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Re: modulator mod
Arv Evans
Allison
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Would it be possible for you do a quick schematic of the changes and store it in the FILES section of this forum? That way it will be available for others who might not understand all that was changed from just the textual description. Thanks, Arv K7HKL _._ On Thursday 28 July 2005 09:20 pm, ajparent1 wrote:
One of the things I didn't like in the 20m proto BITX I'd built |
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modulator mod
ajparent1
One of the things I didn't like in the 20m proto BITX I'd built
was the presence of audio getting into the IF amp on transmit and IF noise in to the audio on recieve. I'd gone the route of adding an 47uh RF choke from the intersection of the balance pot wiper to ground which helped greatly. However, it always bothered me. So I opened it up and tried a design change that I find pleasing and also elimiates a number of components. As an engineer I'm the sort that looks at a design and says "what if..?". The solution was staring me in the face and also eliminates the PI attenuator as well. The change is to turn the balanced modulator around and feed the IF in on the transformer and RF (bfo) in at the balance potentiometer via the .1uf capacitor. This eliminated the need for the 3 resistors and the rf choke. I noted cleaner modulation, less RX noise and more gain available in both RX and TX. Might as well add this mod to the collection. I plan to use this mod in the 6M version. Allison KB1GMX |
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Re: Pre driver output
ajparent1
Hi,
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2mw is very low from the driver. Mine I see nearly 1mw at the output of the bandpass filter (L1, L1,L3). The driver stage brings that up to near 300mW on mine. I don't use the IRF510 as the output is more than sufficient to drive a TenTec 1208 transverter at 100mW, 1mW however was not adaquate. Driver transistor used on mine was 2N2219A with bifilar transformer wound on a 2 hole core of -43 material to match 50 ohms. Without the 5db output attenuator it measures as 3.8V rms across 50 ohms which is actually 288.8mW using a HP rf voltmeter. Thats close enough to 300mW. If you are using a trifilar transformer on the driver and measure the power to the IRF then the driving impedence is around 10-12 ohms and a 50ohm power meter will be inaccurate. Even then I'd expect to see about 1.7-1.9V of rf at that point. In any case 300mV is invalid. The gate of IRF needs to be driven with several volts of RF to develop expected power without instability. On mine the Q14 (predriver) device is 2N2222A and driver is 2N2219A both have FT ratings of 350mhz which is adaquate to get good gain at 14mhz. Measurements at the output of the filter (at 50ohms) is .9-1mw. After Q14 I get 40mW. Adding the driver brings that to 300mW. I used ferrite loaded transformers at T1, t2 and T3 as well as collector of 2n2219A. Also added a choke coil (DC return) at RF mixer (100uh molded type) and at modulator. Transistors used are Q1,Q13,Q7 are 2n2222A, Q2,3,12,11,9,8,10 are all 2n3904. This version uses a different VFO (Hartly with fet buffer). All circuits are bypssed with more than shown is schemtic and some sections are shielded (modulator and bfo). Construction is dead bug (ugly on ground plane OF unetched PCB). A newer version is being built that will use a PLL to provide LO and the output will be for 6m using 9.6mhz filter, 40mhz LO and I may try commercial DBM (anzac MD108) for both modulator and mixer. Since this one is to be small power will be limited to around 3-5W and use a RF transistor 2sc1971 for the final. More information than asked for but, measurements are how I know a circuit does indeed perform as expected. Allison --- In BITX20@..., "vdberghak" <vdberghak@z...> wrote:
Hi Milarepa, |
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Re: Pre driver output
Hi Milarepa,
based on my measurements, it is only a few mw, so the oposite of what Allison measured. I searched for you in the older postings (I have often the feeling that older messages are not red) and you can find my answer in message 375 (containing a mistake) and 387. Good luck, Chris. --- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote: Based on my proto 300mW is correct. If there were 300mV the powerof pre driver should be about 300 mWatts, |
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Re: Pre driver output
ajparent1
Based on my proto 300mW is correct. If there were 300mV the power
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would be about 2mW which is way to little. Allison KB1GMX --- In BITX20@..., "MILAREPA" <MILAREPA@T...> wrote:
Dear forum, |
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BITX PA
