TESTING AND OPERATING

STEP 1: Initial Settings.

(a) Connect a 2K 1W resistor across the Balanced Output Terminals (J3 and J4).

Do not use the jumper for this test.

(b) Place all 7 inductor switches in their down (bypass) position.

(d) Set the TUNE/XMT switch to the TUNE position.

(e)

(f) Position C101 at “10” (fully counter-clockwise).

(g) Connect a transmitter’s output to the input jack J1.

NOTE: The transmitter should be set for about 1 to 2 watts output. The tuner can handle power ratings from 200 mw up to 5 watts. We will be using the 40 meter band for this test, but other bands could be used with similar results.

STEP 2: Initial Tests

(a) Install the battery into the “N” type holder with the negative terminal contacting the spring. Check to make sure that none of the LED’s are lit. If they light, remove the battery and go to Step 4a.

(b) Key the transmitter on the 40M band for no more than a few seconds. The green LED should turn on to show that RF power is being applied. Some or all of the red LED’s may turn on. If the green LED does not turn on, check the switch setting in Step 1 or go to Step 4b.

(c) Set the inductor switches labeled 1 and 2 to “on” thus adding 3 uH. The tuner should be able to achieve a 1.5:1 SWR by rotating the variable capacitor C101 while briefly keying the transmitter. You will notice that the LED’s will start to extinguish from right to left as you get closer to finding a match. When the last red LED goes out the SWR is less than 1.5:1. If only some of the LED’s are extinguished you can add or subtract inductance a fraction of a uH using the lower row of inductor switches. Check Steps 4c and 4d if you have difficulty achieving 1.5:1 SWR.

Typical Settings for 2K Dummy Load Typical Settings for 51 Ohm Load

HINT: When the variable capacitor C101 is near the maximum (10 on the dial) try adding another 330 pF and re-adjust closer to its minimum capacity (0 on the dial).

(d) Exchange the 2K resistor for a 50 or 51 ohm resistor. You will now find that only the fractional uH inductance switches will be necessary to achieve less than 1.5:1 SWR ratio on 40 meters.

STEP 3: Operating the Tuner with your Antenna.

(a) Remove the test resistors and connect your antenna to the tuner. If you are using a coax feed or an end fed wire antenna, add the jumper between the two black binding posts (J4 and J5). For balanced antenna feed lines, connect them between the red binding post and the top black one (J3 and J4).

(b) Set all inductor switches to the down (bypass) position and the capacitor switch to +0. Put the TUNE/XMT switch in the TUNE position.

(c) Briefly key the QRP transmitter while rotating the variable capacitor through its range. If none of the LED’s go out, start adding inductance by using the switches in a binary fashion. Use the following tables if you are not familiar with the binary code.

(d) If you are using a multi-band antenna, tune it for each band and make a notation of the switch settings so you can tune your antenna quickly when changing bands.

Binary Code for Upper 4 Switches Binary Codes for Lower 3 Switches

STEP 4: Troubleshooting.

(a) LED’s LIGHT WHEN POWER IS APPLIED WITHOUT RF. This will occur if Q2 is conducting. Check the following:

1. Verify that the voltages on Q1 and Q2 are correct according to the voltage chart at the end of Step 4.

(b) GREEN LED DOES NOT LIGHT WHEN RF APPLIED. This generally means that RF is not being rectified and applied to the Gate of Q1, or the bridge circuit is not receiving power. If the Transmitter is operating properly, check the following:

1. Switch settings, particularly the TUNE/XMT switch, are set correctly.

2. Battery voltage is 12 V at R12/Q2 pad.

3. If you have a scope available, verify the transmitter is delivering RF to the input of the bridge circuit board at pad R1/R3.

uH 0=off 1=on

4. Check other key voltages (See the voltage chart at end of Step 4).

(c) GREEN LED IS OK BUT RED LED’s DO NOT LIGHT. It would appear that RF is reaching the bridge circuit, but the problem lies in the comparator U1. Check the following:

