Tuesday, April 15, 2014

novice 90

You have transmitters or made one QRP.

WOW ! congratulations for hardwork. Lets have a QSO. You connect it to the dipole and presto there is no signal of 40 meter tx even 100k far ! You make another dipole. tweak it with magic formula found in net. It does not work. get frustrated. request for listening and it results in the downgrade of reputations !

Antenna Not Loading

and blame on your hardly homebrewed qrp tx.

No one is to be blamed except the murphy. The problem of QRP tx not loading on the antenna is age old. Even in the 1959 it was there. One of the ham friend has given the solutions in the form of novice 90 antenna.

please search the google and find the original novice 90 from the popular electronics pages.

I will be putting the source of these resources with note of thanks to original authors. I am trying to use the theory for my communications and writing it in a story style. Technique which works....... if it works for me , then it will surely work for you as i am going to make indepth analysis of it......

Now, musing over the antenna starts.
novice90
 Novice90 antenna roghly drawn.
lc tuners











Wow ! More i read, more i get confused. what is vital thing ? I feel like in a classical chicken and egg situations, You should have an experience before you get one. Pirates are doing fine with their qrp AM transmitters, and why we hams not able to use qrp 5watt, even though we have the previledge of cw also ?

I moved my self from the facebook and opened my eye towards the things around me.Brainstorming session starts. Series of question came.

What is transmitter power ? QRP or QRO ? what instruments you have ?

QRO amplifier uses dipoles , loops, uda-yagis, beams etc. they are balanced, they work better,even you can find commercial antennas, know how is easily available. most of hams use them. dipole are very user friendly.

But,for QRP transmitters with dipoles i am not able to transmit. looked into the web found lots of things. there are many camps and theories and formulas. Mind boggling things. End feds, Half waves, Shortened dipoles, Long wires.....

 Ok Ok. what about my question "i am not able to load the transmiter ?" i litterally typed similar words on the google and one solutions came -use Novice90. then Monoband verticals, Long wire etc.

For qrp, first experience,antenna should be resonant.
What you mean by resonant ? half wave, quarter wave, exactly measured and then trimmed ( increased or decreased the wire length practically).

antenna have self capacitance. Due to its structure and nearby objects, EARTH etc it has an inherent capacitance. dont blame elements but use it. here you will need a good earth or counterpoise.

two things, first- antenna should be tuned (resonated) for your band/freq.
and second- impedances should be matched for optimum transfer of power from transmitter to antenna.

So, this power goes to other ham's radio.

For antenna tuning you need antenna analyzer MFJ259B, GDO. (If your club or nearby hams have ! then your all problem end within an hour............).

For impedance matching you need LC tuner with some sort of SWR meter. These things might be in your transmitter or you have to make one.

Fsm is also vital for this verticals, sigle wire antennas.
If you have a portable scanner or second ham ins some distance or a friend who can tune into your signal then its better to listen to your signal and estimate the Signals stregth. In the south india there is density of hams are high compared to my gujarat state , western part of india ! so, they have success in ham radio.

quarter wave antenna has low impedance (in the range of 25 ohm etc), half wave antenna has high impedance (3k around)

Using formulas , for a given frequency a wavelength is calculated (that is called electrical length). If your physical antenna ( wire !) is shorter then this calculated value then your antenna is short. If it is longer, then  your atenna is big. for short antenna inductor has to be added and for large antenna capacitance has to be added to 'tame' it down to your frequency. there are all sort of formulas. For us imperical values will suffice.

For insulation, end insulators or support you can use "white pvc water pipe" used in water plumbing. Please remember "white". If it is grey or black, dont use them.