Folks
I am working from the (c)2004 circuit on Ashar's web page and have very low output from PA. I am using cheap general purpose transistors (ME4003) and changed pre-driver for 2N2222. Better but still only about 1W out. I have used a very similar PA in the TCF transceiver by VK3XU and it works fine. That is on 40m though. I have read through previous postings and applied mods by Chris, PA3CRX. I now have full 6W output. Well done Chris! I see Ashar has adopted the trifilar transformer and the extra 200pF capacitor in his simple dual band transceiver design. Is there a definitive revision, or is it a case of 'suck it and see'? 73, Steve, G0FUW ___________________________________________________________ Book yourself something to look forward to in 2005. Cheap flights - Bargain holidays - |
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Pre driver output
MILAREPA
Dear forum,
I have read somewhere from the posting messages that the output of pre driver should be about 300 mWatts, but I read from the article it should be about 300 mVolts. Which is right ? ------- I begin to test the tx section, rx section test is good in 3.5; 7; 10; 14 MHz. ------- Thanks. |
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Re: need help for vfo
ajparent1
Hi Chris,
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Rather than guess at Gautams question it is easy to ask. Saves giving multiple conflicting answers. I may add my favorite "cheap" Varactor [tuning] diode is 1n4007 rectifier. It also makes a fair substitute for a PIN diode in switches and attenuators. Not as good as the real thing but far less cost. Allison KB1GMX --- In BITX20@..., "vdberghak" <vdberghak@z...> wrote:
Hi, |
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Re: IRF510 on higher voltage?
Rahul Srivastava
Hi!
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Arv is quite right. Here we also took a similar route. First was the need for a cheap common PSU so we selected a portable BW TV transformer sec abt 20V AC unloaded around 1.25amp. Unreg DC goes to IRF.
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Later I realised that 2N3866 is 24V device so I gave it unreg DC too on collector thru a simple choke on the binocular cores abt 9-10turns. Emitter resistor 10ohms, base to gnd 2k2 and base to 12V TX for bias 10-12K. The collector director?drives the gate via a 0.1 cap?of IRF530. Current drawn is abt 1amp now and power more than 12W.
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Incidently the Mousefet series of TX also drive the power fets in similar manner.
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Rest of the ckt is powered thru reg 13.6VDC by a LM317 as evident from my linear board layout. This scheme of 3866 on unreg DC also reduces some load on 317.
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BTW I have stacked 2-3 nos of tap washer for LPF, the number of turns for required inductance is less and more manageable.
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73
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Rahul VU3WJM
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Arv Evans wrote: Chris
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Re: need help for bitx VFO & BFO
Arv Evans
Gautam
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I am assuming that you are using the same size VFO inductor and capacitors as specified by Farhan. If you are using the original design with the 36V zener diode as a VFO fine tuning capacitor, you might try a different diode. They do not all show the same capacitance value or range. If this does not work, it is possible to use other diodes in place of the zener. My BITX20 uses a Red LED as the tuning diode. It is possible that you have connected the tuning diode using the wrong polarity. Try reversing it to see what the results might be. Since the tuning diode contributes only 10 pf, it can be disconnected temporarily and the VFO tested without it. If you do not have a way to measure capacitance, the value of your variable capacitor can be measured using the simple capacitance test circuit shown in <>. This might help to verify that your tuning capacitor is really 365 pf. With the capacitor completely open it should measure less than 20 pf. Arv K7HKL _._ On Saturday 23 July 2005 09:08 am, ajparent1 wrote:
gautam |
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Re: need help for bitx VFO & BFO
ajparent1
--- In BITX20@..., kumar gautam <fromgautam@y...> wrote:
