thUndeadMod v3.4 - openLRS S**T just got real :)

[Devonian]

I've just made some simple bench tests.
All test are on full power and Tx & Rx are 2 metres apart.

Rx is standard v1 hardware module, running Flytron's v1.11-spectrum_analyzer firmware + Spectrum Analyser software (ver04 from Dennis) and antenna cut for 459MHz (163mm).

Tx is my modified v1 hardware module, running thundead's ver 3.5 firmware, fixed single channel @ 459MHz and antenna cut for 459MHz (163mm).

As always, click the pics to go supersize !!

First up is a benchmark run with 459 (Sander style 'whip') antennas - peak @ 213



I now added a ground leg to the Tx whip (simply clipped on to make a kind of half wave dipole) - peak @ 221



Next up, I added a section to the Rx and removed the Tx section - peak @ 224



Finally, a ground return section on both the Tx and Rx - peak @ 237



By adding a ground leg/counterpoise, it seems I'm getting a bit more RF/efficiency out of my device.

So, how far apart are you guys keeping your Tx & Rx when you post your spec-an plots?

Seems like mine is pretty well up there with peaks always above 200...

Nigel.

[papa_lazerous]

That's pretty impressive Nigel,  I'm running a 433mhz it's the diamond SRH-771 which is obviously not tuned for 459 at all. One thing though is its a monopole antenna, would it be more efficient with a ground plane?

[Devonian]

Mine are monopoles as well.

It should help to have a decent ground plane or ground return for the antenna.
After all, the only other thing providing the ground return is the ground system of the VTx or VRx and that equals the square root of b****r all !!

I'd be interested to see if it makes any improvement to other users findings.

This is all I did to add the ground return/counterpoise, simply croc clipped on a bit of wire (bared end to make good electrical contact)...



See, us 'geeks' may have some use  :D

Nigel.

[papa_lazerous]

I was thinking the easiest way to make an end fed dipole would be to take the plastic off the outer of some coax down to 163mm (that's the calc length I think) then slide the shield back over itself, tricky but can be done then your active element is to the correct length and you have a ground element and it's centre fed. You get me?

[Cat695]

Mine are monopoles as well.

It should help to have a decent ground plane or ground return for the antenna.
After all, the only other thing providing the ground return is the ground system of the VTx or VRx and that equals the square root of b****r all !!

I'd be interested to see if it makes any improvement to other users findings.

This is all I did to add the ground return/counterpoise, simply croc clipped on a bit of wire (bared end to make good electrical contact)...



See, us 'geeks' may have some use  :D

Nigel.

could we just wrap the bare wire round the threads and then screw on the antenna??

[Devonian]

@ papa,
Yes that's do-able.
I've done it a few times.
Strip the outer plastic sheath down to 170mm or so.
Push the braid down until you get a small 'bunch' near where you want the centre conductor to emerge.
Pry a small gap in the braid at 170mm and pull the centre conductor out through, start with a small 'kink' of centre conductor and by pushing on it and pulling the kink, you will get it to emerge completely.
Straighten everything out and cut both elements to 163mm.

@ Cat
You could put it under the captive nut/washer of the SMA panel connector/receptacle  (not the nut of the antenna connector part).

It needs more testing before we can draw any real conclusion, but my initial test is encouraging.

Nigel.

[zitron]

I also saw a large difference between when I just soldered a wire and using a properly sized dipole. I did some experiments for dipoles with 22 awg wire length at 459, here are the results:

Code Select Expand


Length(mm)  RSSI(dB)
16.5     -47.5
16.1     -45.0
15.6     -43.5
15.2     -41.0 *prolly a fluke
15.0     -45.0
14.7     -46.5
14.3     -44.0
13.5     -47.5


Please note that it is very difficult to do these experiments because how sensitive RSSI is to everything, you should probably do your own experiments.

I bought some of these: http://www.ebay.co.uk/itm/5x-30cm-SMA-Male-male-RF-WLAN-Antenna-Pigtail-RG316-Coaxial-Cable-w-Connector-/290674988270

You can cut them in half and make 10 antennas!

