Saturday, 26 July 2014

Cheap Chinese WiFi Yagis - Avoid!

Well, Ive generally found the cheap Chinese imports to be alright, but it seems I lucked out on the WiFi Yagis.

I ran a test, comparing these to a standard 'whip' wifi antenna, and these are actually worse! The more I look at it, the more I realise I should have known from the start!

The main problem I think is that the driven element is so far out of the plane of the antenna.The boom is also far too wide, and the elements far too thick.

 I will see about a mod to put the driven element correctly in the plane. I have two of these and if I dont get them to work im effectively out of pocket by about a tenner (yes, I know its not much for two antennas, and in fairness, the U clamps they came with are probably worth a fiver themselves)

Its a shame, as the little cheapo wifi dongle I bought to improve the laptops connection works quite nicely! Its only about 10dB better than the laptops internal antenna, but since it has an antenna port, it means I can connect a directional antenna to it - If I can get a working one!

I have looked at various homebrew wifi yagis, and will probably make one now and see how it works.

 I finally have the spanner for the Larkspur mast! Thanks to Chris G6HTH.

Ive looked around online and made use of a yagi calculator to create a set of dimensions for a 15dBd gain 2.4GHz yagi, using simple materials that I have knocking about. It should take about 2h to knock one up.

Monday, 21 July 2014

Playing around with Jenny

Jenny, like many of us, takes a little bit of caressing to really get going, and Julie doesnt mind me playing around with her. Of course, Jenny, or 'Genny', is short for generator.

This is the machine I picked up at the rally. After Sam and I had enjoyed our morning of Canadian canoeing, and a fried chicken lunch, we headed to ASK to pick up some two stroke oil for her. She needed a while for the oil and fuel to work into her, but soon she was throbbing away. She does like a little squirt of carburettor cleaner/easy-start to help get her going, and she runs a bit lean, so likes just a touch of choke to keep her from 'hunting', but other than that she works quite well.

She's shown above feeding a small 7A 13.8v linear PSU (it does slightly over volts anyway). 
The blocking diode needed to allow parallel battery operation was lifted from an old PSU card, I think from a transposer. Its a dial diode, each leg rated 15A. It was one of a half dozen semiconductors all mounted on the same block of aluminium, so I also took that ali block to mount it on.

A pair of lengths of my heavy duty DC cable provide the connections to the diode. A layer of tape, and then liberal coatings of liquid insulation, sealed and insulated the +Ve rail.

A small piece of heatshrink tubing, pumped full of hot melt glue, seals the -Ve rail through connection. The whole assembly was then wrapped in 3M PVC electrical tape. The red smudge isnt, for once, my own blood (I managed to save cutting myself for later!) but is actually tamper evident varnish, used to seal the thread on the bolt.

By setting the PSU feeding into the diode such that the output voltage at the diodes cathode is 13.6V, this will allow the big 38Ahr SLAB to be charged and act as a reservoir for the peak current demanded by the radios. An added bonus of this scheme is that the generator can be stopped for refueling without having to stop radio operations.

Ive managed to get a bit further with the WiFi repeater, but need to do a proper air test soon. Still to do is making up the datamode lead for the Yaesu, the 6-pin miniDIN plug I have isnt wired properly. Being a sealed plug, its not easy to change, so ive ordered a plug. I can probably get away with the old plug as a test until the new one arrives.

Sunday, 20 July 2014

Finningley ARS Rally

Sorry, another post with no photos!

Today was the 1st Finningley ARS Rally at Sandtoft, near Doncaster. Myself, Sam and Mike arrived not too early with our selections of bargains (ok - junk) and were directed to an outdoor pitch.

Once we had our stall set up, the other vendors were beginning to make use of 'trader privilege' to seek out bargains before the punters arrived, and I was already taking money before i'd finished unloading!

The target of the day was to raise enough money to cover the insurance costs and some running expenses for the CHOTA station. This was more than achieved! Oddly, the vintage stuff i'd expected to sell easily didnt, and the RF PCBs I thought might be hard to shift went well!

My own wanted items I couldnt find! So I will have to order the dipole center and the 6-pin MiniDIN (unless the old mouse one does work) online. Most of my days purchases were to feed and water my eldest son, who happily had the price of a can of pepsi and a tray of chips from me. But, one bargain I couldnt resist was a small 2-stroke petrol generator for £25! I didnt actually pay that, I paid £20, and the stallholders wife (he was away at the time - it turns out looking at MY stall!) said ok, as she didnt want to cart the bloody thing home! I think the fella might have been a bit disgruntled at this, as she told me later he came back and said "you sold that genny for £20! I know, 'cos the fella that bought its bragging about what he paid!" I have yet to see if it actually works (no two-stroke oil!) but if I have bagged a bargain, i'll be very well pleased.

But, the potential to have a small genny available gives me a bit of a problem - Its regulation might not be great, so I would prefer any sensitive kit - such as HF transceivers, to be run from it via a PSU AND a parallel battery. However, to do this I need a blocking diode capable of taking the full, peak, forward current! This is about 22A! As luck would have it, one of the PCBs I didnt manage to sell today has a pair of suitable diodes on it!