Hello,gang capacitor my VFO shows 4.000 to 4.180 MHz(when trimmer shifted to 4.000MHz) and after tuning Trimmer(shifted to 4.150MHz) it shows 4.180 to 4.410Mhz. After trying various type of variable capacitors i coul'd not findentire range i.e. 4.000 to 4.400MHz. Kindly help me in this regard i.e.Varies depending on the crystal filter characteristics. Ideally it should be tuned to 300hz down the lower frequency edge (assuming upper sideband) of the filter slope. To do that precisely you have to know the filter shape. The alternate way is to listen to good signals and start with the bfo low and tune it up for natural sounding recieve signal. Then there may be some fine tuning of the BFO once you have a QSO for best TX sound. 2. What modification should i do for correcting the VFO.Try fewer turns on VFO coil. The tuning diode the 22pf capacitor connected to the tuning diode may need a slight increase in value. also could i connect T1,T2 and T3 legs in any direction or it isconeected in any direction. ?? I am not certain what you are asking. Allison KB1GMX |
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Re: need help for vfo
Hi,
I think the tuning range is found to be to small. Likely because the tuning capacitor does not have enough capacitance. (the LC combination defines the frquency and if the L is fixed, only the C can be responsible?). If there are more capacitors inside the housing, just connect them also. Otherwise an other type of capacitor is needed. An other possibility is to have the range in two bands, by switching an additional capacitor in parallel. Regards, Chris. --- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote: Hello,wrote: orhi,trimmer i found 4.200 to 4.430 (i.e 0 to 0.230 MHz tuning range). 2x type) i coul'd not achive the desired frequency. i used 2n2222a |
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Re: need help for vfo
ajparent1
Hello,
First the transistor used. The 2n222a or 2n3904 are excellent for this type VFO. I have tried to understand what problem you are having. I suspect the range of tuning 0-230khz is either too small or too great for you. The ability to adjust the frequency using the trimmer says the coil and other components are close. Allison KB1GMX --- In BITX20@..., kumar gautam <fromgautam@y...> wrote: hi,trimmer i found 4.200 to 4.430 (i.e 0 to 0.230 MHz tuning range). aftyer several changing in coil and various types of capacitor(2j or 2x type) i coul'd not achive the desired frequency. i used 2n2222a transistors for VFO and BFO and for rest 2n3904. kindly anyone help me in this regard |
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need help for vfo
kumar gautam
hi,
in my bitx20 vfo frequency is 4.000 to 4.230MHz or trimming the trimmer i found 4.200 to 4.430 (i.e 0 to 0.230 MHz tuning range).?aftyer several changing in coil and various types of capacitor(2j or 2x type) i coul'd not achive the desired frequency. i used 2n2222a transistors for VFO and BFO and for rest 2n3904.
kindly anyone help me in this regard?
with 73's
de kumar gautam
Free antispam, antivirus and 1GB to save all your messages Only in Yahoo! Mail: http://in.mail.yahoo.com |
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Re: need help for IRF540
Rahul Srivastava
Hi!
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Go ahead with 540. Let me know someone coming this side 510 is available at Lucknow.
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73
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Rahul VU3WJM
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kumar gautam wrote:
NEW - crystal clear PC to PC |
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FW: Re: IRF510 on higher voltage?
ajparent1
Hello Hans,
I do hope you got my initial response. The blocking may be enroute, it's not anything I can control. Do try to reply to the arrl.net address rather than direct. High power (greater than 20w or so) solid state amps are not trivial design exercises. As a result experiments can easuly destroy transistors. This is why the IRF510 became so popular, they are inexpensive (compared to true RF power fets) and work acceptably. I do not know the PL5xx Valves but I will assume they are not unlike the US Television sweep tubes. Typically those tubes are rated for 30-40W plate dissipation or around 80w for intermittent SSB service. These tubes are related in design to the famous 6146 final valve used in a large number of transmitters. Running them hot (plates glowing) is not good for their life or quality of signal. It would be better to run several in parallel and abuse them less. Also running higher plate voltages 500-800v will give a better signal and easier plate matching. A suitable mains transformer is always troublesome to obtain but it's possible to wind one. There are sites that discuss this and it's not unreasonable. Finding used equipment that can donate a transformer is another path.. Good luck, Allison KB1GMX (@arrl.net) --- In BITX20@..., Hans Summers <Hans.Summers@t...