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Monday, October 21, 2019

Farhan Visits Northern Virginia and SolderSmoke HQ

Our good friend Farhan came to Northern Virginia last week for the 50th Anniversary Symposium of AMSAT.   We were really delighted that he also came to SolderSmoke HQ.  Elisa and I gave him a lightning tour of Washington DC (including a quick visit to The Air and Space museum) and then we headed back to the shack from some radio work. 

In the picture above you can see my BITX-20 (that Farhan designed) off his right shoulder.  Off his left shoulder you sits my ET-2 rig.  I really wanted to show Farhan how well the N0WVA regen performs -- he was impressed, especially when we started listening to SSB contacts. It was really amazing that we were doing this with just one J-310 FET.  This was great fun.  Farhan tells me that he will soon take up the "two transistor challenge."

When he was here in 2017, I tried to demonstrate my version of Rick Campbell's R2 Direct Conversion receiver.  Unfortunately, when I tried to show off the "single signal" capability that is the whole purpose for this receiver, it was NOT producing a single signal output -- you could hear the signal on both sides of zero beat.   One of the small AF chokes I had used had gone open, knocking our one of the two DC receivers.  This time I had the problem fixed and single signal reception was successfully demonstrated.  

Farhan brought me two pieces of test gear that I have needed for a long time:  A step attenuator and a two tone generator.  Paired with his Antuino, these devices will bring about a big increase in capability on my bench. 

It was really great to have Farhan in the shack.  We had a great time talking about ham radio and homebrewing.  Elisa and I both really enjoyed hearing from Farhan about his travels and about his life in India.  We are all really lucky to be in the same hobby as Ashhar Farhan. Thanks for the visit Farhan.

Here is a quick video of Farhan tuning the BITX 20.  


Saturday, October 19, 2019

QSO #3 with the ET-2 Minimalist Transceiver

The Radio Gods were clearly supporting me on 16 October 2019.  I had sent out a plea for people to listen for the 80 mW CQ from my ET-2 rig.   I had specified 0930 Eastern as the time.  Little did I know that there would be a contest at that hour (on a Wednesday morning!) on 40 meter CW.  There was no chance of my signals getting through.  I leaned that the contest would be over at 1000 hours, so I waited and called CQ again at that hour.  Jim W1PID had guessed that I would do that.  I immediately recognized his call -- he was often at the other end of Michael Rainey's most daring low-power adventures.  He was a participant in the famous Rexpeditions, including a coastal effort to send Michael's voice-powered CW signal across the Atlantic.  His normal operating habitat is in the field.  We had a wonderful QSO.  He told me I peaked at S-6.  

I have worked W1PID on at least two Straight Key Nights and this blog has had many postings about his long-standing involvement in QRP. 

Thanks a lot Jim! 
 


Tuesday, October 15, 2019

Please Listen for My 80 Milliwatt CQ Tomorrow, Wednesday 16 Octoberr

I will be calling CQ from Northern Virginia starting at 1330Z (0930 Eastern) on Wednesday 16 October 2019 on 7038.6 kHz with my ET-2 QRPpp rig.   I have made two contacts so far -- both contacts were at a range of about 300 miles.      I'd like to be able to make at least one per day.   If you are within range please listen for my CQ tomorrow and give me a call.  

Thanks and 73  Bill N2CQR

Monday, October 14, 2019

The First Sunspots of Cycle 25 -- Explained by Space Weather Woman (Video)



Dr. Tamitha Skov explains how Cycle 25 has begun while Cycle 24 is not quite finished. 
She has a very clear way of presenting the space weather.  Very useful. 

YouTube site: https://www.youtube.com/channel/UCkXjdDQ-db0xz8f4PKgKsag

Sunday, October 13, 2019

More on the ET-2 : Better Pictures and More Circuit Description. Some Thoughts on Simplicity


So yesterday I made my first contact using my ET-2 rig.   Last night I got an e-mail from Gary, the fellow at the other end of that contact: 


Evening Bill, N2CQR….Yes I did learn about you from the spot on the DX Summit cluster. I tuned to the freq to see if I could even hear your 80 mW and you were a good real 569 when calling CQ.  You built up to a real 589 on the later transmissions. I did not have either of the two pre-amp positions on in the ICOM 756 Pro II. There was not any QRM on the freq either. Your spot indicating the 80 mW is what really got my attention.

