BATC Forum

Can someone tell me how best to get my receiver on to 13cm. At present I use an SL65 and an SL65/12 on 23cm but would like to have a look at some of the DATV signals on 13cm. I would guess this requires a down conversion to some frequency within the receiver passband. Are there any converter designs around? What frequency is usually used for the first IF? I do have a commercial low noise block with 2GHz to 2.7GHz input and have tested it with a simple VCO local oscillator and it works although requires some filtering but has a reasonably flat output anywhere from 750MHz to 1.7GHz (with suitable LO).
Dick G4BBH

While I can't answer your question Dick I would certainly be interested in any answers as I
am about to add 13cms tx capability to my DATV set up. For receive I planned to
use one of the £10 mmic based preamps that G4DDK sells driving a suitable minicircuits
mixer. For the local oscillator I planned to use an old crystal controlled microwave source.
What I am still hunting for is a 13 cms BPF. I did find these
http://www.abex.co.uk/sales/microwave/f ... /index.htm
filters but I have not been brave enough to ask the price!

I have used a similar setup to translate 1.3 GHz down into the UHF TV band for receiving
my DVB-T transmissions on 23 cms.

- Charles G4GUO

Hi Dick/Charles,

there used to be a number of S-Band LNBs that were extremely useful for 13 cm ATV: ~55 dB of gain with 0.5 dB NF ! IF is typically 950 to 1750, so standard L-Band Sat TV RX can be used.

Common makes included CalAmp but more recently a UK importer (Astrotel?) stocked LNBs too, although I can't find details of their current whereabouts.

20 years ago 13 cm was great fun for ATV but the recent proliferation of 3G/UMTS base stations, with high ERP just below the 13 cm band, means that a good quality band pass filter is now mandatory. Some time ago I bought a couple of filters from this supplier:

http://www.l-com.com/item.aspx?id=22037

Although the filters are designed for WiFi use, they can be retuned all the way down to 2.3 GHz with good insertion loss and return loss characteristics. Here is a plot of one of my filters before it was retuned to 2320:



Without good filtering on 13 cm, most receivers curl up their toes and fail miserably.

73 de Darren
G7LWT

Everything Darren says about interference on 13cms is true and is only likely to get worse as there is a move a foot in international standards bodies to increase the WiFi band down to 2300MHz making the complete band unuseable.

I'm looking at 3.4GHz as the next interesting band - results from professional wireless cameras show there is not much degradation between 2.3 and 3.4. There is a move to reduce the amateur band down from 150 MHz to 10 MHz between 3400 - 3410 MHz but we have lobbied to establish DATV at the top end of that allocation (3406 - 3410).

Rx is easy, just buy a C band LNB from ebay for less than $10 and feed in to your Sat rx. On Tx, I'm playing with an ex Ionica motherboard and PA - the mainboard has 3 complete up converter circuits which take a 2.1 GHz ish LO and mix with your 23cms signals and produce 1 milliwatt out which will drive the PA to 15 watts.

As very few stations are active, there's no need to follow narrow band convention and use horizontal aerials and there are ex Ionica base and home vertical aerials available which would make omni aerial systems easier...

BTW - I've got a DATV repeater application in for 3406MHz in Basingstoke and will hopefully be showing some live off air "tests" at the BATC convention in October.

Best 73

Noel

Hello All,

At Noel's suggestion I have bought a couple of C band LNBs from eBay.
I am not sure yet how to feed the loop yagi into the LNB. I would have probably
been better getting ones with rectangular waveguide rather than circular!
But I only thought about that after I had pressed the buy it now button!

My USRP2 covers 3.4 GHz (about 60mW out) so I have a signal source.

I just need to find some time to play with them now.

- Charles G4GUO

Stop press!
I have had a few minutes to play with the LNBs and they work fine.
I have to point them away from the 3.4 GHz transmitter antenna
otherwise the receiver seems to overload and the picture freezes.