transceivers

Post new topic   Reply to topic

Go down

Re: transceivers

Post by zsolt on Thu Mar 15, 2018 9:09 pm

hi , i built it . Seems to work . Now i plan to build a transmitter . If that could cover 50 m , it will help me to find out where my tools at , or who "barrows " them

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Ivan on Tue Mar 13, 2018 7:09 am

Hi Zsolt,
you are right. You need a transformer or autotransformer to match the resonant circuit (the coil of which is on the ferrite rod) to the rest of the circuitry and to avoid lowering its Q too much.

I found an article about ferrite loop antennas: http://www.sarmento.eng.br/Loop_Ferrite_Rod_Antenna.htm

BR from Ivan

Ivan

Posts : 234
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Re: transceivers

Post by zsolt on Mon Mar 12, 2018 2:58 pm

So my LC will be overall  most complete when it's Z is the highest possible , under the restriction that i still have to take in account the impedance of 1000 ohm of the rest of the circuit ? 
This sounds more like a transformer thing , or maybe autotransformer ?

Endeed the 1K seems to appear about the 25% of the whole LC  bounce 
And what would be the best position for the coil on the rod for best directivity, middle or at one end  (or carefully wound equidistant overall the rod?? ) ?

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Mon Mar 12, 2018 10:35 am

It is easy to calculate the impedance of a tuned circuit.
Wind the coil, add the capacitance to make it resonate at the required frequency.
(Tip: use a fixed capacitor and slide the coil along the ferrite rod to fine-tune the frequency)

Note the capacitor value and use the second calculator on this page:
http://213.114.131.21/begin/calc-00.htm
The inductor and capacitor both have the same impedance at resonance.

If your tuned circuit has an impedance of, say, 1000 Ohms and you terminate it with 1000 ohms then the Q-factor will only be 2.

It is advantageous to get the impedance much higher and use a lower impedance tapping, even this results in a miss-match.
Suggestion, add a 25% turns loop to the ferrite antenna and connect the 25% coil to the transmitter instead of the inductor in the collector.
(if your coil is 20 turns then use a 5-turn coil to couple the TX).

Best regards from Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by zsolt on Sun Mar 11, 2018 9:20 pm

Admin wrote:Hi again,
Yes Ivan, you are 100% correct. Sorry, but in my excitement I often assume other know what I mean. I should slow down a bit and explain more. Thank you for coming to my rescue  Smile

Now Zsolt, if you have 33pf then the impedance of the ferrite antenna is a little low, which means:
a - It will be matched directly
b - The bandwidth will be very wide
So you do not need a second winding.

If you had a higher impedance (eg 10pf and more wire) then the Q would be higher, the BW would be narrower and the efficiency as an antenna would rise, although you will need a tapping on the coil, or a second winding.

But give it a try as it is. It should work.

BR Harry - SM0VPO
ok , so the simple LC  does the job . With no additional winding or tap . I don't understand how do you define the impedance of the paralell LC at resonance . Can you explicit a little the formulas ? My computer outputs strange things .. Thous Xc=XL = value  , Z  goes to infinite  at resonance.  I think because my formulas are for ideal LC , for the real model i need something else ... or maybe i should set lower and upper bounders  for Xc and XL

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Sun Mar 11, 2018 7:05 pm

Hi again,
Yes Ivan, you are 100% correct. Sorry, but in my excitement I often assume other know what I mean. I should slow down a bit and explain more. Thank you for coming to my rescue  Smile

Now Zsolt, if you have 33pf then the impedance of the ferrite antenna is a little low, which means:
a - It will be matched directly
b - The bandwidth will be very wide
So you do not need a second winding.

If you had a higher impedance (eg 10pf and more wire) then the Q would be higher, the BW would be narrower and the efficiency as an antenna would rise, although you will need a tapping on the coil, or a second winding.

But give it a try as it is. It should work.

BR Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by zsolt on Sun Mar 11, 2018 6:51 pm

Ivan wrote:Hi,
I expect Harry missed to say the fact there will be two windings on the ferrite rod:
1-get the number of turns and inductance of the main  coil already wound on the rod;
2-bring it to resonance using a capacitor;
3-calculate the impedance of the resonant LC circuit;
4-calculate the number of turns of the coupling winding;
5-make the coupling winding and connect it to the transmitter.