[Cat695]

@ papa,
Yes that's do-able.
I've done it a few times.
Strip the outer plastic sheath down to 170mm or so.
Push the braid down until you get a small 'bunch' near where you want the centre conductor to emerge.
Pry a small gap in the braid at 170mm and pull the centre conductor out through, start with a small 'kink' of centre conductor and by pushing on it and pulling the kink, you will get it to emerge completely.
Straighten everything out and cut both elements to 163mm.

@ Cat
You could put it under the captive nut/washer of the SMA panel connector/receptacle  (not the nut of the antenna connector part).

It needs more testing before we can draw any real conclusion, but my initial test is encouraging.

Nigel.

something like this??

[papa_lazerous]

Just had a little crack at making an end fed dipole antenna for my Tx,  The first pic shows how I pulled the braid back over the coax (it took allot of patience) and the next pic shows the entire length to show it in full.

I need to cut off the spare coax and fit an sma connector. and then trim the braid and centre to the correct length as they are oversize right now.  The issue I have right now is that its floppy, I need some kind of sleeve to keep it rigid. any ideas on what I can use and where its available?  I'm off to get some sleep

[Splashy]

I use snake outers and inners when making antenna. I use 0.8mm Mig Welding wire so that fits nicely inside the inner and then I use the outer to give it some rigidity. In your case I would just use some outer snake. You can buy replacement EZ* snake sets and they are great but around £4. I also bought a few other snake sets but they are less rigid.

[papa_lazerous]

Figured I would add to the show and tell with some graphs I did today using the spektrum analyser software.

First is my noise floor, I have a dipole on the Rx tuned to 459Mhz



Ok next is with the Tx on, I am using a diamond SRH-771 on the Tx it's not tuned to 459Mhz but I am getting a pretty good result anyway I think.



It would be nice to get the graphs in RSSI or dB, any news if thats going to happen or not?

[zitron]

To convert to dB just divide by 2 and subtract 130.

[papa_lazerous]

So my noise floor analysis is -73dB and with the Tx on its -7.5dB

Ok so now I have these figures what can I extrapolate from them?

[Splashy]

All this antenna talk is going over my head.

This is a little embarrassing since I studied Electronic and Electrical Engineering at University. All I can think of is that antennas have changed since I studied, or I might have been hung over and missed that lecture .. slightly more likely.

What I do have is a load of bits to make antenna and the tools to make them.

I do not quite understand your end fed dipole antenna, what is is trying to achieve? Is it some sort of dipole antenna?

If you can tell me what you want and give me dimensions you require then I will make antenna to that spec for anyone that wants them, and will send them out at cost (which is basically the cost of the SMA connectors plus some snake sections).

I really believe that if we can get the TX antennas sorted out then 459 will again become a viable solution. The range of power outputs we are getting seems so antenna dependent that this could easily explain the range difference seen between 433 and 459.

I have been reading up about 1/2 wave TX antenna (a tuned equivalent of your Diamond antenna) and will make a couple of these if you guys think that would be worth it .. and your results would seem to indicate that this is the case. I have read that the more gain on the antenna the more directional it becomes and that is why I would like to get some real, in the field experience behind the antennas I make.

[papa_lazerous]

Right here we go.... The high'ish gain of my diamond doesn't mean it's directional, it's still omni but the pattern is more like a squished doughnut if that makes sense. I went on the diamond website this morning after work and it's not designed to transmit on 459 (which we know) but 459 is within the band that it's designed to receive.

My thinking with the end fed dipole is this. I wonder if a dipole would be better than running a monopole and no ground plane which we are doing at present. The problem with dipoles is they are usually centre fed like the sanders style dipole Rx antenna. Now if we used a centre fed antenna in the same orientation as the current monopole antenna the coax would run from the middle and parallel with one of the elements to the Tx sma connection. Running the coax parallel with an element will reduce efficency and defeat the object. So the idea of pulling the coax inside out like I did on   my earlier post is that you still have a dipole but the coax feeds through it and not parallel with it meaning it effectively doesn't cause a problem. I'll test it when I get up Wednesday after work, not sure if that's today or tomorrow now lol