My antenna is a 2 element yagi at about 115 ft and it really works great for me.

Thanks for the picture of the great little transmitter. Glad to be your first DX QSO with it. Hi Hi  Maybe again soon.  My pleasure to work you.
73, Gary, K4MQG
Fort Mill, SC

Farhan commented on yesterday's post, saying that it was hard to tell (from my pictures) where he rig started and ended.  He was right.  So this morning I have tried to clean up my bench a bit -- I hope these pictures are better.  

Above you see the whole rig.  The transmitter board is right next to the key that Farhan gave me.  You can see the 7040 crystal.  A C-Clamp holds to the bench the piece of scrap plywood that serves as the base for this rig.  Next to the C-Clamp you see the TR switch -- the just switches the antenna -- both transmitter and receiver are powered at all times.  I can hear the transmit signal in the headphones and this serves as my sidetone. 

Here is a close-up of the transmitter with the schematic below: 

 

The transmitter is VERY simple.  Nine parts, including the low-pass filter.  You can barely see the J310 FET to the right of the crystal. 

Here is the receiver:


I really like N0WVA's regen.  The green diode in the source circuit is the key.  This one does not squeal when you go into excessive regeneration (when you think about it, regens should NOT squeal at audio frequencies -- but most do).  Also, the green diode dims a bit when you are at the right amount of regeneration.  In the picture you can look down the tube of the variometer that Pericles HI8P gave me many years ago.  The big variable cap is from the junk box -- I think it may be from a Johnson Viking transmitter.  Note the long shaft with the insulating connector -- this is to reduce the hand capacity effect.  On the right you see a smaller cap with just one vane -- this is my fine tuning control --- with the smaller cap at mid range, I would just set the big capacitor to put the receiver at 7040 -- with the smaller cap I could tune +/- 12 kc.  I also used an insulating shaft on the smaller cap -- the connector for this one is from an old 1930s era regen that I picked up at the Kempton Part rally in London.

Instead of the audio transformer and Radio Shack headphones, I just used some old DLR-1 WWII Headphones.   They are very sensitive and work well. 

Lots of soul in this new machine:  The variometer from Pericles.   The WWII headphones.  The 1930s era shaft connector.  The circuit idea from the Autumn 2001 SPRAT.  Farhan's key. 

I recently read on Hack-a-Day of a new FPGA chip that has on it 35 BILLION transistors. I'm sure that thing can produce some fascinating results, but can anyone really understand it, or feel that they really BUILT something that has that kind of chip at its center?   On the other hand, I did rely on a lot of modern digi technology in this project:  The Reverse Beacon Network reported back that my unanswered CQs were in fact getting out (one as far as Kansas to K9PA).  And in the end I had to ask -- via the DX Summit Spotting cluster -- for someone to listen for me.   So I can't go full Luddite here.  And I wouldn't want to have to use a rig like this simple every day.  No way.  It is just too hard to use. But there is a beauty and a challenge in simplicity.  There is some virtue in using just two transistors instead of 35 billion. 

Thanks to N0WVA, W2UW,  VU2ESE, HI8P, K4MQG, The G-QRP club and their inspirational journal SPRAT, the RBN and the DX Summit. 

Saturday, October 12, 2019

Success with my ET-2 --TWO TRANSISTOR RIG


In my effort to replicate the ET-1 rig of Glen Yingling W2UW, I had a hard time getting the receiver to work well with the single FET being switched between receiver and transmitter, so I retreated a bit and went with individual FETs for the TX and the RX.  This doubled the transistor count -- to TWO.  So it is an ET-2.

I also boosted the power to 80 milliwatts by putting 12 V on the transmitter.  The receiver was running off the 9V battery you can see in the left in the picture. 

Here is the story of the contact: 


To K4MQG from N2CQR:
Gary: Wow thanks for the QSO today.  I was using 80 mW transmitter that consists of just 8 parts!  The receiver was a regen using one single transistor.  So one transistor on transmit and one transistor on receive.  And it reached South Carolina.

I was about to give up hope.  I had been calling CQ for days.  Then I was talking to Rob VE4GV on 20SSB.  Rob suggested that I "spot myself" on one of the DX clusters.  So I did (see below).  Obviously you saw my spot and a minute or so later, SUCCESS!   I'm really pleased.

