Mike WU2D -- VFO Video #3

Mike WU2D continues to show us how it is done.  I hope to make all my future VFOs using the techniques he describes.  Thanks Mike. 

Exorcism Lite -- Spur Suppressed on 17 meter Transmitter -- Split TX/RX Station On The Air

I spent most of January in the tropics, away from my workbench.  This seems to have had a good effect on my 17 meter split TX/RX project.  As I was leaving, heading south,  I was thinking about several difficult options to deal with my spur problem (see previous blog posts). I thought about turning the transmitter into a transceiver by building a receiver board.   I thought about putting San Jian frequency counters on both the transmitter and the receiver, then doing a visual numerical "netting" by just putting the two devices on the same frequency (I actually ordered 3 San Jian counters).   The counter option was even more complicated than it at first seemed -- I would have to build a converter to shift the RX VFO frequency up.  VK2EMU suggested a tube type "Magic Eye" (interesting idea, but also complicated).   This was getting out of hand. 

When I got back home, I took a new look at the problem.   I decided to take one more shot at suppressing the 8th harmonic of the carrier oscillator.  I had already built a new oscillator and buffer using the circuit from Farhan's BITX20.  And I had put it in a metal box.  Now I decided to do three things: 

1) Tighten up the low pass filter at the output of the buffer by moving the cutoff frequency lower (to around 7 MHz) thereby getting a bit more suppression at 41 MHz

2) Try putting a series LC shunt circuit tuned to 41 MHz  at the output of the carrier oscillator (between the oscillator and the buffer). 

3)  Reduce the voltage to the oscillator/buffer.  I have this on a pot, so I can adjust it down to the point where the remnant of the harmonic is no longer audible, while keeping the main carrier osc signal sufficiently strong. 

It seemed to work.  I could now hear the desired frequency for spotting, without the confusing tone from the spur.  

Why had I been able to do this back in 2002 in the Azores using a simple trimmer cap to ground?  My guess is that I was using my Drake 2-B as the receiver.  The trimmer cap to ground may have reduced harmonic output.  And I was probably cranking back the RF gain on the 2-B to the point where I could hear the desired signal but not the remnants of the spur.  I have no RF gain control on the Barebones Barbados receiver that I am using in this project. 

So, what's the lesson from all this?  Well, if you are faced with a serious technical problem, and you find yourself considering complicated and difficult solutions,  go to the Dominican Republic for about a month (especially if it is January or February), and then take another look at the problem when you return.  If you are unable to travel this far or for this long,  taking a walk or taking a weekend break from a troublesome problem will likely have a similar mind-clearing effect. 

The video above shows part of a February 1, 2022 QSO with Gar WA5FWC using the split TX/RX 17 meter rig.  Gar is an amazing long-time SSB homebrewer who got his start with phasing rigs back in the day. 

The NCDXF/IARU Beacons (very useful website)

 

So there I was, innocently checking the lower end of the tuning range on my now 17 meter SSB Barebones Barbados W4OP receiver.  I had it tuned to the bottom of the 17 meter phone band.  All of a sudden I hear YV5B in CW.  It was obviously a beacon transmission. 

I had forgotten about these beacons.  Some quick Googling brought me to a very up-dated web site: 

https://www.ncdxf.org/beacon/

The site shows exactly which station is transmitting at any given moment.  There is also a very handy map display giving beam headings and distance from your location.  

So far, I'm only hearing YV5B and VE8AT.  I hope to hear more once the Coronal Mass Ejection is behind us. 

Check it out.  Leave your receiver on 18.110 MHz.  Let us know what you are hearing.  

Three cheers for the NCDXF and the IARU! 

Mike WU2D Shows Us How to Do Temperature Compensation in Homebrew LC Analog VFOs

In several of the articles that I have seen about the homebrewing of VFOs the authors seem to throw up their hands when the subject of temperature compensation comes up.   They seem to just say, "This is hard.  Not for the faint of heart.  Good luck with that!"   But in this great video Mike WU2D shows us in very practical terms how to do temperature compensation of VFOs.   This is really great news for those of us who prefer old style coils and caps to Si5351 chips.  Thanks Mike!  

Image of James Webb Space Telescope In Position at L2

https://www.inverse.com/science/james-webb-photo-final

A very nice shot of the James Webb Space Telescope, nearly 1 million miles away, taken from Rome. 

