Yagi aerial design help

[CHE]

Mike,

I think Vin's early trackers were on 27MHz but his later ones were on any frequency you wanted. I know of a well known F1C flyer from the Harlow 'hood who has them on 173MHz and uses a suitable Yagi.

CHE

[Baz599]

Hi PeeTee

Re. “1p less than an unwell cephalopod”

Should I feel happy or insulted ?

[PeeTee]

Baz

Perplexed is more like it Having been brought up on a diet of the Goons, Monty Python & the Bonzos I have a somewhat warped sense of humour, thus:

Unwell cephalopod = sick squid
Sick squid = well just say the words and you'll see
1p less than £6 = 5.99

Just out of interest, what does the 599 represent?

Now back to the subject, was the tape yagi information of any use to you?

TTFN

Peter

[Baz599]

Hi PeeTee

Well, that is a good one now you’ve explained it, 5.99 I would never of worked it out.  The 599 actually refers to the BGA competition number of my first syndicate glider (full size).

Re the tape measure Yagi, it’s on my build list but in reality it will most likely be winter before I have time to do it.

Regards

Baz £6.00 -1p

[JefO]

Getting this back on track...

I need to get a Yagi for 433MHz by Friday 20th Aug.

What do I need? (apart from a miracle or a time machine).

Thanks in anticipation,

Jef

[PeeTee]

Jef

An hour's work plus a quick visit to B&Q and Maplin will see this done and dusted. Ian tells me that he has sent you a copy of all the info i provided to him, together with my e-mail addy - feel free to call direct as I'm having difficulty from accessing FlyQuiet from time to time.

For materials you need to buy a length of 20mm plastic conduit or overflow pipe from B&Q (or elsewhere) plus 2 metres of 5 or 6mm alu tube from the metal racks. From Maplin, you'll need a length of coax cable (I don't know if 50 or 75 ohm is best) together with a connector to mate with your scanner/receiver. Finally some 16swg piano wire is needed (about 28" by my reckoning.

The drawing shows you the element widths and spacing. For the alu elements I just drill a 5 or 6mm hole centre the tube and retain with a smidgen on 5 min epoxy. The 16swg driven element needs to be bent to shape to the drawing dimensions, and the coax inner and braid soldered to it. Fit the plug to t'other end (I allow an 18" lead ) I've added a wooden handle at 90 degrees to make it more comfy to hold and if you do that I recommend plugging the last 2" of tube with dowel.

If you need anything else, just shout

Cheers

Peter

[JefO]

 PeeTee

Thanks ever so much - exactly what I needed.

Already have the plastic tube and the coax (we don't use the telly upstairs anyway  )

Just a couple of bits to get then.

Cheers,

Jef

[PeeTee]

Tres bon

You may find that the info from me via Ian talks about using 16 swg piano wire for all the elements. I chose to use alu tube for the four passive elements as 16 swg has a propensity for poking into people's eyes, damaging model covering and tearing car seats. Unfortunately the total length of the four elements is just over a metre, hence the need to buy two lengths.

What are you using as the transmitter (bug)?

Happy tracking!

Peter

[JefO]

Hi PeeTee

The Txs we have are 433 (434MHz) Radiometrix units, supplied via Ian. Dad has been busy making timers which he has done without mounting them on a board (rocketeers are very weight conscious).

To offer some flexibility within the team, for those that want to use the devices, we have made the battery connections compatible with the Alt - USB LiPos and charger units from Adrel electronics. This means we have no way of preventing polarity reversal, other than religiously looking at the colour of the wires to each half of the plug and socket. Obviously a recipe for disaster in the heat of competition, but the chips and the LiPos are all relatively cheap, and it is easy to tell when a bug is working (unless someone is already retrieving a model with the scanner, but with their walkie talkie switched off).

Will be building a Yagi this evening. Thanks for your help.

Best regards,

Jef

[PeeTee]

Hello Jef

I'm pleased to hear that it's coming along. Just to let you know that the bare boards weigh 0.15 g and tend to use less solder than when joining components individually. Good luck to your dad if he is making up the timer using chip devices (SMDs) as it's bad enough trying to solder 2x1mm chip resistors onto a PCB

Just one word of warning (something that crossed my mind) to ensure that the timer is able to withstand launch loads. As for using Lipos as a power source (I assume a 1S), you are on your own there, although looking at the data sheets it should be OK. If it's a 2S, I'm pretty sure that the Tx module isn't specced to 8.4 v as I gave Ian the part number for the low voltage version which we use with the 3v fishing float batteries.

Anyway, best of luck, especially with the comp - bring home a nice gold medal!

TTFN

Peter

[JefO]

Hi Pete

Using the Tx with 1s LiPo.

Yagi is built.

Not sure that it is functioning correctly. Would have hoped for better directional selectivity, frankly, don't know if it is working or not.

The receiver I bought does not have a signal strength indicator. Perhaps that is where I have gone awry.

