Frog FAB!

Quite some time ago, I dismantled for parts a defunct 10W CML analogue UHF TV transposer. One of the things I kept from it were the thin anodized aluminium sheet covers on the individual modules.

Tonight, I decided on a bit of sheet metal fabrication! Ive measured and marked up one of these sheets, and using my mini-bender, formed it into a U-shaped box half, the first stage in making a cabinet for the Frog Sounds QRP transceiver I built a few weeks back

This sheet is only about 1/64 of an inch thick, and bends easily and accurately, although it is a bit flexible which makes filing the saw cut edges smooth a bit time consuming.

I'll find out some standoff posts to mount the PCB on, and then once I have the lengths of those, will mark and drill the holes for the connectors, controls and LED. The box will be a bit wide, but I really couldnt be bothered to do the necessary measuring, marking, cutting and filing needed to make a narrower box. Its as wide as the CML modules were!

I will also cut and fabricate another U-shaped half to be the lid. This I might have overlap the bottom section by a quarter of an inch or so. Ive yet to decide how to fix them together. I could use four long standoffs (or chains of standoffs) as pillars, or I could see if I am skilled enough to bend a pair of lugs inwards into which I can secure four M3 sized nut-serts.

Tape Measure Satellite Beam - UHF Build, Tested

A big problem I have when it comes to testing UHF antennas is that my analyzer only works up to 170MHz. This means that transmitting on UHF into a homebrew antenna is a bit risky! And its a risk I didnt wish to take with the tape measure antenna.

Luckily, I have a friendly engineer colleague, and he has an Anritsu Site Master test set. This machine will do what my spectrum analyser, antenna analyser, VSWR meters and more do, but from 25MHz to 4GHz! And today over my lunch break I put the UHF beam on it.

Despite the fact that I have inadvertently cut the driven element too short, because I forgot I had marked the whole inches but not yet the tenths, and then went and cut it, the Anritsu showed that the resonant point was only a little high, around 441MHz. The part of the 70cm band used for the FM satellite downlink (Mode J) is around 436MHz, and here the VSWR was still well below 1.5:1. Perfectly usable. And this reinforces the on-air reception test a couple of days ago where I could still copy French and Spanish stations working the SO-50 bird down almost to the horizon.

All thats left now is to decide on a mounting method to join the two beams together for use, and to try the combination live against a satellite pass.

Revox Revamp

As is probably known by regular readers of this blog, i'm a bit of a sucker for a nice bit of surplus! So when I spotted this beauty on its way to the WEEE man, I just had to save it!

This is a Revox B261 FM tuner. Its got to be the most perfectly retro set ive seen! It makes me think of a middle aged bloke, with this and its matching amp built into a teak cabinet, huge headphones on, a pair of cords, slippers, and pipe, puffing away to a good bit of prog rock...

It had a ticket on saying 'dead', but luckily, also naming the engineer who said so! So, a quick email to him and I knew its symptoms - doesnt come on, just makes a click as from a relay on power up. OK, so, something inside is working, even just for a moment! A relay is powering up! My suspicions, as always with a vintage piece, fell on its electrolytic capacitors, and in particular, the power supply.

But first, I had to un-mod it! The XLR's and the Eddystone box of DINs shown here are all part of the non-standard build inside, part of the use this set had been put to in its earlier life.

There were also several PCBs inside as part of the mods. All came out, and theres some very nice parts on them!

 All the mod parts are shown here. Theres relays, audio ICs, audio transformers etc. With these out, the tuner is back to its 'native' state. And I could start work

 The first thing I did, was to continuity check all the internal fuses. Oh look - F4 is open circuit! Could it be as simple as a blown fuse? Rated 800mA slow blow, I didnt have any but found some 1A which will do at this stage. I replaced it, and tried the power - still dead. Rechecking the fuse showed this one had blown as well. So, checking the circuit diagram, I now knew what I was up against. F4 protected the 9.6v windings of the power transformer, feeding the +5V regulator. The picture below shows the regulator card

 Notice the missing component? C1, a 2200uF 16v electrolytic smoothing capacitor, was dead short! Thats it in front of the PCB! With it removed, I fed the LM317 regulator IC with 10v from my variable PSU, and tested the cards output - A good 5V line!
After some digging about I found a replacement 2200uF 25v capacitor that fit nicely. Soldering this in, and adding a wire link to connect two point that previously did so via the three ground lugs of the original capacitor, meant that I could refit the card and try the radio. It failed first time, but only because I forgot to replace the fuse! With a new fuse, powering it up and pressing the buttons, I now have -

Yes! Its on!
 OK, so ive no speakers or antenna attached, so I dont yet know if it actually receives or if theres any output, but it powers on, the display works, the buttons work, the LEDs work! (alright so the display backlights dont work, but they are 36v filament bulbs - i'll replace them with LEDs)

I'll test the audio another day, but i'm quite confident its working. And for the sake of a few fuses and replacing this little bugger

I have a top of the range professional grade FM tuner! And its cost me nowt!

