Linear Amplifier Problem- 3

A friend experienced a problem and solved it. first image depeicts the problem and second image depicts the solutions.

Question :---
My friend Vadivel requested in the Indian Homebrewer forum ::  " Help Needed on MOSFET Linear amplifier. I'm using Linear amp used with Minima TRX. Its working very fine. But the low pass filter is getting too hot / smoke after TX of 10~20 secs. I used 2x TV balun glue together and 3 turns of 28 SWG. SWR is corrected with the use of Pi network ATU. Any suggestions welcome. "

 The problem:---

The RF theory :---

The low pass filter was made with the pig nose baluns. But, IMHO opinion it can not handle the passing of 15watt rf.  If  core gets burned or becoming hot, its probably got damaged due to the heat. Please do not use it further. discard that piece and never use this baluns as filter eliment. they can handle just 1watt.

In my experiments I have found that, You need atleast minimum 4 big pignose baluns stacked for linear amplifier transformer.

The solutions :---

The coil is made over the felt pen body. The sketch pen body is the beast material to make the coil for low pass filter. Its diameter is uniform, widely available and most of the time they are in standard size.

A friend suggested  to use air core. And our great elmer shri  Dev Rama Prabhu say's, let me reproduce in his own word ::
Dear sir, if any inductor core is becoming hot it means it is very lossy! Just replace with one more core as these cores are not repeatable! Otherwise as Mr Rajesh has suggested use aircore and I always use aircore with Teflon formers. 73

BITX, Single Frequency Receiver-2

Peter VK3YE  made a wonderful signel freq transceiver based on the BITX. My previous experiment is here. http://vu3inj.blogspot.in/2015/06/bitx-singlefrequency-receiver.html write up looks similar.

Frequency is 14315kc , ( 20 meter band )

 I had one 14315kc transmitter and made two three single frequency receiver. Those receivers work for Testing my local signal only. I wanted something air worthy. Which can receive other hams signal. So, made this...

Lets start from back-wards.

1.AF Amplifier stage:-
LM386 In standard form with BC549C af preamplifier.

2.Product detector:-
Using subharmonics detector... he he... I don't have third 14.318kc xtals. So used the available 7.159xtal. Also did not had the balun core. If you have balun cores use them please. Another option is to use  differential 3 transistor Single balanced demodulator.

3.IF Amplifiers:-
 As given in bitx. As frequency is higher the gain will be low. Ohh this is the reason for Rx being so much deaf. Need to add one amplifier in Front end. { Read last para, finally found out the true reason, the xtal  had moved a little and loose connection happened. It works fine. No need of extra gain }

4. Front end band pass filters.
Even after making this working receiver I did not put the filter. Could not find the RFC nor a IFT. Was lazy to wind it up. One day legendary VU2DEV suggested to me K&R Filters. Here the tap is taken from the capacitor instead of the L.  My problem with filter was that I could not find suitable component for L and taped L does not work as receiver BPF. You can see VU2DEV use this type of filter for his JOTA, S7 trx, GR40, ISDR etc. Somehow I managed to make a suitable filter.

Have a look at his blog

5.Cabinet and Speakers.
All standard things.... I really homebrew cabinet.  In our kitchen we buy 15Kg oil in metal pack. So, when it is used up, I cut the metal box which is 2foot x1 footx1foot. So, it give a good one box for my projects. I buy paint from local store. Generally black paint . It is a thin metal, so I can do most of the mechanical work without any problem and it last more than 10 years.  After that give a pint job and it look new. He he. this tech is 15 years old.

The schematics and pictures will be updated. With full details.

PCB Sketching:-
I sometimes make the pcb very very old style. Using the oil paint, paint brush and Feric Cloride as etchant. It is no hole , surface mount type pcb. Of course for normal components. This is the process to make a quick prototype. Draw it, etch it, make it and test it. The prototype is ready within a day.


 Here AF amplifier stage pcb patter before it is etched. In the blank right hand side I have put the detector using manhattan style.

Af Pre amp + LM386 audio amp. 

RF amplifier, Second stage is cascade.

RF Amplifier with Xtal filter.

If I make further project then will integrate all the ckt in single board with replaceable filter assembly.

Schematics 
You will often see the similar ckt. reason is simple. The modules have given me time proven performance. So, they are innovated and used.





AF pre amp, LO,detector, IF2,xtal filter, IF1 Amp.

The last write-ups and this write-up looks similar. It should be as it is one and the same thing.
I intend to put up a BPF and do some on air test for my beacon. From one QTH to another QTH and measure its performance.