Am I right?
BR from Ivan
Hi , 
Actually this is what i understood  word by word:
I have 
C = 33 pF :
fo = 4MHz:

 then the Xc  =  10^6/(2* 3.14 * 4 * 33) = 1206 ohm .  ( i think H wanted to say Xc not Zc = R+jXc  ... or eventually = -jXc  ... ) , this value i should pass  to the ferrite rod antenna  as it's impedance .
Then the impedance of the transmitter is  Z=1000 ohm .
ratio1 (didn' get ratio of the what from the text so i call it ratio1  ) Xc/Z  = 1206/1000 = ~ 1.2
then  turn ratio =  sqrt(1.2)= 1.095

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Ivan on Sun Mar 11, 2018 12:05 pm

Hi,
I expect Harry missed to say the fact there will be two windings on the ferrite rod:
1-get the number of turns and inductance of the main  coil already wound on the rod;
2-bring it to resonance using a capacitor;
3-calculate the impedance of the resonant LC circuit;
4-calculate the number of turns of the coupling winding;
5-make the coupling winding and connect it to the transmitter.

Am I right?
BR from Ivan

Ivan

Posts : 234
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Re: transceivers

Post by zsolt on Sun Mar 11, 2018 8:26 am

hi , 
i understand some part of this example . I don't get the point why should i make 4 more turns if i have already 20 turns ? do i have to take of the 20 turns and ad only 4 turns ?
It's to simple , i think i want to make it more like circuitus confusicus : 
I made up a little theory i wan't to throw later in Matlab 

If the above is correct , using an optimization toolbox i have , the program should give me the optimum L value under the given restrictions . Than later on build the coil which is also tedious to calculate (have no idea about the ferite core ). Or maybe i should wind the L , measure it's inductance with my L meter and find the proper C ? and if i don't have that C [pF] than use a trimmer capacitor  (i have one from a radio it's 5- 45 pf , good to experiment with)

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Sat Mar 10, 2018 6:28 pm

Yes, exactly!

If the impedance of the ferrite rod is too high at the ends then two things will happen:
1 - The radiated power (range) will be terrible
2 - The bandwidth will be really wide, possibly allowing spurious and harmonics to be radiated.

It may be wise to make a quick calculation:
1 - Measure (or estimate) the capacitance required to get the correct resonant frequency.
2 - Calculate the impedance of the capacitor at the TX frequency

This will give you the impedance of the ferrite rod antenna. The impedance of the transmitter is about 1000 Ohms.

3 - Divide the capacitance impedance by 1000 and you have the impedance ratio of the to get a good match.

This could be something like 20:1

4 - Take the square root of this value (20? = 4.5). This is the turns-ratio you need to match the transmitter to the ferrite rod.

So if your ferrite rod coil was 20 turns, then add a coil of (20 / 4.5 = 4-turns) to the ferrite rod over the tuned coil.

BR Harry

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by zsolt on Sat Mar 10, 2018 6:52 am

hi , i have some of these ferite rods 

So , if my crystal is 4MHz , i have to build an LC circuit on 4 Mhz in the collector  of the oscillator transistor ?

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Fri Mar 09, 2018 9:13 pm

> ... how would you connect a loop antenna to this circuit ? 

Assuming you are talking about the experimental circuit a few messages down the page, then the antenna connection can be connected to a reasonable HF antenna. Dipole? Ground-plane? Resonant loop? Ferrite "Loop-stick"? All should work to varying degrees of efficiency.

If you use a loop-stick antenna (for shorter ranges) then you can replace the coil in the collector of T1, instead of L1. Just put a capacitor across it to bring it to resonance. You may have to feed the collector into a tapping to get max power radiated. For a kilometer, or so, then the resonant loop may be the best bet.