UPDATE - Ive just slipped out, put a croc clip lead on the antenna socket, and plugged in my cans -
It sounds amazing! This sounds to me how FM should sound! This is most definitely the best thing ive every pulled out of a skip!

What a muppet! - FT-857D CAT fuse

Feeling utterly terrible today, hardly able to think straight. So of course it was perfectly sensible to test to see if the FT-857D's CAT port 12v pin is switched or permanently on during my lunchbreak. It was of course perfectly sensible to do this by plugging in a bare plug, without its shell, to gain access to the pins...

Or not. As I discovered. Measuring the pin with the radio powered but off, showed no voltage. Measuring it with the radio on, showed 12v - for a moment.

And that moment was when the meter probe slipped and shorted the pin to the one next to it - GND! It even made a nice crackling noise until the internal, and ironically, surface mount, fuse blew!

Well, I suppose I have gained the information I wanted, the pin does appear to be a switched 12v line, so I can power the RT-11 from it. But, unless by some fluke I have a suitable SMD or micro sized fuse in my junkboxes, perhaps not for some time.

Crazy Idea? 144MHz Dismantlable/Transportable 4x Long Boom EME Array?

A strange thought occurred to me yesterday - with suitable thickness PVC tube, and 25mm/1inch dia. tape measures, plus various pipe fixings, it should be possible to build an ultra light weight, portable long boom 2m Yagi.

That being the case, it is clearly possible to build four of them, all identical. With that done, some more tube and they are on a H frame. A few more pieces and the H frame is mounted on an A frame...

Some cleaver bearings, a long guide handle, and some form of sighting system - and we have a portable EME antenna array!!!

Used with a 100W linear, a suitable masthead preamp, and a laptop running JT-65....


Just a thought

Tape Measure Satellite Beam - UHF Build, Pt 2

Building the UHF section of this antenna has proved somewhat trickier than the VHF section. For a start, the holes through the boom are a bit more critical, and although ordered my new reamer hadn't yet arrived to widen the holes a little at a time, so I had to do that carefully with a round file.

Once all the elements were in place, apart from the driven element and its support member, and all the sections aligned, the 'plugs' were secured with a liberal dousing in glue. Several coats of this glue might be needed to allow it to fully penetrate and make the joints fully rigid. The mostly assembled antenna was left supported on my workmate for several days for the glue to cure

Whilst the UHF section was curing, I got on with tuning the VHF. The driven element sections were trimmed to bring the resonant point close to the middle of the 2m band, and then a Hairpin match added to adjust the feedpoint impedance. Its actually resonant close to the middle of the band, but the match around the FM simplex calling frequency 145.500MHz (S20) is very good and the picture below shows just what it is around the satellite frequencies

Im quite happy with that! The Hairpin came out as about a 5 inch length of wire. The 50ohm RG-58 feeder is wound for 6 turns around the boom to form an ugly balun. Eventually, I might change the M3 bolts to some that are a bit shorter, as they are a bit too prominent and could catch on things during use.

Ive not yet tried the VHF beam on air. I'll test it at the weekend against several local repeaters.

The UHF section does now have its driven element in place, and is just awaiting connection of the feeder, and then testing and adjusting for the best match. I dont possess an analyser or SWR meter that works up to the required frequencies, so once complete I will take it to work and test it on the Anritsu Site Master testset in the service center.

Low cost Chinese components and modules

Its probably not gone un-noticed that I order quite a few components and modules from the Far East. One of the suppliers I use what has proved very good for low cost and/or bulk parts and modules, particularly for Arduino and Raspberry Pi related modules, is Banggood.

I have no connection with these guys other than I buy LEDs, Lasers, small modules etc from them. If these sorts of things are something you wish to buy (and if your following what im doing on here then theres a good chance you do) then if you follow the link below, and order from them, you become one of my referrals and I get a little bit of a discount!

So please, help me save money! - Banggood - electronics, toys, gadgets

Ive also noticed a large increase in traffic to  my blog recently, mostly form Europe and the US. I'd be interested to know what people think and what it is im doing that you find interesting. Feel free to leave a comment!