Testing:-

I  finally boxed up with last screw.  I want to make it as a black box. Literally its painted black. The VXO does not deviate much... I need to make some components change in VXO... add one rfc.

It is quite sensitive. There was one glitch. signal was intermittent. Did the screw driver test. I put screw drive at the second IF amp. It did sound loud. Then put at antenna side. No signal. so somewhere is dry solder. Pressed one xtal. Presto the signal boomed in. Did heat up all joints. Then suddenly once again signal went down. So, I looked minutely. Oh the real culprit was second leg of xtal. It was loose. So soldered it. And all is well.

Now.....Installing the bandpass filter. Installed and working fine. Will do some field test ..........



 

One  ham  VU3YFD, informed, he had also made the transceiver for single freq. But, I have not seen his ckt  nor the picture of that project.

 

VK3YE , Peter had made it and worked successfully. He has put it website. Both hams done transceiver in 40 meter, mine is just single receiver.

 

 I have tested and found working. Will try to design the pcb and offer kit also so that  others do not have struggle.

 

The wheel is re-invented  Worth try it.

On air , part-5

Tale of two transceivers:-

I have promise of the SSB transceivers on 20 meter an another on 40 meter. I have all types of wire antennas, dipoles etc, power supply for QRP and one or two liners.

Licence is valid for next years.  And upto next year will be in and around at my present QTH. After that it's possible I will not operate, not renew my license ! Who knows.....

I have plan to print the QSL CARDS. Will send it for one months QSO. Then 100% on demand only. Will be regular on band and will finish up my bitx and other transceivers and will gift them. Will print card without call sign so other friends SWL can also use it.

If this does not realise or there is some problem, then what ? Nothing. My region, district is a ham desert. There is no one around me. I have know how to teach. I can initiate/encourage some new guys into becoming hams. For that, I require a working Transceiver  to give demo. I could not give them the feel of being on air with a sinleband xtal CW TRX.

As a seed some trx was needed, I have nothing to test my home brew stuff. Loss of digital marine receiver was serious loss. It's not just money, I lost a friend also. I dislike loosing the friendship, for me friendship is more important , as its hard commodity to get by easily.

May be I will be getting the JOTA transceiver 40 meter and BITX-20.

Enjoy,
73
De VU3INJ
INDRAJIT,

Wheel has moved.....

Ha Ha Ha ........ where is the wheel ?

As of 15 july :-
May be in this week I will be getting this JOTA transceiver at my shack... But, somehow my desire to be on air has been killed by "build the bitx dialogue by many senior/juniour hams...".  But, for me this is it. I am not buying any HF transceiver after I receive above Jota Trx and BITX transceiver.....

23 July 2015:-
I have received the Jota transceiver. Its modulations is nice. vu2dev has specifically made for me. And for making it he made another rig also to test this rig. The metal body is good. VFO is quite stable. Very kind of 2dev. He has gifted the mic-handset of ahuja make. Also, did not charge any curier. Thank you Dev Ramaprabhu sir. 

25 July 2015:-  
I did test with long wire and power meter. It seems its a real QRP of 2watt. Today bought the 12 volt relays each costing rs70/- (about 1 dollar).  I asked the shopkeeper give me 8 terminal relays. He  smiled at hearing this. I should have said, give me two c/o relay. We are in this business since last 15 years.... he he. Ya, i said, this is the layman's language..... 

I am not using the existing 20 meter PA by output changing LPF coils, I will make another 40 meter Linear  based on IRF840. Let's  make and see that it gives me the contacts. With long wire antenna i was able to listen only. Will erect the dipole tomorrow. If  this set-up does not give me anything then i am QRT and will be running the beacons only ( pirate)  or CW on xtal based transceiver.

Peoples using smallest efforts, little money and easily come on air. What is problem with me ? Spending this much time , effort, resources, still not able to put myself on SSB fone. Many peoples have helped me. Still this problem ! VU2KD, VU2DEV, VU2UPX VU2PTR, with pcb, materials, instruments, books, tech support. They are the masters of the masters.
May be my ham-karma is bad. and frankly I don't know how to balance it !!!!!

I have no local support. My support is from DX places. Time and time, again its proved that the QRP never works for me. I need atleast 15watt to 20watt pure RF power, just to be heard at some nearby stations.

