Thursday, 19 July 2018

30MHz and Above.

He's got a point - although the proliferation of VHF/UHF digital modes is not completely to blame for the demise of analogue signals on the bands above 30 MHz. The release of HF bands, including digital modes, to Foundation class licenses has, in my mind, caused the problem. If a 24 month period of analogue operation on bands above 30 MHz, to include QSL proof of operation, was made a stepping stone to the next license class this problem would not have come about. Exposure to the 6m, 4m and 2m band SSB and FM would have made these operators aware of the DX possibilities of these bands and given them a life long appreciation VHF and above. As it did me as a Class B operator under the old license scheme. I often still sit on hilltops listening for summer tropo signals to appear on hot days and for Sporadic-E openings just before a good Autumn thunderstorm. They have missed all these mystical and magical phenomenon which are still a delight to me even after all these years.

https://youtu.be/LaGT4QurBcc

Monday, 11 June 2018

Eazy Hi-Z Phones

I was looking at throwing out some scrap office telephones at work but we are not able to dump electronic waste in to our refuse. So I stripped them down to recover the plastics for recycling and was left with a pile of electronics. 

All good stuff , Jolly Useful Necessary Kit (JUNK) - switches, electret mic. inserts, medium impedance earpieces and other goodies like piezo sounders. Seeing the sounders took me back to an article I saw a couple of years ago where an enterprising SWL had fashioned a couple of these sounders into a pair of high impedance headphones.

Now from time to time I like to build a crystal sets just to remind myself why I got interested in radio, trouble is the only devices I have for listening on is one of those uncomfortable crystal earpieces, salvaged from an old hearing aid. So I decided to build a pair of high impedance phones using a cheap pair of ear-defenders and two of the piezo sounders.

The sounders have a very high impedance, too high for normal use, so I wired a 43k Ohm resistor in parallel with each sounder and then placed a sounder each defender ear-cup. I wired them with the cable salvaged from one of the phones in the same configuration as a stereo headset, terminated in a miniature stereo jack plug. This enables the inserts to be wired in series or parallel, in parallel the impedance of  21k Ohms is just about right for crystal set use. 

Any sounder can be used, from the type you may find in musical greetings cards to the old trim-phones - bigger the sounder the better the low frequency response.

I'm very pleased with the result, my new headphones are comfortable and have a nice frequency response for communication use, together with a couple of useful resonances for peeking morse signals against - particularly good when used in conjunction with one of my simple valve regen receivers.

Link to original article


Selection of salvaged piezo sounders

Piezo sounders installed in cup including 
original sound deadening foam behind each insert

Finished phones including salvaged curly wire

Sunday, 29 October 2017

Sound Powered VOX Digital Interface


Just finished and tested a new simple self powered VOX operated digital interface for my IC-703 rig. One good thing to come out of this weekend, a poorly foot stopped me going too far from the shack. This is based on my interface posted on Thursday, 19 May 2016. 👻




Friday, 20 October 2017

Modified End fed matcher

Since my original post regarding my linked end-fed halfwave antenna and matcher I've decided to extend its range to include 80m. The switch I fitted to add the 60m band was replaced with a centre off change-over type. The extra place on the switch puts a 600pF silver mica cap in parallel with the original tank circuit - 600pF is not a common value so I made it up with several devices in parallel. So with the new switch in the central position the matcher covers 40m  to 15m, first position on the switch enable the 60m band and the second the 80m. The test button that was fitted to put a 3.3k termination in place of the antenna was replaced with a toggle change over type as the original was too hard to operate with cold fingers. The 1k resistor in series with the VSWR dip indicator LED has been replaced with a 4.7k to improve the dip indication - see the accompanying circuit diagram.

Saturday, 10 September 2016

Waste not want not.

I've just recently gone around the house swapping out all the 50W GU10 spot lamps for their LED equivalent. Prices on the web have dropped to well bellow £3.00 each when purchased in bulk. The only trouble is I now have a box full of partly used 50W incandescent spot lamps.  However, as I have a workshop and a little used studio, all populated with old drawing office angle-poise lamps I decided to re-cycle the lamps in these beautiful old fittings. The CFL (compact fluorescent light) spot lamps are really expensive and give a very poor light when they get old. So having dredged through several of the auction sites I came across these nifty little adapters shown below. 


