SINUS B1 PROJECT

[radium98]

Thanks.
Another point that I don't understand how.
How the AFC system.work in the receiver that say when the transmitter drift the receiver track it ? Something magical.

[sinus trouble]

The AFC works similar to a PLL (Sort of)

A DC voltage is given out from Pin 7! When the 10.7Mhz IF signal drops in amplitude due to the Local oscillator or receive frequency drift? The voltage on Pin 7 will either rise or fall to correct the drift!

As Albert mentioned! You can configure the Local oscillator to track the receive frequency simply by adding a varicap to the Local oscillator!

The DC voltage from pin 7 fed to the varicap would then control the Local oscillator!

So in theory, If the receive frequency drifts up? The Local oscillator will follow it! And vice versa!

[radium98]

Thank you as always.

[Albert H]

The beauty of the AFC system is that the link frequency is entirely controlled by the stability of the transmitter, so if your link transmitter is PLL controlled, the receiver will stay on frequency even if its local oscillator tries to drift. If correctly dimensioned, the AFC will hold on to the signal under all conditions.

[sinus trouble]

The beauty of the AFC system is that the link frequency is entirely controlled by the stability of the transmitter, so if your link transmitter is PLL controlled, the receiver will stay on frequency even if its local oscillator tries to drift. If correctly dimensioned, the AFC will hold on to the signal under all conditions.

I can confirm that the voltage on Pin 7 (AFC) does track!

I monitored this voltage varying with changes to my Band 1 TX frequency!

I have yet to add a Varicap? But i see no reason why it should not work!

[Albert H]

You'll need to put a resistor in the way, and sometimes I used two resistors in series (usually 10k each) with 100n to ground at the junction of the resistors. This ensured that the AFC didn't try to correct the mod!

[XXL]

Has anyones band 1 receiver ever unlocked the pll before ? My driver goes crazy when I put the receiver on it. Like the static is making it unlock but with the volume down it’s fine. It unlocks at low and high levels.

[Albert H]

Your white noise from the receiver is obviously way overmod! You need to set the levels so that white noise from the receiver is the same level as no carrier white noise - that means that if your link is off, the white noise from your main rig will sound just as if there's nothing there!

My link receivers always have squelch, so that their output is muted on link carrier loss. I also used sub-audio tone as a "keep alive" - so that the main rig would switch off automatically when we shut down the link!

[sinus trouble]

Has anyones band 1 receiver ever unlocked the pll before ? My driver goes crazy when I put the receiver on it. Like the static is making it unlock but with the volume down it’s fine. It unlocks at low and high levels.

Yes!! It is very common for the main transmitter lock indicator to blink when white noise is present!

If you look at the CA3089 datasheet, 400mV is the typical audio output! White noise is full of allsorts and at times could possibly peak @ 1V!

Once the B1 receiver obtains a carrier signal, The main transmitter will settle!

[sinus trouble]

Also just to add!

My Receiver does not have the squelch feature as standard? But i do not see why you can not activate it if you wish?

The reason i did not implement it was that it effectively mutes the white noise! Which can give the false impression that it is linked or malfunctioning?

White noise may be unpleasant for some? Yet i find it reassuring that everything is working as it should!

[Albert H]

It's easy enough to use the RSSI output (pin 13) on the 3089 to drive a comparator (I used an LM311) and switch an LED on when the link is received at sufficient signal strength.

[sinus trouble]

Your white noise from the receiver is obviously way overmod!

Yes Albert raises a good point!

Whilst it is possible to setup the audio by ear? The correct way of setting the audio would be to feed the receiver with a test tone! (Say a continuous 1Khz signal) The quadrature coil can then be adjusted for best spectural purity of the waveform on the output!

During setup, The receiver input would be fed directly from a function generator @ the Band 1 frequency! Input filter and mixer would in turn be peaked for max gain!

Once peaked! The function generator would be set to modulate the Band 1 frequency (1Khz) this would give a good reference to set the quadrature section!

It can be done without a function generator! Your Band 1 TX is technically a function generator!

The TX is fine to use as such providing there is low distortion and it is stable!

[sinus trouble]

Welcome back Necks!

I have some additional updates to the Sinus B1 Project which i would like to share!

Lets start with the B1 Receiver! These are minor changes that should improve stability? But are not critical!

The two circled components can be changed! Image below!

[sinus trouble]

Sinus B1RX Schematic.png

R10 has been substituted for a 47 Ohm resistor to reduce CA3089 operating temperature @ 15V

C12 has also been substituted for an 82p capacitor to align the Quadrature coil to a more central position!

[sinus trouble]

Now to the B1 VFO!

I have been researching allsorts of options to improve gain! Choosing the components fit for the job and keeping it simple has not been an easy task!

As my B1 VFO uses a "Class A" output stage, The signal is ideal for driving something like the NRG PROIII output stage!

The stage in question is pretty simple once broken down and should in theory produce a decent 4 Watt boost to the "Link Box"

I have alot of testing to do, However here is the basic layout below!

[sinus trouble]

Schematic_B1 Amplifier_2022-09-19.png

[sinus trouble]

As can be seen, There is no input tuning required! Direct coupling to the VFO should be OK (In Thoery)

L1, L2, C4 and C5 will need optimising to improve gain and efficiency!

L1 will most likely be a 2.2K resistor with the coil wrapped for damping!

[radium98]

Good experiments my freind.Hope you the best.

[sinus trouble]

Good experiments my freind.Hope you the best.

Cheers Radium!

[Albert H]

One word of advice - the 2SC1947 has incredible amounts of gain at 50 MHz. When I tried them on Band 1, I found that it was necessary to either include a small value emitter resistor, or use negative feedback from collector back to the base with a resistor, inductor and capacitor in series. This kind of negative feedback will reduce the gain, and will open out the bandwidth, whilst improving stability.

I used a 2SC1971 as a 5W final on Band 1, and found that it also had a huge amount of gain, necessitating negative feedback. I found that I could get over 5 Watts out with just 300mW of drive!

As usual, the little rig had a discrete CMOS synthesiser, but because of the lowered frequency, the usual "prescaler" stage wasn't necessary. I could clock the 74HC4040 reliably at half the carrier frequency (I used a diode doubler to get to the output frequency), so my whole PLL was a 4060 reference with a 4 MHz crystal, 4046 phase comparator and lock detector, a 74HC4040 for the preset divider, and a dual op-amp (NE5532) for the loop filter and modulation buffer. The whole rig cost around £14 in parts - the most expensive part being the Eddystone diecast box that I used to house it! The 2SC1971 was loafing along at around 5 Watts out, and was heatsunk to the lid of the box - I didn't need anything else.