Showing posts with label g3xbm. Show all posts
Showing posts with label g3xbm. Show all posts
31 Oct 2016
G3XBM video channel
Just a reminder that I have a video channel at https://www.youtube.com/user/G3XBM . This channel has many of my projects. Most videos were created before my stroke. I hope you enjoy these.
30 Sept 2014
RSGB president request
Today I was asked if I could provide a photo of my 8.97kHz TX so the RSGB president could use it at a convention in Northern Ireland. I was happy to oblige.
If anyone else needs to use photos from my website at www.g3xbm.co.uk or this blog I am usually happy to say "yes" but it is polite to ask first.
If anyone else needs to use photos from my website at www.g3xbm.co.uk or this blog I am usually happy to say "yes" but it is polite to ask first.
21 Mar 2013
The current G3XBM (operating) shack
G3XBM QRP shack in a bedroom corner |
The maximum power I can run currently is around 7W from the K1 and about 12W out on 472kHz from the transverter (about 5-10mW ERP) and 30W from the 136kHz transverter (about 50uW ERP). I have no great desire to run much more power. The FT817 is only used at 2.5W or less.
16 Mar 2013
100 subscribers - thank you
Just noticed that the number of people who subscribe to this blog has now reached 100 for the first time. Many people just drop in from other links, but it is good to see that so many people actually subscribe. I try to post things that interest me, and I hope interest you too, here. Please let me know if the blog can be improved in any way.
Things (such as designs) that are of longer term use are added to my main website www.g3xbm.co.uk so check there too if you've not visited it.
Things (such as designs) that are of longer term use are added to my main website www.g3xbm.co.uk so check there too if you've not visited it.
Labels:
100,
g3xbm,
rss,
subscribers,
website
3 Feb 2013
Website woes
In the last few days I've done a major overhaul of my main website www.g3xbm.co.uk . All was working fine, but for some reason the web forwarding is not working correctly. Landing on the www.g3xbm.co.uk site you should automatically be forwarded to https://sites.google.com/site/g3xbmqrp3/ which is where the site is now located on Google Sites. So far so good, and this happens, although the address bar, which should change to the new site address based on how I've got my forwarding set up does not. Not only that, but clicking any images does NOT bring up larger, clearer images as it should although this works fine when you start with https://sites.google.com/site/g3xbmqrp3/ . So, I think it is a problem with the web forwarding, which I will try to fix.
In the meantime, you may want to go directly to https://sites.google.com/site/g3xbmqrp3/ if you want to explore the revised site.
In the meantime, you may want to go directly to https://sites.google.com/site/g3xbmqrp3/ if you want to explore the revised site.
20 Nov 2012
Tenbox 10m AM RX video
It is hard to contain my enthusiasm for simple transceivers and super-regen receivers! This video shows just how well the RX breadboard for the little Tenbox 10m AM transceiver works. 1uV (-107dBm) is a very good signal and it will still detect a well modulated AM signal at -120dBm. Selectivity is not good with this type of receiver, which is the main drawback. However for its intended application - a simple transceiver for local nattering across town - it should be fine. Some people use super-regens as the IF stage of AM receivers. If a filter is added ahead of the super-regen IF this overcomes the selectivity issue but makes the RX design more complicated.
Labels:
10m,
28mhz,
AM,
amplitude modulation,
g3xbm,
qrp,
super-regen,
superregen,
tenbox
6 Nov 2012
Lesser Chirpy 10m transceiver
You may recall that some months back I did a tiny transceiver for 10m CW ....that chirped. Well, this is the latest version that does NOT chirp! Instead of keying the oscillator current, I now key the capacitor that sets the oscillator frequency instead i.e. FSK keying. The latest version is shown here. Have a go: 10m is is good shape and you may get a few QSOs.
If the going gets tough (the RX audio level is low!) try adding an extra antenna change-over switch so you can receive on an external receiver instead. or add a 100n from TR2 collector and feed the signal into a sound card and SDR so you can use the PC's audio gain to help with copy and tune either side a few kHz.
If the going gets tough (the RX audio level is low!) try adding an extra antenna change-over switch so you can receive on an external receiver instead. or add a 100n from TR2 collector and feed the signal into a sound card and SDR so you can use the PC's audio gain to help with copy and tune either side a few kHz.
14 Aug 2012
Autumn project list
My wife often calls me a "fireside fusilier" as I am always gunner (going to) do this or gunner do that.
Well here is my current projects ideas list, some of which I hope to address in the coming weeks and months. How many will be replaced with other ideas first?
Well here is my current projects ideas list, some of which I hope to address in the coming weeks and months. How many will be replaced with other ideas first?
- Finish the 472kHz transverter and write this up.
- Simple 28MHz QRP WSPR transceiver to use with a netbook.
- Stand alone 137kHz receiver (for use with PC).
- Semi-permanent E-field probe antenna and on-line 137kHz/472kHz grabbers
- More non line-of-sight light beam experiments (get better distances).
- Semi-permanent 481THz QRSS beacon for NLOS light beam tests.
- Alternative HF antennas - maybe re-erect my Par Electronics 40/20/10 end-fed.
- Further earth-mode (ground conduction) experiments - tests at around 30 and 73kHz as well as more tests at VLF aiming to improve best though ground DX (currently 6km with 5W).
- Experiment with horizontal loop antenna on TX at VLF (maximising coupling into ground).
