BATC Forum

G3UVR on the Wirral managed to rx my 437MHz DATV transmission from IO83LR (Lytham) and I was only running 125mW also got a D5 report from G1LWX Mike located at Ashton-in-Makerfield.

Not managed to rx anyone though which is a little worrying even though the rx seems to work down to -106dBm on 437 and - 105.5dBm on 1248MHz.

I can see my out going signals ok.

I was wondering what others get rx sensitivity wise ?

73 Tim G4WIM

Hi Tim,

It is probably not just a matter of sensitivity - the SUP 2400 needs quite a bit of gain in front of them but more likely need some good filtering as there's a lot of (very loud) rubbish around on 70cms.

Take a look at http://www.batc.org.uk/forum/viewtopic.php?f=15&t=3704 for more ideas...

Noel - G8GTZ

HI Noel,

thanks for the link - as it happens I had stumbled across that one already.

As for my rx line up it is a SUP2400 preceded by a BATC 435MHz bandpass helical filter which is fed by a WJ LNA about 1.5dB NF and 15dB gain not sure what the IP is though.

I also have a DCi filter for both the tx and rx path but have not put that in circuit yet - maybe it is something out of band blocking the rx and hopefully the DCi filter will fix it. It's this 4 pole 10MHz bandwidth one - 0.3dB insertion loss and can handle 200 watts

http://www.dci.ca/?Section=Products&SubSection=Amateur

73 Tim

Hello Tim g4WIM

Re sensitivity of 70cm DATV, hope the following helps.

I have an permanently connected low level signal injection on my DATV Rx using a -29db coupler.
The RX line up is g4DDK pre amp, 8MHz (to 3db points)6 pole filter with side notches set to reject 433 area. C/F is 437 and out of band is good.
Convertor is home made with SBL mixer IF is 1525Mhz gain across convertor is 38db ...437 to 1525.
I use a Toutune and a Technomate 1500 on a splitter.
The Technomate lock threshold is -114dbm and the Tutoune about 3db poorer.

In this mode my antenna is connected so I see antenna and site noise, when I beam at he local hospital threshold drop by up to 4/5db but towards France over the see its quite and the -114 level is reliable. I see Frence Sysedis (not the correct spelling) quite often in the direction of Cherbourg.

Without the notches the whole system is much poorer.

Regards Peter g3pynb

Hi Peter,

thanks for the feedback on your system.

I suspect my 437MHz front end is quite good and the sup-2400 is not the limiting factor - I'm beginning to think my Samsung STB might be rather critical as to what it'll decode. I have a good 437MHz band pass made by DCI to keep jammers out of the pass band.

The STB is a SMT-S7800 - quite high spec device I've borrowed from the lounge, maybe a lower spec device might have a lower threshold !

Will have to get my hands on another STB and see how it compares - especially as it looks as though I might be nearly 10dB adrift - probably the same on 24cms as well.

73 Tim G4WIM