Attached is a picture of the rig.  The transmitter is around the crystal and the blue pot on the right.  The headphones are from WWII.  The receiver was powered by the 9V battery.  The regen uses a variometer given to me by a friend in the Dominican Republic in 1992.  The main tuning dial is connected to the cap by an adapter from a 1930s-era regen.  Antenna was a 40 meter dipole at about 25 feet.  Obviously your 3 elements a 115 feet were doing the heavy lifting.

Thanks again Gary!

And thanks to Rob for the suggestion on the spotting.

73  Bill N2CQR





The BGCD: A Regenerodyne Receiver built on Pencil, Candy, and Tea Tins. Circuit from 1937 QST


David Newkirk recently put up a nice website on ham radio.   The page below provides details on the amazing creation pictured above:  The BGCD:   "The Byron Goodman -- Clinton DeSoto Regenerodyne." It is a beautiful piece of work, made more beautiful by the metal containers used in construction: pencil, candy and tea tins.  The circuit is based on a 1937 QST article. 

David's site reminded me of the wonderful writing of his father, Rod Newkirk of "How's DX" fame.   More on him in due course.

More on the BGCD here:

http://dpnwritings.nfshost.com/ej/pictures/pictures1.htm?fbclid=IwAR2-lmJ8E1kEBT_jsB3Q8UnPaN0vc472dP783ifABK7eSxgpe5M1Pl0N77g




Wednesday, October 9, 2019

Very Useful: Copper Tape with Conductive Adhesive

This copper tape is really useful, especially when doing "free style" homebrew.  At first I didn't even realize the adhesive is conductive.  This tape is great for creating a common ground among several printed circuit boards, especially when you are using a wood board as the base.  You can solder to it very easily.  You could even use it (with a wood or plastic base) in lieu of a copper clad board. Lots of possible applications for homebrewers. This stuff deserves a place on the workbench shelf right next to the Gorilla Tape and the Crazy Glue.   I'm using it in my Single Transistor Rig project. 

You can get it from Amazon -- there are many varieties and vendors.  This one is similar to the one I am using.  

https://www.amazon.com/dp/B01I1XNY1E?aaxitk=I9X2Na8Gu23M3nrhlpSzYw&pd_rd_i=B01I1XNY1E&pf_rd_p=44fc3e0f-4b9e-4ed8-b33b-363a7257163d&hsa_cr_id=3252618550401&sb-ci-n=asinImage&sb-ci-v=https%3A%2F%2Fm.media-amazon.com%2Fimages%2FI%2F71sJrx27%2B-L.jpg&sb-ci-a=B01I1XNY1E

Tuesday, October 8, 2019

Analog Waterfall -- The Hallicrafters Skyrider Panoramic


We were talking about this a short time ago.  I was trying to reproduce the effect using my Rigol oscilloscope and my Feeltech scanning signal generator.  Hallicrafters did a much better job.  Thanks to the K9YA Telegraph for this picture. 

Monday, October 7, 2019

Organic Electronics


This made me think of the OLED screens.  But they are not, as far as I know, gluten-free. 

This guy would probably be a QRPer, probably running an HW-8 off solar panels. 



Friday, October 4, 2019

Single Transistor Transceiver On the Air

I got my version of the ET-1 transceiver working.  As I described in previous posts, I first got the transmitter and the receiver working separately, each with their own J310 FET (oh the extravagence!) Then I built a switching arrangement that allowed for just one shared FET and very short leads.   I used a 4PDT "push button" switch from an old Ramsey Electronic LC meter. See the last picture for details. I use the tube from a pen to operate the switch (that's the green thing in the picture). 

It is inhaling and exhaling.  My 20 mW signal is being picked up on the Reverse Beacon Network, mostly in New England, but today in North Carolina.  

No contacts yet.  I may have to resort to scheduled contacts.  OM Yingling W2UW was operating during much better propagation conditions (2001), so I don't think I will ever get close to his impressive (23 states!) operating record.  

But it has been fun getting this thing going.  The N0WVA regen design is one of the best and simplest regens I've ever built.  It is really nice --hardly demonic at all.  

I can run the whole thing off one 9V battery. I think it is a cool looking machine. 



