[Milsurplus] Free - running osc at 7 MHz

[howard holden]

There's a TM-11-310 which has the BC-156 schematic on Radionerds.com. 
The oscillator looks like a Hartley, although the coil is pictured in a 
somewhat unusual manner. Besides a stiff Dc supply, you also need a very 
stiff antenna - if the antenna flaps around too much in the breeze the 
signal will wander (antenna capacitance to ground). The coil in the TX 
side should also be very robust and relatively low inductance (high C), 
even at 10 watts input. With that input, expect maybe 3-4 watts out. But 
it certainly could be OK, unless you're comparing it to a YaeComWood 
radio.....Sounds like my kind of transmitter! No, not interested, got 
too much on the plate now.


73, Howie WB2AWQ

On 8/22/2019 1:26 PM, Kenneth G. Gordon wrote:
> On 22 Aug 2019 at 20:11, Hubert Miller wrote:
>
>> I have a U.S. Army trans - receiver type BC-156. This is very similar
>> to the "loop set" BC-148 which you may have seen. The BC-156 however
>> tunes around 5 MHz and has instead of the large loop antenna, a
>> transmitter coil inside, and worked into a wire antenna. The
>> transmitter is one type 10, free running, and the receiver, 3x #30
>> tubes, autodyne.
>>
>> Now, if the frequency is pruned up to 7 MHz, and using a stiff B+
>> supply for the transmitter ( about 10 watts, I think ), will this be
>> stable enough to use on the air ?
> Yes.
>
> These types of transmitters are being used regularly on the air, especially during the
> Antique Wireless Association's Bruce Kelley Event which takes place yearly, usually around
> January.
>
> Might you have a schematic of this transmitter I could see? What type of oscillator is it?
> Hartley, Colpitts, TNT, TPTG, what?
>
> I have a push-pull pair of 211s in a TNT configuration I will use on the air this winter.
>
>  From experience with these 1920s designs, I can give you a better idea of what to expect
> from it on 40 meters once I know what type of oscillator it is.
>
> FYI, KM1H used a push-pull self-excited oscillator somewhat like yours to earn DXCC
> recently. No one he contacted even knew what his transmitter was from the sound of it on
> the air.
>
> Your "stiff B+ supply" is primarily the key to getting it to sound good.
>
> Ken W7EKB
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