DATV on 70MHz.

The place to discuss reduced bandwidth fast scan amateur television on 70cms and below
g8gtz
Posts: 920
Joined: Wed Apr 07, 2010 6:26 pm

Re: DATV on 70MHz.

Post by g8gtz » Thu Jun 28, 2018 1:30 pm

Grrr - despite saying I wouldn't, I have!

It's amazing what the junk box throws up and I now have 20 watts out on 71MHz from a RA30H0608M module driven by the Portsdown / Express combo - I do wonder how far a barefoot Portsdown at 10mw would go.

On rx I have an upconverter (old 70MHz to 1100MHz unit designed for testing modulators), just needs some gain and a filter - found this which looks nice and easy to build http://pa3csg.hoeplakee.nl/WP/?page_id=62

I even found I had a birdthru line element covering this band!

Just got to sort an aerial - maybe a dipole is a good place to start??

EDIT - just knocked up one of these - http://www.70mhz.org/coaxdipole.htm - seems a reasonable match after some tweaking - not sure how it will work but cost me £5 for the tubing and an hours work so worth a try - but even this is very big!

73 Noel

BTW - for more ideas there's a 71 MHz feature in CQ-TV out this week

g8vpg
Posts: 226
Joined: Fri Oct 11, 2013 9:35 am

Re: DATV on 70MHz.

Post by g8vpg » Thu Jun 28, 2018 5:59 pm

Oh good, that means at least one station for me to work /portable! I have now built the Spectrum upconverter and it seems work quite well, with pictures from the Express being received across the bench. I have a borrowed Pye filter and lined it up on 71MHz today. It is a really lovely filter with 0.27dB insertion loss and 3.4MHz -1dB bandwidth. I have all the components needed to build the Mitsubishi based amplifier, so that is the next task. I have ordered an Innovantenna 3 ele OWL type yagi, which is lighter and more compact than their other models. After talking to Justin, he is going to cut me a special for 71MHz for the standard price, but it will take two weeks to arrive. With a bit of luck, I might be ready for the next activity day!
73 Shaun.

g0mjw
Posts: 500
Joined: Sat Sep 20, 2014 9:15 am

Re: DATV on 70MHz.

Post by g0mjw » Thu Jun 28, 2018 8:46 pm

M0SKM wrote:
Thu Jun 28, 2018 12:02 pm
Arthur G4CPE now has a 4m horizontal dipole on a rotator down the garden and my 3 element beam has just arrived. We were both wondering if anyone else apart from Mike G0MJW is ready to do 4m tests?

On Sunday morning I could be on one of the local hills for a test; either Dunstable Downs or Ivinghoe Beacon.

@Mike From this afternoon Arthur will be ready to test with you.

73 Steve
steve (at) m0skm.com
I can be around tomorrow afternoon hopefully. Was at work today.

Mike

g0mjw
Posts: 500
Joined: Sat Sep 20, 2014 9:15 am

Re: DATV on 70MHz.

Post by g0mjw » Thu Jun 28, 2018 8:48 pm

g8gtz wrote:
Thu Jun 28, 2018 1:30 pm
Grrr - despite saying I wouldn't, I have!

It's amazing what the junk box throws up and I now have 20 watts out on 71MHz from a RA30H0608M module driven by the Portsdown / Express combo - I do wonder how far a barefoot Portsdown at 10mw would go.
What level are the shoulders at 20W output? Seems a little high for a 30W module, I have a 5 element beam for 4m.

Mike

G4CPE
Posts: 28
Joined: Mon Oct 31, 2016 3:59 pm

Re: DATV on 70MHz.

Post by G4CPE » Fri Jul 20, 2018 3:53 pm

My second 2 way contact on 4mtrs. I have just worked Don G0WFT on 71MHz. Only 3.5km but Don was only running 10MW to a dipole.
Attachments
don71.png
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G1BVI
Posts: 68
Joined: Wed Aug 02, 2017 7:32 am

Re: DATV on 70MHz.

Post by G1BVI » Sun Jul 22, 2018 8:28 am

Hi Arthur
I wonder what you used to up convert to Mini Tiouner?
73

Nick

G4CPE
Posts: 28
Joined: Mon Oct 31, 2016 3:59 pm

Re: DATV on 70MHz.

Post by G4CPE » Sun Jul 22, 2018 12:00 pm

Hi Nick
The converter is an old CML TX up converter which has a L.O. on 930MHz and was used to convert 70MHz to !GHz.
I have also got a CML SAW filter amp on the I/P to keep out unwanted signals.
The set up appears to be good but my aerial is only a dipole which may grow a couple of extra elements when the XYL isnt looking.
73 Arthur

G1BVI
Posts: 68
Joined: Wed Aug 02, 2017 7:32 am

Re: DATV on 70MHz.

Post by G1BVI » Sun Jul 22, 2018 7:13 pm

Hi Arthur
I noticed it said 10Gig on your RX Gui.

I am way behind most people on this project but enjoying putting enjoying putting everything together,

My problem is my eyes are not 20/20 any more hi hi,

Good luck with the upgrafes.

I keep looking at 4/6 antennas and imagining how big they are.... Not got one yet but whatever I get it will never be big enough :-)

Good luck on next contact

73

Nick

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