Just go to http://soldersmoke.com. On that archive page, just click on the blue hyperlinks and your audio player should play that episode.
http://soldersmoke.com
Coming home from the Dominican Republic, this was a major item on my list of desired mods for the uBITX: a narrower passband for CW. Using the 2.3 kHz SSB passband, you could have many CW QSOs audible in your headphones. Narrow that passband to 200-300 Hz and life gets a lot easier. Farhan had discussed adding a 12 Mhz IF filter of suitable CW bandwidth, but this seemed difficult to me. Besides, I have long wanted to use an active audio filter for this purpose. The Hi-Per-Mite filter from 4 State QRP Group is just what I needed. I built the kit without problems in about an hour, then I put it in the uBITX box, with switch on the front panel that lets me put it in the circuit or take it out -- this is very satisfying and a lot of fun. The Hi-Per-Mite just goes between the uBITX audio out and the speaker/headphone connection. I built mine for "no gain" -- the uBITX provides plenty of audio. The selectivity with the Hi-Per-Mite compares favorably to that of my Drake 2-B with the 500 Hz LC filter. You can get an idea of the performance in the video. Three cheers for the 4 State QRP Group and their Hi-Per-Mite! Here is the page with all the info: http://www.4sqrp.com/hipermite.php
They say it's easier to make a narrow ladder filter than a wide one. Many a receiver in the old days got by with a single crystal filter, which then got loaded down with resistance to broaden for voice. Of course at 455KHz the IF transformers would help more with skirt selectivity than at 12MHz.
But then you have the SSB filter to provide skirt selectivity, so maybe a simple single crystal filter in series would be fine for CW.
The hardest part might be adding switching of some sort to remove the CW filter when doing ssb.
The neat thing about using a synthesizer controlled by a computer is that you can shift the frequencies as needed just by changing software. So if the filter isn't on the same frequency, just shift the local oscillator, and the BFO. So much easier than in analog days. If the IF strip is otherwise broadband, you can use that commercial crystal filter on 9MHz for SSB, and that 2MHz wider filter for AM, and some third frequency for a CW filter. No need to add mixers to make an odd filter compatible with an existing IF frequency. Of course, this may affect other things, like image rejection or where the spurs land.
Digging into the material for this audio filter, it derives from an article in "73" for May 1994. I have no idea how much was changed, but someone could just go back a quarter century and build from scratch.
I forgot, whatever happened to commutating filters?
The first issue if QST I ever saw, April 1971, had an article about tgem, though called a "digital filter".
Some capacitors of the same value, and something to switch them sequentially, and a divider to drive them. The center frequency set by the frequency of the oscillator, so easy to change.
The Tayloe mixer derives from the concept.
There were articoes decades ago, including one in Ham Radio that was well detailed, but not much in recent times. There are limitations, but you can't get much simpler. I've onky seen them used for audio, I don't know if they can translate up to low IF frequencies
"SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
http://www.amazon.com/dp/B004V9FIVW
April 19, 2024. An Audio Amplifier you can Build.
-
I find that data is very useful in making decisions. How startling a
statement to make on a ham radio blog. For instance, when I post subjects
about how t...
No birds do sing
-
Hi FastRadioBurst 23 here letting you know of our forthcoming shows this
week. On Sunday 21st April 2024 at 0900/1300 hrs UTC on 6160 kHz and then
at 2000 ...
An Inline RF Step Attenuator for QRPp Work
-
I don’t need to explain the attraction of low power operation; if you’re
reading this, the chances are that you are already a convert. I’ve been
operating ...
Using an external clock with the RX-888 (Mk2)
-
*The RX-888 (Mk2) and external clocking*
*Figure 1:*
The RX-888 with external clock input *(right)*
The enable/disable switch is barely
visible behind the...
A 51S-1 Restoration Story
-
I came across my Collins 51S-1 in a big junkyard in Ankara, Turkey around
2012. It was in a pile with a lot of other electronic scrap, probably from
one o...
New QRP Cluster Online From OM0ET and OM6APN
-
By DX EXPLORER
DX EXPLORER
Paul OM0ET and Peter OM6APN recently launched a new cluster dedicated to
QRP operations. Have a look and I hope you will enjoy...
3D Printing The Hadley 114mm Newtonian Telescope
-
Yes, we’re building a 3D Printed Newtonian Telescope called Hadley. It’s
being printed in PETG and in the video below, I give a quick tour. My build
isn’...
3D printed project boxes
-
I have been busy with some other things that have kept me away from
electronics projects for quite a while. Now I can get back to them, but
realize I n...
Daylight Again – An all Analog Radio
-
What’s all this? In 10 seconds, A high performance, 7MHz, 5 watt SSB rig
Draws just 24 mA of current 90 dB dynamic range, 80 dB close-in dynamic
range 3D ...
Adding Enclosure to your sBitx Boards Order
-
The early buyers of the sBitx board set who bought it for $270 USD might
want to also add the enclosure (box) for in the kit. What you will now get
is a f...
Digi-chirp! Digital synthesis of ‘nostalgic’ CW
-
The bottom ends of 80, 40 and 20m are not what they used to be. For
starters, the busiest part is the digital segment where computers talk to
computers – l...
-
A Simple Speech Processor
(For QRP/SSB Homebrew Transceivers )
Over the last few weeks I had been thinking to build a small AF speech
processor to add to...
A New Look for your uBitx!
-
Adding a "Cool Blue" Display to your uBitx!
The standard "green background" with black lettering frequently reminds me
that I suffer from Chronic seasickn...
It is indeed a very good addition for the uBitx.
ReplyDeleteI have also implemented it in my uBitx.
https://www.ph2lb.nl/blog/index.php?page=ubitx-mods3#ubitx-mod14
IMHO a must have.
They say it's easier to make a narrow ladder filter than a wide one. Many a receiver in the old days got by with a single crystal filter, which then got loaded down with resistance to broaden for voice. Of course at 455KHz the IF transformers would help more with skirt selectivity than at 12MHz.
ReplyDeleteBut then you have the SSB filter to provide skirt selectivity, so maybe a simple single crystal filter in series would be fine for CW.
The hardest part might be adding switching of some sort to remove the CW filter when doing ssb.
The neat thing about using a synthesizer controlled by a computer is that you can shift the frequencies as needed just by changing software. So if the filter isn't on the same frequency, just shift the local oscillator, and the BFO. So much easier than in analog days. If the IF strip is otherwise broadband, you can use that commercial crystal filter on 9MHz for SSB, and that 2MHz wider filter for AM, and some third frequency for a CW filter. No need to add mixers to make an odd filter compatible with an existing IF frequency. Of course, this may affect other things, like image rejection or where the spurs land.
Digging into the material for this audio filter, it derives from an article in "73" for May 1994. I have no idea how much was changed, but someone could just go back a quarter century and build from scratch.
I forgot, whatever happened to commutating filters?
ReplyDeleteThe first issue if QST I ever saw, April 1971, had an article about tgem, though called a "digital filter".
Some capacitors of the same value, and something to switch them sequentially, and a divider to drive them. The center frequency set by the frequency of the oscillator, so easy to change.
The Tayloe mixer derives from the concept.
There were articoes decades ago, including one in Ham Radio that was well detailed, but not much in recent times. There are limitations, but you can't get much simpler. I've onky seen them used for audio, I don't know if they can translate up to low IF frequencies