Thursday, October 3, 2019

The Collins Mechanical Filter -- An Advertisement from Australia, 1963

Peter VK2EMU sent me this ad a while back.  He said he regretted being unable to send a filter -- all he could send was the ad.  Thanks Peter -- I think that ad is a work of art.  Radio art. 

Thanks too to all those who sent me mechanical filters.  Pete sent the first one (it is currently in my HRO-ish receiver), then two more (both inside SBE transceivers, where they will remain -- it would be a sin to cannibalize those beautiful rigs.)  Then Mike Herr WA6ARA sent one as did Brad.    Brad assures me that the one he sent was boxed up by Art Collins himself! 

Thanks again guys. 

Brad wrote: 


To:soldersmoke@yahoo.com
Jun 23 at 7:49 AM

Kudos to Pete for 60 years! And I've always thought he was much younger than you......

Catching up on your podcast, I was surprised to learn that no one answered your call for a spare filter.  

I'm one of those older guys who is making his way back after leaving amateur radio in 1968 for girls and/or recreational drugs.

No one told me that The Force (electro-motive, that is) would require me to catch up on all the junk I would have acquired during my nearly 50 years away from the hobby (see list below).

A recent impulse purchase, the most beautiful thing with tubes ever made (SX-42), happened to be near Newington.  On the way home I visited ARRL HQ hoping they had some sort of a chapel where I could perform an act of penance and ask for guidance in dealing with my affliction.   Apparently, this is the equivalent of asking a crack dealer where the closest Narcotics Anonymous meeting is held. I ended up buying a copy of "200 Meters and Down" and have since acquired a couple of Atwater Kent projects. 

My place is full now, and my sweetheart would like back the half of her garage I've slowly taken by electronic eminent domain.   It seems that for every 100 pounds that departs to a ham fest, 125 pounds comes back.  Is this considered a normal ratio?

In order to be able to tell her that I have, indeed, gotten rid of something, I'll be sending you a F 455 filter (QRZ address OK?).

Thanks for you help,


--Brad 




Sunday, September 29, 2019

W4AMV's Beautiful Receiver


Hi Guys,

We had our Knightlites annual BBQ this past Saturday. I wanted to share one of the radios from one of my Elmer's, Alan Victor W4AMV.
Pictured is him standing beside the preselector and receiver.
I hadn't ever heard a Collins mechanical filter vs Murata crystal filter side by side. The Collins was amazing. Single signal extracted from the band. The rig is line powered with a built in power supply.
There is a note (pictured) that has some specs.
Alan's work is to be savored, true analog engineering at its best. I wanted to share it with you.

Chris
KD4PBJ



-------------------------------------

FROM W4AMV'S QRZ.COM PAGE:


Here is a receiver that started out as a regen for the grandkids to copy code.
Digging through the junk box un convered parts that I forgot I had. Included a wide and narrow band set of filters. So, the unit wound up as a single conversion superhet. A fun radio to build as well to listen. The wide band filter provides super fidelity on sideband as well uncovers plenty of CW signals within a 10 kHz bandwith of the tuned frequency. A switch to either a 800 Hz audio filter or a 500 Hz CW filter permits focus on a single signal. I was going to package the whole unit, however I was prompted to leave it OPEN to show what makes it tick! 
Left side front is the RF preselector, mixer and pre amplifier with RF gain control. The rear double deck card is the IF and selectable wide and narrow band filters. The IF and pin diode IF gain control is bottom deck. The HF VFO is center stage with a 6:1 gear reduction. Right rear is power supply and voltage regulators. The active product detector and a BFO is just to the front of the power supply. The BFO is able to tune product detector output over a full 10 kHz of the IF. And finally the audio filter and 5 watt power amplifier. There is no AGC. Instead it is FUN to control every aspect of  gain control of the receiver; RF, IF and audio. Its a fun receiver to operate, dedicated to 40 meters and hopefully will spark the kids! 
Going forward a receiveing station is setup to copy code. Although a nice long high wire would be proper, I settled on something a little more compact. A 40 meter small loop, 2 turns, about 18 inches on a side is connected to the preselector thru a pickup wire. This arrangement works quite well. W1AW will knock the speaker off the desk if your not careful. However, rotation of the loop to the E-W knocks down W1AW to a whisper. The pix shows the little 25 W infinity speaker in a 8x8x8 inch cardboard box, works well and the single conversion receiver sporting a new front plexiglass panel is illuminated for evening tuning. 