I know using the 50W lamps is wasting energy but throwing them away is too. However, they were use four at a time in the fittings we have in each room, that 200W just to light the lounge, reusing theses lamps one at a time isn't too bad! I reckon my supply of pre-used lamps should see me OK for the next twenty years. These adapters are also available in ES (Edison Screw type). You could,  if the fitting allows, use them to put LED spot lamps in your favourite retro angle-poise! When looking for these adapters use the terms "BC to GU10" or "ES to GU10 adptors". 

73 Rick G6AKG




Monday, 27 June 2016

UT5JCW 4 Meter Transverter Reveiw

I was lucky enough to spend this weekend playing with an old Deecom 4m HB9CV beam antenna and as this coincided with the 4m cumulative contest I decided to give my portable station a workout. This flurry of activity was spurred on by the many thunderstorm that have triggered sporadic-E openings well into this summer. My hope is to go and activate a local SOTA site this Autumn.

My backpack station now consists of a 70MHz transverter, a fishing pole mounted HB9CV beam antenna, a Yaesu FT817ND transceiver and a homebrew 12V power pack.

Supplied transverter PCB
Serge (UT5JCW) produces transverters for bands from 50MHz right though to 430MHz and I can confirm the 4M PCB is slightly larger than a credit card, it makes use of mainly SMD components with the exception of Inductors and the PA transistor. The PCB is supplied fully aligned and produces in excess of 10W when running from my gell-cell portable power pack. After carefully adjusting the transceiver drive level I did some quick tests which proved a nice clean output on 70MHz, with a second harmonic 39dB down on the fundamental. The close in emissions noted at 84MHz (2 x the local oscillator crystal at 42MHz) were better than 40dB down on the output signal.

So after extensive bench testing, I've finished boxing up my transverter and made several successful 4M band SSB contacts using my newly acquired Yaesu FT817ND as the driver. 

Rear of supplied transverter PCB
The receive sensitivity seems similar to that of the drive transceiver on 28MHz and the only problem noted was a slight frequency skew in transversion, of plus 5.8kHz. However, I didn't view this as a deal-breaker as this can be programmed out in my home QTH transceiver and mentally accommodated when out portable .

Serge did suggest that a suitable inductor could be connected in series with the crystal to drag it on frequency, but the PC board is so neat it seemed a shame to start hacking it around. Surge commented that in order to keep the price down of the product he had used computer grade crystals that were not noted for their accuracy.

Included in my box is a variable 30dB power attenuator, as suggested by Serge in the application data, as the transverter only requires 100mW drive - maximum! I also added to my project an RF activation circuit to operate antenna changer-over relays, as the barefoot transverter PCB has no switching hardware. A separate socket was added to make use of the grounded PTT line which is available on the ACC socket of my FT817. 

My boxed transverter including power attenuator and relays, the heat sink is from a faulty industrial PC
Overall this transverter represents good value for money and since I purchased mine, Serge has added some accessories that make its application even easier - as he now offers a ready made relay and power attenuator PCB. In fact you can buy a whole kit including the case for approximately £80 - see his  Ebay Transverter Store.

Many thanks to Serge UT5JCW for his prompt help in answering my technical queries and use of his circuits diagrams and photos in this blog. 

Transverter technical specifications
  • RF range  -   70 ... 72MHz
  • IF range  -  28 ... 30MHz
  • IF input power  -   1 ... 100mW (0.1W max.) or 0 ... 20dBm
  • LO frequency  -   42 MHz
  • LO frequency stability  -   +/- 3ppm
  • Output power  -   10 ... 15W
  • RX gain  -   typ. 20dB
  • Noise figure  -   typ. 1.0dB
  • Image rejection  -    typ. 70dB
  • PTT control  -   Contact closure to ground
  • Supply voltage  -   +13.8V DC (+12 ... 14V DC)
  • Current consumption  -   typ. 2A (TX)
  • TX Output transistor  -   RD16HHF1
  • RX Input transistor  -   BF998
  • Dimensions (mm)  -   80 x 45






Sunday, 22 May 2016

FT817 RF Clipper Microphone Review

DF4ZS RF Clipper  

A couple of months ago I purchased an audio RF clipper module, designed by Joachim Münch DF4ZS (SK), to fit inside the microphone of my new FT817ND. I based my purchase on some enthusiastic reviews posted on eham (www.eham.net/reviews/detail/2732).