"From Crystal Sets to Sideband" -- A Great Book about Homebrew Radio by Frank Harris K0IYE (FREE!)

I first came across the above picture of K0IYE's inspirational, completely homebrew station many years ago in the pages of "World Radio" magazine. I have already linked to Frank's book many times over the years, but it is so good that I regularly feel compelled to write about it again. Frank updates the book. Just check out the introduction to his website. Frank even has a Spanish language version of his book. All for free. Thank you Frank.

The introduction to Frank's web site:

Over the last century amateur radio has evolved into numerous different

hobbies. Some hams enjoy weekend contests in which they try to

contact as many stations as possible. Others talk to as many of the

world's 341 call areas as possible and collect QSL cards to prove it. Other

hams just like to ragchew with friends. Still others communicate over

long distances at UHF frequencies using satellites, meteorites, aurora and

other substitutes for a sunspot-charged ionosphere. Some hams provide

communications for their communities during emergencies.

Many of us have returned to the early days of radio by building our own

equipment from scratch. Most home builders start by building QRP (low

power) transmitters. If this doesn't satisfy your urge to build something,

you can move on to build the entire station. That is what this website is about.

https://www.qsl.net/k0iye/

Mike WU2D on VFOs (with additional Tribal Knowledge from Frank Harris K0IYE)

Great stuff from Mike and from Frank Harris K0IYE.   But when I put the VFO in a box, I usually try to put the frequency determining components (the coil and most of the caps) in the box, with the powered components (transistor, Zener,  voltage dropping resistors) outside the box.  If I put these powered components in the box, I find there is some drift as these components slowly heat up the interior of the box. 

Dean KK4DAS and he VWS Builders have just stated building analog VFOs, so Mike's video is very timely for them. 

Looking at the Galaxy's Spiral Arms with a Dongle, a Raspberry Pi,and a Homebrew Antenna

I told Farhan that the world NEEDS a homebrew Raspberry Pi observatory at Lamakaan in Hyderabad. They are on it.  

This looks very do-able.  And fun.  And UHF.  And SDR. And Raspberry Pi. 

I'd like to build one too.  I was encouraged by the video demo -- it was done in Alexandria, Virginia, very close to where I live. 

A while back I was lamenting to Dean that I reluctantly threw away a DISH or DIRECT TV  satellite TV antenna.  I worried that I had discarded something that would have been useful for radio astronomy.  Turns out I didn't need it.   This video and the associated .pdf shows how to look at the galaxy with a simple homebrew (Home Depot!) horn.  

https://www.gb.nrao.edu/~glangsto/aas2020/Langston2020AasTelescopeWebinar.mp4

https://drive.google.com/file/d/1ssS_zBQWDEXMENc2_aqqPGxGkEEU5Ea3/view

Thanks to Thomas K4SWL of the SWLing Post for alerting us to this. 

Exorcism Not Quite Complete -- Thinking of Other Options

As often happens, I may have jumped the gun in declaring the exorcism of my 17 meter transmitter to be a success. As readers of this blog will recall, my problem was that when trying to "net" my separate 17 MHz receiver and transmitter, at around 18.116 MHz I could hear more than one tone as I tried to get to zero beat.  The 8th harmonic of my 5.176 MHz carrier oscillator was mixing with the 23 MHz VXO signal and producing a spur.  I could probably knock the level of this spur down below FCC limits, but -- and here is the problem -- I probably could never knock it down to the point that it would not be audible in the sensitive receiver that sits right next to the transmitter.  So this is really a netting problem, not really a spur problem. 

I don't want to try another filter frequency -- I have VXO crystals that really work only with a filter at 5.176 MHz.

So here is my current idea:  Build a receiver board and turn this thing into a transceiver.  Switch with relays the input and output of the 5.176 MHz filter, and use relays to switch to the receiver board the VXO and carrier oscillator signals. 

Making this thing a transceiver would eliminate the need for netting.  This should solve my problem. 

What do you folks think? 

73  Bill 

Roy Lewallen W7EL Gives Us All EZNEC for FREE! Thanks Roy! (Video)

Free download here: https://www.eznec.com/

Thanks to Roy Lewallen W7EL for this great gift to the amateur radio community.  

And thanks to G-QRP for the excellent video (above) of Roy talking about antenna modeling.