BR Harry - SM0VPO

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by zsolt on Fri Mar 09, 2018 7:46 pm

oook so getting back to my transceivers , how would you connect a loop antenna to this circuit ? I remember when fox hunting we had a ~ 30 cm loop on 2 pieces of wood in x form .I absolutely don't remember how it was connected but for shore not to antenna pad and gnd, probably  the antenna itself  was a part of the LC tuning circuit . I remember that they worked  bounce i cached a fox even without having a battery in the unit .

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Wed Mar 07, 2018 12:39 pm

Hi Ivan,
At the time I was just trying to get the telephone bill down, which was my first objective.
No CPU at all, just TTL and diode logic (plus the odd OpAmp) - really simple logic.

I never even thought about marketing it, and had I done so I would probably have lost my job with PYE Telecommunications.
At that time I was studying in Cambridge to get my BSc and trying to feed a family.
Besides that I didn't think it was particularly clever.

In retrospect perhaps I should have sought a sponsor?
Anyway, it is too late now.

BR Harry  - SM0VPO  (30,000 feet over Northern Spain)

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by Ivan on Tue Mar 06, 2018 7:21 am

Hi Harry,
what a clever system you made, probably without any MCU! I admire it. If you sold it
into the world, you could be a very rich man now and Lythall Labs Ltd. would be a
worldwide famous mark. Cool 

BR from Ivan

Ivan

Posts : 234
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Mon Mar 05, 2018 7:52 pm

Now this is extremely interesting.

In the learly 80s, TTL was popular, and so was my former wife popular on the telephone to neighbours. So I built a local telephone network, with no exchange.

Telephone 01 generated a 0 - 99 timeframe with short pulses, and a very long end-pulse. If telephone 01 was unplugged then telephone 02 would generate the timeframe. Any telephone could generate the timeframe. All telephones were connected (T-fashion) to a long coaxial cable.

If for example, telephone 36 dialled 07, then +5 was put into timeslots 06 and 35. Telephone 07 would then ring. No other telephone could call either 07 or 36 since they were busy. The +5v was amplitude modulated (sample-hold each timeslot) at about 6kHz with +/- 0.75v audio variations on the timeslot. Every timeslot was repeated every 6.66kHz.

With 100 timeslots it was possible to have 50 simultaneous telephone conversations, no exchange/switch. It was a bit crude - if you put down the called telephone before the callers telephone then the called phone would ring. Audio was quite clear, but slightly treble-limited.

I had about 40 telephones on the system before I left the village. A few of those were multiple phones in one house, but there were over 30 homes fed.

Just a bit of interesting history .-)

BR Harry

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by zsolt on Mon Mar 05, 2018 3:13 pm

Ivan wrote:Hi Zsolt,
it is not widely known that Ethernet originally started on RF and coaxial cable - so called Thick Ethernet.

You wrote about a coax with antennas conneceted - how do you mean it?

BR Ivan
hi ,
well i would not call my little network ethernet , that's a big word .. Basically i have one master and 44 slaves . It is bidirectional in the sense that the master sends on the bus a little datapack (6 byte's) containing principally an address and some instruction (+crc) , and the addressed slave responds with a 36 byte datapack (adress, sensor data + crc....) . 
I managed to make the databus a 0/+24 V databus , originally i started with the RS485 standard and all that goes with it (differential tx/rx lines , protocoll ...) as i mentioned that didn't work well , and to be honest i don't like complicated industrial stuff and standards . So now 0 V (...actually no voltage) means a logic zero and 24V (...actually some voltage) means a logic one . The software is also not standard , i made a simple software serial link .
An now after visiting these pages i came up with the idea that one's and zero's could be transmitted with these simple transceivers  Very Happy , 
The below transceiver has an antenna , if i build 44 of these and connect their antenna pad to the same coax cable , i think i have same thing like above described, just that a is RF signal transmitted  in a shielded cable . 
I   i don't know is this was done before or not , and i have no idea if it works like this .
Thick net is interesting i google -ed  about it and i found some articles on Wikipedia  Shocked , i see this first time , is exactly what i need

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Ivan on Mon Mar 05, 2018 7:56 am

Hi Zsolt,
it is not widely known that Ethernet originally started on RF and coaxial cable - so called Thick Ethernet.