(for this antenna) lower swr alway does not mean that it will radiate more, check with FSM, (Emperical) little mis-match on swr but high FSM reading is okey with qrp.

what is VSWR ?  standaing wave. answer is complex ! but practically be understood by little experiment. put a water in a bucket, with a little stick or pen -vibrate up and down with a constant motion, you will see the waves propagate to corners and move back to centre and due to this to and from movements of waves there is a pattern on the surface. this sort of things happens with rf in antenna, coax etc.

the power which does not get radiated due to this VSWR comes back to the coax, tuner and heats up the coils, capacitors and make complex things... that's the reason for qro amplifier swr should be 1:1, our goal should be to throw last bit of rf power onto the ether....

wave travels in duality. up-down, if we are using single radiator there should be some sort of earth to compensate it. counter poise is a piece of wire which provide earth for radiating element. remember the famous parasets. they used halfvave wire as antenna and quarter wave as earth. good. Military is using this comm. we should carefully see their wwII radio antennas were....

in our novice90 tuner is supposed to be near the transmitter, also the earth is nearby. Warning- long coax line is not encouraged. it will create problem due to return currents, heat, TVI, harmonics interference to (the legal services, very bad , if your shortvave tx harmonics interfere  neraby police  station vhf ! an ugly situations is ready for you. wpc is will be late but they will reach to you first with siren blaring wehicles ). hence we dont find this antenna in a full power or medium power transmitters, commercial transceivers. Thats the reason most hams don't use this atenna.

This is your first antenna. and with upgradation you have to migrate to other antennas. happy ! thats why you will not find anyone using this antennas but it works mirculously first time and any time, good for camping, temporary, clandestine work (he he) etc ......Don't loose hope. It worked for 1959 American Novice and even today it will work for you, me with just 5 watt.

Make a good earth. How?. Make a deep trench of 2 feet deep. Soil should be moist. Bury the old unsused cloth iron plate and few small metal, copper etc things with salt and black coal deep into the earth. dont forget to wrap copper wire for more contact. rod etc. pour water from time to time and you are done. Main element is, there should be no gravels, sands, stones etc, it should be wet. and if not sufficiently wet, then you got to insert a pipe to pour water before use. With multimeter measure the voltage. There should be no drop of line voltage and you are ready to go.

Your local electrical store can provide you the brass plates and little more know-hows,even a handy-man for a price.
In the railways they still make earth for signaling purpose. Ask a friends in the signals department (the PWay inspector or Signal Inspector). They have measuring tool like "megar" a resistance measurement tool. only thier instruments are regularly used in fields.

What wire should be used for L ? for antenna use any wire easily available say "1/18 " electrical wire inside the insulating coating there will be a single copper wire of 18swg. It seems electric wires copper is little different from the motor windings copper...,

Use of copper enamalled 22swg, 20swg is ok, still better is 18swg. copper enamalled will cost less then common electrical wire. You can scrounge the copper wire from burned winding of big electrical motors. but buying new is really cheap.

peoples have used the normal aluminium pipes in the telescopic fashion (fitting one end inside other pipes end) with success as monopoles. here you dont have to worry about supporting the wire or buying the bamboo. this is also a good option. but care should be taken to tight fix the aluminum. as it can not be welded. better mechanical works gets good results.

40 meter is all day night, all time band. terresterial. (neighbour hood band if there is no local qrm due to mobile tower smps etc) for a given place,situation one antenna works and for different place situation that does not work!

There is also another third options. As the legendary spy set and paraset transmitter used. halfwave as antenna and quarterwave wire as counter poise. I think i will try this last antenna first and then other things. or may be make all the antennas.... or may be somehow use the QRO-linear..... and not try any of this.

Brain storming ends here. What a topsy turvey journey.still there from where we started. thats called chicken egg problem.

Now,,,,,I am making ANTENNAs and will  upload more fotos, end results. And possible first contact.using vwn tx.


mp-10, minipig
 this is the simplest bridge to handle the qrp tx.

I intends to make this led based bridge to get hang of the swr meter.
antenna and tuner coil. short antenna whip, vertical, half wave , long wire.... all sketched on paper same but, there is big difference.....






(to be continued.......)



No comments:

Post a Comment