50MHz 500Watts Linear Amp Using IRF510

I came across this site with a super design that uses 16 cheap IRF510 power transistors to get 500 Watts of RF power. Now, this is an Ideal amp for hams in India as these transistors are available very cheap over here.

Here is the link to the site. You can find the entire PCB layout, Schematics etc there.

http://frenning.dk/OZ1PIF_HOMEPAGE/50MHz_IRF510.htm

I have put this in my to-do list and in the mean while, i hope you like building it.

Labels: amateur radio, electronics, ham radio, HF, power amplifier, radio, RF, RF amplifier

Bitx20 Version 3 from VU3SUA Construction Notes

I have been building this board from past few days and was searching for some help regarding the tuning parts of various sections. And I asked Sunil to help me with some images, notes and he updated his blogs with a couple of pictures. His blog is available here. When I looked closely, I found that those images and tutorial work was actually done by Leonard L Leeper (KC0WOX). His home page is here. The complete set of instructions he wrote is here. Great job Leonard!!.

Update on 05/03/2008

I couldn't access Leonard's site most of the times for checking up information, So I am just copy pasting the information i found in leonard's page along with the images so that the visitors can see them, basically a mirror.

Bitx20 Version 3

After building a Far Circuits Bitx20 and a Hendricks's QRP Kits bitx20a kit, I decided to build another bitx after seeing this posting:

A new batch of Bitx PCB, in glass epoxy ,masked, roller tinned and with
component place-ment is in ready stock for delivery world-wide.
Also available is the pcb for Avala 01 Sdr monoband tcvr.

I am giving a very special discount on the pbc's. To know further about
the discount, kindly send me a mail at suillakhani123@ gmail.com

I sent off my email and received this back:

Dear Leonard,
The Bitx Version 3 PCB is for $10 PCB +Coils+1 No 2570 transistor.
The Avala sdr pcb is for $5.Shipping is extra $ 10.

I looked at this web page to get an idea what the Avala sdr was and decided that I couldn't pass up a deal like this.

After a trip to paypal, the boards for the bitx and the avala were ordered. Soon I received a package in the mail. In it was 3 pcb's. This was the bitx board along with some of the specialized parts. The other boards were the PA board and the Avala board,

There was enclosed, a schematic, a component layout, and a few other pages of documentation.

After examining them, I decided to make an "exploded" layout drawing using a section-by-section approach to the assembly and testing. I will function test each section as it is assembled. This will almost insure that the board will function when everything is completed. I already had an head start on the project as this would be the 3rd Bitx I had built. I already knew what the signals should look like in each stage.

Bandpass filter section

RF Driver stage

VFO Section

Bandpass filter section

I decided to start with the antenna end and soon I had the following parts placement diagram for the bandpass filter section.

Next I assembled it and connected a sweep generator to the input and my oscilloscope to the output.

After a little tweaking, this was the final result. The scope is displaying from 10mhz to 20 mhz. Each division is equal to 1mhz.

Rf Driver Section

Following my plan to work from the antenna back, the next section was the RF driver stage. It was the next logical section of the board to populate also.

With the drawing done, the next step is assembly, then add a little power, no smoke, that's good, and a signal input.

Then on to test with the scope. 100mv 14.2mhz in, 1.5 volts out. That was open circuit and we probably won't get that when we hook to the PA, but for now, thats a gain of 15. On to the next stage!

VFO section

The VFO section stands on it's own and will be easy to test so I choose that as the next section. A transformer was furnished with the boards but it would have to be rewound as the VFO needed about 9uh's of inductance and the transformer maxed out around 5uh. Depending on the variable capacitor you tune with, the turns on the inductor may have to be adjusted but 50 should be plenty and then you can remove some to adjust the frequency up. My test capacitor tuned from 15-377pf and the VFO had almost a 500khz tuning range so setting the frequency shouldn't be really critical. I didn't tweak the range on mine as I will do that when I install it into a case.

Next I assembled it and connected my oscilloscope to the output. You can see the power connection for the test

I checked it out with the scope. A little over 3.5 volts. This will be less when the transformer is hooked up due to it's loading. There is some distortion of the sine wave so we know there is some harmonic content.

A quick look with the spectrum analyzer to see what the 2nd harmonic looks like.

1 Mhz/div horizontal. The left is 0hz and the right is 10mhz. Each vertical division is 10db. It looks like the 2nd harmonic is down about -25db.

Time to drink a cool one and then pick a new section to do next.

First Mixer section

This section is a little harder to understand. I've included a picture to help show the diodes placement. The colors below are the wire color connections if you use red, brown, and green wire. If you use different colors, substitute them for mine.

