Thursday, March 10, 2011
Ten Steps to QRP Success
1. Use efficient antennas
A half wave dipole or better is preferred.
2. Know your capabilities - do not expect DX every time
It would be nice to work Europe with one watt to a mobile whip on forty metres, but do not expect such contacts to come easily (if at all). Instead, you should cast your sights a little lower and enjoy the closer-in contacts that are more achievable.
3. Have frequency-agile equipment
Many articles describe simple crystal-controlled QRP transmitters that can be put together in an evening. These are fun to build but frustrating to operate; 99 percent of such rigs sit on shelves, unused, gathering dust. Instead, use a VFO or 3.58 MHz variable ceramic resonator on eighty metres, or a VXO with at least a 10-15 kHz tuning range on the higher bands.
4. Use 'tail-ending' to advantage
When your signal is weaker than average (such as when operating QRP), 'tail-ending' is the most effective way of obtaining contacts. Simply tune across the band, noting the contacts that are ending. When all stations sign clear, call one of the stations. They will most likely reply to your call, even if only to give a signal report.
5. Have a quality signal
A transmitter that clicks and chirps is harder to copy at the other end than a signal from a clean and stable rig. This is particularly the case when the receiving station is using narrow CW filters.
6. On CW, know the relationship between your transmit and receive frequencies
It is possible for a station to miss your call if you are transmitting on the wrong frequency. Set direct conversion QRP rigs so that they transmit about 800 Hz below their receive frequency. Conversely, if calling CQ, tune around your normal receive frequency (with the RIT control) just in case a station is calling you on the wrong frequency.
7. Have an efficient transmit/receive switching system
A homebrew station that requires the operator to flick two or three switches to switch from receive to transmit is inefficient and may result in missed contacts (particularly during contests). Use just one T/R switch or experiment with the many break in and timing circuits available.
8. Use the best receiver you can afford
Most of the complexity in a QRP station is in the receiver. While simple receivers are fine for casual SWLing, active operating requires a somewhat better class of receiver. Aim for good frequency stability, adequate bandspread, reasonable selectivity, good strong-signal handling and an absence of microphonics. A well-built direct-conversion receiver should satisfy on all five counts for all but the most hostile band conditions.
9. Enter contests to boost your operating skills
Many people think that high power is necessary to participate in contests. This is untrue, particularly for the local VK contests. Contest rules are given in Amateur Radio magazine and on the WIA website.
10. Don't be afraid to call CQ
On bands such as ten metres, the band can be wide open, but no one would know as every body is listening. Call CQ, particularly when you have grounds for supposing the band is open, for example reception of beacons or 27 MHz CB activity. Automatic CQ callers using tape recorders, computers or digital voice recorders are particularly handy here.
Wednesday, March 9, 2011
L Match Tuner for End-Fed wire antenna
In this tuner. a variable inductor made bv mutual coupling between two coils of near equal inductance is used as the L match inductor. The object is to have a variable inductor with no taps or rollers. These coupled coils, LI and L2 are connected in series (see Figure) to get total inductance.
A reverse switch connects the two coils either for additive or subtractive M to accomplish a wide range of total L. With LI = L2 = 10 uH and K = 0.8 the range is about 4 to 36 uH. One coil is wound on the plastic case of
a 12 ga empry shotgun shell and the other on a 20 ga empty shotgun shell . The winding is #23 magnet wire so that the outside diameter of the 20 ga coil slides nicely into the 12 ga shell to allow variable coupling by sliding the smaller coil in and out of the larger coil.
1. Use a low base 20 ga empty shotgun shell and drill out the primer end to clear a 114 inch screw.
2. Take a 1/4-20 nylon hex nut and glue it over the hole just drilled. This gives the shell a threaded nut that will run on a lead screw to move this coil in and out of the 12 ga shell.
3. In preparation for winding the coil cut off and discard about 318 inch of the crimped end of the 20 ga plastic so that a well formed coil form remains.
4. Locate and drill a 1132-inch dia hole in the plastic about 114 inch from the end just prepared. This is for the start of the $23 magnet wire winding.
5. Locate and drill another 1132" dia. hole in the plastic about 7116 inch from the fust hole toward the base. This allows 15 turns between the holes from start to finish, Drill a 1W-inch hole close to the base that will serve to bring both ends of the winding out for connections clear of the sliding fit. .
6. Wind 15 turns of #23 magnet wire between the two 1132 dia holes. Start with one end into a 1132 dia hole, into the shell and out the 118-inch hole. When 15 turns are on, put the end into the nearby 1132- inch hole, down the center of the shell and out the 118-inch hole pulling the wire tightly to maintain tight turns.
7. Take a 12 ga shell, cut the crimped end off to make a uniform coil form and wind on 13 turns of #23 magnet wire. No holes are used for the start and finish of the winding so tape must be used hold the winding and dress the leads. Clear fingernail polish may be useful as well.
8. A 1/4-20 x 2 inch nylon machine screw along with an extension of 114 inch wooden doweling is used to make the lead crew shown in the diagram in Figure
Subscribe to:
Posts (Atom)