------------------------------------------------










Loop antenna used with the receiver



Saturday, September 28, 2019

Radio Art -- Zenith Tube Ad


This ad was recently shown on the K9YA Telegraph.  I was wondering about its origins.  I asked noted thermatron guru Grayson Evans -- he referred the question to fellow tube guru and author Ludwell Sibley.  OM Ludwell gives us the origins: 


She’s in a promo for Zenith, an Italian prewar brand that sold European triodes of types originated by Philips, and a few equivalents of American types.  She’s based on classical Italian art.  Doing a high-wire act while holding a small early-‘20s European           radio! I have an 11 x 17 glossy color print framed on the wail in the display room.  I ran       her as the cover art in a long-ago issue of “Tube Collector.”  “Three cheers for the red,       white, and green!"
Ludwell Sibley is the editor of "The Tube Collector."   Great stuff.  Their web site is here: 

Sibley's book "Tube Lore" can be purchased here: 

https://www.amazon.com/Tube-lore-reference-users-collectors/dp/0965468305/ref=sr_1_1?keywords=Tube+Lore&qid=1569660647&sr=8-1

Thanks Grayson, Ludwell, and to the K9YA Telegraph. 




Sunday, September 22, 2019

Pete Juliano N6QW on Homebrewing and SDR (Video)



Pete recently spoke to the Peel (Canada) Radio Club about SDR and homebrew.  The first 13 minutes show the club members but then it shifts to Pete.  Great stuff. 


Another Amazing Rig from VK3HN (Video) (EI9GQ Design)

Monday, September 16, 2019

ONE VOLT rms Reaches New Hampshire from Virginia

 My son Billy was back from college over the weekend (he came back to help me celebrate the completion of yet another orbit of the sun).  I was showing him my 8 part rig and telling him that it puts out 20 mW.  He asked a good question (he is a scientist):  What is the voltage at the antenna terminal.  I checked:  ONE VOLT rms.   About 1.414 volts peak.  Think about that.  My transmitter is sending a signal to New Hampshire from Virginia on less than the voltage of  AA battery.  

Two more spots on the Reverse Beacon Network (see above).  Another skimmer station in New Hampshire.  My signals seem to like the granite state. 

Sunday, September 15, 2019

Virginia to New Hampshire (one way) on 8 Parts and 20 mW


Having gotten the regen receiver portion of the ET-1 transceiver working nicely, I'm now working on the transmitter.  This is a much easier circuit to get going. (Check out the right hand side of the schematic below --- that is the transmitter.)  I have not made any contacts yet, but yesterday I called CQ on 7050 kHz and watched the Reverse Beacon Network to see if any of the skimmer stations picked me up.  Success!   W3UA up in New Hampshire received my signals. 

I was running about 30 milliwatts to my doublet antenna. The transmitter consists of EIGHT parts.  And three of them are the low pass filter. 

Next step:   Bring the transmitter and receiver together by using the switching scheme that OM Yingling used.  The RX and TX will share the same single FET (MPF-102 or J-310) with all three leads from the FET switched from TX to RX.   Then I will try for the elusive QSO with a single FET. 

More ET-1 related posts here: https://soldersmoke.blogspot.com/search?q=ET-1





Saturday, September 14, 2019

16x2 in Juliano Blue! The CRAP Single Board Transceiver by N6QW (VIDEO)



Another amazing rig and another very useful acronym from the wizard of Newbury Park.   

More here: http://n6qw.blogspot.com/

Saturday, September 7, 2019

SolderSmoke Podcast 213 WE'RE BACK!

N6QW's Analog CW QRP Transceiver
SolderSmoke Podcast #213 is available. 

http://soldersmoke.com/soldersmoke213.mp3

7 September 2019

The dire consequences of our summer absence. 

50th PODCAST WITH OUR FRIEND PETE! 
THREE CHEERS FOR PETE! 

