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Panasonic / National Panasonic,
Matsushita Electric Industrial Co. Ltd., Osaka
DR - 48 / RF - 4800 LBS

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überarbeitet am 21.10.2010

Panasonic's DR-48 / DR-49 Receiver were the high end sets of the series of shortwave receivers with conventional design still without PLL synthesis constructed by Panasonic.
I'm not yet absolutely sure about all differences between the DR-48 and the DR-49, the older set comes with a red LED frequency readout only active on the shortwave bands 2 - 7.

Double conversion, I.F. 2 MHz, 455 kHz

Digital frequency counter, 1 kHz


coverage 145 kHz - 30 MHz, UKW 88 - 108 MHz

Sensitivity MW 60 uV,
5-30 MHz AM 1,1 - 1,4 uV, SSB 0,6 - 1,0 uV

Selectivity -6/-60 dB
1,7/6,0 kHz, 2,5/15 kHz

S Meter, RF Gain

The Panasonic RF-4800 LBS has been sold in Europe as DR-48, it covers also the longwave band.
The DR-48 is a quite bulky desktop receiver with it's dimensions of 48 x 20, x 35,5 cm and it's weight of 8 kg; two metal handles give protection to the front panel, when the set is turned face down - the give the set the aspect of a semiprofessional receiver.

The RF-4800 can be powered from 110 / 220 V mains, from a 12 V car battery or eight UM-1 / mono cells accomodated in two battery compartments.

At the left side of the frontpanel, You find the big speaker and below the mains switch, the jacks for an external speaker and a cassette recorder at further right the rotary controls for volume, bass, treble and the BFO pitch control.
In the middle of the display window at the right, You find the red LED display of the frequency counter active on shortwave bands SW 2 - 7 and the auxiliary dials for long-, mediumwaves, tropical bands (SW 1) and the FM broadcast band at the left and the shortwave bands SW 2 - 7, each 4 MHz wide, at the right.
In the middle of the frontpanel the huge main tuning knob is located, it is equipped with a crank and can be set to slow and fast tuning speed by pressing the knob in the centre - this knob will tune the shortwave bands. The frequency display is active on these band segments and the receiver operates as a double conversion receiver.
The second smaller tuning knob tunes the long-, mediumwave, SW1 and FM broadcast bands, in these bands, the set operates as single conversion set and the frequency display is not active.
The signal strength meter tends to read high, in the RF-4800 it has a white background, this is a possibility to distinguish the set from the RF-4900, the S meter of the successor comes with a black background. Below You find a row of switches: the switch to activate the AFC in FM mode selects between the two AM bandwidths in AM mode, the middle switch activates the noise limiter and the third one the BFO: use the BFO pitch control just below for an optimum BFO note when receiving CW transmissions and for optimum speech reproduction in SSB mode - voices should no sound like mickey mouse.

The bandswitch for LW - MW - SW1 - FM and the band segment switch for SW 2 - 7 are located below the right auxilitary frequency dial. The frequency counter can be calibrated from a 5 or 10 MHz time signal and frequency standard transmission from WWV / WWVH or even from another station transmitting exactly on a known frequency. Tune in to "Radio Deutsche" Welle on 6075 kHz and wait for news and station identification, then tune to maximum S meter reading and use the SW 2-7 CAL control to set the frequency display exactly to display 6.075 - with this control not set correctly, the frequency displayed can be 2 - 4 kHz off the actual frequency. Keep in mind, the RF-4800 is no PLL synthesized set.
In the right lower part of the front panel, You find the ANT TRIM to match an external antenna, the R.F. gain control. This should be set to maximum position or "DX" as a standard, in case of overloading of the receiver front end due to high signal level conditions in acrowded shortwave broadcast band wit ha long antenna, You can reduce the R.F. gain. In fact, this knob acts more like an attenuator as there is no switch to turn off the AGC (automated gain control) completely. Three more switches activate dial illumination, frequency display and set the S meter to indicate battery power.

At the rear face of the DR-48 / RF-4800 LBS, You find the two folding out ferrite antennas for long- and mediumwaves, the international variant comes with only one ferrite antenna. Next to the antenna sockets, there is a PL / SO 239 antenna socket for SW 2 - 7. The DIN socket can be used to feed the DR-48's audio signal to a cassette recorder and also to feed a signal from an external audio source to the receiver, set the switch at the rear to "PHONO" to use the DR-48 as audio amplifier.

The operation scheme of the DR-48 is quite straightforward: turn on the set, make sure the RF gain control is turned to the MAX setting, the AM bandwidth to wide and the BFO turned off. The right bandselector should be on SW 2 - 7 and the left on "2" to select the 3 - 7 MHz range, the use the big tuning knob to find the "Deutsche Welle" from Cologne on 6.075 MHz. If the signal peak is one or two kHz higher or lower then 6.075, use the SW 2-7 CAL to adjust the frequency display setting to the correct frequency.

Due to it's conventional design as a double conversion receiver with a quite low first I.F. and a frequency counter, the receiver shows a certain frequency drift even after warm up, CW or radioteletype decoding with an automatic decoder and even reception of SSB signals need slight retuning of the set from time to time, automated recordings won't work properly.
The skirt selectivity of the two I.F. filter's is mediocre. quite often, You hear an 5 kHz interference whistle from a adjacent channel carrier.
As the receiver operates as single conversion set below 3 MHz, You might encounter mirroring or "ghost signals" appearing 900 kHz from the original signal away. As the internal ferrite antennas cannot be switched of, the DR-48 / RF-4800 is not well suited as a longwave / mediumwave DX receiver.

Conclusion: the DR-48 / RF-4800 represents the state of the art from the early eighties as desktop receiver with double conversion circuitry connected to a frequency counter, stability, suppression on unwanted signals and selectivity of the I.F. filters is all below the expectations for a shortwave receiver in the 21st century.
The DR-48 / RF-4800 looks very impressive and makes a decent secondary or entry level shortwave radio, for real Dxing, You would need a set with better filters, maybe a notch filter and passband tuning and a few memories to compare different frequencies.
If You find a DR-48 / RF-4800 for a bargain price, get one, and You might have lot of fun with it. The technical built quality is not superior, so You might encounter some work until the receiver is running properly. In my sets, the wave band and shortwave band switches all did contact poorly and needed cleaning, as well as the AM narrow / wide switch and even the rotary volume and tone controls.

Variants sold in different regions of the world: 
DR-48 /
RF-4800 LBS
red LED display, aktive only in the SW 2 - 7 ranges;
longwave reception (two ferrite antennas), FM 87,5 -108 MHz
RF-4800red LED display, aktive only in the SW 2 - 7 ranges;
no longwave coverage (only one ferrite antenna), FM 87,5 -108 MHz
RF-4800red LED display, aktive only in the SW 2 - 7 ranges;
no longwave converage (only one ferrita antenna), FM 76 - 90 MHz

© Martin Bösch, 14.7.2010