[MRCA] Giant leap backwards

Wed Aug 9 18:13:47 EDT 2023

Consume a small tin of sardines and then fill the empty tin with lead, 
makes a nice base for the key.
Z

On 8/8/2023 3:29 PM, Christopher Bowne wrote:
> Good on ya Ray.  As you’re probably aware, the Command Set 
> transmitters were designed to work into short wire antennas in the 
> aircraft with relatively low fees point impedances especially at low 
> frequencies such as the 3-4 Mc range of the T-19.  They can be loaded 
> to put out 40-50 watts in CW with a simple matching network, 
> increasing the number of turns on the output coupling coil on the 
> transmitter plate tank coil, or using a 4:1 balun in reverse with the low
> impedance end connected to the transmitter and the high impedance side 
> connected to the 50 ohm feed line. My favorite method has been to use 
> a matching network that Walt Hutchens published in ER’s Electric
> Radio in Uniform around 1989.  Consists of a
> parallel LC resonant circuit with the bottom end grounded, the 
> transmitter fed to a rap about 3 turns above the bottom of the coil, 
> with a nominal 150 pf cap in series  between the transmitter output 
> and the tap on the coil. The 50 ohm antenna feedline is  connected to 
> another tap about 3 more turns above the transmitter feed tap.  Of 
> course both the transmitter chassis and the feed line shield are both 
> connected to the bottom of the coil.  Essentially a high Q tunable 
> resonant auto-transformer, will certainly provide some suppression of 
> 2nd harmonic energy.  I still have an OO card for out of band 7 Mc 
> emissions from my first forays onto 80 meters with a T-19 back in high 
> school 55 years ago when operating with a dipole connected directly to 
> the transmitter output!
>
> I made my KJ4KV matching circuit with an junk box Eico 720 pi network 
> coil, the full coil resonated nicely with a 3-4 Mc Command Set plate 
> tuning cap.  For 40 meters, a clip lead jumper shorts out the large 
> low frequency section of the coil.  Be sure to use a fairly wide 
> spaced variable cap, I had occasional arcing even with the  Command 
> Set variable cap.
>
> The matching network also works well to match TCS transmitters to a 50 
> ohm antenna.  They are also designed to work into low impedance short 
> antennas at low frequencies.
>
> When you get comfortable with CW, check into the Old Military CW Net 
> on Sunday nights at 2030 Eastern on 3558 kHz!
>
> 73 de Chris, AJ1G
>
> Sent from my iPhone
>
>> On Aug 8, 2023, at 14:01, Ray Fantini <RAFANTINI at salisbury.edu> wrote:
>>
>> 
>>
>> When I was out at the Hamvention picked up a AN/PRC-74 with all its 
>> accessories, that included a CW key. So, I have decided that the next 
>> great challenge in life will be mastering CW and maybe using the 74 
>> to check into the pack net this year at Gilbert (MRCA). It makes way 
>> too much sense to just set the 74 up with a power supply and practice 
>> that way so I decided to build up a CW operating position. Common 
>> sense would dictate using a more modern transceiver like my URC-94 or 
>> the big rack that’s used for RTTY but no, all that is to simple, the 
>> solution was to build up an entirely new operating position and use 
>> something that would be way over complicated.  I decided to use the 
>> 1938 HRO RAS along with a T-19/ARC-5 type transmitter. The power 
>> supply for the transmitter came from an old military sweep generator 
>> and provides 450 volts for the plates of the 1625 and a regulated 200 
>> volt source for the MO tube in the transmitter and with keeping all 
>> the original tank can generate a whopping fifteen watts into fifty 
>> ohms. The panel provides a place to turn AC power on and off to the 
>> transmitter, a fat multi contact switch that works as a T/R relay, 
>> key line interlock and spot switch that allows the MO to receive B+ 
>> but not the PA and a high voltage relay is located on the back of the 
>> panel that is controlled by the key to provide HV and B+ to the 
>> transmitter. Now all I have to do is to develop my ability of being 
>> able to receive code to some level of proficiency.
>>
>> Ray F/KA3EKH
>>
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