- Build some better LF/MF test gear such as resistive SWR bridge, 50W dummy load and a noise bridge.
27 Jul 2012
Updated MF transverter schematic
The current Rev D version of the 10W MF (472/500kHz) transverter is shown below. There are a few changes around the PA and output filter.
Revised 10W transverter schematic (27.7.12) |
The Lesser Chirpy 10m CW transceiver
SPRAT 151 had my article on Chirpy, an ultra-simple, very basic crystal controlled CW transceiver for 28MHz. This does work and has even managed a few decent QSOs but, boy, does it chirp! So, today I followed up on an idea I had to reduce the chirp by FSKing the oscillator when on TX. The schematic is attached.
The basic idea is to switch to TX by closing S1 (increases the oscillator output to around 150mW) then key a capacitor in series with the crystal. As the oscillator is on at full power with the key off or on (FSK shift) the chirp goes. There are a couple of disadvantages (a) the rig is no longer full break-in, and (b) when the key is up there is the "opposite" morse about 1kHz up the band, which is wasteful of power and may confuse. Still, this is a "for fun" rig and, with virtually no chirp, a much better radio. As before, a small low pass filter on the output is advisable unless your ATU provides this.
I also adjusted the turns on the main collector inductor finding that a tap 3t from the cold end worked better. You will almost certainly have to experiment with the values of capacitance around the crystal and key to get the right amount of TX-RX offset.
UPDATE 29.7.12: corrected the circuit diagram (crystal going to wrong place!)
The basic idea is to switch to TX by closing S1 (increases the oscillator output to around 150mW) then key a capacitor in series with the crystal. As the oscillator is on at full power with the key off or on (FSK shift) the chirp goes. There are a couple of disadvantages (a) the rig is no longer full break-in, and (b) when the key is up there is the "opposite" morse about 1kHz up the band, which is wasteful of power and may confuse. Still, this is a "for fun" rig and, with virtually no chirp, a much better radio. As before, a small low pass filter on the output is advisable unless your ATU provides this.
I also adjusted the turns on the main collector inductor finding that a tap 3t from the cold end worked better. You will almost certainly have to experiment with the values of capacitance around the crystal and key to get the right amount of TX-RX offset.
UPDATE 29.7.12: corrected the circuit diagram (crystal going to wrong place!)
472/500kHz video
20 Jul 2012
472/500kHz TX transverter - first schematic
10W 472/500kHz TX Transverter (CW, WSPR, OPERA, QRSS) |
Next stage is to add the RX preamp and filter and sort out RX-TX switching. I also want to try to go for a higher PA output power which will require changes to the output network.
Labels:
472-479khz,
472khz,
500kHz,
g3xbm,
qrp,
transverter
11 Jul 2012
My first ever website - 1996
8 Jul 2012
G3XBM Shack - 1977 style
My shack in 1977. I still use the same Morse key. |
14 Feb 2012
Non line-of-sight optical path profile
This is the path profile of my successful 3.6km QRSS3 cloudbounce non line-of-sight 481THz (red light) test on Feb 12th 2012. Sorry it is in feet and miles. The vertical scale is exaggerated, but it shows how non line-of-sight the path was. I used http://www.heywhatsthat.com/ to produce the data. This is a very useful site. It is fascinating that such paths can be used successfully for optical frequency communications.
Labels:
481thz,
g3xbm,
heywhatsthat.com,
optical,
path profile,
red light
22 Nov 2011
28MHz WSPR with 50mW
14 Nov 2011
10m Chirpy Measurements
Last week G6ALB made a copy of my Chirpy 14 component transceiver for 28MHz CW. Andrew had access to some better calibrated test equipment and carried out some RF power and sensitivity measurements both on his version and on my second original unit - the first was just a rat's nest on the bench.
Both on my version and G6ALB's version the measured RF power out was in excess of 200mW, which is around 2-3dB more than I had crudely measured. The RX sensitivity on both was such that below -100dBm (around 2uV) was audible in our earpieces in a quiet room. Backwave carrier on TX was rather too high at around -10dBm. Second harmonic was also only around -6dB, so a low pass filter is really a necessity apart from casual short tests.
It does seem that the simple design is reproducible and its performance not at all bad for something this simple. The only major shortcoming is the chirp.
Both on my version and G6ALB's version the measured RF power out was in excess of 200mW, which is around 2-3dB more than I had crudely measured. The RX sensitivity on both was such that below -100dBm (around 2uV) was audible in our earpieces in a quiet room. Backwave carrier on TX was rather too high at around -10dBm. Second harmonic was also only around -6dB, so a low pass filter is really a necessity apart from casual short tests.
It does seem that the simple design is reproducible and its performance not at all bad for something this simple. The only major shortcoming is the chirp.
6 Nov 2011
The "Chirpy" 14 parts QRP 10m transceiver video
17 Aug 2010
ICQ Podcast: LF/VLF and QRP stuff
Last week Martin M1MRB interviewed me by Skype for an ICQ Podcast mainly about LF/VLF and QRP . My contribution starts about half way through the podcast. Thankfully Martin edited out many of the "ums" and "errs" that littered the piece!
17 Dec 2009
Video of the G3XBM shack
Just for fun, I've put a very short video of the G3XBM operating "shack" (actually a corner of the smallest bedroom) onto YouTube. It shows the current set-up of homebrew and commercial equipment in use as well as the 500kHz transverter. I do most of my construction elsewhere.
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