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 

Thursday, 19 May 2016

FT817ND VOX Interface

A month ago I built a rough copy of the Wolphi VOX interface to go between my Yaesu FT-817 transceiver and my Android Tablet - its shown on my now largely defunct Facebook blog. It worked OK with the Tablet but was somewhat "hit & miss" on my Chinese copy Samsung phone. The Wolphi interface uses the DC bias available on the Tablet audio port to power a single stage audio amplifier, it's normally used to supply an electret microphone in a headset.

It would appear this DC level is not standard across all Android devices and on my phone it was a dismal 1.4V, far too small to provide a decent rail to power the audio amp. This resulted in my interface failing to key the FT-817 in several of the digital-modes I tested, even with the phone volume set to maximum. 

Needless to say I was rather disappointed, but to be fair if I'd used a Darlington pair transistor rather than an FET to control the PTT line, as in  the original design, it would have worked. The FET requires twice as many volts to put it into conduction - so there's nothing wrong with the Wolphi design. I'd decided to use an FET because it's is less likely to be biased on by stray RF fields which are often present in the shack  and portable installation where RF grounds are less than perfect. If  the interface were to be effected then the transceiver PTT line would hang in transmit mode, because the PN junction in the control transistor rectifies the RF and biases itself permanently on.




I finally settled on a circuit designed WA8LMF which uses a step up transformer rather than an audio amplifier to generate the high level of audio needed to drive the VOX circuit and in order to make the rectifier circuit more efficient I used a Schottky diodes which have a much lower forward volts drop, of approximately 0.2V, giving me more power to switch the FET. If you have some germanium point contact diodes, like those used in crystal receivers, will work just as well.

My interface uses transformers culled from my extensive scrap box, however, after a search I found some suitable replacements available from Rapid Electronics. Unlike the original interface design mine has additional flying leads enabling the use of  Notebook PC in place of the Tablet - the number of digimodes available for Android is still relatively limited, so I like to use FLdigi and MMSSTV as well.

Just as a final note, if you see any old PC keyboards floating around at the tip or a junk sale, the type with a light green PS2 plug, salvage the cable with plug, as it can sometimes be used to connect the interface to the data socket on the FT-817 as its the same plug - unfortunately later keyboards use a cheaper cable with the spare cores removed. :/


Monday, 16 May 2016

I need the Sea


Hamworthy Sunsets

I couldn't live away from the sea its in my blood, three generation of my family have work, next to, or on the sea. My maternal grandfather George was a shipwright diver, my father Gordon was an Electrician in Bolsons Ship Yard and I worked for Greenham Marine as a marine electronics service and installation engineer. I was born under a water sign, if you believe such stuff and away from the sea I get restless. Here are a few of my Poole Harbour sunset photographs taken from the Hamworthy shoreline - they are a comfort to me when I'm inland. :0)

Sunset from Lake Pier, the dolphin (mooring post) is
a relic of WWII when a shorts flying boats would
have been stationed here as a coastal patrol.

Low tide at Hamworthy Park (late winter)

Same sunset but earlier on, boy it was cold.