SINUS B1 PROJECT

[reverend]

The other option (obviously) is to use a PLL. At Band I you can use the 74HC4024 as a "prescaler" to divide the carrier frequency by either 4 or 8. I then use a diode-programmed 74HC4040 to select frequency. The reference is (usually) a 4MHz crystal and a diode-programmed 74HC4060.

I've found that these CMOS type PLLs are fine in transmitters but having all those 5 Volt square waves near a receiver can cause lots of birdies. A 1MHz square wave from an 'HC' style CMOS will have harmonics up to 100 MHz or higher. If any of these are within 100 kHz or so of the wanted receive frequency, it can easily interfere with the weak wanted signal. Very careful board layout would be necessary to separate the two, or the receive frequency needs to be carefully selected.

[sinus trouble]

Just made some adjustments to the Tx and now getting 300mw out at 12v and 500mw at 15v. I changed c16 from 47pf to 100pf. And removed c19.

Before I was barley getting 50mw from the original parts list.

Nice work XXL!

The circuit itself is heavily restricted so there is room for squeezing a bit more out! Just keep in mind the temperature of the devices.

If you do decide to build the Low pass filter add on? I can confirm it works great! However due to the abundance of ground plane proximity? The 10mm 4 turn coils fall slightly short of the 120nH target! Maybe try 5 turns per coil?

[sinus trouble]

The other option (obviously) is to use a PLL. At Band I you can use the 74HC4024 as a "prescaler" to divide the carrier frequency by either 4 or 8. I then use a diode-programmed 74HC4040 to select frequency. The reference is (usually) a 4MHz crystal and a diode-programmed 74HC4060.

I've found that these CMOS type PLLs are fine in transmitters but having all those 5 Volt square waves near a receiver can cause lots of birdies. A 1MHz square wave from an 'HC' style CMOS will have harmonics up to 100 MHz or higher. If any of these are within 100 kHz or so of the wanted receive frequency, it can easily interfere with the weak wanted signal. Very careful board layout would be necessary to separate the two, or the receive frequency needs to be carefully selected.

Thats a good point Rev!

I never even considered that side effect!

[Albert H]

The other option (obviously) is to use a PLL. At Band I you can use the 74HC4024 as a "prescaler" to divide the carrier frequency by either 4 or 8. I then use a diode-programmed 74HC4040 to select frequency. The reference is (usually) a 4MHz crystal and a diode-programmed 74HC4060.

I've found that these CMOS type PLLs are fine in transmitters but having all those 5 Volt square waves near a receiver can cause lots of birdies. A 1MHz square wave from an 'HC' style CMOS will have harmonics up to 100 MHz or higher. If any of these are within 100 kHz or so of the wanted receive frequency, it can easily interfere with the weak wanted signal. Very careful board layout would be necessary to separate the two, or the receive frequency needs to be carefully selected.

You're not wrong!, However, screening the digital ICs from the rest of the receiver and making sure that the supply rails are well filtered (and that you have a long loop time constant) go a long way to making for a good receiver. Most of the battle is won by screening.

[Albert H]

IF sensitivity can be improved, and the IF bandwidth tightened up by adding an extra stage or two. My Link Receivers would usually have two transistor IF stages with SFE ceramic filters - the sensitivity and selectivity could be massively improved.

The other things that I did for my receivers was to have an aerial input amplifier stage with additional filtering, use a dual-gate FET mixer with a bit of gain, and when I needed extreme sensitivity, I'd use a PLL demodulator (an Elektor circuit). I could get a fully noise-quietening sensitivity of a couple of µV!

When I wanted Band IV and V receivers, I usually used the Philips TV tunerheads - they were really cheap, and had a better performance than I could easily get with something built from scratch, The only disadvantage of the tunerheads I used was that their IF output was at ~35MHz, so I needed an extra crystal-controlled down-converter stage to get the usual 10.7 MHz IF. Back in the 80s, I used the FM IF board kits from Ambit - they came with all the components and could be built in a few minutes. They included a squelch circuit which muted the output in the absence of input signal, and had a metering output that could be used to drive a comparator (LM311) switching a relay to operate the main rig. Sometimes - when the station was stereo - I used the 19 kHz pilot tone on the link ANDed together with the carrier detect to switch on the main rig.

Band IV and V have vast open spaces between the TV channels, and TV aerials never look out of place. By using 24-element TV aerials at each end, I got a 300mW Band IV signal (carrying stereo) to link reliably over a noisy path of around 19km! It's trivially easy to make your link transmitter match into 75Ω instead of 50Ω, and good quality TV downlead coax is really cheap because it's so common. You can also buy really good link aerials quite cheaply in any DIY store!

UHF really isn't the "Black Art" that many rig builders claim - it's just that they're not used to building very neatly and taking every component lead and board track into account when laying stuff out!

[radium98]

Good explanation...thanks albert

[jvok]

A good modern-ish source for TV tuner heads is old pc tv capture cards. These are obsolete after digital switchover so can be had very cheap (£10 odd) on ebay. Search for "hauppage wintv".

