The Fish Soup 7 QRP Rig -- On the Air on 40 Meters (video)

I don't know why, but this weekend I got the urge to get on the air with a very low power homebrew QRP rig.   I reached for my Tuna Tin 2 -- Herring Aid 5 combo.  I call it the Fish Soup 7 (seven transistors in total). 

I first tried to turn this rig into a transceiver by taking the VFO signal from the receiver (it is direct conversion) and using it to excite the Tuna Tin 2, but it just didn't work out.  The oscillator in the Herring Air 5 is very bare bones -- no buffering and an LC circuit that is mostly L (10 uH).  It became very difficult to get a stable amount of CW offset.  So I went back to crystal control for the transmitter.  I did replace the 5K tuning pot in the RX with a 10k 10 turn pot (thanks to W8NSA).  Tuning is now very smooth.  I used my old UK freq counter to monitor my receive freq. (Thanks to Tony Fishpool G4WIF-- back in 2009 he sent me the CMOS chip that brought this counter back to life.) 

I was putting out about 750 milliwatts.  

I had a very quick contest-like contact with K2D -- one of the "13 Colony" stations.  Then a longer chat with Hank K1PUG (see video above).  

I had lost my 7050 crystal, but this morning it re-appeared.  TRGHS. 

As you can see in the video I am using the beautiful VU3XVR  key that Farhan brought me from India. 

This was fun.   I may try to put a VFO of some sort into the TT2, just to get more agility.  But I want to keep things simple.  

Look for me on 7050.  

Homebrew RF Design Contest -- Win $3,000!

https://www.nxp.com/products/rf/rf-power/homebrew-rf-design-challenge-2019:Homebrew-RF-Design-Challenge-PG

Building Spark-Gap Transmitters -- And a Very Cool Coherer (video)

The creators of "Plasma" and "Blueprint" YouTube channels have collaborated on this very interesting video about spark-gap radio transmitters and receivers. Really nice work.  Especially impressive was the coherer build by Blueprint.  I detect the spirit of Nikola Tesla in his lab!  

LightSail 2 -- Solar Sailing Cubesat with a Beacon on the 70cm Band

Once deployed, LightSail 2 will automatically transmit a beacon packet every few seconds, which can be decoded into 238 lines of text telemetry describing the spacecraft's health and status, including everything from battery status to solar sail deployment motor state. Every 45 seconds, the spacecraft will transmit "LS2" on the spacecraft's frequency of 437.025 MHz, within the Amateur Radio 70-centimeter band.

Further details can be found online at,
http://www.planetary.org/explore/projects/lightsail-solar-sailing/ 

Caption (or meme) Contest!

Please supply a caption for this picture.  Or turn it into a meme.  

Place submissions in the comments section below (or e-mail them in) 

Feel free to use the hosts of the SolderSmoke podcast. 

Antuino's Cubesat Origins, and How it Works (with video)

In a series of e-mails to the BITX20.io group, Ashhar Farhan VU2ESE provided background information on the origins of his new "RF Lab in a Box' -- the Antuino. He also explained how the device performs the SWR meter, Power Meter and  Scalar Network Analyzer functions.  

Farhan's Antuino Page: http://www.hfsignals.com/index.php/antuino/

Dec 27, 2018 to BITX.io

peeps,

while trying to measure the swr on the cubesats, i figured i couldnt use any of the analyzers i had access to. they were simply too big to be stuffed inside a 10 cm cube. my simple resistive bridge was too insensitive for any reasonable work. so, i sat down and made an antenna analyzer from a spare raduino. 

the code is wobbly and just about enough to get my work done. it works on a superhet principle. this is not my clever idea, rahul had mentioned this approach taken by a russian builder. i havent seen the original design. it would be interesting if rahul or someone can point me in the right direction.

the code and a pdf of the circuit is on https://github.com/afarhan/antuino. i am attaching the circuit for the lazy bones.

have a great holiday and get some dx !!

- f

Dec 28 2018

Jerry,

first, thanks. there is substantially your code in there.

second, onto the circuit. it uses two clocks. not three. the third is a spare output. more on that later.

the circuit here uses a resistive return loss bridge. the clock 1 drives the bridge through the R22 to a low level of -10dbm. If the bridge is perfectly balanced (that is, the antenna, R21, R29, R16, all the four are the same ohms), then, there will be no RF developed across pins 3 and 4 of the ADE mixer. Under ideal match conditions, there is no RF across the R26. As the mismatch increases, so does the RF across R26. 

We could directly detect the voltage across the R26 with a diode detector. This is quite a popular configuration with most of the simple resistive kind of SWR bridges (like the one designed by Dan Tayloe). This simplicity comes at a cost. The problem is that the detector responds to all the RF between the arms. For instance, if another ham down the block starts to transmit, that energy will show up across the R26 and you will get crazy SWR. I had that problem with broadcast FM showing up on my 7 MHz dipole! Even if there was no RFI from elsewhere, harmonics and spurs from your own transmission can show false readings. 