I had previously built and tested an audio compressor based around the SSM2216 chip which was trialed on a fellow amateurs FT817 (thanks to Mark 2E0VOV).  It suffered terribly with RF feedback problems, even though standard EMC design practices were adhered to, with respect to layout and earthing. Needless to say it did leave me with the impression that any audio circuit left out side the transceiver chassis was going to suffer a similar fate.



When the RF clipper arrived I eagerly unpacked it and inspected the hand crafted PCB with its mix of conventional active devices and surface mount discrete components - all looked to be in order however, my heart sank when I saw that there were no installation instructions included - just a QSL card! I need not have worried, as all the data I required was available on Joachim's website , I also found it useful to download the MH-31 microphone data provided by Roy Frettsome G4WPW web pages.
 
Circuit diagram of Yaesu MH-31 mic.
I sat and pondered all the information for a while and once I'd  got my head around taking spare components out of the mic.  PCB and adding a 1.2k resistor, the installation of the clipper went easily. I even re-wired the tone switch to enable the processor to be switched in and out of circuit.
 

Note: There is a service offered by the supplier of the module to install the clipper for you, although  once you've factor in the postage both ways for the microphone it looses its appeal. However, for those not gifted with the necessary skills it is a nice option.

The newly modified microphone uses an electret type insert mounted of the rear of the clipper PCB, which I though was a neat idea (more of that later). Once the Clipper PCB was wired in place I button up the microphone assembly and it all worked first time, I found it necessary to reduce the transceivers microphone gain down to approximately 15 (with the clipper out of circuit) and adjust the clippers output to match the normal microphone setting using a small preset on the clipper PCB (I was a bit premature completely reassembling the mic!).


The mic. gain and ALC adjustments were made by ear, aided by the use of a second receiver fitted with a decent pair of over-the-ear headphones, to prevent audio feedback while monitoring the FT817 transmission.  Setting the FT817  ALC is very "hit and miss" using the LCD bar graph provided, however, I did managed to eventually adjust the gain settings to produce  a few meter bars on speech peaks, both with and without the clipper. 

After satisfying myself that I was not overdriving the transmitter I finally re-assembled the microphone and then did a couple of videos showing the modulation envelope of the transmitted RF signal, with and without the clipper in circuit. I'm sure once you've viewed both videos you'll be able to instantly see the increase in peak envelope power made by the clipper. 

Un-processed 

Processed

I decided to perform a couple  on-air tests with another amateur, fortunately Mark 2E0VOV lives within 2 meter QRP range so I set a schedule using both FM and SSB. Mark can always be relied upon for an unbiased audio report, he's spent some time with me fine tuning his FT817 audio, which now uses an electret microphone insert, his logbook bares whiteness to its clout in chasing QRP DX.

It's fare to say the results on both FM and SSB were disappointing, the overall increase  in average signal level was good but the audio quality was very poor - this was using the supplied electret mic. Mark commented that both microphone setting were like listening to me through a wet sock, at this point I got frustrated and a little confused, as the audio was poor with and without the clipper in circuit! After some thought I decided to try mounting the  supplied mic. insert in a baffle plate (as shown), after all this is the way Mark and so many other amateur have modified their standard Yaesu microphones to take an electret insert.

The upshot of my experiment has finally produced audio  quality that now matches the increase in talk power provided by the clipper. :0)

However, I can only recommend this mod. to those with a steady hand, a good set of eyes and decent fine tipped soldering iron. 

73 to Ivonne Glaser (DO2AL) and Harry Gödde (DO5AL). Thanks to Harry and his partner for all their help in perfecting this modification, they have now taken over the production and development of the DF4ZS RF clipper.

Note: Having discussed the above modification with Harry, he has promised to investigate my findings once he has finished re-designing other products in their range. The clipper sells well as it is and my modification just adds icing to the cake. 

I hope you have found the review useful and interesting, I have yet to do any serious DX chasing with the RF Clipper Microphone, because as soon as the project was finished HF propagation took a very rapid downturn.  I live in hope of better times with the onset of the  sporadic-E season. 

73 Rick DE G6AKG