Rather than charge Mike his share of the booking fee (I took the pitch booking fee of £5, so Mike's fee was just £2 for an additional trader pass) I just made him brew bitch for the day!

Thursday, 17 July 2014

1st Sandtoft Rally - This Sunday

This Sunday sees Finningley ARS hold the 1st Sandtoft Rally. This is on the grounds of the old Sandtoft airfield, near Doncaster. See their website for more details Finningley Rally

I shall be there, along with a considerable quantity of junk to sell. Please come along and buy some of my junk! It will be mostly RF circuit boards, mainly UHF, with some very nice RF parts on; but also cable, various loose bits, some odd bits of untested equipment etc. All proceeds towards the CHOTA station's expenses.

Come along and support us and the rally! I believe rally entry also gets you free entry into the Trollybus museum!

In the meantime, the WiFi repeater progresses. The 5v regulator board is now fitted.  A power on test with the unit connected by LAN cable to my laptop showed the board to be working, at least as far as logging in and configuring, and able to see some local WAN networks. Oddly it didn't seem to see my own network, but then in the workshop neither can my phone! Even with the yagi's, there probably isn't sufficient signal penetrating into the workshop to pick up.

The regulator board looks very home-made, but this is in order to get the decoupling capacitors as close to the 7805 regulator as possible.

It turns out that the antenna port at the lower left of the photo is the 'source' network antenna, which means it is the antenna port on the right of the unit when viewed from the front. This is ideal, as in my mind the source signal should be on the right, and the destination signal, or new network coverage, to the left.

Still to do, is the U-clamp plate for the lid of the case, and an actual 'air' test - I have to prove that not only will this pick up and connect to a network, but it will also generate a new, relayed network.

Sunday, 13 July 2014

WiFi Repeater Progress

The box has been completed, the board modified, and all installed into the case

The purple wire is the thinnest I have at the moments. Unfortunately its not thin and flexible enough and has led to one of the pads coming off the board. Luckily, this was for the WAN  LED, which was to have been the green one. I can live without this, but subsequent wiring was done with far more care! It had proved impossible to remove the original SMD LEDs, so these had to be destroyed in situ, to prevent running parallel LEDs and ramping up the current. One of the coax's also had to be redone as the dielectric melted and shorted out.

With care, the remaining two LEDs (PWR and RF) were connected up, along with the reset switch and fitting the RP-SMA connectors. I dont know if the LEDs are wired correctly yet, that will become apparent when the unit if finally powered up. Apart from the sheet of insulation behind it, the board is only currently held in place by hot melt glue along the edge and around the LAN connector. Much more hot melt will be added to the top corners later.

The device bolted to the side of the case is a 7805 5v regulator. A set of bypass capacitors are still needed on this before the board can be wired to it, and the DC socket connected up. Prior to this, the antennas will be fitted temporarily and the boarded fed 5v from the variable PSU on the bench, with the laptop connected, just to prove the board is still operational.

When the 2nd repeater arrives, i'll meter out the WAN LED connections and find a way to reconnect the LED.

Apart from the PSU and testing, there remains the mounting plate. This will bolt to the lid of the case, and hold two U-clamps. With this in place, a section of pole with a base plate attached will be fashioned to allow a free standing repeater unit to be set up.

Hopefully testing of the unit can start in the next day or two.

Saturday, 12 July 2014

WiFi Repeater Ruggedization Build

The project to build a ruggedized WiFi repeater ready for the church station is underway. The RP-SMA connectors and the extra Yagi have both arrived from Hong Kong,

The repeater has been removed from its cheap plastic shell, and the outrageously poor SMPSU removed and discarded. The two silly little PCB dipoles have also been removed.

The PCB pads for connecting the new antenna connectors are not very big, but just about workable. The hot melt glue holding the original coax in place was very carefully peeled off, and the coax cut to leave just the smallest bits soldered to the board to unsolder. Attention then turned to the new housing

This is a die cast aluminium 'Eddystone' box ive had kicking about for a long time waiting for a suitable project. Some very fine needle file work and we have a snug hole for the LAN connector. Holes were then marked for DC power input, the two antenna sockets, a reset switch, and the status LEDs.

The reset switch on the board is a tiny push button, this is being replaced by a good sturdy toggle - latching one way and momentary the other. The momentary contact will be used as the reset control, but the latching side will be used as a 'parked' position, helping prevent resets due to the switch being knocked.

The LAN socket cutout is so arranged that the whole board sits a few millimeters above the case, and will be held in place by hot melt glue. Other spacers will be used to ensure the board cannot short to the case.

The 5v regulator circuit will be installed against the left hand side of the case, and the three status LEDs through the bottom surface, in a vertical row. These are likely to cause the greatest headache, as the LEDs on the board are incredibly small, and i'll have to remove them and wire the case LEDs in their places.