You wrote about a coax with antennas conneceted - how do you mean it?

BR Ivan

Ivan

Posts : 234
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Re: transceivers

Post by zsolt on Sat Mar 03, 2018 2:01 pm

Even in digital transmission data collision is a big deal , i have to address with one master 44 slaves   .. at first 13 slaves already had trouble with that (didn't use flow control , only timing ... ) First i used RS485 modules to interface the 1.5km long bus , thous they where heavily protected against data collision they kept burning out from time to time (had big problems with electrostatic discharge also , i made up the bus from the cheapest un-shielded  UTP cable ) , after that i got smart , i give up on those rs485 modules and made up a dirt simple circuit that toggles 0/24V to transmit data bits on the line and believe it or not i'm using the simplest software RS232 library (a little adapted ) @ 9600 baudrate (still with no flow control , handshake , or other fancy stuff ).
Anyway i'm still interested in using this simple circuits for digital transmission . I taught that this could be a good idea to replace the data bus with a simple 75 ohm coax cable , and since only the antennas are connected to it data collision is no problem .  An other idea was that if this works and transmission can take place in the air it could help me to make connection between 2 parts of the factory  (the 2 are separated by an access road )
It doesn't matter even if i have to go down to 2400 bits/s or even lower , the slaves transmit some sensor data which is not critical in time

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Ivan on Sat Mar 03, 2018 11:22 am

Hi,
several stations on the same frequency and within the common range form a radio network. Their operators must keep some rules to reach a connection. Only one of the stations in the network may transmit at any moment. If two or more stations transmit CW or AM at the same time, an unreadable jam occurs. In the case of NBFM stations, the receivers will hear one transmitter only, the one with a stronger signal. Digital modes make advantage by addressing packets, but require much more complicated equipment.

BR from Ivan

Ivan

Posts : 234
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Re: transceivers

Post by zsolt on Fri Mar 02, 2018 7:56 pm

Ivan wrote:Hi Zsolt,
digital circuits including MCUs usually generate squares. If you put the squares directly or after simple amplification into an antenna, you would transmit lots of harmonics together with the wanted frequency. Squares of 50% generate mainly odd harmonics: e.g. if you set an MCU to make 2MHZ, you would transmit 6MHz, 10MHz, 14MHz etc. together. Some filtering is necessary to obtain the basic sinewave from the squares. A passive lowpass filter will probably do.

BR from Ivan OK1SIP
hi, i can generate also sine signal or triangular , just that it cant go high frequency , i have built a DDS signal generator from the net . It uses a lookup table stored in eeprom memory with the amplitude of the signal , than it passes those values to a simple  R-2R digital-analog converter . Didn't modify his code , it worked as is . But i read on the net (https://en.wikipedia.org/wiki/Direct_digital_synthesizer) about DDS that it can go even in Mhz range with special cip .

Oh , an i still don't understand something : if you talk that QRP stuff with Harry on let's say 4 Mhz with your transceivers  , and i build that circuit also , will i get you both go mad when i start beeping around with those two transistors on same 4MHz  ? Or let's say all on this forum build them and start signaling   , how can you still talk ?

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Ivan on Fri Mar 02, 2018 10:03 am

Hi Zsolt,
digital circuits including MCUs usually generate squares. If you put the squares directly or after simple amplification into an antenna, you would transmit lots of harmonics together with the wanted frequency. Squares of 50% generate mainly odd harmonics: e.g. if you set an MCU to make 2MHZ, you would transmit 6MHz, 10MHz, 14MHz etc. together. Some filtering is necessary to obtain the basic sinewave from the squares. A passive lowpass filter will probably do.

BR from Ivan OK1SIP

Ivan

Posts : 234
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Mon Feb 26, 2018 8:32 pm

> What is QRP?
It is one of the international Q-codes (QTH = home location, QSY = change frequency ... etc). The code helps morse-code operators send more information using fewer and shorter words. It also helps operators to understand each other when language fails, using standard code-words.

QRP means lower TX power; the opposite of QRO, which means to increase TX power.

