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Latest Posts

Topic Author Posted On
28-V, High Current Power Supply - Adjustable? Steffen 3 days, 9 hours ago

Chapter 17 is the RF Power Amplifier Chapter. But, I see a suitable project on page 11.36 of the 1999 ARRL Handbook.

There is an schematic error--rather than go to pin 2, R7 should go to the common of R2, R3, R4, and R5.

Typically, there are two distinctly different 723 circuits--one goes from 2 to 7 volts, and the other goes from 7 to a much higher voltage. Thus, you won't be able to go down to 5 volts with this circuit.

A problem with a wide voltage range linear supply that can supply a lot of current is that you will be dissipating a lot of heat when supplying 5 volts at 6 amps. When putting out 5 volts instead of 24 volts at 6 amps, the pass transistors will need to dissipate an additional 114 watts. De-rating the supply from 10A to 6A isn't enough to compensate for the extra heat--you actually need twice as much heat dissipate to provide 5V at 6A than to provide 24V at 10 amps. Assuming 31 volts, I calculate 156 watts compared to 70 watts.

It may be more practical to built two separate supplies, one to cover 2 to 7 volts, and another to cover 7 to 24 volts.

Zack Lau W1VT
ARRL Senior Lab Engineer

What is an accepted range for a DX contact? WN6WJN 1 week ago
As you can see, when you get to the higher amateur bands, even 100 miles is enough to set records.

Zack Lau W1VT
ARRL Senior Lab Engineer
RF Suppressor Ground System KK6CXF 1 week ago

The best way to handle the second floor shack grounding issues is to run coax from the antenna to single point ground that is line of sight and bonded to the electrical service entrance, and then bring up the coax to the 2nd floor station. Some antennas, such as verticals and long wires, may require a good radial system for decoupling, as ground rods are typically inadequate. A balanced antenna, like a center fed dipole, will often work with just ground rods. A half wave dipole is likely to be the easiest antenna to get working well from a 2nd floor station.

A program like EZNEC can be used to model this type of ground. The outside shield of RG-213 coax can be modeled as a 0.4" solid copper conductor. You can then connect a transmission line of the appropriate velocity factor (0.66 for solid polyethylene up to 0.84 to foam) to model the center conductor and inside of the shield. While you can't "prove" anything, you may learn enough to satisfy your curiosity, or justify spending the time and effort to make a few measurements with real hardware.

Zack Lau W1VT
ARRL Senior Lab Engineer
looking at MFJ 31' vertical /portable antenna KB9YUT 1 week, 2 days ago

Instead of leaving a dipole up, perhaps you could install support ropes that can be used for future operations?

Zack Lau W1VT
ARRL Senior Lab Engineer
Air Conditioner RFI KD4LN 1 week, 2 days ago
Quote by NZ2Z
I just moved into a new home and am contemplating where to put the shack in the basement. On one side is the incoming power, and Internet/cable feed. Very close to that are 3 ac external units. I need to determine a location for the radios as well as the location for a sleeve to feed the antenna wire from the shack to the outside antennas. I can locate the radios anywhere inside, but the antenna wires will in all probability have to come out near the ac ac units. Is there any general guidance on 1) how far from the ac units or electrical power box (outside) to place the radios, and 2) if it is a good idea to have the antenna coax exit the shack near the electric box or the ac pads?

Bob - KG2RP

Ideally, there should be a line of sight path from your service entrance to your shack's single point ground--that way, if there is lightning strike on the service wiring, there will be a simple and direct path to the station grounding. Typically, lighting will take a path through the home instead of going around a corner to follow a bad ground path.

The service entrance ground and the single point ground can be the same, but you will need to work harder remove electrical noise from the single point ground. Ground rods aren't as effective as a good radial system in decoupling noise from grounds.

In terms of overall station performance, it may be worthwhile to sacrifice a little bit of transmit signal if you can significantly reduce the noise on receive--typically, we are talking about a fraction of a dB on transmit and many dB on receive, if there is a low SWR on the transmission lines.

Zack Lau W1VT
ARRL Senior Lab Engineer

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