Pete's Bench Report

-- Transceiver Count:  FORTY!  
-- SDR RADIGS 
-- Colorful OLED screens
-- Pilgrims and Paisanos -- "Left Coast Homebrew SSB"
-- Pete builds a CW transceiver (see picture above)


Bill's Bench Report: 

-- Going minimalist
-- Tuna Tin 2 + Herring Aid 5 = Fish Soup 7 (and later 10)
-- My QRPp QSO with K1PUB overheard in Canada
-- Glen Yingling's ET-1 
-- Bill attempting a single transistor transceiver

SPACE NEWS

-- Antuino's Cubesat Origins. Farhan's Antuino Mods
-- Apollo 11 Anniversary
-- Possibly the best space book ever:  "Carrying the Fire" by Michael Collins
-- Chinese microsat sending eclipse pictures from the moon
-- LightSail 2 success
-- India has spacecraft in lunar orbit. 

Eric Sears ZL2BMI and Dino Papas KL0S on "QSO Today" Podcast

MAILBAG: 

ZL2PD's Sugar Cube VFO
N8WQ gets free samples
N5RWF Getting started, wisely wearing beret
VK2EMU Australian Ad for Collins Filters
W1PJE on new LDMOS PA transistors
KA4KXX Al Fresco 75 meter SSB rig with model plane engine mufflers!  

Forgot to mention:  W9TH still has manuals for whover owns Drake 2-B #4215.  Check your serial number! 

Monday, August 26, 2019

Single Transistor Regen Has QSO Potential (Video)



In my previous blog post I'd expressed skepticism about using a single transistor regen on the air.  But over the years I've learned to give new receivers a chance.  They usually don't work perfectly on the first try.  You have to work with them.  It is almost as if you have to peak and tweak a lot in order to get them to properly inhale signals from the ether.  

That has been the case with this little receiver.  I found some silly mistakes in my construction.  And I decided to try some more sensitive headphones.  I ditched the 1000 to 8 ohm AF transformer.  And I added a very small variable cap for fine tuning.  

The results are amazing. See video above. It performs as well as most of the direct conversion receivers I've built. It is remarkably stable.  

I do think I could make contacts with this receiver.   I might eventually go the full ET-1 route and try to do it with a single switched FET, but I think my next step will be to built a single transistor crystal controlled transmitter on the same piece of wood, and try to make some contacts with a two-transistor rig. 

Wednesday, August 21, 2019

Another Bout of Minimalist Regen Madness

My success with the Fish Soup 10 QRPp transceiver got me interested in further minimalization.  About ten years ago I built a rig presented in SPRAT 108 as the ET-1 by Glen Yingling W2UW.   It re-appeared in modified form as the FETer by G3XBM in SPRAT 137.  

This rig uses just ONE active device, an MPF-102 FET that is switched via a 3 pole double throw switch from transmit to receive.  The transistor is switched.  The receiver is a regen and the transmitter is a very simple crystal controlled one stage oscillator. See: 
https://soldersmoke.blogspot.com/search?q=ET-1  for info on my ET-1 effort. 
The transmitter was the easy part.  I don't think I made any contacts with this thing.  That has been kind of bugging me.  

So I tried it again.  Again, I had trouble with the receiver.  So I looked around for another single FET regen receiver design.   I found one on AA7EE's page.  It was designed by N0WVA:  
https://aa7ee.wordpress.com/2015/02/07/n0wvas-one-fet-regen-optimized-for-ssbcw-sounds-great/


I've had a variometer in my junk box since about 1994. (Given to me by Pericles HI8P. QEPD.) It was time to use it as the coil and ticker for this rig.   I liked the green LED in the source, and the promise that this thing would not oscillate at audio frequencies.  

I built in on one morning.  See pictures. It works.  I can hear CW stations.  But I think I would have a tough time making contacts with this thing.   OM Yingling worked 24 states with his ET-1.  Respect.  


Tuesday, August 6, 2019

King Hussein JY1 Speaks to Owen Garriott on Shuttle Columbia



I thought this was a very nice contact -- the recording provides a nice bit of radio history.  I wonder how the German station got the JY1 portion of the QSO.

Saturday, August 3, 2019

Antuino Mods and Updates from Farhan





Both messages from the BITX20.io email group.

26 July 2019  

Peeps:


The Antuino has been in use for over a few months now. We had produced 100 of them that were sold at the FDIM. These work quite well for an SWR meter and Antenna Analyzer, but they were sub-optimal for serious RF work. For those who bought it for SWR measurements, you can continue to use it. For those who want to improve it, read on.

