Is that a new Rack I see??

Talk about anything related to GB3YT, ATV or anything!
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Wolfie
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Re: Is that a new Rack I see??

Post by Wolfie » Tue Jul 03, 2018 9:39 pm

Temperatures must be playing havoc with otherwise reliable equipment all over the country.. good to hear it wasn't too serious a problem.

I missed it anyway. Was busy playing Bikes all weekend, then playing with a BIG train set yesterday.

I had a bit of time to look at the coverage on my usual route to work today, sorry to say there are some of the locations missing. Just by the Canal on Mill St East always gave a few seconds of image and I always used to get a couple of seconds image just passing Jct31 East M62, but there was nothing, and then my spot on our lane where I usually do my fiddling was also erm.. nothing. :(

However, passing the Card factory gave a sudden image (a first) and across Saville Bridge and also for a greater distance up Leeds Cutting there were live images, where usually it is lucky to receive anything.

Could you just hoy that mast up another inch or three next time you visit please?

But the new cards are looking good, difficult to make out what they are on my tiny screen on the rear parcel shelf and in a mirror too.
It's good to see something other than caravans once in a while.. Gra.
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G8NZR
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Re: Is that a new Rack I see??

Post by G8NZR » Wed Jul 04, 2018 6:55 am

Hi Graham

Yes - the temperatures have been really excessive as the rack temperature reached just under 50 degrees when it failed! I have got another PSU ready to swap it out again, but have increased the air flow with a bigger fan - but it doesn't help much if it's already sucking in warm air! Don't forget the cabinets are up towards the roof of the building as well.

The transmitter rack and aerials haven't changed, so coverage should be exactly the same - strange how it seems a little different :o . Rob says he can still see a weak signal from home, so that hasn't changed either. We have a couple of new test card/sequences to show from time to time, like you say something a bit different from caravans.

It would be great to be able to get a full mast up on site, but the site owner won't let us do much more than we already have. :cry:

73's Kay

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Wolfie
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Re: Is that a new Rack I see??

Post by Wolfie » Wed Jul 04, 2018 7:38 am

The difference might be due to the temperatures, or more likely my own equipment, although nothing has been changed as such, it does get shaken around in the car 24/7.

I'll keep an eye on it.
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GaryM1EGI
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Re: Is that a new Rack I see??

Post by GaryM1EGI » Sun Jul 15, 2018 9:36 pm

Today I have been to my new portable site to run various ATV tests...
The site is pretty much the same location (IO93fl61), but higher up the hill, with better coverage to the east and north, I am also off the road which should be a massive help with both noise and personal safety!

Unfortunately nobody was around to test my new 5.6GHz rig with, so I swung the aerial around to see if I could open up GB3KM, but nothing seemed to change on the stream.

I then set about running tests on GB3YT, nothing seen! :shock: so I then did a sanity check and swung the beam around to look for GB3VL, I did manage to an image from that repeater, so at least I know my gear was working as such...
BUT VL was a little hit and miss with getting a steady decode with the new software (0.8) for the mini tuner (V2 hardware)!

Now I seem to remember having a similar issue before, and reverting back to my V1 tuner, but I will now have to buy another USB module to run the same test, as the recent software requires a small mod to the USB module to tell it which tuner is in use.
Another issue I have is the PSU inside the V2 hardware is acting as a VHF noise source and knocking out 144.750 talk-back!
Once I fit a new PSU, and buy another USB interface I shall go back and run the same tests using both RXs.

The next test was to fire in some good old fashion analogue TV into GB3YT, I managed to trigger the logic and open the squelch, I heard verbal confirmation via the streamer that I had managed to get in successfully!
But watching the streamer I could see either blue screen, or FM noise, no image.

The location isn't quite LOS to the repeater due to Emley Moor, I was also only running ~13watts to a dipole/reflector antenna, so I still have scope to improve at my side.

73s Gary M1EGI

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G8NZR
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Re: Is that a new Rack I see??

