[Boatanchors] SLAT BOARD Transmitter

[Bry Carling]

K9EID, Bob Heil has a very interesting slat board transmitter project that you can build. The video series includes plenty of step by step instructions.

https://youtu.be/UorZKKLthqI

Best regards - Brian Carling, AF4K

Tel: 321-262-5471




On Mar 29, 2017, at 9:25 PM, Bry Carling <af4k at hotmail.com<mailto:af4k at hotmail.com>> wrote:

Thank you Roy. For me it will just become a source of 240 V DC very regulated!

Best regards - Brian Carling, AF4K

Tel: 321-262-5471




On Mar 27, 2017, at 2:50 PM, Roy Morgan <k1lky68 at gmail.com<mailto:k1lky68 at gmail.com>> wrote:

Bry,

The HP 415 is a 1000 cycle detector/voltmeter usually used in the measurement of rf devices and transmission lines with a slotted line.*  The 1000 cycles was the common modulation frequency (400 cycles was sometimes used) so the detector could measure the signal picked up by a movable probe and diode detector on the slotted line.  The meter circuits and meter movement in the 415 allowed for accurate measurement of the detected audio signal enabling measurement of the RF present along the length of the slotted line. There was of course a functionally equivalent General Radio instrument - it appears that the latest version was the Type 1234.*

The 1000 cycle filter Bry reports was needed to reduce extraneous noise, set the detector response to the desired 1000 cycles modulation frequency, and to tune out audio harmonics from the use of square wave or other non-sine-wave modulation signals.  The HP and GR detectors were able to accurately measure signals at levels where the normal crystal detector was operating in either the square law region or the linear region.  (Can you say 1N21B?) . They also had provisions for alternate detector devices such as crystal diodes, and bolometers.  (A bolometer is an element like a low current fuse whose resistance depends on total power dissipated, and was used in a circuit that could reduce the DC current in the thing to exactly compensate for RF power dissipated, thus measuring the RF power by substitution.  The most highly accurate low level RF power measurements were made with this method.)

This system enabled determination of SWR and related values.  Computation, or often use of the Smith Chart, provided indictions of transmission line performance, load impedance, system tuning element settings (for instance stubs and series line length adjustable sections),  line loss and other related transmission line parameters.

I presume that clever application of 1000 cycle modulation tones to a transmitted signal from your transmitter, with a carefully built moni-match type detector (directional coupler) , or the Johnson SWR detector, would let you make a measurement of transmission line SWR.


On Sun, Mar 26, 2017 at 8:05 AM, Bry Carling <AF4K at hotmail.com<mailto:AF4K at hotmail.com>> wrote:

I think the only thing that my HP415B needs is a new AC cord. This will make a great source of stable HT for the xmtr osc.

It has one other interesting thing to offer! A series of 12AX7 tubes with a mysterious 1000 Hz audio filter between them. This thing may have some uses for receiving as well!


** The manual for the GR 1234 is at:
http://www.ietlabs.com/pdf/Manuals/GR/1234%20Standing%20Wavemeter.pdf
and the HP 415E manual can be seen at:
https://www.valuetronics.com/Manuals/keysight-Agilent-HP-415E.pdf


--
Regards,
Roy

Roy Morgan
k1lky since 1958

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