Here is an example: a 7 MHz transmitter with a 14 Mhz harmonic that is 20 db down is connected to a 7 MHz dipole. The dipole is perfectly tuned to show 1:1 SWR, hence, it should show no RF across R26. However, as the antenna is reflecting back the 14 MHz energy, the 14 MHz shows up across the R26.

What's the solution to get a clean dip?The solution is to substitute a simple detector like a diode detector with a simple receiver that is tuned exactly to the frequency that you want to measure the antenna at.

So, the ADE-1 mixer, Q2, Q1 together form a very simple superhet receiver with 25 MHz IF andCLK2 as the local oscillator. The RF at the IF is directly detected and converted to db range with the AD8307. This simple configuration makes this a very powerful instrument.

Here are things you can do with it:

1. Switch off the CLK1, now you have a receiver that can very accurately measure RF levels at any specific frequency in db range. For instance, you connected your transmitter with a suitable RF attenuator to P3, you can tune to various harmonics and measure them very accurately. If you inject a two tone signal into an amplifier, you could easily measure the IMD and IIP3. 

2. With the CLK1 on, the instrument now measures the return loss. you can measure the SWR of an antenna, S11 parameters of an amplifier, filter, etc.

3. With CLK1 off, CLK 2 on, the CLK2 can now tune to the frequency tuned in by the receiver's LO (CLK0). By connecting a device/filter between P3 and P4, you can sweep it to measure the gain, frequency reponse.

4. As the diode mixer (ADE-1) has harmonic response, a local oscillator at 135 MHz, will also convert a 430 MHz signal into 25 MHz IF (430 - (135 x 3)). This is possible because we are driving the diode mixer with a square wave from the Si5351 and the local oscillator at 135 MHz also has a 405 Mhz harmonic in it. Hence, the range of this instrument extends to UHF.

The ADE-1 mixer is quite similar to the ubitx mixers. You could even use ubitx kind of discrete version of a diode mixer, it doesn't work too well beyond 50 MHz. The pins 4 and 3 of the ADE-1 are the primary winding of the RF-input side transformer. The documentation recommends that we must ground 4, but that is not essential. We need a differential drive between those two pins, that is what the bridge provides anyway. 

73, f

jerry,

i built it so i could stuff it inside the cubesat to measure the antenna. an external spectrum analyzer and its cables were upsetting the RF model hence, i needed something that could read the return loss sitting inside the cubesat. then, i borrowed by daughter's DSLR with a monsterous tele lens and sat 100 meters away to read the the LCD display as it swept through the range. 

the analyzer was removed once we knew the correct dimensions and the actual payload went inside the bird.

- f

Mike KL7R's Web site on Way Back Machine

Thanks to Karl K5KHK for digging this up.  Excellent.  Three cheers for the WayBack Machine.

And thanks again to Walt K3ASW for voicing concern about the disappearance of Mike's site.  Good to know that all is not lost.

https://web.archive.org/web/20131126190933/http://kl7r.ham-radio.ch/

Pete N6QW's RADIG SDR On The Air!

Hi Bill: 

So far I have made about two dozen contacts with the new RADIG. Just finished one with a ham I know in New Mexico and he is an RF Engineer –he was a designer at Alpha. I asked that he do a critical review of how I sounded and looked on his SDR –  a good report and his comment was that if I hadn’t told him he would have guessed it was a $4 or $5K box.

So another goal achieved –on my 60^th year anniversary and this makes #37.

Pete

For more info: 

http://n6qw.blogspot.com/2019/06/sdr-radig-tsunami-of-new-ham-radio.html

SolderSmoke Podcast #212 HDR, Boatanchors, SDR, Antuinos, Spurs, QSX, Mailbag

Dale Parfitt W4OP's  SBE-33 with modern digi freq counter

SolderSmoke Podcast #212 is available: 

http://soldersmoke.com/soldersmoke212.mp3

22 June 2019

CONGRATULATIONS TO PETE:  Licensed 60 years today

Pete Juliano during Field Day, 1959

Sideband Engineers Models 33 and 34 -- Thanks Pete! 
Hans's QSX SDR Rig at Dayton-Xenia and FDIM
W8SX FDIM interviews

Pete's SDR Projects -- Update

The Peregrino SSB transceiver in the summer SPRAT

Why no rare earth cell phone speakers in ham projects? 

