Another Great DSB rig from New Zealand

So many great Double Sideband projects come from Down Under.  There are the various versions of the famed ZL2BMI rig.   And Peter Parker VK3YE has long been the acknowledged guru of DSB. In fact, Peter sent me an enthusiastic e-mail about the new ZL DSB rig pictured above -- his e-mail arrived before the message (below) from the intrepid builder.  I detect a bit of the "Tucker Tin" influence in this rig. (But perhaps this one is more Tupper than Tucker!)  Charlie's work has graced out blog posts before: http://soldersmoke.blogspot.com/search?q=zl2ctm

Be sure to check out his video:   https://youtu.be/JsAuWGkyvmE   (and below).

Hi Bill.

You asked recently on the podcast for listeners to let you know what they had on their work bench. Well I’ve been working on a tramping (hiking) radio, which is now complete. It’s a DSB 5W rig designed for 80, 40 and 20m, as well as our New Zealand mountain safety radio system. I designed everything in LTSpice as was suggested by Pete, N6QW. That was great, as I could ‘desolder’ components with the mouse and instantly see what impact it had on the output. An amazing tool that’s free! I highly recommend it.

Once again I’ve used upside down strip board for each stage, which are tacked down onto an un-etched copper board (earth plane). That seems to work really well for me.

The rig uses an Arduino mini driving a small OLED screen and a Si5351 DDS. The Si5351 is going straight into a SBL-1, which seems to work fine too. The AF strip is a 2N3904 before a LM386, which has enough drive to run a speaker. The TX amplifier is a three stage one with shielding between each stage. It’s made up of two 2N2222A stages followed by a BD139. That in turn is followed by three simple filters, one each for 80, 40 and 20m.

All-in-all it works really well. I’ve uploaded a quick video at https://youtu.be/JsAuWGkyvmE

The next project will be a proper SSB rig using a crystal filter salvaged from an old Codan 7727. Like this one, it will use an Arduino and a Si5351.

Finally, I am certainly no expert in homebrew, but I hope my ‘dabbling’ will help inspire others to pick up the soldering iron and give it a go. If I can do it, then anybody can! There is certainly a great sense of achievement to operate a rig you built yourself.

Regards, and thanks to you and Pete for all your inspiration.

73’s

Charlie

ZL2CTM

I.G.Y., The Nightfly, Donald Fagen, Jean Shepherd and SolderSmoke

OK, so from time-to-time we  talk about IGY, the International Geophysical Year. I was born during that scientifically momentous period.  A lot of cool stuff happened.  Amazing propagation conditions too.  So for a while (around SolderSmoke 149) I was using the opening bars of Donald Fagen's song I.G.Y. as the intro for the podcast.  That song comes from Fagen's album Nightfly.  The album cover appears above.

This morning I got two e-mails from Steve N8NM about another connection between SolderSmoke and IGY.  At first I thought he was pulling my leg.  But  before I show you the e-mails, let me show you another picture:

That's Jean Shepherd.  Can you dig it?

Steve writes:

Hey Bill! 

I'm Listening to #149, where you introduced Donald Fagen's "I.G.Y" as the new theme song.  Have you heard that the protagonist on that album is based on none-other than Shep, K2ORS.  Don't know if that's necessarily true, but the album title (The Nightfly), Fagen being from NY, and the era depicted certainly make that plausible...

I guess it's factual - This is from an interview Fagen did with New York Magazine:

Your first solo album, The Nightfly, was inspired by fifties jazz disc jockeys. Which ones were your favorites?
Symphony Sid was very popular. Mort Fega was probably the best all-around jazz D.J. Ed Beach on WRVR would do this very scholarly afternoon show, and I’d listen to that when I came home from school. But the figure of the Nightfly was based more on a guy who didn’t play jazz records, Jean Shepherd. He was a monologist who used to just talk and tell stories and say funny things. He was a social satirist.

Speaking of Shep:  You've done him proud, not only in your HB radio efforts, but in proving yourself to be a very capable monologist for the several years between Mike's passing and Pete's arrival.  Three Cheers for Bill!  Give that man a brass figlagee with gold leaf palm!

73!  Steve N8NM

By the authority vested in me by having once spoken to Jean Shepherd, I award Steve Murphy N8NM, the coveted Brass Figlagee with Gold Leaf Palm.  

EXCELSIOR!  

TRGHS

Farhan on What's New in the BITX 40 Module

Writing to the BITX e-mail group, Farhan provides some very interesting information on the philosophy behind his new BITX 40 module, and on how it differs from earlier BITX designs:

The new builders are often caught in a catch-22 : to get on air they need to build a rig from scratch. but to build a rig, they need lots of experience. A way out was to provide working boards where we can get on air quickly, and then start improving and modding the circuit. this is the spirit behind the new boards. Consider them like you would consider a raspberry pi or an arduino : simple, working circuits around which you can grow your own radio.

In the new bitx boards, I have tried to keep as close to the original bitx as I could. however, there are a few departures that I thought the bitx builders here would like to know about.

i have to admit though, strangely, i am less familiar here with bitx than many others on this form. arv, leonard, dan,  andy and others have build far many more version than I did. I just happen to be the first one to build a bitx. this as much an acknowledgement of their inputs. without all you folks, bitx would not have had the kind of traction that it now enjoys. I suspect that it is the most built transceiver in the world.

So, here are the changes from the original bitx.

