Q Mark Schoonover, KA6WKE, asks, “I’m just getting started in low-power (QRP) operating and I have two questions. How do you establish an RF ground while out in the field? In the Army we pounded in ground rods for field operations. Most of my QRP will involve hiking to various sites and the thought of dragging along a ground rod and hammer is not too exciting.”
A Depending on the type of antenna system you use, grounding in the field may not be all that important. Many antennas, such as dipoles, Yagis, and so on, do not require ground connections for proper operation. Consider the space shuttle; it is nowhere near a ground, but it works just fine!
Other antennas do require grounds—end-fed wires, most verticals, etc. In those cases, you establish the best ground possible with a counterpoise, which can consist of one or more 1/4-wavelength wires connected to the “ground” point such as a short ground rod. Counterpoise radials work best if they are a few inches above the soil.
RF notwithstanding, don’t forget the role grounding plays in lightning protection. If you are truly in the field, however, you shouldn’t be anywhere near the antenna if lightning is about.
From QST August 2000
Showing posts with label QRP transceiver. Show all posts
Showing posts with label QRP transceiver. Show all posts
Friday, July 30, 2010
Wednesday, July 7, 2010
Is it possible to create a QRP transmitter using little more than a CMOS logic chip?
Q Is it possible to create a QRP transmitter using little more than a CMOS logic chip? It would seem that you could get one to sustain an oscillation and generate RF at HF frequencies.
A It is indeed possible! Lew Smith, N7KSB, designed a 1/2 watt CW transmitter for 10, 15 and 20 meters and it has been featured in The ARRL Handbook. The transmitter design is based on a 74HC240 octal inverting buffer. One section acts as a crystal oscillator (with a crystal for the desired fundamental frequency) while four sections amplify the signal (see Figure 3). The 74HC240 can get fairly hot in this application, so you must attach a heat sink. The supply voltage must also be held to a maximum of 8 V to help ensure the survival of the chip. Finally, this transmitter can be a prodigious harmonic generator, so you must use an output filter composed of capacitors C1 and C2, as well as inductors L1 and L2. See Table 1 for filter component values. L1 is sensitive to lead length, so keep its leads as short as possible.
Figure 3—The 74HC240 transmitter designed by N7KSB.
Table 1 Output Filter Component Values for the 74HC240 Transmitter
From QST December 1999
A It is indeed possible! Lew Smith, N7KSB, designed a 1/2 watt CW transmitter for 10, 15 and 20 meters and it has been featured in The ARRL Handbook. The transmitter design is based on a 74HC240 octal inverting buffer. One section acts as a crystal oscillator (with a crystal for the desired fundamental frequency) while four sections amplify the signal (see Figure 3). The 74HC240 can get fairly hot in this application, so you must attach a heat sink. The supply voltage must also be held to a maximum of 8 V to help ensure the survival of the chip. Finally, this transmitter can be a prodigious harmonic generator, so you must use an output filter composed of capacitors C1 and C2, as well as inductors L1 and L2. See Table 1 for filter component values. L1 is sensitive to lead length, so keep its leads as short as possible.
Figure 3—The 74HC240 transmitter designed by N7KSB.
Table 1 Output Filter Component Values for the 74HC240 Transmitter
From QST December 1999
I am having a hard time tuning my QRP transceiver for zero beat on CW ...
Q Dan, KE6LBX, “I am having a hard time tuning my QRP transceiver for zero beat on CW. It seems as though the stations are always telling me that I’m off frequency. With low power on a crowded band, I know that zero beating is important, but I don’t really know how to do it. Can you help?”
A All you need to do is to match the tone of the received CW signal to the receiver’s offset. If your rig has an offset of 800 Hz, that’s what you would tune for. Most transceivers have offsets between 600 and 800 Hz, and they are usually adjustable so that you can select the tone that is most pleasing to you. If you don’t know what your rig’s offset is, and you don’t have the equipment to measure it, then you have to use trial and error to find the right tone. (This assumes that the transmit-receive offset is set via the VFO and there isn’t a separate fixed-frequency BFO employed.) One word of caution: If you’re using a direct-conversion receiver or a wide filter, you may end up on the wrong side.
From QST December 1999
A All you need to do is to match the tone of the received CW signal to the receiver’s offset. If your rig has an offset of 800 Hz, that’s what you would tune for. Most transceivers have offsets between 600 and 800 Hz, and they are usually adjustable so that you can select the tone that is most pleasing to you. If you don’t know what your rig’s offset is, and you don’t have the equipment to measure it, then you have to use trial and error to find the right tone. (This assumes that the transmit-receive offset is set via the VFO and there isn’t a separate fixed-frequency BFO employed.) One word of caution: If you’re using a direct-conversion receiver or a wide filter, you may end up on the wrong side.
From QST December 1999
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