The Hammarlund HQ-145A is a shortwave receiver with bandspread dials covering the amateur
radio bands, below 10 MHz, it acts as single conversion, above 10 MHz as double conversion
|HQ-145AX||11 crystal controlled fixed frequency positions|
|HQ-145AC||equipped with electric 24h clock|
(type Telechron, with timer functions)
In contrast to the original HQ-145, the "A" version which appeared in 1966
has a slightly darker front panel and a hinged lid, instead of the rectifier tube
5U4GB, two silicon diodes are used.
The tabletop radio can be powered from 117 or 230 V mains.
The receiver's dimensions are 48 x 26,6 X 33 cm, a hinged lid gives access to the
chassis for tube replacement.
In the middle of the frontpanel, You find the two dial windows, the
round main and bandspread frequency dials are rotated behind the fixed pointer line.
The square signal strength meter is located in between.
The huge tuning knobs for the main tuning and the bandspread dials are located below
the corresponding dial windows, the bandswitch between them selects from the
following band segments: 0,54 - 1,6 MHz (mediumwaves), 1,6 - 4 / 4 - 10 MHz (single conversion
in all these band segments) and 10-30 MHz (double conversion), the position
20BS selects the spread 20 m ham band.
The bandspread dial should be set to "100" for a correct reading of the main tuning
dial in general coverage mode.
For use of the bandspread dials, the main tuning dial should be set to the upper
edge of the corresponding amateur radio band mark, so that the readings from the bandspread
dial should give correct results. When the optional crystal calibrator is installed,
which will give You a marker signal every 100 kHz through all ranges,
tune the set to the 100 kHz signal of the crystal calibrator in the region of the
upper edge of the ham band, You want to receive. Now the matin tuning dial
should not be touched anymore, You might search for the next crystal calibrator
mark on the fine tuning dial 100 kHz down.
Two switches next to the band selector activate the AVC (when turned off, regulate
the R.F. gain manually with the SENSITIVITY control) and the crystal calibrator.
On the left side of the front panel, You find the rotary operation switch marked with
SEND (receiver is on standby, for use in connection with a matching transmitter),
REC (for reception in standard AM mode), CW/SSB (BFO is activated for the reception of
CW and single sideband transmissions) and CAL (crystal calibrator is active).
The other three controls are used for the crystal filter, which is activated by the
CRYSTAL SELECTIVITY switch in the left lower corner. You can control the slot frequency
of the passband of the filter, the filter depth and the phasing, the frequency
rejected by the crystal filter. This feature is used to "notch out" an interfering
carrier an a very close frequency.
On the right side of the front panel, You find just below the electric 24 hour clock
the BFO control for the reception of CW and SSB signals, the sensitivity control (which acts
in fact as a R.F. gain control) and the AUDIO GAIN control, which acts as volume control
and is combined with the main power switch.
For reception of an AM signal under standard conditions, the operation switch
just left of the dials should be set to REC, the SENSITIVITY control should be turned
to maximum fully clockwise. For normal reception, the crystal filter can remain turned OFF. The receiver
is switched on with the AUDIO GAIN control, after a while (it takes a while until
the tubes are glowing), You hear a slight hiss in the headphones.
Radio "Deutsche Welle" can be found in the 49 m broadcast band in the lower frequency
part of the 4 - 10 MHz shortwave range. The bandspread dial should be set to
"100", so the main tuning dial readings are more or less accurate, then look out for
the signal of the transmitter on 6075 kHz somewhere below the 6.1 MHz dial mark.
When You have identified the station, You can use the antenna tuner to tweak for
maximum reading on the signal strength meter.
The antenna signal is fed via a tuned antenna circuit and a R.F. amplifier stage
(V1: 6BZ6) in the ranges 0,54-1,6 / 1,6-4 and 4-10 MHz to the mixer(V2: 6BE6),
with the oscillator signal (V9: 6C4), the standard intermediate
frequency of 455 kHz is generated.
In the 10 - 30 MHz range, the first intermediate frequency of 3035 kHz is mixed with
a 2580 kHz oscillator signal (V3: 6BE6) to result in the second i.f. of 455 kHz, too.
After two I.F. amplifier stages (V4/V5: 6BA6), the
crystal / phasing filter is switched in between them, the signal is fed to the demodulator stages.
One diode system of V6 (6AL5) is acting as AM detector, the second system is used for the noise limiter.
For the reception of CW signals, the signal of the beat frequency oscillator (one system
of V7: 12AX7) is added. The second triode system of the same 12AX7 is used as A.F. preamplifier,
V8 (6AQ5) in the final A.F. amplifier stage. A 6BZ6 tube is used in the optional crystal calibrator.
The rectifier V11 (5U4GB) and the voltage stabiliser V10 (0B2) were both used in the power
supply section of the original HQ-145, in the A version, the rectifier tube has been replaced by two
silicone diodes CER72C.
The Hammarlund HQ-145 A is a well constructed general coverage and ham band receiver,
with a combined single / double conversion design. The receiver with it's "boatanchor" weight can still be used
as a reliable mediumwave and amateur band radio, high precision readings in the amateur
band bandspread dials can only be achieved, when the optional crystal calibrator is installed
or You have an external calibrator signal to adjust band spread dial calibration properly.
The HQ-145 is one of the receivers which makes most of the Hammerlund crystal filter arrangement.
© Martin Bösch 26.4.2008 / translated 15.11.2010
e: Osterman, F.: Shortwave Receivers - Past and Present