26july 2015:-
Opened up the JOTA TRX top lead. A very professional approach. The metal body is a very strong one. May be 16 SWG sheet metal. Which can be very hard to bend. Inside there is big relay. There is one copper plane in middle. Which shields the VFO as well as the modulator. The PIC counter is neatly placed behind the LCD panel so it does not occupy too much space.  It smells fresh. No smell of anything burning. There is no loose connections. Everything seems to be in order. But the 13watt linear is not producing the power ? I have run CW tx in those its a continuous power, in the SSB its peak power.  OK ? OM Sunil  TT also has the similar trx, but he has dds vfo. May be there is no problem at all. I just need to put a big antenna and a very big linear due to my living in the dry western part..... ok
***
27 july 2015:-
I opened the top lead and staring at the linear. Trying to figure out the connections. I am tired of the "miss murphy". Requested for the ckt diagram. If possible will start trouble shooting. Most probably I will remove that linear card and put  my own "2watt linear" into the box.

I wished that VU2OO had gifted me that RM96, which he promised three years ago. Anyway sometimes you have to let it go.....

I AM NOT ON AIR-40 METER as of 28july2015.

there is no wheel !  the wheel has not moved. End of searching the wheel.

ENJOY
(Each time I say I am QRT and still try to mess with Miss Murphy, hope one day she will yield to me and she will give birth to the child called success ! )

BITX Making part-1

BITX making will start this 1st week of the 2015.

Actually I wanted to finish my DSB transceiver and a linear project. But due to persistent request from a friend I have to make the bitx-20/bitx-40. I have all the materials, components, tools, and friends with expertize. But there is shortage of quality time due to MQTH and work.

I am also supposed to find the fault with my own bitx--20 and a friends bitx-40. There has been a classical mistake. All the components are soldered with big lead. All the coils are wobbly. There are dry solders. Did not write its making. there is no documenting the process and components changes etc. Thanks ,it has landed on my lab. Nothing to worry my friend i will find the fault. Some time I also do same type of mistake, every body has some ENTROPY. Well, I am 100%committed to solve and send it back.

Well as  promised I am starting with printing the bitx schematics and other hams write-ups...

First will be the bill of materials... as per  BITX-40......HFI2014.
BLOCK DIAGRAM

BITX

 Now bill of materials...

03jan2015
prepared the list of resistors

Bitx bill of materials. Bitx-20 or bitx-40

Component number	Value	Module	Transistor
R1	2k2	RF Rx input amp	q1
R2	1k
R3	10
R4	220
R5	220
R6	100
R7	2k2	Rf TX output amp	q2
R8	220
R9	100
R10	220
R11	10
R12	1k	Rx, If amp-1	q3
R13	2k2
R14	1k
R15	10
R16	220
R17	220
R18	100
R19	2k2	Tx, if amp-2	q4
R20	220
R21	100
R22	220
R23	10
R24	1k
R25	100	Rx, if amp-2	q5
R26	220
R27	2k2
R28	1k
R29	1k
R30	470
R31	2k2	Tx, if amp-1	q6
R32	1k
R33	4r7
R34	470
R35	100
R36	220
R37	2k2	Rf tx output amp	q7
R38	1k
R39	10
R40	100
R41	100
R42	2k2	Vfo amp	q8
R43	1k
R44	10
R45	220
R46	100
R47	100k	Xtal vxo	Q9,10
R48	1k
R49	1k
R50	1k
R51	100
R52	220	Mod/demod	pad
R53	22r
R54	220
R55	4k7	vfo	Q11
R56	220k
R57	10k
R58	10k
R59	100
R60	4k7		Q12
R61	2K2
R62	1K
R63	10	Audio amp	LM386
R64	100
R65	220
R66	4K7	Af pre amp	Q14
R67	120k
R68	2k2	Tx af amp	q14
R69		Not needed
R70	10k
R71	220
R72	2k2
R73	4k7
preset

 and capacitors. ...