> wrote: simpler and suitable for many people with no microcontroller etc skills. ThoughI built a microcontroller-less DDS: valve linear for quite a while. I have accumulated more than sufficient number ofPL519 / PL509 TV sweep valves - there are several designs on the internetproviding for 400+ W using four PL509/519's paralleled. Very cheap andreliable. What I am lacking is the HT transformer. I quite liked Arv's idea of a solidcabinetted! makes the idea even more expensive. From what I hear, those PL5xx sweepvalves are virtually indestructible, even if you make them practically red hot.RX at: to QRO either, just so long as it's homebrew. I've never touched acommercial rig and gonna keep it that way!finished yet, some trouble with the crystal oscillator multipliers. Needs a bitmore work. time ideas!to work on it at the moment. The pictures are in the G0UPL folder onHello Hans, turn itI was thinking of using this PSU with switching, as a variable thoseinto a solid state linear? 50V should suit MOSFET's quite well for which tocaps elsewhere which would leave quite a lot of space, I think enough morefunction as front panel for metering, low pass filter switching, etc.Opinion, doing that would represent the hard way with limited success. designs for RF power use known RF transistors (bipolar or fet) that areare fast enough to operate at RF but Miller capcitance and input capacitancefollow. down from 400W. Generally parallel devices are touchy and each has todid Also yousome googling but didn't manage to find anything particularlyYes they do but, not for common HEXfets or other low cost power fets. can find some of the appnotes on the net. However, nonefoward and well documented. A 3-500 or 4-400 in grounded grid with 2000V onand the FETs may destruct on power up it's not too hard to visualize.tubes(valves). may add that I prefer VHF and up for my experiements. |
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Re: need help for IRF540
ajparent1
Hello,
That IRF540 will be very difficult to drive with increasing frequency. The input will be very reactive and will require a more complex network to get the needed RF power (and voltage) impressed across that gate capacitance. That takes greater power and the driver may not be up to the task. A first order calculation says driving impedence will be 1/10th (.1) times that of the IRF510. None of the input or output networks used will perfom as well with the irf540 due to it's differences. At 80m this will not be as bad as 20 or 10m. I'd try it but do not be surprized if the results require redesign to achive adaquate gain. If you are successful you may be rewarded with greater power than the IRF510. A scratch evaluation suggests if accomodated the IRF540 could be capable of 60-80w output with about 4-5W drive at the lower HF frequencies aassuming it's not bandwidth limited. There are several parameters to look at besides those quoted. Gate turn on voltage (lower the better). Output capacitance as well as Drain to Gate capacitance are also functional parameters of importance. The drain to gate capacitance is can be thought of as a negative feedback capacitor from Drain to gate and limits gain with increasing frquency. The result is that you need to feed both the gate and extract power from the drain at low impedences or the implied feedback will reduce gain to below zero (less out that in). At 20m these will look like around 7 and 2 ohms for the IRF540 where the IRF510 they are around 65 and 10-12 ohms. Accomodating these new conditions were not anticipated in the original design. I hope this gives a starting point to a successful design. Allison --- In BITX20@..., Heinz Schnait <oe5eep@q...> wrote: Hi Kumar,as if the 540 has more junctions wired internally in parallel. This is also540. I am afraid this might cause problems for the gate driving circuit,especially at higher frequencies.some experiments with a IRF540 replacement? Please share your results!SUBSTITUTE THIS FET. WITH 73'S |
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Re: need help for IRF540
Heinz Schnait
Hi Kumar,
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The datasheets give the following parameters: IRF510: RDS = 0.54 Ohms; ID(continous) = 5.6 A; maxPower = 43W; Input capacitance = 180 pF IRF540: RDS = 0.077 Ohms; ID(continous) = 28A; max Power = 150W; Input capacitance = 1700 pF The IRF540 is a more robust version than the IRF510. It looks to me as if the 540 has more junctions wired internally in parallel. This is also reflected in the input capacitance, which is much higher for the 540. I am afraid this might cause problems for the gate driving circuit, especially at higher frequencies. Is anybody out there with a working IRF510 amp who would like to do some experiments with a IRF540 replacement? Please share your results! 73 Heinz, OE5EEP Am Freitag, 22. Juli 2005 07:33 schrieb kumar gautam: HI, |
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FW: Re: IRF510 on higher voltage?