1. Pin 3 of U1 (LM339) should be at or near 12 v when RF applied.

2. The anodes of all red LED’s should be at or near 12 v when RF is applied.

3. Check other key voltages on U1 (See the voltage chart at end of Step 4).

(d) NOT ALL THE RED LED’S TURN OUT WHEN ADJUSTING TUNER WITH 2K DUMMY LOAD ATTACHED. The most likely cause of this problem is in the tuner section of the project. Remove the RF input, the antenna or dummy load and the jumper for coax if installed, then check the following:

1. Carefully check the wiring of all coils and switches in the tuner section.

2. Set Switch S8 to +660 and all the inductor switches in the down position.

Measure the continuity between the top two pins of S8. It should be less than 1 ohm. If this measurement is high, there is likely an open circuit in the Coil/Switch chain.

3. Perform the same check as above, only turn all the inductor switches to the up position. The reading will be a little higher by about 0.2 ohms. If there is a very high measurement, then one of the inductors is open.

Close the switches one at a time until continuity is restored and the faulty switch/inductor combination identified.

4. Measure the resistance between either of the top pins of S8 and the ground plane of the pcb. The reading should be between 2K and 3K. A high reading will indicate an error or short in the wiring of C101 or the antenna connection circuitry. A low reading will indicate an error or open circuit in the same wiring.

DC Voltage readings using the SW-40+ Transmitter at 2 Watts XMT OFF <1.5:1 SWR >5:1 SWR

BATT + 12.8 V 12.0 V 10.7 V

Q1-G 0 6.3 7.3

Q1-D 11.9 0 0

Q2-B 12.1 11.1 9.7 Q2-C 0 11.8 10.2

U1-1 0 10.6 0.4 U1-2 0 10.6 0.4 U1-3 0 11.9 10.0

U1-4 0 0. 6 7.0

U1-5 0 1.3 1.5

U1-6 0 0. 6 7.0

U1-7 0 2.1 2.4

U1-8 0 0. 6 7.0

U1-9 0 3.1 3.7

U1-10 0 0. 6 7.0

U1-11 0 4.3 5.0

U1-12 0 0 0

U1-13 0 10.6 0.4 U1-14 0 10.6 0.4

All material in HOMEBREWER is copyright 2005 and may not be reprinted in any form without express written permission from the American QRP Club and the individual author. Articles have not been tested and no guarantee of success is implied. Safe construction practices should always be followed and the builder assumes all risks. HOMEBREWER Magazine is a quarterly journal of the American QRP Club, published on CD-ROM. Each issue typically contains over 200 pages of QRP-related homebrewing construction and technical articles intended for builders, experimenters, ham radio operators and low power enthusiasts all around the world. HOMEBREWER features include construction projects for beginners all the way up to the advanced digital and RF experimenters. Annual subscriptions are $15 (for US & Canada) and $20 (for foreign addresses). For information, contact editor/publisher George Heron, N2APB at [email protected] or visit HOMEBREWER Magazine home page at www.amqrp.org/homebrewer.

If the rig in this picture looks familiar to you, it should! It looks a lot like the 40m Nuts and Bolts design that was detailed in the previous two installments. There is there is a major difference – this one is a 20m rig that was the product of taking that original design and bringing it a step forward. The result is a useful rig for one of the most popular HF DX bands.

As can be seen in the photo above, the construction layout and building method were the same as those used in the Nuts and Bolts 40. However, in order to put the rig on 20 Meters, several parts of the circuit required changes, and there were some additions, as well.

The 40 Meter transceiver described in the previous two "Nuts and Bolts Approach" articles is fun to operate, has a very clean transmitter signal and a nice sounding superhet receiver, and has a stable VFO, which provides coverage of the entire CW portion of the band.

It was even more fun designing it, building it, testing it, modifying and tweaking it so that it actually performed as desired. In this article, we will look at the changes necessary to make this basic design work, and work well, on a higher band.

Because 40 and 20 Meters have always been the two most popular HF bands, it seemed only natural to design and build a transceiver for 20 Meters, since the first Nuts and Bolts transceiver was designed for 40.

DESIGN REVIEW

In document HB#5 (Page 37-52)