground plane surface it has around the transistors. Something completely absent on the larger "1000" board, where it's required even more.
To me, this board screams of parasitic oscillation...
The layout - too ordered - well thought out, but not in the approach of RF and it's needs in mind, more like ease of assembly and repair. - which raises a question about the builder, that being said; NO - I'm not trolling just making an observation.
When you have trace layouts that structured, RF is a lot like water, takes the easiest path to get there, this board is a clean layout - looks nice to the eyes, but the RF path needed to reduce the problems of reactive elements in the pathways, isn't there - potential problems are evident.
Anyone whom has done their own amps or have had to chase down impedance bumps, squeals and ground loops knows this - and these boards are not setup to provide the best and most direct pathways for RF pipelines.
Ever try to work on strip line? This is what amazes me about him, he knows these problems exist and with a plastic enclosure this may have been his saving grace - not shielded so you have the initial tuning to accommodate the RF path (but do your calculations in the effort of less inductive effects along the pathway) - but woe be to they that place this too close to another noisy RF spot in their vehicle.
I've already had to work on several T/S and Palomar amps that the customers, in order to provide clearance UNDERNEATH their vehicles seats - have removed the covers of their amps and have generated other issues around the running amps with covers removed - a different SWR mess and beast can occur from this.
Although someone can think of this as a hilarity, but a bad amp can leak so much RF out of it's system they can set off an Air bag - which one customer visit at the shop did have occur - at least not admittedly at first - only when the amp was removed could it bee seen.
You can blame the wiring, or the proximity - but either way - my approach to plastic cases and their protection they can provide, I can only caution you.
They had to test and refine it to make it work. - but is it the best concept you can provide a customer?
The layout - too ordered - well thought out, but not in the approach of RF and it's needs in mind, more like ease of assembly and repair. - which raises a question about the builder, that being said; NO - I'm not trolling just making an observation.
When you have trace layouts that structured, RF is a lot like water, takes the easiest path to get there, this board is a clean layout - looks nice to the eyes, but the RF path needed to reduce the problems of reactive elements in the pathways, isn't there - potential problems are evident.
Anyone whom has done their own amps or have had to chase down impedance bumps, squeals and ground loops knows this - and these boards are not setup to provide the best and most direct pathways for RF pipelines.
Ever try to work on strip line? This is what amazes me about him, he knows these problems exist and with a plastic enclosure this may have been his saving grace - not shielded so you have the initial tuning to accommodate the RF path (but do your calculations in the effort of less inductive effects along the pathway) - but woe be to they that place this too close to another noisy RF spot in their vehicle.
I've already had to work on several T/S and Palomar amps that the customers, in order to provide clearance UNDERNEATH their vehicles seats - have removed the covers of their amps and have generated other issues around the running amps with covers removed - a different SWR mess and beast can occur from this.
Although someone can think of this as a hilarity, but a bad amp can leak so much RF out of it's system they can set off an Air bag - which one customer visit at the shop did have occur - at least not admittedly at first - only when the amp was removed could it bee seen.
You can blame the wiring, or the proximity - but either way - my approach to plastic cases and their protection they can provide, I can only caution you.
- - the heat can soften, they can stink
- - and crack from the abuse they will get sitting in a vehicle
- - Bouncing around or bolted - can it hold up to accelration and torque problems in ordinary driving let alone highway...
- - Thermally stable plastic or not - whether it would be a sunny hot day, or the cold of winter - are you sure you can trust this build construction?
They had to test and refine it to make it work. - but is it the best concept you can provide a customer?
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In my 2010 hhr the airbag control module is mounted to the FLOOR BOARD UNDER THE PASSENGER SEAT under the carpet. The Body Control module is mounted to the center hump under the center console. One needs to do their homework as to where the computers, modules and sensors are mounted in their vehicles before installing the amp imo.
I never even looked at the plastic case and only considered the board itself. I actually thought at first glance the cabinet was molded aluminum until I noticed the threaded inserts in the plastic!
No high power RF amp should EVER be placed in an unsheiled cabinet. The flaws on that board that my eye can spot are the absence of negative feedback and the output combiner not being centered between the two output transformers, creating an unequal path for RF. The collector traces to the output transformers are also longer than they need to be. If you see more that I've missed, please share? Having said that, this board is still WAY better than the Rocketbox.
OK, upon further inspection, it's missing thermal tracking bias. There are several strikes against this board including parts being spread apart too far. But, I still see a lot of improvement in areas that are typically lacking. Like the right transistors and great low inductance grounding around all of the emitter tabs.
PS: I also have to admit I am a bit confused why we see two RF combiners and splitters being used? At first I thought the second one on the output, may be a double choke, to feed DC into the collectors but that sure does not explain the second one on the input.... What's going on here?
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I just thought I would mention that if you're tempted to cut costs by using a plastic enclosure, at least spend some of that savings, on installing a thin metal shield to cover the PA board.
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