Inside The Galaxy DX 2547 AM/SSB CB Base Station Radio
The first thing I noticed after removing the top and bottom covers was the mobile chassis mounted in the base chassis. At first I was disappointed thinking this was a cheaply made base radio. What they have done was use the aluminum chassis of their mobile CB radio and designed a base chassis that accepts this sub -assembly utilizing the mobile chassis for the heat sink.
Most base radios were nothing more than a mobile circuit board in a box with extra features and a built-in power supply. Even the very popular Cobra 2000 was a Cobra 148 in a nice box with a frequency counter two meters and extra features. So there’s really nothing different here.
The transformer is a small version of the one used in the 100 watt RCI base radios. It’s a toroid type and I would expect it to power this radio with the dual final modification and still have more in reserve. In addition, the power supply regulator has a large heat sink attached to the rear of the radio.
Speaking about a dual final modification, the circuit board has spaces for another 2SC1969 and other components required to increase the output power to that of a 10-meter dual final 30 Watt radio. To get optimum output and truly clean sideband transmission a matched pair of 2SC1969 should be used. I mention this because the modification sheet I have seen calls for one 2SC1969 not a matched pair. I will cover this in another article sometime in the future.
DX 2547 Transformer
The following are some power supply voltage measurements made at no load, receive only, and at different transmitter power levels:
|SSB 14 Watts PEP||13.72V|
|SSB 22 Watts PEP||13.69V|
The layout is very clean. There are no components on the back of the circuit board. The main circuit board is through hole technology. This will make many dealers happy. Most dealers don’t like working on surface mount circuit boards. There are some boards in this radio that are surface mount. It’s the coming technology whether we like it or not. More and more components are are only available for SMT.
Peaking the transmitter was disappointing at first. sideband wouldn’t increase at all. The AM carrier would increase to around 6 Watts and the peak modulation would only swing to 12 Watts. After going over and over the tune-up, I realized the the heatsink by the final was getting very hot. Finally I was able to get 22 Watts PEP sideband. and 6 Watts with a swing to 18 Watts on AM by spreading L29 out. The heatsink didn’t get as hot after spreading this coil.
The controls for power and modulation are as follows:
|AM High Power||VR14|
|AM Low Power||VR18|
Mechanically it is well structured and should last for many years. The components on the main PC board are well marked and easy to locate. The top and bottom covers may be a tad too large. I recommend putting the side screws in first and lining up the covers while tightening them. Then install the top, bottom, and rear screws. I found installing the top and bottom screws first, the covers overlapped at the side seam and was impossible to line them up without doing damage.
And for the operators that like toys in their radios, There’s room for echo boards, speech processors, sound recorders, noise toys and whatever your heart desires. There isn’t a lot of room on the front panel for switches though.
The front bezel has knockouts for other switches and maybe controls. It seems that there are other plans for this bezel. I hope it’s only for Galaxy. I’ve seen to often what happens when a radio case is used for another product.
The end user thinks they are the same inside, when in fact they can be quite different. The cheaper model gives a bad rape to the better unit, after all it’s the same, it looks the same, it must be the same. Just the company that charges more is screwing the public…right? As wrong as these theories and assumptions are, the public hasn’t learned that a radio can look the same but be totally different inside. One example is the Magnum 257.
Magnum International did many hours of engineering on this unit. Most of this engineering didn’t go into the look alike radios. This radio has been hurt by other look alike radios produced by the same Korean factory. Some were single final radios.
The distributors and dealers didn’t go out of their way to point this out. And we didn’t see Radio Shack advertise their copy was unconvertible. In fact Radio Shack had it in the contract that the radio must not be convertible and if it could be the factory would pay dearly in damages. It’s psychology, would you pick up a snake that looks like one that bit you before?
|Support, support, support…The Galaxy support department was gracious enough to send the Galaxy Noise Filter schematic with out a request! This is what is missing in most instances these days with large consumer electronics companies. Their either to big to follow up on details, don’t know were to get the information, or plain don’t care. Another reason for the lack of support for many radios is that the radios are designed, built and documented off shore and shipped directly to the distributor. The distributor doesn’t understand radio technology nor do they understand end user customer support. All they see is the chance to make higher profits by cutting out the important link between the factory over seas and themselves. Most of these radios end up in yard sales or the trash soon after the purchase. Sure you can save a few bucks, but what do you do when the thing quits or there is a technical design flaw. Who’s out their to follow up on it. Don’t think the distributor or mail order company will. They’ll drop it like a hot rock and find a new product to make profit on. Not at Galaxy, they support their product 100% and beyond. To be honest there are a few companies that support their products, but increasingly I see more products that are not supported at all. Have you ever tried to get a service manual for the Uniden Washington base radio? They haven’t supplied them for many years! Need more be said?
REQUIRED TEST EQUIPMENT
Galaxy Noise Filter Schematic
|Figure 4-2, Receiver Test Setup|
This transceiver has been aligned at the factory and does not require any adjustments at installation. The required test equipment listed is used for the test setup or alignment shown in Figure 4-1 Transmitter Test Setup and Figure 4-2 Receiver Test Setup. This test setup is used in part or total during the following adjustments. Refer to Page 43 for adjustment location.
