W1VT
| Joined: | Sat, Apr 4th 1998, 00:00 | Roles: | N/A | Moderates: | N/A |
Latest Topics
| Topic | Created | Posts | Views | Last Activity |
|---|---|---|---|---|
| Antenna analyzer vs feedline type | Sep 21st 2012, 14:37 | 1 | 1,001 | on 21/9/12 |
| USB to Serial Port problems--Prolific Drivers | Aug 3rd 2012, 18:27 | 1 | 1,222 | on 3/8/12 |
| Italian Phishing emails! | Dec 13th 2011, 14:20 | 1 | 1,140 | on 13/12/11 |
| John K0GMO needs help designing SS Amp | Nov 17th 2011, 15:53 | 1 | 1,020 | on 17/11/11 |
| 1 Farad Capacitor to Eliminate Headlight Flicker? | Oct 19th 2011, 13:14 | 4 | 1,792 | on 9/11/11 |
| History of Relay Rack Dimensions? | Oct 17th 2011, 12:58 | 2 | 1,248 | on 25/10/11 |
| Miswired Selsyn | Oct 13th 2011, 17:51 | 1 | 1,076 | on 13/10/11 |
| Stealth Antenna wire | Sep 12th 2011, 12:51 | 2 | 1,591 | on 13/9/11 |
| Designing a ham bench | Aug 29th 2011, 12:38 | 2 | 1,672 | on 29/8/11 |
| Can't find recent Hint and Kink | Aug 26th 2011, 13:01 | 1 | 1,539 | on 26/8/11 |
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 |
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| What is an accepted range for a DX contact? | WN6WJN | 1 week ago |
| http://www.arrl.org/distance-records 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 |
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| 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 |
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| 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 |
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| Air Conditioner RFI | KD4LN | 1 week, 2 days ago |
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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