Post by G8NZR » Mon Jul 16, 2018 6:26 am

Hi Gary. I did notice someone was trying to get into YT. Since it was activitiy day, I was monitoring at the time you tried. I've had a look at the coverage map, and that area where you tried from looks a bit on the fringes? Would you agree? I have done some tests from home with analogue sensitivity during late afternoon, and can open YT with a few mW into a rubber duck antenna from my workroom - okay, I know I'm only a couple of miles from YT!

The analogue receive detector (15.625Khz) is very sensitive and will trigger YT long before any perceived signal can be seen, and moving a few inches with the aerial can make a massive difference to getting a signal into the repeater or not (I've experimented with Graham in the past). The joys of 23cm! We did add a small cheap line amplifier before each receiver input (as well as the LNA after the filters), so not sure what sort of difference (if any) they have made. We may have to invest in another good quality LNA or two, although we don't want to overload the receivers with noise. The other problem we have with too much amplification, is the analogue detector starts to false trigger too much - even the synce from the outside camera and testcards can trigger it!

The transmitter section has not been changed so the signal should be the same as it was previously. I know Rob hasn't noticed any difference in that, and he's a good reference point being so far away from YT.

Interesting about your VHF noise generator :lol: . Switch mode PSUs have a lot to answer for, and I'm presuming the blue screen you saw was from your end and not YT? The new logic will have sorted that blue screen problem that we had with the last controller.

73s. Kay
G8NZR

GaryM1EGI
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Re: Is that a new Rack I see??

Post by GaryM1EGI » Tue Jul 24, 2018 7:19 pm

Hi Kay,

The spot I was operating from is shown as in coverage, but I agree that this would be a fringe area - after all, the coverage map is only a prediction.
On this occasion I didn't try moving the antenna location, but the next time I go out I will try a more portable arrangement to see how that goes.

Regarding the sync detector, I have found the same with the logic for TT, it will detector a valid sync pulse long before an image comes out of the noise!
One thing you may want to investigate more are those line amplifiers... they are known to have a poor noise figure and probably not a good device inside in general, a good cheap alternative (£13 each) would be PGA103+ preamp board from G4DDK:
http://www.g4ddk.com/PGA103amp.pdf
The nice thing about having too much gain is you can always place an attenuator in-line to bring it down, this also results in creating a nice 50ohm match between stages.

The noisy PSU inside my mini tuner has now been replaced, this still generates some noise, but is more in keeping with the other unit I compared with, and it looks like the noise is more or less contained in that area rather than travelling back down the power lead as it was before!
Time with tell when I take it out to test with this week...

I'm sorry to say Kay, that the blue screen I witnessed was on the streamer, that was the best method for me to test access to the repeater to see if I was getting in/triggering it.
Would it help if I recorded a video of it the next time I do some tests?

73s Gary M1EGI

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G8NZR
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Re: Is that a new Rack I see??

Post by G8NZR » Wed Jul 25, 2018 5:00 pm

Hi Gary

Interesting comments about various things :geek:

Yes, I knew the modules could be a tad noisy, but the noise floor on the spectrum still looked quite low when I tested it out, so thought we could give it a try. I do have some modules on order similar to the PGA103, but they use the SPF5189Z. Once I get them built into small rf boxes, I shall replace the 'poor' cheap ones on all the receivers. The SPF5189Z datasheet is viewable on the Farnell website.

The blue screen must be coming from the DTX1 when a noisy analogue receive signal with poor sync is present - thats the only explanation I have for that. I must admit I thought the new system would get rid of it, but I think we would need a sync inserter to stop it totally - so we'll have to live with that one I think. I did try and replicate it the other night from home, and I did get it to come up a time or two, but that was with a very low level (marginal) signal. One other thing I did try was the quad screen which worked quite well receiving both 70 and 23 at the same time!

Thanks for the update - I think there will always be a quirk or two with whatever we do, but that all adds to the fun of amatuer radio/TV lol.

73s, Kay
G8NZR

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