Launch loads - the bug will sit inside a snug and cosy cylindrical blue foam and Depron capped capsule in the middle of the rocket, so it should be OK there as far as launch loads go. However, at the end of the launch phase a secondary charge strikes the bottom of the capsule and accelerates it pushing the nose-cone and parachute out into the air. There is no easy way of evaluating the forces on the piston from the deployment charge - each motor is different, each parachute and nose cone has differing mass. Having a 4 - 5g weight in the piston is uncharted territory in itself (the piston usually weighs 0.5g or less) and the subsequent increase in pressure under the piston may have a catastrophic effect on the body tube and boat tail, so the first boost with a tracker fitted will give us a lot of information either way.

Thanks for the sentiment regarding a medal. A team medal in anything would be really good, but I am sure I don't have the ability / International exposure to get a medal on my own merits.

For the WSMC in 2012 though... who knows?

Best regards,

Jef

[JefO]

...
4. (PeeTee) I have already made a pistol grip for the 'holding end'....from a lump of pine, should really be oiled mahogany but I am a cheapskate.

Don't you just love toys? I will probably use the Yagi in anger infrequently but its cheap to make and has that aura of je ne sais qua that encourages a venture into the esoteric.

Regards Ian

Conscious of the aerial weight comments by various on here, I built my pistol grip from Balsa - in the vain hope that the good air god (who seems to appreciate things made from this wood) looks favourably on my freeflight rocket models (which are shamelessly wood free zones).
 
Totally agree about the toys comment. Yagi aerial has the Maximum toy factor, even if the bloomin thing doesn't tell me in what direction the model is.

Thanks to all the contributors in this thread for their comments,

Jef.

[PeeTee]

Hello Jef

I don't know what range you were checking the Yagi at, but they are better for directionality at greater distances - 400-800 yds. To get the best performance at short range, it is normally necessary to tune 'off frequency', and I don't know whether you can do that with your scanner.

To get this into perspective, at the Nats I had two flights land in the barley field over the Ancaster road (the model was completely submerged in the barley on both occasions). I was getting a reasonable signal and direction while still on the drome, but it became more difficult to home onto the model when I got into the field. By progressively de-tuning the receiver in 1kHz steps I was able to walk the tractor lines, and finally end up a few feet away from the model. For me this was a great result - sad aren't I .

One of the benefits of a decent scanner is that it has functions such as a signal strength meter and smaller frequency step sizes (e.g 50 Hz & 1kHz as opposed to 5 & 10kHz) which makes tracking easier. Unfortunately they also come with loads of functions that we are unlikely to use, but that's life. What many people do is use the Yagi for long range tracking, and when close to the model, switch to a stub aerial of 1-2" of wire soldered into the connector. That used with body shading is good enough in most circumstances.

Incidentally, was it you that lost a model in the oil seed rape at the Nats, as when I was searching for mine, I came across a lady peering into the multi-acre field and saying "my rocket's in there somewhere"

Peter

[JefO]

My Scanner is a much lesser beast unfortunately Pete.  

The tuning is in 12.5 KHz steps, in the 430 - 440 MHz range.

In the street last night, Dad thought there was a directionality (is that a word?) when the bug was  110m away. Unfortunately, Dad didn't have his hearing aids in though, and I was 110m away, so perhaps the aerial is working, but when I could hear the receiver, it was too close to be directional "in tune".

Will have to persevere with the Ebay Yupis, but with less than 40 hours to go before we are at Heathrow, I don't hold out much hope.

Benedykt, the youngest 2010 Senior team member, will be very pleased that you thought he was a lady (best said in Little Britain-esque falsetto). The loss of Benedykt's heli-roc (S9 gyrocopter recovery rocket), in low cloud after about a minute of flight at Barkston, was the last straw that triggered my desire to get the equipment to prevent such near flyaways. Experience has taught me that it isn't that simple - so yes I can recognise your glee at finding your model (with technology actually helping).

In your sketch which deals with 16swg elements, the dimensions relate to a spacing of 143mm. Does the spacing have to increase to maintain the same gap between elements when using 6mm Ali tube instead?

The spacing between front elements on my Yagi is 137mm, distance between centres of all the mounting holes is 143mm. The rear element on my one is 134mm behind the driven element. Is this too close?

Thanks,

Jef

PS We do have a small stub aerial and will give it a go with that (THANKS for the body shading tip!).

Modified to add garish tablecloth photo... and modified again to show a pic of what I look like (I pity anybody that looks like that - so if you do see a lady with these looks, report her to the ugly police)...

[PeeTee]

I'm still having problems accessing FlyQuiet from time to time. For completeness here is the information I sent Jef by e-mail...........

On my yagi the 143mm dimension is taken from the centre of each tube, as for the distance between the active and rear elements, mine is also circa 134mm as I took the measurement from the forward wire. I dunno if it makes much (any) difference, but my antenna seems to work well. One of these days I'll build another with the spacing taken from the OD of each element and see if there is any  discernable improvement.

On the rocket retrieval front, either it was a 'mature' lady, or I need some specs for other than reading
Happy flying & good luck

Peter

Peter