10 - Building & Testing an RF Amplifier

[@jackhaefner9237]

Hi Nick. I'm working on Pete Juliano's DCR; learning from Tony Fishpool and others about how to test the stages. Your video is very helpful to that end.

[@M0NTVHomebrewing]

Hi Jack! I'm glad you found the video helpful. You can't go wrong with those chaps (Pete and Tony). Happy homebrewing! 73 Nick

[@martsmiscmix]

Nice video, once again Nick, and I too am a fan of the "Julian Ilett Blu-Tack Third Hand"technique!

[@M0NTVHomebrewing]

Thanks Martin :)

[@williamglew2851]

Hi Nick i found a laundry marker pen was a good choice when it came to marking the boards as it as a fine tip

[@M0NTVHomebrewing]

Thanks William. Good tip ... if you pardon the pun! 73, Nick

[@franklewon4646]

In the old days your right would keep you warm! Have you seen any of the 1960's QST magazines? Quality home brew rigs.

[@M0NTVHomebrewing]

Hi Frank, thanks for watching and commenting. Yes, I quite enjoy having a look at some of the homebrew creations that have gone before. There is always something you can learn I find. Best wishes, Nick

[@InteraliaTony]

Hi Nick. Great example of how useful relatively "budget" test equipment can be. Your 'scope has far better FFT than my Siglent bought in 2016 - and of course the TinySA is dead brilliant - also along with great value signal generators from the far east. For cleaning PCB can I recommend a Garryson "gentle abrasive block" (mine is fine - 240 grit). It won't leave nasty bits of wire wool around and it will last so long that you will be passing it down to your grandchildren. Mine was seven quid when I bought it around seven years ago and it has cleaned a lot of boards since then. Thanks for the video. - de G4WIF

[@M0NTVHomebrewing]

Hi Tony, thanks very much. Yes, you can get some pretty reasonable test equipment that doesn't have to break the bank. I may upgrade in time but it all meets my current needs at the moment. Thanks for the tip about the Garryson block - I'll have to check that out too. Hope you're keeping well. 73, Nick M0NTV

[@TheArtofEngineering]

Thank you 🙏 for sharing …. Just started home brewing again! This is most helpful.

[@M0NTVHomebrewing]

Thanks very much. Glad it helped. 73 Nick

[@Paul_VK3HN]

A classic! Only one problem, it is fixed gain, not ideal as an IF amp which you really want to be AGC aware. The Bitx es omit AGC and the after market AGC options all use audio gain control, a compromise. Thanks for sharing!

[@M0NTVHomebrewing]

You're absolutely right Paul. I've built a few of these for my latest transceiver project but I'm forgoing AGC on this occasion. You might be able to vary the gain by varying the voltage that feeds the module but I must confess I haven't tried this. Thanks for taking an interest.

[@groovethaang]

@@M0NTVHomebrewing By coincidence, I built one of these yesterday. Although they are not gain adjustable, they are very useful for compensation in the stages of a RX stage where gain is lost, such as a mixer or a crystal filter. I’m currently using a combination of TIAs and an old IF stage I built in the 1990s using dual-gate mosfets (nostalgic sigh) which are easy to design with AGC on G2. It’s possible to replicate dual-gate mosfets with two J310s in cascode.

[@M0NTVHomebrewing]

@@groovethaang Hi Paul, yes I think they are really useful little circuits. I too have cascaded J310s in an Eamon Skelton design for an IF amp. I had three pairs in mine. It took a while to build but worked very well. Happy homebrewing! 73 Nick (M0NTV)

[@skydm2402]

Fantastic build! Just got my ham license and am digging into some first projects. Thanks for sharing! Can you point me in a direction to a book you recommend to build amplifiers of different frequencies? (HF, VHF, UHF)

[@M0NTVHomebrewing]

Thanks & congratulations! The best suggestion for a book is Eamon Skelton & Elaine Richards’ ‘Building A Transceiver’ Building a Transceiver amzn.eu/d/bUayIuy It’s a great resource. All the best. 73 Nick

[@phitrow]

have you linier parameter this amplifier? Very interesting.. How many gain* on 100 mhz?

[@M0NTVHomebrewing]

Hi! The amplifier was designed to work over HF (

[@UKSimon4170]

W2AEW has just put up a video on making measurements on this amplifier using a VNA.

[@M0NTVHomebrewing]

Thanks Simon. Yeah, it's very good - like everything Alan produces!

[@danielraducu9073]

can i use this schematic for a 27mhz transmitter ? i need a range of 2km for a aeromodel...?

[@M0NTVHomebrewing]

Hi Daniel, you can certainly use it in a 27 MHz transmitter but remember it is a small signal RF amplifier i.e. it is designed to produce milliwatts of power. You'll probably need a few of these plus then a higher power driver amp and then a proper power amp. It largely depends on what power output you need. The idea is to work backwards i.e. start with your desired output power e.g. 5W, then design an amp to give you that. Then calculate what you need to feed the amp to get that output e.g. 500 mW. So perhaps your driver will take 50 mW with a 10dB gain to 500mW and the PA has another 10dB gain to 5W. Then you need to get to your 50mW etc. etc. Building up the power stage by stage lets you build in modules and also helps not to overdrive any one stage. Hope this helps. 73 Nick

[@Musicroombar]

Hello and thanks for good videos I have a question iwant to buy lna module there is some types like 20db gain I know If I put 50mv pp in input I will have a 500mv output but ididnt tested it for 400mv input will I have 4v pp at output on 50 ohm load If not why???