Capacitor

Component number	Value	Module	Transistor
C1	*text	BPF
C2	22pf trimmer
C3	*text
C4	100n
C5	22pf trimmer
C6	100p
C7	10p
C8	22pf trimmer
C9	100p
C10	68p
C11	0.1	Rx, RF input amp	q1
C12	0.1		q2
C13	0.1		q1
C14	0.1		q1
C15	100n*/0.1		q1
C16	0.1	TX, RF output amp	q2
C17	0.1
C18	0.1
C19	0.1		q3
C20	0.1		q4
C21	0.1	Rx,If amp-1	q3
C22	0.1		q3
C23	0.1		q3
C24	0.1	TX, If amp-2	q4
C25	0.1		q4
C26	0.1		q4
C27	100p	Xtal filter
C28,28a	100p,100p	Xtal filter
C29	100n/0.1	Rx, IF amp-2	q5
C30	100n/0.1		q5
C31	0.1	TX, IF amp-1	q6
C32	0.1* not needed
C33	0.1		q5
C34	0.1		q6
C35	0.1		q6
C36	0.1		q6
C37	0.1		q6
C38	0.1	Tx, RF PA	q7
C39	0.1		q7
C40	0.1		q7
C41	0.1		q7
C42	0.1	VFO driver amp
C43	0.1
C44	0.1
C45	22pf trimmer	Xtal OSC	q9
C46	47p		q9
C47	220p		q9
C48	220p		q9
C49	0.1		q9
C50	0.1		q10
C51	50micro henry
C52	22pf trimmer	Mod/demod	d12
C53	10p	Mod/demod	d11
C54	0.1	VFO	q11
C55	0.1		q11
C56	10p		q11
C57	22pf trimmer		q11
C58	47p		q11
C59	220p		q11
C60	220p		q11
C61	220 micro H,25v		q11
C62	1 micro H, 25v
C63	0.1	Af amp LM386
C64	220 micro H,25v
C65	0.1
C66	1 micro H,25v	Af pre amp	q13
C67	50 micro,25v	Tx, AF amp	q14
C68,68a	1 micro H,25v, 100p		q14
C69	1 micro H,25v		q14
C70	50 micro H, 25v		q14
C71	50 micro H, 25v		q14
C72	0.001 / 1000pf		q14

One thing I noticed , total R-73 total C-72, nice combinations. wow !

Now other components
Transistors :-2N3904 / BC549c
IC:- LM386
DIODES:- 1N4148
balun cores,














 

BITX Making part-0

Last year, during our brief one minute meeting VU2UPX gave me one packet. This packate contained a good selection of the PCB,PIC for DDS VFO, DVD.  I am thankful to Om Charudatt -ji for  this gift. He had specially commercially ordered those pcb.  Whatever my karmic problem, I was not able to assemble the DDS VFO ( see the previous post ). This costed me a years homebrewing time. Really appreciate and make further projects. Most of project were dependent on the DDS_VFO. I gave it a second chance.  Lastly from that package I made the R7 receiver successfully. ( see preious post)

Due to work, could not visit the HAMFEST INDIA 2014 at Banglore. They gave one BITX40 PCB to all the delegates. and there was arrangement for low cost kit components for Rs.500/-.

Well, I missed that bandwagon. I was felling little desperate. So requested for spare pcb In the HOMEBREW forum. Few promised, but arrived none. (piece be on them atleast they promised). . I wanted to brag about this bitx.  Seeing this, my neighbor and senior ham VU2BGH, Om Bhogibhai sent me his pcb.  Few days later , as a good gesture for participating in homebrew project in the HOMEBREW FORUM, Om Shinos sent me one PCB( also to 6 other friends).

Thus I got two BITX40 pcb , so I remarked that...

Now my time for bitx making has came.... all the bragging will be on vu3inj.blogspot...... pls bear with me.....  My friend @2UPX remarked the following to me.........all the best, but you already have your hands full, Oh humble peasant. He was right but I replied that, you know that commons and kings, never satisfied with their greed.... to make new things.., to acquire more things......to get more beautiess.... he he he.... but actually i never had the cance to make the bitx & brag.......before bitx actually i wanted to make ararinha and one dsb tx......
 

This is the beginning part, all the bragging and other thing will be from the bitx40 making part-1
I will stat wit the pcb, components lists, links..... I am not giving any time frame..... I might need few 10mhz xtals and cores from some vendor....

so work in progress..... 2015...............

xtal filter making 2

Crystal filter making :- Part Two

In the first part we explored the theoretical part of the filter. Now, at this time we will actually try to find the suitable xtals for the bitx transceivers. Then try to measure the  bandwidth, frequencies of the xtal so that we can put the BFO accordingly.

First thing :- The oscillators to measure the series frequencies...



xtal series frequency test oscillator

*************************************************************************

As discussed on the part -1, measured the xtals series frequency with & without 33pf. All the data is given below.

I used the PIC frequency meter. all readings are in Khz. the minimum reading is 10hz if you get more accurate reading it will be better to use it. All  xtals are standard HC49.

