STL link RX

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radium98
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STL link RX

Post by radium98 » Thu Oct 04, 2018 5:24 pm

here it is if anyone is interrested to build and try ,can you explain the local OL part and the mixer .
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3metrejim
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Re: STL link RX

Post by 3metrejim » Thu Oct 04, 2018 8:32 pm

Looks like a band III link receiver - covering 140-164Mhz if the model number is anything to go by.

Converts the amplified antenna signal to 10.7Mhz to be recovered by the ca3089.

The MPSH10 is the mixer, with the incoming signal and local oscillator signal applied to the base.

To use it, you will need an external local oscillator applied to the LO connection - 10.7MHz above the incoming signal.

If it can tune band III it will be safer to use there rather than the 140-164Mhz the model number is suggesting. There are a lot of services in the 140-164Mhz range you wouldn't want to interfere with...

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Re: STL link RX

Post by Albert H » Fri Oct 05, 2018 12:12 am

With those recommended transistors, replace the input filter coils with Lecher Lines, build a Colpitts Oscillator (Crystal controlled or PLL) that delivers about 1V p-p 10.7MHz above (or below) your required Band IV frequency. Building a >500 MHz transmitter will be above the abilities of most of the usual solder-jockeys, unfortunately.
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Re: STL link RX

Post by radium98 » Fri Oct 05, 2018 5:17 pm

3metrejim thanks ,also Albert but you speak in a way more complicated as always and i dunno why ,i never forget that you want to post a link receiver ,and this will be in my dreams that one day you will post it ,i dunno if u will take it with you for next LIFE.Share and help man we wont bring anything with US,you know that .

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Re: STL link RX

Post by Albert H » Fri Oct 05, 2018 11:56 pm

The problem with sharing circuits and layouts is that the stupid solder jockeys who can only copy other people's work will usually fail to make a receiver work properly, and then will blame its designer. We used to have this problem with the NRG gear - if you followed the instructions and could solder neatly, you'd get a working transmitter. Unfortunately, many people can't solder and many just won't follow instructions....
"Why is my rig humming?"
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radium98
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Re: STL link RX

Post by radium98 » Sat Oct 06, 2018 7:08 am

Do you think i am not able to do that then ? so in a PM it could be .And maybe i could not get the components to do .so no helping from the part of you ,then i will have to try the one i posted above till it work.Because i know the principle but i lack from some old components.And remeber that electronics is a kind of experiments and you have to fail many times to be then on the right way to ..
thanks regards.

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Re: STL link RX

Post by sinus trouble » Sat Oct 06, 2018 10:16 pm

Hello Mr Radium :)
I do not think Albert is doubting your competence at all! However he does become Responsible for posts in a 'Good Will' sense only!
The circuit you posted looks like a conventional receiver to me and as Mr Jim and Albert suggested, a simple Colpitts LO should get you started!
In all cases you will need significant test equipment to align the antenna input trap and mixer stage!
Failure to do so will almost likely end in poor results
I am as stupid as I look! :|

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Re: STL link RX

Post by Albert H » Sun Oct 07, 2018 12:31 am

Actually, the receiver board posted above could be modified to work well on Band 1, and has a signal strength meter which is a great help in alignment. Way back, I used a little ½ Watt band I exciter as my signal source for setting up receivers. It was built into a diecast box, and had a 50Ω BNC aerial socket. The little rig was connected to a couple of 100Ω resistors in parallel as a dummy load and modulated with a reasonably high quality audio source, so that it was easy to identify the signal once it was received.

The Link Receiver was connected to a monitor amplifier at the other end of the work bench, and it was usually possible to hear the transmitter immediately if the local oscillator in the receiver was on the right frequency. The first step was to adjust the tuning of the input filter whilst monitoring the received signal strength on pin 13 of the CA3089 IF chip. When no further improvement was possible, the link transmitter was taken down the garden - about 120m - to the shed, and connected to an audio source, whilst still connected to its dummy load.

Back in the workshop, the receiver was fitted into its box then connected to a 75Ω aerial load (a couple of paralleled 150Ω resistors with a short piece of wire to sniff some signal). Final tune-up was done - getting the RSSI as high as possible, and minimising distortion on the received signal (which can be done "by ear" to a remarkable degree of accuracy - with practice). Lastly, the receiver would be connected to a Band I folded dipole (300Ω, through a ferrite 4:1 transformer for 75Ω, then down 20m of TV coax to the receiver), and the link rig would be put inside a metal box with the door ajar to give a really weak signal, and the carrier detect switch would be adjusted - I used to use an LM311 driven by the RSSI on the CA3089 to switch a relay for either muting the audio to the main rig or switching the main rig on and off......