[@M0NTVHomebrewing]

Thanks. If I understand you correctly you are asking why an amplifier rated at +20dB gain might not give the expected output. Your question is a good one and not quickly answered in a comment. If you think of a transistor - it has three areas of operation: 1) the cut off zone where it is not amplifying at all; (2) the linear region where an output is proportionate to the input (e.g. a 3 dB increase in input gives a corresponding increase in output); and (3) the saturation region where the gain is compressed. Once the gain has reached the threshold where it compresses then higher levels of input signal will not produce the corresponding output gains. If you overdrive the transistor not only will you not get the expected gain but it will also be distorted with lots of harmonics. This is usually to be avoided at all costs in RF amplifiers. Depending on how "hot" the transistor is (i.e. how much power it can handle in the linear region) will determine how large an input signal you can put into it and get a clean output. The amplifier in this video is primarily a small signal one so good for most parts of a radio but not beefy enough for the power amplifier stages (at least in it's current form). Check out W2AEW Alan Wolke's KZbin channel and some of these excellent videos: www.youtube.com/@w2aew/search?query=transistor 73 Nick

[@Musicroombar]

@@M0NTVHomebrewingthanks for complete answer.

[@josedasilva4904]

Excellent project!. Thanks for sharing. Is it capable to handle 900Mhz ?

[@M0NTVHomebrewing]

Thanks. I doubt very much you would get much out of it at such a high frequency. Personally I wouldn't use it at more than about 50 MHz as the losses increase substantially from this point. At 900 MHz you'd have to have circuit boards very carefully designed and produced. 73, Nick

[@josedasilva4904]

@@M0NTVHomebrewing Thanks again. All the best!

[@markkennard861]

My only comment is you should have used double sided board so the bottom layer is the main ground. Any grounding should go through the board. Even at VHF you should have ground points all the way through. Give RF a chance to ' take off ' and it will. See you on the dark side.. ( eme )

[@germanjohn5626]

Use a paper cutter to cut boards it is working great and square I found an old one for a couple of bucks at a yard sale. It works like a charm

[@Carl-zg5jd]

Absolutely brilliant thankyou

[@M0NTVHomebrewing]

Thanks very much Carl. Glad it was useful. 73, Nick

[@M0XYM]

Really appreciated. It would be nice to see a whole project - with each module built and tested separately and showing now they are connected warts and all. I seem to trip up at stage-to-stage impedance matching and I would like to see how others attempt the stage connections. Thanks and keep 'em coming. Kevin M0XYM

[@M0NTVHomebrewing]

Thanks Kevin. Yes, I know what you mean about impedance matching. That was one of the things I really struggled with at the beginning. These days I tend to build all my modules with a 50 Ohm input and output Z. This will sometimes mean using a matching transformer or maybe a pi attenuator if you can afford to drop a few dB in order to present a consistent 50 Ohms. That's why the Wes Hayward TIA is so useful. Thanks for the suggestion though. You should also check out Charlie Morris (ZL2CTM) who does exactly what you describe in terms of designing, building and testing. He has a great KZbin site. 73

[@jerryneel1965]

Douou have info on an rf amplifier for 13.56 mhz ?

[@M0NTVHomebrewing]

This amplifier is pretty wideband and will certainly cover 13.56 MHz easily. It is only a small signal amp though i.e. it will produce milliwatts of power. But it is relatively cheap and simple to build and performs very well.

[@obenggetok5693]

For what frequency is that?

[@M0NTVHomebrewing]

Hi there! It is a wideband RF amplifier and this one should cover at least 1 - 50 MHz with a pretty flat gain over this range. I've not tried it any higher or lower than this.

[@hamidbesharati3688]

Hi .is it pussible to amplify a fast edge squre wave (rise time=30ns) with 10 Vp-p to 100 Vp-p and with rise time being less than 60ns?

[@M0NTVHomebrewing]

Hi Hamid, I don’t think so. It’s only intended as a small signal amplifier with a few volts max input over a 50 ohm load. Thanks for watching. 73

[@CreativeHarshRaj]

Can I use this circuit with my 108Mhz FM radio transmitter ?

[@M0NTVHomebrewing]

Hi! Wes Hayward designed it to work in the BitX i.e. an HF SSB transceiver. It will probably work at VHF but with much poorer performance. You'd really want a different amplifier that was designed for the frequency and mode that you are using. 73, Nick

[@CreativeHarshRaj]

@@M0NTVHomebrewing can you please suggest me some other simple amplifier circuit which will work with my radio transmitter

[@M0NTVHomebrewing]

Hi, sorry but I don't have any experience building at those frequencies - I rarely stray above 30 MHz. There should be plenty of stuff out there though. Remember Google is your friend. Hope you find something. 73, Nick

[@CreativeHarshRaj]

@@M0NTVHomebrewing Thanks ❤️

[@hubercats]

Great video! Thank you!

