DATV on 70MHz.

The place to discuss reduced bandwidth fast scan amateur television on 70cms and below
g8gtz
Posts: 899
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: 208
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: 474
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: 474
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

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