|ITEM||U.U.T. (UNIT UNDER TEST) SETTING||ADJUSTPOINT||MEASUREMENT|
|RegulatorVoltage||Connect Voltmeter positive lead to power switch.Connect Voltmeter negative lead to PCB ground.||VR701||13.8 VDC|
|VCO||Disconnect ‘short PCB’ from TP7, TP8 and TP9.Set radio to CH 1 AM RX mode.Connect Voltmeter to TP2.||L14||2.5 VDC t 0.1|
|Set CLARIFIER Control to 12 o’clock.Connect Oscilloscope to TP3.||L15||Adjust for max.|
|Connect Frequency Counter to IC3 Pin 8||VC1||10.2400MHz t 20Hz|
|AM Frequency||Set radio to CH 1 AM RX mode.Connect Frequency Counter to TP3.||L20||16.2700MHz t 20Hz|
|USB Frequency||Set radio to CH 1 USB RX mode.Connect Frequency Counter to TP3.||L21||16.2725MHz ± 20Hz|
|LSB Frequency||Set radio to CH 1 LSB RX mode.Connect Frequency Counter to TP3.||L22||16.2675MHz ± 20Hz|
|TX OffsetFrequency||Set radio to CH 1 AM TX mode.Connect Frequency Counter to TP3.||VR7||16.2675MHz t 20Hz|
|AM OSC||Set radio to CH 1 AM TX mode.Connect Frequency Counter to TP5.||L23||10.695OMHz ± 10Hz|
|USB OSC||Set radio to CH 1 USB TX mode.Connect Frequency Counter to TP6.||L24||10.6925MHz t 10Hz|
|LSB OSC||Set radio to CH 1 LSB TX mode.Connect Frequency Counter to TP6.||L25||10.6975MHz:t 10Hz|
|BIAS Current||Set radio to CH 19 USB TX mode.Modulation Off.Connect current meter to TP7(+) and TP9Connect current meter to TP7 (+) and TP8||VR12VR10||50 mA100 mA|
|SSB APC||Set radio to CH 19 USB RX mode.Connect Multimeter to TP7.||VRI7||12.5 VDC|
|SSB TX Power||Connect “short PCB” to TP7, TP8 andConnect RF Power Meter to antenna jack.Set radio to CH 19 USB TX mode.AF signal 30mV, 1 KHz to microphone.Set RF PWR Fully Clockwise.Set MIC GAIN Fully Clockwise.||L40,L42,L43,L44||MAX > 12WSpurious EmissionMinimum.Balance PowerBetween CH1 andCH4O.|
|SSB ALC||Set radio to CH 19 USB TX mode.AF signal 3OmV, I KHz to microphone||VRI3||11.5 W|
|SSB CarrierBalance||Set radio to CH 19 USB TX mode.Set MIC GAIN Fully Counter Clockwise.Connect Oscilloscope to antenna connector.||VR6||Spurious Emission toMinimum.|
|AM TXHigh Power||Set radio to CH 19 AM TX mode.Modulation Off.||VR14||3.8 W|
|AM TXLow Power||Set RF POWER fully counterclockwise.||VR18||0.5w|
|RF PowerMeter||Set radio to CH 19 AM TX mode.Set RF POWER fully Clockwise.Set SWR/MOD/PWR Switch to PWR position||VR9||For a needle readingof “4” on TX PWR scale.|
|AM ModulationMeter||Set radio to CH 19 AM TX mode.AF signal 30mV, 1 KHz to microphone.Set MIC Gain fully Clockwise.Set SWR/MOD/PWR Switch to MOD position||VR16||For a needle readingof 95% on theModulation scale.|
|FrequencyCounter Adjust||Set radio to CH 19 AM RX mode Set CLARIFIER Control to 12 o’clock.||VC1 onfrequencycounterPCB.||Display should be27.1850|
|AM Sensitivity||Set radio to CH 19 AM RX mode.Set RF GAIN Fully Clockwise.Set SQ Fully Counter Clockwise.Set VOL Control at 2 o’clock.Set NB/ANL switch to OFF position.Set TONE Fully Clockwise.Set CLARIFIER Control to 12 o’clock.Connect RF SG to antenna jack Frequency 27.185 MHz, lmV. Mod 30%.||L2,L3,L5,L6,L7,L8,L9,L10||Audio Output > 2VS/N > 10 dB.|
|Set radio to CH 40 AM RX mode.RF SG setting 27.405 MHz.Set radio to CH 1 AM RX mode.RF SG setting 26.965 MHz.||L5,L6||For Balance BetweenCH 1 and CH 40|
|USB Sensitivity||Set radio to CH19 USB RX modeSet VOL Control Fully Clockwise.RF SG setting 27.186 MHz, 0.5uV. Mod off.||L11,L12||Audio Output > 2VS/N > lOdB|
|LSB Sensitivity||Set radio to CH19 LSB RX modeSet VOL Control Fully Clockwise.RF SG setting 27.184 MHz, 0.5uV. Mod off.||L11,L12||Audio Output > 2VS/N >lOdB.|
|NB Adjust||Set radio to CH 18 AM RX mode.RF SG setting 27.185 MHz, 1000mV Mod off.Set NB/OFF switch to ON position.Connect Multimeter to TP1 (D2 cathode).||L1||DC Voltage to max.(> 2.OV)|
|AM Squelch||Set radio to CH 19 AM RX mode.Set SQ Control Fully Clockwise.RF SG setting 27.185 MHz, 2OmV. Mod 30%.||VR4||Adjust very slowlyuntil squelch just closes.|
|SSB Squelch||Set radio to CH 19 USB RX mode.Set SQ Control Fully Clockwise.RF SG setting 27.186 MHz, 20 mV. Mod off.||VR3||Adjust very slowlyuntil squelch justcloses.|
|AM S-Meter||Set radio to CH 19 AM RX mode.RF SG setting 27.185 MHz, 100mV. Mod 30%.||VR1||For a reading of “9”on the “S” scale.|
|SSB S-Meter||Set radio to CH 19 USB RX mode.RF SG setting 27.186 MHz, 100mV. Mod off.||VR2||For a reading of “9”on the “S” scale|