A PA Tuning Setting a frequency on a WS no 19

[Robert Bergeron]

( A PA Tuning .) I am new to the set . I have experience on HF , VHF and UHF aviation radio’s but zero on the No 19 set . I understand i have to set the frequency on the right dial first . Let’s take for example CHU on 3.33 or 7.85 MHz. The dial readings are very coarse but i can tune in somehow and there is a knob to turn to select 2-4 1/2 and 4 1/2 to 8 MHZ. What does the A PA Tuning stand for ? I know it’s the left dial and i am supposed to turn the variometer in conjunction with it .Somehow the signal become clearer and louder when i turn that dial . What are the readings for ? What does it do ? Sorry for the very basic questions but i am very interested of making the most of my radio truck by knowing more about it’s main purpose : Operating the radio set . Thanks .

[Bruce MacMillan]

"A PA" is "A" set (HF) and "PA" is power amplifier. This control is used to tune the PA output circuit and receiver rf amplifier to resonance with the variometer. To get the most transmit signal radiated the aerial should resonant at the frequency in use. By adjusting both controls this is achieved. Being adjustable allows for change in aerial length and frequency. The same principle applies to the receiver circuit. At resonance the maximum received signal is applied to the receiver rf amplifier resulting in a stronger signal in the headphones.

It's calibrated in frequency to allow some pre-tuning. The variometer is also calibrated and this is used in conjunction with the flick mechanism to speed band change.

The meter switch in the AE position indicates rf power through the variometer. The maximum the better.

The AVC position shows receiver is properly tuned when at maximum dip.

Read the manual section on netting drill in harbour and practice.

[Mike Kelly]

I've not used a 19 set on the air . A radio tech. friend of mine tested a 19 set RF transmit output on a modern spectrum analyzer and the total RF output seen from the 19 set is actually a sum of the frequency you want ( if the PA is set correctly ) , plus various spurious emissions . The meter on the set can lead you astray because it measures the total RF output , it doesn't care what frequency it's measuring, it adds the whole RF output together . I think the PA tuning circuit has a low 'Q' , meaning its a rather broad filter in effect. Because the PA tuner is so coarse , you can easily tune the PA for the wrong side of the mixer output, meaning you will actually be on the wrong frequency .

[Bruce MacMillan]

I agree Mike, the ws19 is not the most pure in spectral output. I don't beleive Robert is licenced so we won't have to worry about that, will we.

I didn't take photos but the rf spectrum of my 19 set driving the Canadian amplifier was nasty, not to Industry Canada standards.

[Robert Bergeron]

Thank you Bruce and Mike . I have a licence restricted to aviation so no i will not transmit . I am just trying to familiarise myself with the set . Certainly nothing wrong listening ! So in simple terms i find the frequency on the right dial first and then «* adjust «* the left ( PA ) one to amplify the signal and best legibility and then «*tune «* the antennae with the variometer . Correct ? I am using a 100 ‘ plastic covered copper wire hung between a few lamp posts and got a news station in Romania transmitting in English . I am in Canada . That’s pretty far and neat as hell !

[Bruce MacMillan]

You will find that that different stations on different frequencies will vary through out the day. This is due to the effect called propagation. Besides commercial broadcast stations there are several other things to listen to. Aviation volmet, military HFGCS, ham operators, etc. It makes a display more interesting when visitors can actually hear wireless coming from a wireless vehicle.

Next step is to get your ham licence. It's very easy these days and allows you to put your set to full use. You and David could chat when his WS52 is on the air. Years back a group of 19 set users organized an event called Atlantic Hop. It was to communicate across the Atlantic using 19 sets. It was successful although operating from Vancouver I only made it as far as Brampton, about 3300 Km.