[@M0NTVHomebrewing]

Glad you found it helpful. 73 Nick

[@eugenepohjola258]

Howdy. Nice. I would suggest etching the board. Use ferrochloride (iron chloride) availe from any drug store. Solve it water and neutralize with chalk after use. Cover the copper with adhesive film and cut out the borders with a hobby knife or scalpel. Then drop the board into the solution. Another popular way is to cut a piece of board into 7 x 7 mm or 10 x 10 mm tabs. Then just glue the tabs on the board. Regards.

[@M0NTVHomebrewing]

Thanks Eugene. I've never fancied playing around with ferrochloride to be honest. What puts me off is not just that it is horrible stuff but it is disposing of it responsibly when you've finished. Give me a Dremmel or a MePad and a tube of superglue any day! If it works for you though then all power to you. Thanks for watching. 73 Nick

[@eugenepohjola258]

@@M0NTVHomebrewing Howdy again. Yes. You are correct. Ferrochloride is evil. Gluing pads has another good feature. There will be a continuing ground plane. This is good experimenting with UHF signals. I like Your sketching technique. That step is actually what I have missed. In regards.

[@louiskatzclay]

Thanks!

[@M0NTVHomebrewing]

You are welcome! 73, Nick

[@Greg_Chase]

I offer you a design we built relying on tunable RF. Several of our group have radio, antenna education and work history, both military and in industry. 1) 10 layers of store-bought aluminum foil, each layer separated by a thin insulation layer 2) RF applied via eddy current coils placed radially, and adjacent to (but not touching) the 10 layer lamination 3) the aluminum/insulator 10-layer lamination is positioned horizontally on the workbench 4) the initial RF frequency was 16.28Mhz, due to the skin depth of store-bought aluminum foil 5) a vertically-oriented and axial (through the midpoint) magnetic field is applied through the lamination Vertical B field, and horizontal, radial electric current (induced at 16.28Mhz by the eddy current coils) results in the Lorentz force (right-hand rule, recall), creating coherent accelerations of the charged particles in the metal, at the 16.28Mhz rate. We work at artificial gravity devices, and this was our first design. This is easy work for anyone with an RF background, who is familiar with the Lorentz force. The waves created by the Lorentz force in the metal layers are: - coherent (all charged particles accelerating together, in unison, back-and-forth at the 16.28Mhz rate) - acoustic in nature ('acoustic' does not necessarily mean 'audible' - an acoustic wave is not a transverse wave like a radio wave, an acoustic wave is a *_longitudinal_* type of wave) Later designs adjusted the working frequency, and the dimensions of the 10-layer lamination so that resonant standing waves became possible EDIT: the motive and background for why we settled on this, our first design, is extensive and the physics is not obvious. But one symptom was interesting. One of the very early 'symptoms' we keyed in on, were the huge number of witness reports of radio interference of their car radio when a vehicle was near. We recognized that, since a car radio exhibits the same symptoms driving past an antenna next to a roadway, "aha, the vehicle must be inducing acceleration of charged particles" since that is how EM waves are created, and is a way to create enough RFI/EMI to interfere with car radios. Since the 1940s/1950s reports were filled with this 'interfered with our car radio' symptom, our radio/antenna background told us "the hull is creating noteworthy accelerations of the charged particles in the hull of their vehicle" and the vehicles are creating enough of it to interfere with car radios. Another symptom reported by witnesses can be created by focused beams of RF - see for example "Active Denial System", a version of which was seemingly deployed in the 11/4/1957 Fort Itaipu incident in Brazil. Since we found the tech being developed in germany in the 1940s, we figure after they relocated en masse to south america, they used 'demonstrations' like this to extort money from governments, including the 1965 east coast power grid takedown in the U.S. They were developing EM devices in the 40s that relied on focused EM beams relying on the photoelectric effect. It works on spark gaps - including spark plugs - by creating misfires. It will not work on diesel engines, which have no spark plugs. All the witness reports from gas-powered cars of "our engine shut off" when a diesel operated vehicle was nearby reported the diesel-powered vehicle was unaffected. .

[@M0NTVHomebrewing]

Sounds fascinating Greg. 73, Nick

[@ذكيذكي-ط7ظ]

Thanks

[@eletronicaetelecomunicacoe7821]

Hi from Brazil

[@M0NTVHomebrewing]

Hi to you too 👋

[@RumpaRazz]

Circuit diagram plz sir

[@M0NTVHomebrewing]

The download link to the original article is in the description. 73, Nick

[@multilecful]

Nick, this is where the bitx came from over 20 years ago. You would have to live under a rock not to have seen it yet. Enjoy your experience.

[@M0NTVHomebrewing]

Actually Nigel the original Bitx used a different design for the bidirectional amplifiers. The one I build in the video was adopted by Farhan because of the Wes Hayward and Bob Kopski article of June 26th 2009. I don't know about living under a rock but as I'm relatively new to the hobby I'm discovering all kinds of things that are new to me even if not for others. My aim is simply to give some encouragement to others in having a go at building radios.