Hans Summers
Apologies list, for the bandwidth - I am having some trouble emailing
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Allison on private email. Seems I am blocked somewhere :-( 73 Hans G0UPL -----Original Message-----
From: Hans Summers Sent: 22 July 2005 15:40 To: 'Allison' Subject: RE: [BITX20] Re: IRF510 on higher voltage? Hello Allison I love Huff & Puff. These days DDS is so easy, but H&P is still simpler and suitable for many people with no microcontroller etc skills. Though I built a microcontroller-less DDS: Thanks for the advice. I actually have been planning to build a valve linear for quite a while. I have accumulated more than sufficient number of PL519 / PL509 TV sweep valves - there are several designs on the internet providing for 400+ W using four PL509/519's paralleled. Very cheap and reliable. What I am lacking is the HT transformer. I quite liked Arv's idea of a solid state linear because the PSU is there, all ready and waiting and cabinetted! Thanks for the links, I had a good look around. You're right, it doesn't look very cheap. The very real possibility of frying the transistors makes the idea even more expensive. From what I hear, those PL5xx sweep valves are virtually indestructible, even if you make them practically red hot. All of my ham stuff to date has been at 10W or below. See my TX and RX at: I had my first ever QSO in March 2002 (a mere 8 years after getting my license!). I've had over 500 QSO's now, all using that 1-valve crystal controlled CW transmitter. Mostly on 80m, but also on 40 and 30 once I'd converted the transmitter for those bands. I'm not a committed QRP'er, I like to operate QRP but I'm not averse to QRO either, just so long as it's homebrew. I've never touched a commercial rig and gonna keep it that way! I did make a 2m AM handheld see - it's not finished yet, some trouble with the crystal oscillator multipliers. Needs a bit more work. Tnx again for the advice and links. 73 de QTH nr London, UK Hans G0UPL -----Original Message----- From: Allison [mailto:ajp166@...] Sent: 22 July 2005 13:30 To: Hans Summers Subject: Re: [BITX20] Re: IRF510 on higher voltage? Hans Summers wrote: Hi AllisonHello Hans, I have built and experimented with you milimal H&P circuits. Good ideas! I was thinking of using this PSU with switching, as a variableOpinion, doing that would represent the hard way with limited success. To get to 400W is a significant endevor and trying with unknown RF performance power fets is likely failure prone. All of the 100W or more designs for RF power use known RF transistors (bipolar or fet) that are expensive (.5-2$/watt US). Most of the high voltage switching FETs are fast enough to operate at RF but Miller capcitance and input capacitance will make themm very hard to drive at HF especially 10M. I may add that the IMD performace for IRF510 and friends is terrible and that translates to RF polution. They were not developed for linear service, they were intended as power switches. The other thing is the TO220 tab cases have poor thermal dissapation. That makes getting thermal stability hard. IF you were into AM phone, it's possible to use switching fets in a class E design (Not FOR SSB). There are several here doing that with power to 1.5KW. There are websites that discuss this. Now, if you really still up for the idea.. Heres a possible path to follow. Expect to use parallel devices (seperate bias for each device) in push pull configuration. You will need to accomodate the very high (800-2000pF) input capacitance and low impedences involved. Expect elaborate groundplanes and input/output transformers with quality ferrite. A design of four IRF510s in pushpull (pairs of parallel devices in pushpull) might get you to 80-100W at 24V or about 1Sunit down from 400W. Generally parallel devices are touchy and each has to be biased independent of others. So, I wondered what you thought of this crazy idea, and can youYes they do but, not for common HEXfets or other low cost power fets. DEVICES like MRF140 and the like are used and they are not inexpensive. Typical Vdd for these parts is in the 50V region (at up to 20A!). Start with this site: Comm Concepts sells kits for power amps based on Mototrola app notes. Browse the site for examples, schematics and some of the apnotes. Also you can find some of the appnotes on the net. However, none specify low cost fets and likely would not support low cost power fets. Also, what is your opinion about valve vs solid state? It seemsSimple, valve designs using obtainable valves are fairly straight foward and well documented. A 3-500 or 4-400 in grounded grid with 2000V on the plate will easily hit 400W for 80-10m. A pair of 811/572B are in the same league as well as a long list of other Valves that maybe had used or surplus. Why Valves(tubes)? They are known, durable within experience of most hams and often can be had inexpensively. When you consider a 3-500Z can often be had new for around 150$us and MRF150(x4) will cost 200$us and the FETs may destruct on power up it's not too hard to visualize. This outfit sells RF power transistors and other items like tubes(valves). While I've done commercial work at high power I choose to do most of the ham activity at under 20W. My unusual twist on that is my station while low powered is supported off of solar pannels and batteries. I may add that I prefer VHF and up for my experiements. Regards, Allison KB1GMX |
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need help for IRF540
kumar gautam
HI,
HERE IN?MARKET IRF510 IS NOT AVAILABLE, ONLY IRF540 IS AVAILABLE. ANY ONE HELP ME THAT IRF540 IS EQUIVALENT OF IRF510 OR I CAN SUBSTITUTE THIS FET.
WITH 73'S
DE KUMAR GAUTAM
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