It was noticed that the db scale was not accurate. Antuino was designed to be an accurate and precise instrument. The db readings should be within +/- 1 db accuracy. However, they tended to vary by as much as 2 db on the upper range of power measurments. This was finally tracked down to having too much gain. I had prototyped the original with 2N3904 transistors but in production we used BFR93W as I guessed it would have 'better' performance. It turned to be a bad choice. The higher gain resulted in compression of signals above -30 dbm. This restricted the useful range of the Antuino to about 50 db. 

I am attaching the new (Version 2.1, it is a minor edit of the V2 that was sold at the FDIM). In summary, these are the changes:
1. The new software with a cleaner way to calibrate is on https://github.com/afarhan/antuinov2.1. Please upgrade to it even if you don't want to carry out the other hardware modifications.
2. Replace the Q1 and Q3 transistors to 2N3904. Although the PCB pads are SMT, you can solder the leaded type by twisting the legs around.
3. In the first IF amplifier (that immediately follows the mixer), we decrease the emitter resistor (R18) from 100 ohms to 51 ohms (you can also parallel a regular 1/4 watt 100 ohms with the original 100 ohms to get to 51 ohms). We also parallel the (R19) 220 ohms collector load with a 10 uh inductor (you can use 10 turns on FT 37-43), the exact value is not important.
4. In the second and third IF amplifiers, we replace the 100 ohms emitter resistors (R7, R34) with 10 ohms and remove the 4.7 ohm resistors (R32, R4).
5. In the last IF amplifier, we change the load resistor(R33) from 51 ohms to 220 ohms.

You need a few 10 ohms resistors and a 220 ohm resistor. You can resuse the R31 at R18.


Attached are the images and the circuit.

73, f 
_._,_._,_

August 3, 2019

Every instrument has limits on its accuracy. While making the Antuino, I was well aware of its deficiencies. 
I made a decision to keep it simple to a point where a radio ham could throw this thing together in an evening or two.

In order to overcome the limitations inherent in the Antuino design, the complexity could have been prohibitively complicated and expensive.
On the other hand, it is an extremely useful instrument that grows on you. I no longer use a frequency counter or the specan. I rarely use the oscilloscope. Antuino does most of my measurements.

There are two very important things you must be aware of while using the Antuino :
1. In the power measurement mode (the problem is non existent on swr or sweep mode), any reading above 25 mhz could be an image. Thus, if you see something at 35 mhz, you will have to do some mental math to figure out if it is not an image. An easy way to know is to add an external low pass filter with 25 mhz cutoff.
You have to use it like a radio in this mode. If you want to measure the harmonics from your pixie radio with 7040 crystal, tune to 14080, 21120, 28160 and measure. It is as accurate as any spectrum analyzer with more than 80 db of usable bandwidth. Raj and I struggled to get this for a month.
2. Unlike a full fledged spectrum analyzer, Antuino has just one bandwidth of about 7 KHz. This is enough to made IMD measurements at 20 KHz tone separation. The sweep plot does only 128 readings. Thus, if  you sweep a low pass filter from 0 to 20 mhz, it will measure the filter response every 120 khz. If there is something lurking between the steps, it will miss it. This is a common challenge with spectrum analyzers. So, a crystal filter should be swept at less than 100 khz. 
There is a software hack to mitigate this. First : introduce another control for step size. This can slow down the plot. A 30 Mhz sweep at 5 khz steps will involve 30 x 200 =60000 readings.It could take minutes. The Second : write a more optimal Si5351 routine that changes frequencies faster. I know that smaller jumps can be instantaneous on Si5351. I don't know that hack. If someone wants to take a stab at it, I am willing to work with them.

In a nutshell, Antuino is a very useful instrument. You don't have to buy it. You can build it. It is just as challenging as a direct conversion receiver. It does a fabulous job though. It can measure oscillator frequencies, it can measure amplifier gain, distortion, frequency response, it can measure filter response, it can show mixer behaviour, it can tune your antenna, it can measure power from a few uV to 100 mv and more with attenuators. It does all this slowly but surely. Like any precision tool, you must know its limitations and use them as an aware user. I would wager that if you have to choose just instrument for your lab, it would be this; Apart from a DVM.
And (I repeat) don't buy it, build it (grin)

- f

Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column