{ Please be aware  11059kc halfsize xtals did not oscillated in this ckt ....No.8 is not the typo it was actually 10mhz mixed-up in the 5mhz bag. }

(wire open-with 33pf,)  ( wire close-direct , shorted the 33p)

xtal no.--- Open---- --------Close

1.        4999.38       4998.39

2.       4999.37       4998.38

3.       4999.38       4998.41

4.       4999.39       4998.46

5.       4999.36       4998.36

6.       4999.34       4998.33

7.       4999.33      4998.35

8.        ---------      --------

9.       4999.36      4998.34

10.     4999.40      4998.40

11.     4999.37      4998.37

Now, what 3 or 4 xtals should i choose for 5mhz ladder filter. ?

(1,2,5,7,11 would be my selection dear Rathorejee! replied VU2DEV and all concluded on 1257 for filte and 4 for oscillator)

filter from the  xtal no.........1,2,5,7
and for oscillator use the xtal no.,,,,,,4

In the selection we have to see that the xtal frequency should not deviate from each other about 50hz.
THUS this part concludes with success.........
****************************************************************
The xtal filter as brewed :: How to test it.How to describe a filter ?Measuring other parameters. i.e Xtal activities, frequency will write on these later on...pls..... meanwhile........
****************************************************************
One friend popped up the question "what shoud be the position of bfo freq. if the IF is 4 MHz and VFO is 11 MHz... to tune 40m LSB... should the BFO be below ladder filter central freq. or above the ladder filter freq. ..." .. i checked your blog first.. ... din found the topic... so can you brefly let me know...
Interesting question actually i made a little write up and forgot to upload here. Well answere is simple but somewhat lengthy.... consisting three parts.

First part::- consider filter as a gate. This gate has a centre frequency, actually a band of frequency between those frequency it allows to pass and for others there is steep rejection. These frequecies can be measured by feeding it a RF Signal from DDS_VFO and measuring the voltage at the output. At some freq it peaks then at some freq it drops down. now is the interestng part we have to find this steepness. at one point filter has 3db bandwidth these are two important frequency. It can be represented by the Voltage (y-axis) -----> Frequency(x-axis)... a flat dumpbell shape.

Every xtal-filter has different characteristics as it is not a commercially made filter for a fixed frequency. In our homemade ladder filter we accept whatever frequency band-pass our filter gives. so each fitler differes from other homemade filter.Bandwidh can be increased / decreased by ckt topology and components emperically.

Second part:: - Amplitude Modulation is the basis for all the analogue modulations. In the Amplitude modulations there is carriers and two sideband containing acutal informations. (about 66% rf power is at useless carrer. In the DSB signal we suppressed teh carrier by balanced modulations. Now our signal contains only informations in two sideband. But by using the DSB singal we still waste our RF power in another sideband. As both sideband contains same informations. Is there any way to remove this another side band. Well we have to trim the sideband by some filtering. And here the role of the filter comes.

In DSB modulations ,now our information is on the two side bands. USB is the signal where the information is on upper side band. in the LSB the information is In the lower side band. Another concept clerance this side band is related to the carriers frequency.


where should the bfo need to be put..... Now, there is steep dumpbell like shape of the filter and the dsb signal is without the carrier unlike the AM signal. We have to play with it.

Now, we have the steep ness of the filter. Our signal with two side bands. We have to fix the signals carrier frequency so that it collides with its steepness and let pass only the single side band of our choice out of two side bands.

Third part::-
For LSB The carrier frequency should be high i.e high side of the filter steepness

For USB the carrier should collide with lower side of carrier steepness that is its frrequency should be lower.

To lower the oscilattor frequency use the choke and to increase the xtal osc freuq use the capacitor. Well using the LC in xtal oscillator will give you good tuning range, as we don't know where our filters freuqncy is exactly ? Xtal filters generally shift little down from their xtals marked frequency. To shift the freq down we need L in osc.

hope you got it. some time i also get confused, so i draw it on the paper.... will upload it with full diagrams Actually these all are the practical things once you understand the theory afterwards it has be done practically.



graphical presentation of AM signal & xtal filter
 



After passing through filter we got LSB signal



After passing through filter we got USB signal

Query and answere ends here.

Chat Conversation End

It will be ALSO interesting to read the PY2OHH. he has published god work on farhans BITX. I HAVE FOLLOWED THE 2ESE in xtal making. As many people have successfully made xtal filter following him. Why re-invent the wheel ? Lets use it, as invented by the VU2ESE.
(work in progress ,,,, )