The receivers were cheap to build - the coils in the front end were all hand wound, air-spaced and adjusted by stretching and compressing them! The discriminator coil was a cheap Toko part, and the ceramic 10.7 MHz filters were pennies each. The local oscillator was usually crystal controlled, but I did make a run of receivers with VFO local oscillators that had AFC, so the receiver would "lock" to the incoming signal. This allowed the use of VFO link transmitters, since the receiver would "follow" the drift of a transmitter! This made for some really cheap "throwaway" link gear!

Band I wasn't used much - I preferred Bands IV and V because the aerials were smaller and nobody looks twice at a TV aerial on a rooftop! The earliest Band IV rigs and receivers were hacked Pye Pocketphone 1 units. I bought a huge boxful of these from a junk dealer for about £3 a pair! The transmitter was hacked about to remove the oscillator and phase modulator, leaving the multipliers and "power" amplifier (about 100 mW output!), and a PLL driver was added. This gave a nice clean, stable signal with minimum hassle. All the UHF part was done for me! The receiver posed a bit more of a problem. It had to be cut about to remove all the audio and IF stages, just leaving the front end and oscillator strip. The output of the mixer was modified for 10.7 MHz output and connected to a conventional IC-based IF strip. This transmitter / receiver pair could link ridiculous distances when connected to 20-element TV aerials! Back in the early 80s, one of these Band IV systems would sell for £250 - 300 since there were only two or three people who knew how to make them!
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Re: STL link RX

Post by 3metrejim » Sun Oct 07, 2018 10:01 pm

You will probably have difficulty locating a ca3089 IC, they have been obsolete for some time.

If you want to build a link, then it is interesting to know that a cheap analogue FM radio (not one with a tda700 type chip or it's variants - they have difficulty passing a bandwidth suitable to carry a stereo signal) can be used as a tunable IF (intermediate frequency) receiver. You can lower the reception frequency of most fm receivers by adding capacitors in the correct places. You also have to lower the de-emphasis capacitor to allow a full stereo signal to pass.

For a UHF link receiver, you can use an old analogue TV tuner. The more modern ones require a data input to set the frequency so some data sheet searching for the chip used in the tuner, and programming knowledge will be required - Arduino?. Feed the IF out from the tuner to your frequency lowered FM receiver (around 36Mhz is the frequency for the IF in TV receivers), and that should do it. It's about the least complicated way I can think of.

A UHF transmitter will be more difficult if you want frequency stability, but you won't need much output power to get distance if you use TV antennas at each end - 50 to 100mW will likely be plenty. Be sure to not cause any tv interference as that will bring in a lot of complaints quickly.

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Re: STL link RX

Post by yellowbeard » Sun Oct 07, 2018 11:31 pm

3metrejim wrote:
Sun Oct 07, 2018 10:01 pm
You will probably have difficulty locating a ca3089 IC, they have been obsolete for some time.
Donberg, enigma and cricklewood all have them in stock.

radium98
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Re: STL link RX

Post by radium98 » Mon Oct 08, 2018 6:46 am

LA1235.
CA3089.
CA3189(?).
TDA1200
all the same :) i used to use tda1200 pin to pin compatible for 3089 and 3189 and 3089 can be swaped but need little mod.thanks,if it is possible someone can pass a LOCAL oscillator easy bf199 bf494 etc ...as a vco to try with the pcb i posted in UP first.or i have to play with an MC1648 that goes to 225mhz my interrest is arround 205,30 mhz for 1KM.

download/file.php?id=729
download/file.php?id=731
download/file.php?id=730

i have a question regarding the MIXER pic number 2 please tell me from the toko transformer output how this work if i need to have Fin1 +Fin2 +10.7
and if i need to have Fin1 +Fin2 -10.7 mhz
thanks

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Re: STL link RX

Post by sinus trouble » Mon Oct 08, 2018 10:37 pm

Hello again Mr Radium! :)
I can upload a schematic of a nice Colpitts that I have used many times but I think it would be pointless? Etching a PCB for it would be a waste of time unless it is built into the whole receiver circuit!
It is literally less than 8 components and would be better prototyped on a small piece of plain clad board!
stability and overall frequency will vary? If you keep the amplitude low, connections short and temperature under control, it should be a reasonable performer!