In general, 5-Watts or less is generally considered to be QRP operating.

Such low powers rely on the fact that TX power is NOT a major contributing factor to long distance. If you improve your receiver sensitivity from 3uV to 0.3uV then this is the same as the transmitting station increasing the TX power from 5-Watts to 500-Watts, which is only 3 S-points difference on a calibrated receiver signal strength meter.

A base-coil-loaded vertical ground-plane antenna and a full 1/2-wave dipole at 25-metres height, have a similar difference and the dipole will improve both transmitter radiation and receiver sensitivity. This is one of the reasons there is so much work done on antennas.

Gota go now, past my bed-time- Have a house show in the morning.

Google keywords: "Q-Code", "QRP", "QRP antennas", "QRP circuits"

BR Harry
(Q-code joke: QSS = "Quit Sending Sh##")

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by zsolt on Mon Feb 26, 2018 7:20 pm

Admin wrote:Hi again,
Yes, a tone is exactly what you would hear. The frequency of the tone would be the difference in the TX and RX oscillators.

I tried searching for the TX/RX circuit but could not find it in Google. I did find a simple circuits that has:
   sensitivity = -100dBm  (2.2uV)
   TX power = 70mW (+18dBm)
This should give you quite a long range between similar units, with decent antennas. There is absolutely no reason why you cannot work intercontinental with this type of QRP transciever - onlyu 3 S-points difference at the receiver staion if you use 60mW or 5-Watts.

The author does recommend an LPF in the antenna "for serious work".

BR Harry

Ok , it's simple i'll try it out .
What is QRP ?
So if i build this little circuit , you say that you can receive the signal produced from 1 transistor over all those km's in Sweden or Spain ?  
It sounds so unbelievable that i would all most try out    bounce

I recognise the oscillator at first transistor . 
I have an idea , with the microcontroller i can generate square wave up to 8 Mhz with no problem . How could i feed this to the antenna ?
Is this a good idea 

What if the difference of the 2 frequencies is zero ? (lets say the two units are at perfectly same frequency )
If this is true (f1==f2) than would be enough to monitor the emitter current of T1 like in the GDO , to see if the antenna is picking up ?

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Mon Feb 26, 2018 6:39 pm

Hi again,
Yes, a tone is exactly what you would hear. The frequency of the tone would be the difference in the TX and RX oscillators.

I tried searching for the TX/RX circuit but could not find it in Google. I did find a simple circuits that has:
   sensitivity = -100dBm  (2.2uV)
   TX power = 70mW (+18dBm)
This should give you quite a long range between similar units, with decent antennas. There is absolutely no reason why you cannot work intercontinental with this type of QRP transciever - onlyu 3 S-points difference at the receiver staion if you use 60mW or 5-Watts.

The author does recommend an LPF in the antenna "for serious work".

BR Harry

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: transceivers

Post by zsolt on Sat Feb 24, 2018 7:38 pm

OH8GAD wrote:As the circuit stands, it's just a TRF receiver with an audio amp acting as a detector.
Press the CW key, and you groung the input to the amp so the the signal from the crystal goes through the transistor and out of the aerial.
It is pretty much the same as the Pixie tranceiver.
As it is, it will only send CW. Though it can be modded to send AM voice, but that will be just horrible...

Ok , so what would i hear in the speaker , a kind of beep , because the 2 oscillators (a pair of these circuits ) are not exactly at same frequency ?
I'm not after sending AM voice , i'm after sending 0's and 1's Smile 
I have some experience with this ''analog transmitted digital'' with a disEQ (USALS) equipment i built in the past ... 22kHz tone was sen't in the 75ohm coax cable along with the SHF coming from the LNB. Different duration of the 22kHz was used to distinguish 0's and 1's . I used a PIC16F628  to decode the disEQ message and drive the antenna motor .  ( i also made a small pdf to share it  https://www.slideshare.net/JakabZsolt/diseqc-51558703  )
With this transceiver i would try out something similar with an Arduino...