1. SMD

The SMD components make for virtually error free boards assembly. We used the biggest sized SMD components. In fact, the resistors and capacitors are about the same size as a quarter watt resistor that is soldered standing up. They are very easy to desolder without messing around with the desoldering wick and solder pumps. All you do is to lay the soldering iron's bit on the component such that the flat end touches both sides at once and after a few seconds just drag the component away. I soldered the sample boards with my regular, 2 dollar, 25 watts iron without using a magnifier (I wear reading glasses). 

1. 40 Meters

It is just that with the sunspots fading away, 20 meters in the tropics is far less active than before. Many of the us South Indian hams hang out on the lower end of 40 meters every morning and evening. Hence, the choice. That doesn't mean that i can't be converted to 20m! There are several ways to change to 20 meters. Keeping the VFO same, change the crystals (and hence the IF) to 8.833 MHz and rework the band pass and the low pass filters. I will work out the details in a few weeks and post them here.

2. A new bandpass filter

The original bandpass filter was quite lossy. I didn't know how to use any CAD tools when i sketched it. I was actually on a long haul flight when I designed that filter. The new filter configuration is very interesting one. I saw it on PA3AKE's site. This is a triple tuned circuit with very good out of band attenuation while maintaining very low loss. 

In the last then years, ecomm has made it possible for us to globally access good quality toroids anywhere in the world. Hence, we have used T30-6 toroids with excellent low loss. I measured it at just 2 db, the original had more than 6db loss.

3. VCO

The original oscillator on the BITX used a variable capacitor. These were noisy, and often of inferior quality. In any case, they are no longer available. Instead, we have used a varactor diode for tuning. The greater benefit of using a varactor to tune the oscillator is that the tuning control only carries a DC voltage. You can install it anywhere. If you need finer tuning control, you can add a second lower value tuning pot in series with the main tuning pot. It is easier to add FLL to a VCO.

4. Audio muting

The original BITX used just a switch to move from receive to transmit. The receive voltage charged receiver's audio preamp's decoupling capacitor and it took time to discharge. this kept the audio preamp active even on transmit and caused a very sharp audio noise on the transmit change over. Now, the other section of the T/R relay is used to cut the audio off to the LM386 as soon as transmit line is energized.

5. A better T/R system

The original bitx didn't have a PTT. this one has two relays to switch the linear amplification chain in and out of the circuit, mute the audio and change over the antenna. These changes lead to a very stable linear amplifier and smoother change over. 

6. Mic amplifier

The original mic amplifier easily saturated. The new design, thanks to dan tayloe, has a better head room and provides very clean modulation.

7. The fixed BFO

Though the PCB has the provision for a trimmer and an inductor to pull the crystal frequency. I discovered that with five matched crystals, if you used 4 in the ladder filter, the fifth's frequency fell right into the perfect sweet spot for LSB work. You might need to add the trimmer and an inductor back for USB work.

8. DDS connector

To use the DDS, you will have to remove L4 (the VFO inductor) and inject the DDS/PLL output into the connector provided.

There are some smaller mods that people can try out:

* The current in the receive amplifiers can be reduced if you don't have any radio hams in your neighbourhood who run kilowatt amps. 

* The capacitor between pins 1 and 8 of the LM386 can be removed if you prefer headphones to speakers. 

VK3HN: SOTA, HB, SSB, and QRP FB!

Peter VK3YE sent me the link to this amazing site.  Wow, Paul VK3HN does great work, both with the homebrew rigs and in describing his work on them.  Check it out: 

https://vk3hn.wordpress.com/2016/10/25/summit-prowler-one-a-homebrew-7mhz-ssb-qrp-transceiver-for-sota/

Great stuff.  Thanks Peter!  Thanks Paul!

Video of BITX 40 Module in receive mode

A Package from Hyderabad: Farhan's BITX 40 Module Arrives in Virginia

I am having a really EXCELLENT radio morning here at SolderSmoke East coast HQ.  I made some progress on the Armand HRO receiver -- just squaring away some of the too-long leads and improving the shielding a bit.  Then I was looking out the window as the mailman arrived.  What was that little box he was leaving us?  Wow! A box from Hyderabad!  The BITX 40 module arrived, wrapped in a very interesting piece of Hyderabad newspaper. Very FB. Thanks Farhan.  I will surely be writing and talking about this rig in the weeks to come.

UPDATE:  I just realized that the BITX module fits very nicely into a TenTec TPC-45 cabinet that Armand gave me a while back.  TRGHS.

Cool Jazz from New Zealand as Heard on a Homebrew Superhet Receiver (VIDEO)

I'm making slow but steady progress on this one.  The origin of the project was the beautiful National HRO dial and gearbox that Armand WA1UQO gave me. 

I decided to use a 455 kHz IF because;
1) That was the IF of the old HRO receivers (the ones that won WWII)
2) I had a nice TOYO CM455 crystal mechanical filter that would be good for SSB.
3) I figured it would be easy to add in a wider filter that would be good for AM shortwave listening.
4) I like to keep the IF below the frequency of the VFO.

The wide filter turned out to be harder than I thought, but I think I have finally achieved the selectivity I was looking for.  I'll have a switch on the front panel that will allow me to go from "AM-Wide" to "SSB Narrow." The switch will change the filters and the detectors, and will turn the BFO on and off.

Still to do:  I need a high-pass filter to knock down RFI from nearby AM broadcast transmitter. And an RF gain control would be nice.

I'm really glad Radio New Zealand is there.  It provides welcome relief from the shortwave fire and brimstone.   Radio Romania is also doing a fine job on shortwave.