MiniTioune/r Help Please!

[Basil]

Not wanting to derail the thread, but just a quick interjection. I have never bothered covering the POTY at all, it's totally exposed to the elements and I have never had any issues even when TX'ing in a serious (for the UK) deluge and thunderstorm. Have I been lucky or are people spoiling their POTY's and giving them an unnecessarily sheltered life?

[g0mjw]

You have been lucky not to destroy your PA. A few drops of water around the connector would cause a bad match. Now if you have a lot of cable loss then it probably won't be an issue, but if you are thrashing an EX UMTS PA to the edge of its existence and have removed the circulators because they didn't work on 2.4 GHz, it doesn't take much to be terminal.

Mike

[Basil]

Thanks Mike, it's a 20W SG Labs PA feeding the POTY with about 7 or 8 feet of LMR-400. It probably runs about 70% of max power tops. Guess I have been lucky, will look at some sort of rain hat.

[GM0SCA]

Hi Simon,

I did wonder, picture explains all as that is actually around a 60cm dish equivalent, so really too small for DATV. You will find Iceland bags more robust for protecting the feed. Try and find a 1m or 1.2m dish, but note for an offset dish it is the shortest dimension you need to look at because of the way these dishes work.

Mike

Hi Mike

Thanks for your comments - it does make sense about the dimensions and I shall look very carefully now at dimensions shown in adverts for a larger dish!

I was also interested to read and think about Gareth's post. I have ordered another Bullseye LNB and I will try and receive using that on it's own i.e. without a POTY and see what the difference is. I am not sure about using a POTY stuck down the throat of an LNB - it doesn't quite make sense to me. The LNB mount on the dish is presumably at the optimum distance for the LNB to be mounted; given the short wavelengths involved and the (approx) 15cms between the POTY Tx and LNB Rx, I'm not sure how efficient that system would be given that the POTY is likely to be in front of the 'optimum distance' (there's probably a correct term for that) and the LNB further away. Hope that makes sense!

Certainly an interesting learning curve and a good distraction whilst 6m is quiet!!

73 Simon.

[G0MXW]

Simon,
The lens at front of POTY focuses signal into tube which acts as a waveguide transfering signal into LNB. Tube length doesnt matter. The POTY effectively moves the focal point of the LNB forward to approx 10mm in front of POTY. Focal point of the patch is about the same point. Looking at your dish its hard to make out under your bag but if your mount is the black shadow immediately in front of the red cap of the LNB then your focal point is way too close to the dish. See http://www.hybridpretender.nl/poty.html half way down under "mounting"

Dave G0MXW

[GM0SCA]

Hi Dave

That's a great explanation, thank you, it corrects all my (incorrect!) assumptions. The rear plate of my POTY is just under 4cms in front of the LNB mount so I will look at bringing that back towards the mount tomorrow when I get a bit of time. The other interesting point is that the tube length doesn't matter so I will look at shortening that which should reduce any wobble or vibration of the LNB hanging off the back.

Thanks again - very much appreciated.

73 Simon.

[g0mjw]

Hi Dave

That's a great explanation, thank you, it corrects all my (incorrect!) assumptions. The rear plate of my POTY is just under 4cms in front of the LNB mount so I will look at bringing that back towards the mount tomorrow when I get a bit of time. The other interesting point is that the tube length doesn't matter so I will look at shortening that which should reduce any wobble or vibration of the LNB hanging off the back.

Thanks again - very much appreciated.

73 Simon.

Simon, you want the lens for the POTY, a proper one incidentally, not one of those cylinder things, ideally one removed from a rocket LNB, to be where it would have been, so for example, if you get a rocket LNB to salvage the lens, then before you do anything, mount it and measure where the lens is. Then when you replace it, get the lens back where it was. The critical measurement is in-out, it it is a bit up or down that's less of an issue, within reason as you can re-point the dish to compensate.

If you don't know what a Rocket LNB lens is, it is the plastic bit at the front that looks like a small cylinder, but isn't as you will find out when you take it off - here is a dead link from Amazon so you know what it looks like. https://www.amazon.co.uk/Venton-Rocket- ... B008CNTVV6

Alternatively an HB9PZK style lens will work, (google it) if you can find one. Don't consider anything else for a standard satellite dish. If you come across a larger prime focus dish, it might be better without a lens at all, depending on how deeply curved it is. https://twitter.com/therealmike/status/ ... 3293381637 Ideally a 1.2m channel master offset is the thing to have. They often come up on Ebay, collection only. As you live in a relatively remote area as far as DATV goes, you might be lucky.