Mobile HF antennas and tuning

At present for mobile HF im using Hamstick type  single band antennas. The problem with these is they are rather big for a little car, and its quite a faf to change them to go to another band, especially if im just listening about, where I might be outside the amateur bands.

So, at the risk of reduced efficiency on lower bands, im considering installing my LDG RT-11 remote auto ATU alongside the FT-857D, which hopefully will give me some improved frequency agility, and particularly, allow me to use a shorter antenna for general utility listening.

The RT-11 is capable of fully automatic operation, retuning itself on any frequency change greater than 10kHz. But the manual states that the control line for this should be grounded momentarily on powering up, it doesnt say if it can be left grounded. It would be quite awkward to add yet another remote control cable between the radio installation and the control position at the drivers seat, so I need to find out if it will work as needed.

Unfortunately im not in a  position to test the theory for a few days!

I also need to haul out any junk I wish to take to sell at this years Finningly rally on the 16th!

Tape Measure Satellite Beam - UHF Build, Pt 1

After a lot of deliberation, and careful testing (ok, waving about) of 1/4wave lengths of tape, I came to the conclusion that the cheap 19mm width 3m long tape I had was just as good as the 22mm I was going to us, and so have saved the slightly wider tape (which is also 2m longer) to use for its originally intended purpose.

Each of the five elements of the UHF section of the satellite antenna is between 11 1/2 and 12 inches long. Above they are all cut to the nearest higher whole inch. Below, they are cut to exact length, again using steel rule and digital calipers, the corners trimmed diagonal to remove the sharp edges, and the driven element cut into two halves

Next I needed to find a plastic tube to cut the plugs from. What I found was a two part PVC elasticated pole from an old toy pop up tent! Another one of those things I kept because it looked useful! from this, four 1inch, and one 3inch, plugs were cut, again just like the VHF plugs, using a pipe cutter for nice neat edges

Two things I have yet to decide on are A- Do I make a seperate UHF boom, or drill the UHF holes onto the VHF boom already made? And B- How to attach the feeder to the UHF elements.
Question A will be answered by examining the spacings on the VHF boom and the balun positioning. This antenna doesnt have to stay as intended and be separable into two for VHF ARDF, as ive more than enough materials to build a second VHF beam just for Foxhunting. Question B will depend on what M3 bolts I have and how sturdy the 3inch plug is when inserted into the boom.

A more pressing task for tomorrow though is to test the match of the VHF antenna, and add and adjust the hairpin match section.

Tape Measure Satellite Beam - VHF Build

A couple of hours today, and I have the VHF section of the tape measure beam built. The hardest part is getting the holes marked and drilled accurately. There are three 3/4 inch holes to be drilled on each side, and these have to line up with each other on each side, and with each other on either side! This was done by first drilling a pilot hole all the way through, and then expanding it out with a tapered reamer bit.
The boom is 1 inch diameter, the holes are then plugged with 1inch long sections of 3/4 inch tube. These are cut using a pipe cutter, which leaves nice tidy edges.

 

With the tape element in place, the plug is pushed tightly home. By reaming the hole more on a particular side, the hole can be adjusted to get the elements in best alignment. Once complete, these will be made permanent using a PVC welding solvent glue.

 The picture above shows the director and reflector element installed, and the driven element 'mocked'up' using Jubilee clips. You can see that some alignment work is necessary, although it would probably work just as well without.

The next task was to attache the driven element sections. A circular wire brush and mandrel in the pillar drill made light work of removing the paint from the ends, and then three M3 fitting holes were drilled.

The 'plug' section here is 3 inches long. Carefully marked and drilled to correspond with the element that will be attached. The reverse side has 6.5mm holes that allow screwdriver access to the bolts. Each element is fitted with a pair of 'contact' bolts, with M3 solder tags on each. A third bolt secures the element near the end of the plug.

The antenna with all elements installed is shown below. At this stage some adjustment of the element lengths on either side was needed for the director and reflector, this being done by measuring both sides and pushing out the plug, adjusting the tape, and pushing the plug back in, until all was equal.

 In this final picture, both sides of the driven element are attached.

Since taking these pictures, ive attached the coax feed to the driven element, wound the 6 turn balun onto the shaft, and added the BNC connector. I have yet to put the antenna onto the antenna analyser and check the match, which is why I havent yet installed the hairpin matching section. I should get this done in the next few days. All being well, the VHF side will be complete soon, and I can work on the UHF section.