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Minitune Front End
Posted: Wed Feb 07, 2018 7:11 pm
by G4uvz
Over the last couple of weeks I have been trying to find the 'best front end' for 146.5MHz
I have come to the conclusion that the MK2 tuner is quite sensitive at 2M. Putting a tight 5 chamber filter in front of the Mini allowed me to rx G4BVK 60K distant when he was transmitting just under 1 watt.
I then added
https://www.ebay.co.uk/itm/5V-0-05-4GHZ ... 2749.l2649
in front of the filter. With this in place I can rx BVK at 400mWatts which we think is pretty good!
What is confusing is that when we drop below 400mW I still get carrier / sr and full lock light AND an MER of > 10dB ...but no locked picture?
Would be interested to hear if other have the same experience? The tests were on H264 and H265.
Interestingly on 1316MHz Mpeg2 I can copy good pictures down to an MER of 4-6dB
Adrian
Re: Minitune Front End
Posted: Thu Feb 08, 2018 2:37 pm
by G4uvz
Surely someone else is using Minitune on 2M ???????!!!!!!!!!!
Would be interested in hear about other front end arrangements?
Adrian
Re: Minitune Front End
Posted: Thu Feb 08, 2018 3:26 pm
by G4FRE
I used the dg8 masthead preamp by gm3sek. It has onboard bandpass filtering and has been tested to 400W. I also have the 4m version, should any NOV ever be issued!
Dave
g4fre
Re: Minitune Front End
Posted: Fri Feb 09, 2018 1:05 pm
by g0mjw
I have an nov but nobody to work
Re: Minitune Front End
Posted: Fri Feb 09, 2018 9:41 pm
by g3zgz
g0mjw wrote: ↑Fri Feb 09, 2018 1:05 pm
I have an nov but nobody to work
It may help if we knew where your QTH is?
It's an activity weekend this weekend, you may hear some stations you can try to work
73
Dave.
Re: Minitune Front End
Posted: Sat Feb 10, 2018 8:46 am
by g0mjw
This was a reply to Dave FREs comment on 4m NOVs. I am in Oxford. That information won't help though as at the moment, I am the only one with a 70MHz NOV, as far as I know, so there isn't anyone else to work.
Mike
Re: Minitune Front End
Posted: Sat Feb 10, 2018 11:37 am
by M5TXJ
Hi Mike,
I'm looking at a 4M NOV for when I get my build completed but can't get my head round the different field strength measurements and what is acceptable in the application, any advice would be greatly received.
73 Dave.
Re: Minitune Front End
Posted: Sat Feb 10, 2018 11:54 am
by g0mjw
I just went for 100W ERP and worked it out from there. You need to know how far it is - 10m, 20m, 100m. Probably OK to assume far field to calculate the E and H field strengths.
Mike
Some links - don't know if RSGB has anything similar.
http://www.arrl.org/fcc-rf-exposure-reg ... evaluation
http://www.rfwireless-world.com/calcula ... lator.html
Re: Minitune Front End
Posted: Wed Mar 07, 2018 7:04 pm
by G4uvz
Getting back to the original posting !
https://www.ebay.co.uk/itm/0-01-2000MHz ... 2749.l2649
Using this amplifier followed by a Pye Europa front end works extremely well on 146.5 ...The Europa front end is pretty tight keeping out strong 2M and out of band paging etc.
The Europa front end has the middle section septum removed, giving around 7dB insertion loss
Re: Minitune Front End
Posted: Thu Apr 05, 2018 8:42 am
by Richmmm
I am new to DATV, just constructed a MiniTioune Rx and am now planning to put up a dual band 2M/7cm Yagi. I assume I will need a preamp at the mast head, how much gain do i need to plan for and does the preamp need filtering? I am quite close to the Sutton Coldfield TV mast so I would rather not use a wideband preamp. Any suggestions on filter bandwidth needed for each band?
Regards Rich