I've thought about designing a link rx around the sa605, which is still in production unlike the ca3089. Only issue now is getting hold of if filters which have all been discontinued although nos are still easy enough to get for the time being.

Tbh though I think the modern solution is one of the cheap sdr boards paired with a raspberry pi. You'd probably need an FM bandstop filter because they're quite sensitive to front end overload but even then it would probably still end up cheaper than a homebrew rx.

[XXL]

No way, a band 1 rx is about £5, raspberry pi and SDR, about £50

[sinus trouble]

I agree both with XXL and Jvok on certain aspects!

Software is looking like the way forward and works great! However whilst these technologies are widely available today? My sceptical (Dooms Day) side always relies on the simple hardware solutions!

Receivers are not that hard to build! They can be built from junk if you know what you are doing!

One of my first receivers was built with no fancy electronics! I will dig it out and post a pic below!

[sinus trouble]

Pulse Count Receiver.jpg

[sinus trouble]

The pic above was a full functioning 'Pulse Count' Receiver before i butchered it for parts!

The top half is a Colpitts oscillator with buffer stage (local oscillator) Tuning this would select different stations!

Bottom right used to be a mixer stage where the Receiving antenna would enter!

Bottom left was the IF amplifiers and Pulse count Demodulator!

The audio quality was not bad considering its simplicity! The circuit could easily be refined and improved!

After all there are ICs that work on this same principle! Not bad for a piece of junk!

[Albert H]

No way, a band 1 rx is about £5, raspberry pi and SDR, about £50

The Raspberry Pi Zero (£7.50) has more than enough "grunt" to drive an SDR, and there are cheap SDRs around for ~£10 - 12. I built a little UHF link receiver using this approach a while ago. I built a simple, passive high-pass filter for the aerial input of the SDR, and fitted it all into a small tinplate box.

The recovered audio baseband was found to only be up to around 10 kHz (OK for AM, but not for FM stereo), and I found that I had to remove a couple of capacitors at the output of the SDR board to get composite multiplex through it. The SDR board was originally designed to plug into a PC through a USB connector, so I just hard-wired the USB terminals to the Raspberry Pi PCB USB socket point.

[jvok]

Where are you getting all the if filters, quad coils and a 3089 for less than a fiver? Maybe 20 years ago but I'm impressed if you can still do that nowadays. Modding a radio is fine while there's still enough old radios out there to use, but look inside any modern radio and it's all in one chip with no scope for mods.

I've definitely picked up wideband fm (in stereo) before on a nesdr board which is 25 quid on amazon, no need to mod anything. Like albert says, 7.50 for a pi zero. Band stop filter can be done for less than a quid in passives and some hand wound coils. An external dac for the pi is about 5 quid from adafruit.

[sinus trouble]

I managed to put together another B1 RX and have been testing it for the last few days!

The unit worked first time on power up, However the setup proceedure is tricky! Especially if you do not have the right tools?

I will make a series of videos to explain the basic functions and setup, Both the proper way and the simple way!

B1 RX.jpg

[XXL]

Just sent off for some rx boards using your gerba after several failed attempts using different circuits. Even using this one but I modified it slightly. If it doesn’t work this time it must be my components, not the circuit.

[sinus trouble]

I am sorry to hear you have not had much luck in previous attempts!

My RX uses probably the bare minimum of parts required for a decent receiver? Ofcourse there are more complex versions around which may perform better?

I have built 4 of these so far (+ prototype) and i can assure you that they do work! Infact i have one playing tunes for me as we speak

As i mentioned previously, Some moderately precise adjustments need to carried out for it to operate correctly!

Twiddling trimmers and hoping for the best wont cut it!

I am in the process of making some tuning videos, However i am finding it difficult to hold the camera and work at the same time! (I am certainly not a pro film producer)

I may have to re think my approach?? Maybe an instruction guide of some sort??

[Albert H]

Sinus
I shot a couple of very basic training videos on a (good quality) mobile phone. I used a vacuum-attached mobile phone mount with a gooseneck that's meant to be used on a car windscreen. This held the phone in just the right position, and recorded the audio too.

ScreenMount.png

[XXL]

Please post as I have tuned my band 1 rx to the strongest signal but probably won’t work once it’s up the site judging by what you said. I need to know it’s going to work first time.

[sinus trouble]

No worries XXL!

You most likely have it on point? Just better to be safe that sorry eh!

I am working on a written guide including some diagrams and should have something within the next few days?

I will also update and improve wherever i can!

[sinus trouble]

Sinus
I shot a couple of very basic training videos on a (good quality) mobile phone. I used a vacuum-attached mobile phone mount with a gooseneck that's meant to be used on a car windscreen. This held the phone in just the right position, and recorded the audio too.

ScreenMount.png

Thats a neat trick Albert!

I am defo gonna make some videos! Its more interactive than just words! Keeps the attention of those who wish to learn!

I find it strange that there is literally nothing on the net about Band 1?