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These Radio's were origionallydesigned for use by Trappers and similar who would travel out into the unpopulated area's away from a what we like call civilisation. The 4 channel limitation was not a problem with only a few stations to communicate with. Of course, being for comercial use, they normally use Upper side band rather than lower side band as amateurs do on the frequencys these sets are capable of ( 2 to 10 megahertz). They are simple built and capable of taking the knocks of rough use but still keep working. The ones that I have gained, were retired from expedition use as believed faulty. The only faults I have found, have been battery terminals and switch faults, most were just off frequency. Output power is claimed to be 10watts pep. I have managed to get 20 watts plus out of one set, but this defeats the design and benefits. With an Rx current of 25 ma, and 10 watts out, they will work for a very long time on a 2 amp hour sealed lead acid battery or D cells.
The information below, is for people who are conversant with radio repair and modification,
I am not responsible for your actions
Amatuer Radio Modification
The
SBX11 radio's, use a 2 crystals, a tank coil and two
filters for each channel in use. Mine all came with 2.182 mhz, two
80mtr and one 60mtr frequencys set. However, as long as you have one
set of components for the band you require, You are in luck as you can
parallel the filters etc up, and have the switch gear just changing
crystals. in fact you can then add as many crystals as you want to,
more switch contacts. All the coils etc are colour coded for band
coverage, white = 1.6 to 2 mhz, black = 2 to 2.82 mhz, brown = 2.82 to
4mhz, red = 4 to 5.6 mhz, orange = 5.66 to 8 mhz and lastly yellow = 8
to 10mhz. Changing from upper to lower side band can be achieved
in two ways, (unless you havea simpler way, I dont want to know ).. The
first is to change the intermediate frequency crystal and filter,
(expensive if parts are available). The other way is in fact free if
your set is not already very close to the frequency you require, And
this is as follows, The manual claims, that when choosing your crystal,
ADD the if freq , 465.5 khz to the chosen frequency to get your crystal
frequency. We take the if freq OFF the chosen frequency and get the
correct sideband.. More savings now, as the board is built to hold two
crystals per channel. With a bit of carefull wiring, we can add a relay
to the ptt circuit, and switch our solitary crystal between holders.
Dont be tempted to parallel the holders up, the clarifyer will shift
both Tx and Rx, bit difficult to use !.
Local oscilator tuning
Adjust clarifier to center position, and connect a frequency counter to TP101 via a 10pf capacitor.
Adjust the appropriate trimmer to set the rx frequency.
Adjust the appropriate trimmer to set the rx frequency.
Now connect to TP108 via the same capacitor, and press ptt, and tune tx frequency.
Rx Rf Stages
Connect a signal generator to the antenna socket, adjust the generator to get approx 1000 hz
tone from the set. Then reduce level to get around 1 volt from the speaker, Adjust the rx filter slugs from all out position to get best signal, adjust signal generator as you go to keep around the 1 volt level on the speaker.
Tx tuning
Connect a 50 ohm load to antenna socket, then using a scope or rf milliameter, press the tune button and adjust the tx filter slugs from all out for highest output. When satisfied, transfer to the tank coil slug and tune from all in for a peak in the output power. Go through the tx chain again to get the last bit of power. BUT if the current consumtion goes above 0.3 amp on tx, DETUNE the input coil of the transmitter filter ANTI CLOCKWISE.
Rx Rf Stages
Connect a signal generator to the antenna socket, adjust the generator to get approx 1000 hz
tone from the set. Then reduce level to get around 1 volt from the speaker, Adjust the rx filter slugs from all out position to get best signal, adjust signal generator as you go to keep around the 1 volt level on the speaker.
Tx tuning
Connect a 50 ohm load to antenna socket, then using a scope or rf milliameter, press the tune button and adjust the tx filter slugs from all out for highest output. When satisfied, transfer to the tank coil slug and tune from all in for a peak in the output power. Go through the tx chain again to get the last bit of power. BUT if the current consumtion goes above 0.3 amp on tx, DETUNE the input coil of the transmitter filter ANTI CLOCKWISE.