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by OH8GAD on Sat Feb 24, 2018 6:21 pm

As the circuit stands, it's just a TRF receiver with an audio amp acting as a detector.
Press the CW key, and you groung the input to the amp so the the signal from the crystal goes through the transistor and out of the aerial.
It is pretty much the same as the Pixie tranceiver.
As it is, it will only send CW. Though it can be modded to send AM voice, but that will be just horrible...

OH8GAD

Posts : 2
Join date : 2013-12-12
Location : Finland

View user profile https://satans-kittens.neocities.org

Back to top Go down

Re: transceivers

Post by Glenndk on Sat Feb 24, 2018 2:53 pm

zsolt wrote:Hi ,
i'm in search of a simple transceiver

This is pretty simple when compared to the coverage 0-30MHz (except around 20MHz). It only have two challenges; flashing of ATMega328P and the Si570 90mA current drain. But it does not have AGC ( http://www.qrptransceiver.com/#agc ):

Minima -A general coverage transceiver:
http://www.phonestack.com/farhan/minima.html
http://www.phonestack.com/farhan/minimackt.png
http://www.phonestack.com/farhan/bidiamp.pdf

Minima source code for ATMega328P:
https://github.com/afarhan/radiono

Glenndk

Posts : 40
Join date : 2017-01-06
Location : Copenhagen, Denmark

View user profile

Back to top Go down

Re: transceivers

Post by Admin on Fri Feb 23, 2018 9:41 pm

Hi again,
This does look quite simple, but I once saw a CW transciever using nothing more than an OC45 (germanium IF transistor).

I cannot remember the exact circuit as I was about 11 at the time.
It was basically a loop-stick (ferrite rod) antenna with feedback from collector to base to give a simple regenerative receiver. The CW key bypassed an un-decoupled resistor in the emitter that caused oscillations to increase and be radiated by the loop-stick antenna. I seem to recall that a diode was used to rectify the received signal and feed the audio back into the transistor for audio amplification.

I will google a bit and see if I can find the circuit. I will know it as soon as I see it.

As regards range, this circuit worked over about 250 metres.

If you have ½ decent antennas (GP or dipole) then at 3.5MHz this sort of circuit could give you a pleasant surprise. The formula for pathloss between two antennas includes adding together three dB items: "A Constant***" + 20xLog(distance) + 20xLog(frequency). At 432MHz the frequency figure will be about 50dB, but at 3.5MHz it is about 10dB - ie - a 40dB improvement (100x the range).

(*** the "constant" is about 33dB, depending on km/miles, dBd/dBi, etc)

Ok so the receiver will be a bit deaf and the TX power low, but you may still get a fair few kilometres between this and a conventional hamradio station.

When I give my radio courses I use a GDO and an 8.2m length of wire in the (indoor) classroom. The 17MHz is predictable and has been received by a colleague, more than 2.5km away. GDO power more than 1mW (0dBm). If my antenna demo was on the roof of the building then I would reckon with 12km, or more.

I used to use a 20µW (-0.03dBm) transmitter in Haddenham for 39.7Km to the local repeater (GB3PI) on 145MHz.

Sorry, but I do get a bit carried away with low power comms.

BR Harry

_________________
(no text given)
avatar
Admin
Admin

Posts : 565
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

transceivers

Post by zsolt on Fri Feb 23, 2018 7:10 pm

Hi ,
i'm in search of a simple transceiver (for a crazy idea i don't want to reveal yet ) . I find one claiming being the simplest 

How does this work ? I can see something like an oscillator attached to an audio amp
Let's say i have 2 of these . Another one transmitting and this one receiving , so what do i hear in the speaker ? a beep ?  Shocked
Oh , and can this circuit cover 12 km flat  distance ?
And if 3.5MHz is for all radio enthusiasts on the globe , lets say all readers of this post build 3.5MHz transceivers , and all start conversation with them about same time , what would this result ? (compared to digital circuits there is no addressing , how can different connections not interfere with others? )

zsolt

Posts : 85
Join date : 2017-12-19

View user profile

Back to top Go down

Re: transceivers

Post by Sponsored content


Sponsored content


Back to top Go down

Back to top


Post new topic   Reply to topic
 
Permissions in this forum:
You can reply to topics in this forum