We need to wind the trifilar transformers. Use the small binocular cores and wind 13 turns of trifilar wire onto the cores. 1 turn is a trip through both holes ending up where you started. We need 2 transformers. I had red, green, and brown #28 wire. The cores aren't big enough to use larger wire. The original drawing called for #32 but the size doesn't make much difference as long as it will fit into the core. The different colors make keeping the windings straight easier. When pulling the wire through the holes in the cores, be careful not to scrape the insulation off. The binocular cores can have sharp edges. When you are done, it should look like this.

Now you can place them on the board as shown above. The final placement should look like this.

Notice the direction of the bands on the diodes. Make sure the leads don't short together.

2nd IF Section

Before we start installing components, now is a good time to install all of the wire jumpers on the top of the board. It will make testing easier as we will connect to the rx or tx line plus the 12 volt line to power the appropriate circuit during test.

This section is almost identical to the the RF Amplifier section so it shouldn't present any difficulties.

I found a board problem on mine. On the left picture, notice there is no right hand hole for the 100 ohm resistor in the lower left corner. It's easily fixed simply by soldering the right lead of the resistor to the wire adjacent to where the hole should go.

Your board should now look like this.

Lets test it!

Testing the receive side is a problem as there are many frequencies present after the mixer and when looking at them with a scope, it is confusing. Lets look at the receive side using a spectrum analyzer.

Here's some of the frequencies at the input to the crystal filter. It's a good thing that most of these will go away because they won't go through the filter. Part of the reason there are so many frequencies here is because we are overdriving the antenna input circuits with 10 millivolts input. Lets look at what happens when we reduce the input to the mixer. This is normally done by decreasing the RF gain, either with a manual control or agc on the rf amplifier.

This is a reduction of 10db of input signal. That made a big difference. The VFO harmonics are still there but a lot of the mixer products are drastically reduced. Remember, each vertical division is 10db and a reduction to 1/10th of the power. Lets reduce the input another 10db.

That almost eliminated all of the excess mixer products. This is a 20db reduction from the first picture. 20db is 1/100th of the original power or 1/10th of the original voltage so we now have 1mv input at the antenna connector. Under normal operation, that's still a big signal. Our receiver should see signals down to around .3 micro volts.

Labels: amateur radio, DIY, electronics, ham radio, how to, radio

Bitx20 Kit from VU3SUA

Yay!!, I received my Bitx20 kit from Sunil Lakhani(VU3SUA) today. I was jumping with joy as i received it. The postage + the time in transit was very normal. And he had included Front end coils, Balun Cores, Dumbbell cores, and a transistor that is a little difficult to obtain in local shops. He also sent me a free Frequency Counter PCB!!! I love this guy!!.

The boards were of excellent quality, some spacings are some times a little large and some time a little short, but its okay since it is totally designed here. The PCBS were all plated and masked. Very well made I would say.

Here are the contents.
1. 1x Bitx20 Main Board,
2. 1x Power supply and Linear Amp PCB,
3. 4x Front end Transformers (Already wound),
4. 7X Balun Transformer Cores,
5. 2x Dumbbell transformer cores,
6. 1X 2SC2570 Transistor.

The packing was excellent, he had taken utmost care to pack them properly with a polythene cover, then a paper cover (had a contents listing), and a thermocol protection around this cover and then all these covered in the standard cloth based packing used for Speedpost. Yes, I did spend a lot of time unpacking it :).

I will post the photos of the PCB as well as the contents of the kit in this post as soon as I can arrange a digital camera.

So, I am back to building the kit now, have fun :), and hang in there for more.

Labels: amateur radio, electronics, ham radio, HF, power amplifier, Power supply, radio, RF, RF amplifier

ARF448A/B

When my Ham friend Biju visited me last week, he mentioned about a low cost RF power amp circuit using MOSFETs called ARF448A and ARF448B (ARF448A/B). Here is the circuit(PDF File). And the datasheet for the same is available here.


Soon afterwards I started searching for these power MOSFETs and could not find even a single source over here in India. So, I finally came to this person from china who supplies these in bulk. Now the problem is how to buy around 500 pieces of these and how to get it to India without paying exorbitant duties and stuff like that. I am interested in a group buy. So, If any of you readers are interested, we can work something out, Please comment me with the desired number that you are willing to buy and how can you pay me etc. I will soon update this post with the invoice this contact of mine provides.

Lets see if we can have a cheap solid state linear amp for the HF spectrum.

Say good luck, Suckers!!! ;)

Labels: amateur radio, ham radio, HF, power amplifier, radio, RF amplifier

AVALA-01 SDR

AVALA-01 is an excellent monoband SDR (Software defined Radio, PC Controlled) design.
It was designed by Tasić Siniša (YU1LM), a Serbian Radio Amature.
His words. "New mono-band SDR transceiver AVALA-01 is ADTRX-2 transceiver with built in power amplifier and band oscillator all on one board. Transceiver is optimized for work with one sound card and Duncan M0KGK software. With unique PC control setup AVALA-01 is working in all other programs and with all types modulations SSB, CW, DIGITAL....also."