My HDR "waterfall" project

Farhan's Antuino
Cubesat origins
RF Lab in an box
SWR, PWR, SNA
Superhet receiver with ADE-1 at front, and log IC at the output
Adapters (SMA to BNC) help
DON'T BLOW UP THE INPUT RESISTORS (LIKE I DID!) 
My dirty DIGITIA -- Denial, then acceptance
FFT 
Useful programs:  SPURTUNE and ELSIE
A better bandpass filter for the DIGITIA 
The importance of a good test set up with Antuino

Manassas Hamfest: WA1UQO, W4WIN, AI4OT

MAILBAG: 
KG7SSB
WA3EIB
VK4PG
W3BBO
Jeff Tucker -- Who owns Drake 2-B #4215? 
KN4BXI
KC5RT
K3ASW

Wall Warts

Thank you to Michael Rainey AA1TJ who posted this cartoon, which I'm sure speaks to us all. 

Face the TRUTH! LOOK at Your Signal with an Antuino!

At first, I didn't want to believe it.  I was in denial.  I wanted to shoot the messenger (in this case, the Antuino). How could my beloved HB 40 meter DIGITIA transciever have an output that was so.... so DIRTY!  Everyone tells me it sounds great.  But the little Antuino screen told a different story.  Strong spurs up at 9 MHz and down at around 5.4.  And lots of places in between.  (In these display images, the center frequency is 7.2 MHz and each division to the left or right is 1 MHz.) 

Farhan tried to get me to face the truth: "The frequency domain viewing of RF Signals is the opening of the third eye. Once you start seeing signals as a bunch of simultaneous  sines, you will always be wary of the waveforms on the scope. In fact, time domain readings make little sense."

At first I blamed strong VHF RFI and my somewhat hay-wire test set up.  My homebrew Rube Goldberg 20 db attenuator was probably picking up some of the VHF RF. But as I looked more closely at the output of the transceiver in the frequency domain, I gradually accepted that it was true.  There were a lot of spurs.   I have a general coverage receiver in the shack, and with it I could hear the little devils. And after some adjustment I could see them in the FFT display on my Rigol o'scope.  An exorcism was definitely needed. 

But first came a tightening up of the test setup.  Pete advised me to do this.  I had in the shack some really nice dummy load/attenuators from the HP8640B Signal Generator that Steve Silverman had given me (and that Dave Bamford had hauled across New York City for me).  I ordered the necessary N connectors and adapters and soon my test setup improved a lot. 

All this got me thinking about spurs.  I consulted EMRFD and was reminded of a really great program in the LADPAC software pack that came with the book.  The SPURTUNE program predicts spurs and tells you what to look out for.  It is really illuminating.  Try SPURTUNE. 

Through this, I gained a better appreciation of the importance of the bandpass filter in an SSB transceiver.  I'd always thought of it as something that allowed the other mixing product to be eliminated while passing the one you want.  But I came to realize that it does a lot more than that -- it also helps get rid of spurs.   If it is designed right.  Mine was not.  I had plucked it out of an old QST article and had not paid much attention to it. All it needed to do was knock down the unwanted mixing product, right?  And in my transceiver (9 MHz IF,  VFO running 16.0 - 16.3) MHz that unwanted product would be way up at 25 MHz.  It wouldn't take a lot of selectivity to knock that down.  But I'd forgotten about the closer-in spurs.   Antuino reminded me of them.  And SPURTUNE explained where they came from.  

For the exorcism, I decided to use the bandpass filter design from Farhan's BITX-40 Module.  I had made the BP filter on this rig "plug-in" so it was easy to build a new filter.

I even checked out the filter design in a simulator.  For this I use ELSIE.   Another very useful program.  Here is what ELSIE predicted for Farhan's BITX40 Module filter: 

I plugged the new filter into the DIGITIA and... SUCCESS!  The big spurs that were bothering me were gone and the remaining spurs were all below 50db down from the main signal. Here is what it looks like now:  

The Antuino is a very useful device.  You can learn a lot from it, but you have to realize that this is not plug and play radio.  You have to think about what you are testing, make sure you have the test gear set up properly, think about the circuit you are looking at, and be careful not to put too much RF into the device.  

Three cheers for Farhan and his new Antuino!  More on this soon.  And we will talk about this on the next podcast.  

First Use of Farhan's Antuino Scalar Network Analyzer

I was learning my way around Farhan's new Antuino this morning.  Very cool.  I decided to start with the Scalar Network Analyzer.   I've spent so much time measuring and plotting filter response curves BY HAND... the Antuino is an opportunity for me to move into the 21st Century.  

In the picture you see the results.  I was using a Heathkit SSB filter with the center frequency at 3.395 Mhz.   The Antuino was set for that freq, with the screen range set at +/- 10.  That means each division on the screen is 1 khz (right?).  The Heath filter is advertised as being 2.1 khz wide at 6 db down.  That pretty much matches what we see here.  

You can see ripple in the filter passband.  This is almost certainly the result of an impedance missmatch.   It looks to me like the Antuino is set up with 50 ohm inputs and outputs.   The Heath filter probably needs higher impedances to have a smooth passband.   I will try later to set it up for a smooth passband. 

It is easy to see how useful this device will be.  Thanks Farhan! 

More on the Antuino here: 

http://www.hfsignals.com/index.php/antuino/