To put into simple terms? The local oscillator will be your tuning knob or dial like on a standard radio receiver! As you turn the dial, the mixer stage will select a frequency from your antenna that is 10.7mhz away!

For example if you want to tune or listen to 100mhz? Your local oscillator will be on 110.7mhz or 89.3mhz!
I am as stupid as I look! :|

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Re: STL link RX

Post by radium98 » Tue Oct 09, 2018 8:38 am

Thanks sinus trouble i appreciate the help from the patt of you .In a pm.should be or here .Look i just experiment that than i will see if i add a pll yo it .i need yo be working from it s values lc in the 150/300 mc .
Could explain the second picture of the mixer how i can have the plus ol + 10.7 or the ol -10.7

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Re: STL link RX

Post by Albert H » Tue Oct 09, 2018 12:45 pm

The "Superheterodyne" receiver principle doesn't really care whether the Local Oscillator is above or below the received frequency. The input filtering is meant to take care of the unwanted frequency (the "image" frequency). Just assume that you want to receive 200MHz exactly (that's to keep the numbers simple). The Local Oscillator could be at 210.7 MHz or at 189.3 MHz. The thing that changes with high side or low side injection is the image response.

If your Local Oscillator is at 210.7 MHz, the image response is at 221.4 MHz. That should be far enough away that the input filtering - carefully peaked on 200 MHz - will reject any image signal.

Similarly, if your Local Oscillator is at 189.3 MHz, the image will be at 178.6 MHz - 21.4 MHz away from the wanted signal. Again, the 200 MHz tuned filter at the input of the receiver will reject the image frequency.

The problems arise when there is something really strong locally on the image frequency. I've frequently had this on "Facilities Sites" where lots of transmitters and receivers are co-sited. This is why it's essential to do a "radio survey" with a Spectrum Analyser (at best) or at least a good quality Scanning Receiver which has a field strength meter before you start building your receiver.

There are a number of issues with transmitters and receivers in close proximity to each other. Planning a Facilities Site is a complex task, and if you're to avoid the use of lots of very expensive cavity filters, careful planning and design is vital. That's why Radio Engineers like me earn the Big Bucks!

If you want a link on 205.3MHz, your Local Oscillator can be on either 194.6 MHz or 216.0 MHz. If you go for 216 MHz, you'll have to check if there's anything on 226.7 MHz. Your 216 MHz LO could be a 54 MHz crystal multiplied by 4 (two doubler stages). A 54 MHz crystal is quite easy to obtain. Be thorough with your radio survey, and be prepared to choose a completely different frequency if you find that your choice is a bad one!

One of my favourite Band III frequencies used to be 202.7 MHz, because you could use a standard 48 MHz crystal! My Colpitts crystal oscillator used a FET with the drain circuit having a resonant tank at 96 MHz. This was inductively coupled to the base of a bipolar transistor in Class C, with a 192 MHz tank in the collector. An inductive pick-off gave a big enough Local Oscillator signal (about 1.5V p-p) to mix effectively in a BF961 dual-gate FET. The receiver input had a double-tuned circuit, feeding a current-biased BFR91, with a further double-tuned circuit from the collector of the transistor feeding the other gate of the dual-gate FET. I found that the LO injection voltage was quite critical for optimum sensitivity - YMMV!

Later receivers injected the LO into the source of the dual-gate FET, and used the redundant second gate for gain control, allowing a certain amount (about 22 dB) of AGC action and allowing the receiver to use the minimum amount of gain consistent with a fully noise-quietening signal. This minimised the risks of image reception and receiver de-sense due to close proximity to transmitters.

The drain of the dual-gate FET had a first IF transformer - a standard Toko 10.7 MHz coil. This fed a transistor to do an impedance conversion into an "SFE" 10.7 MHz ceramic filter. There was then a "cascode" transistor amplifier at 10.7 MHz driving through another "SFE" ceramic filter into the CA3089 IF chip.

I generally used a double-tuned discriminator circuit, since this reduced distortion significantly. Again, later receivers used a PLL discriminator, which gave even better results and increased the overall receiver sensitivity by almost 10 dB. My last run of Band III receivers could cleanly receive signals that were virtually inaudible on a conventional scanner!

Really effective receivers aren't trivial to design and build. Any solder-jockey can throw something together that will transmit, but the real skill is in receivers.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

radium98
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Re: STL link RX

Post by radium98 » Tue Oct 09, 2018 5:40 pm

thanks Albert .i appreciate the big help .

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