You can get the circuit details here.



You can get the printed circuit boards from Mr. Sunil Lakhani VU3SUA. His blog page with the details are here. Let him know that you have been to my site :).

Labels: amateur radio, electronics, ham radio, radio, RF, SDR

Bitx20 Transceiver

Here, I will explain briefly about this transceiver. This is a design done by Ashhar Farhan, an Indian Amateur Radio Operator and an electronics engineer. It is a bidirectional SSB transceiver. His original design can be found here. This is an excellent 20 meter radio which is quite cheap to build. You can build the entire thing within $15 or around Rs.650/- . You can also find another one of his designs here.

And once this design was released for the public, there were many enthusiasts who devoted their time and tweaked it to perfection. And they formed a Yahoo group called Bitx20. If you are interested in the project, I suggest that you sign up there. You will need a moderator to approve your subscription, but the wait time is negligible.

There are many kit manufacturers promoting this design and you can find some of them here.

QRPKits: A full kit for Bitx20. $90USD.
VU3SUA BITX: Pre wound front end coils and Balun cores, rest of the components has to be bought locally. $8USD or around Rs:300-350 including postage within India. Please contact Sunil Lakhani and he will send you the information required to purchase the board.

Here is a picture of his board.


Or, In case if you like to etch it yourself, the pcb layouts are available within the files section of the Bitx20 Yahoo! group.

So, thats it for today. Good luck on building your Bitx20. Have a good one.

Labels: amateur radio, electronics, ham radio, HF, radio, RF

Dealing with RF interference

Here is a guide that deals extensively into RF interference.

Here you go.

RADIO FREQUENCY INTERFERENCE (RFI) Notes
M.D.Lowell, N1LO October, 1998

Progress: Through July 1999 archive

Check http://www.qsl.net/n1lo.


Another very well documented guide here.

http://www.kyes.com/antenna/interference/tvibook.html

Make sure you make good use of these guides.

Labels: amateur radio, cable, computers, electronics, ham radio, hardware, HF, interference, radio, RF

Build your own Vacuum Tube?

This guy is crazy!!, He even makes his own vacuum tubes!!

http://paillard.claude.free.fr/

The page is in French, but use the Google translator link provided to read. Very interesting video there.

Labels: amateur radio, DIY, electronics, geek, generic, ham radio, hardware, HF, how to, radio, RF

Elektor 1987 20 meter SSB Receiver

Searching out this article took painstakingly long. This was featured under the retronics section in a recent Elektor magazine. Even though they said there is a free download of this article available in their site, there was nothing. It took long hours of search to pull it out from a cache. I am posting it here to save the trouble for any one interested.

Have fun with it people :)

87051u.pdf

Labels: amateur radio, electronics, ham radio, HF, how to, radio, RF

QEX Magazine

There is a good collection of QEX magazines I came across in rapidshare.


Have a look.

http://rapidshare.com/users/Q52ZAP

Labels: amateur radio, DIY, electronics, guides, ham radio, HF, radio

Hack your radio for Airband

Here is a simple hack you can do to your cheap AM/FM radio. With a few adjustments, you can receive AIRBAND (Flight to Tower Comms).


http://www.make-digital.com/make/vol09/?pg=29&u1=texterity&cookies=1

There are dedicated receivers for these and here is one from Elektor if you want to have a dedicated receiver.

http://www.elektor.com/magazines/2002/march/vhf-airband-receiver.55620.lynkx

Enjoy.

Labels: amateur radio, electronics, hack, ham radio, HF, radio, RF

Frequency Counter.

A nice freq counter.

While browsing the web, I came across a cool freq counter that you can add on to your home brewed radio. Here it is.

http://www.cumbriadesigns.co.uk/kits.htm

Enjoy!

Labels: amateur radio, DIY, electronics, ham radio, HF, radio, RF

Hooked on to Amature Radio.

The radio bug bit me again....

I have been modding, tuning many radio circuits these days to (mis)use them for other purposes ;). So the thought flashed again, why not take up the Amature Radio Exam and get a call sign and home brew a transceiver. So I am on it from the past few months. The biggest issue, is learning Morse code. One of the main criteria here to pass the ASOC exam.

Here are the details of the stuff I am using to learn for the Exam.

ABCs of Amature Radio, EFY Publications Rs: 75/-
G4FON Koch Morse code Trainer. (Free)

I have setup a 40 meter band simple dipole antenna. I will post the image, and constructions details here later.

Labels: amateur radio, electronics, ham radio, HF, radio, RF