Once complete and tested, the lid will be fitted. But the lid itself will have been heavily modified - It will have a plate bolted to it through which pass a pair of U clamps. This will make it possible to fasten the repeater and its Yagis to the same short pole, with the battery underneath.

Sunday, 6 July 2014

'Jaybeam' Slim JIM

Many of us began our ham radio career as the then Class B licensees, confined to the frequencies above 50MHz, and for many of us, our first antenna will have been the ubiquitous 'Slim-Jim'. Some of us, those with money, might have bought a commercial antenna, but those like me, impoverished school kids with an agonising paper round, spent our birthday money on a radio, and built an antenna. My first radio was a Kenpro KT-22 2m Handheld. This was actually stolen off my belt in Doncaster market, but one day i'll get another for nostalgia!

To go with this, I built my first slim jim. This was made from mains wiring stapled to the cardboard backs of several A4 notepads. Incredibly crude, but it worked, stood against my bedroom wall. I only abandoned it after it folded over whilst on air on night, across my bare arm!

Most people these days build them from a length of ladder line, which is what ive done here. 300 ohm window line. I used dimensions from G0KYA's blog, where he discusses a problem found when converting from 300 ohm ribbon to window line, with the velocity factor. To prove a point, I started with the original measurements, then swapped to his new set of 53" overall length, 16" for the matching section.

The insulation on this stuff is quite thick, and takes some baring back. Once about 1/4" is bared at one end, its tinned, folded over and soldered together. This is done at both ends of the section of line.

The bottom few inches are also bared back to provide a location for the feedpoint. This is found experimentally, and is usually the most tedious part of the build - this one being no exception! A sharp knife is needed to expose the wires.

The gap cut into one side, which separates the 1/4 wave matching stub from the 1/2 wave folded radiator, usually makes the whole thing go floppy, here ive reinforced it by taping a wooden coffee stirrer splint over it! This is a 1" gap cut 16" from the bottom.

I used an offcut of RG-58 with an N-type plug on it for the feeder, about 2" long. After a lot of experimentation, I found that 2" from the bottom gave me an acceptable match, 1.6:1, when the antenna was enclosed in its fibreglass tube.

Now, a word about enclosing these antennas. Im using the remains of an old commercial antenna, but even so, putting the antenna into the tube drastically detunes it! So much so that the resonant frequency of my antenna is about 138MHz. Attempts to compensate for this by cutting the antenna for 145MHz resonance when in the tube failed, im not at all sure why, but I reverted to the original dimensions and found a workable feedpoint.

 The antenna is now in its fibreglass tube, with the metal mounting hardware attached. This is being reattached using epoxy filler. Once cured, four bolts will firmly attach the mounting, and the bottom of the tube will have some sealant pumped in.

I also found time to get around to sectioning the 4" Heliflex feeder offcuts. The outer copper on this stuff is so thick that in the end, it was removed with an angle grinder!

 I now have the two sections with connectors sectioned, and apart from a bit more filing to remove some swarf, they are ready for classroom use.

Saturday, 5 July 2014

New 2m Vertical

Its about time I had a portable vertical for 2m FM work. Now, I do have one, but its extremely heavy! Ive used it on the Clansman masts at the show before, but it takes some serious effort to raise.

So ive decided another Slim Jim is in order. Like the last one, this one will be made from 300 ohm window line, but this time enclosed in the radome of a now defunct Jaybeam collinear.

The antenna itself is now built, and the collinears fibreglass tubing cut to size. However, I have not yet had it on the analyser to see where the correct match feedpoint is. Thats a job for tomorrow.

Friday, 4 July 2014

Laptop power

OK, so this really belongs on the CHOTA blog....but I suppose it comes also under the general radio and electronics stuff I do...

I have an old(ish) Toshiba Equium A200 laptop, this is alright for general radio use, but the battery is shot, and I cant justify paying the price of a new battery! Now, I really want to be able to use this in the field, or car. Ive tried it on a 12v SLAB, but it wouldnt power at that low a voltage. The specified supply is 19v (although its battery is rated 10.8v???). So ive decided to invest in a 'car charger', like this one 

With any luck, this will solve the problem of running the machine from a 12v DC supply. This will allow me to run WSPR etc mobile (well, parked up!), and especially at the church station. I will have to measure the current taken when running just WSPR on the laptop, to work out what battery capacity I really need for a days working.

New blog for CHOTA

I have decided, since theres a lot of information and a lot of tests involved, that this blog was getting a bit cluttered with posts about the St Marys CHOTA station, and so ive started a new blog just for CHOTA

On there you will find the info and pictures of the various antennas, masts etc, and of the church itself, as pertains specifically to the GB0SML station.

On here though, there might still be some stuff related to Lead church! This is because, the landowner, Simon, has been nice enough to allow me to use his field for the Backpackers contests! Of course the same ban on ground penetration still applies! So, im now considering how best to get my little 3 element 2m beam in the air from the church! I would normally use a 5.4m Clansman mast, but these need guying! Time to see if the 10m fibreglass mast can take it! It will be nice to get the FT-290 back out portable!