Simple 146.5MHz RBW receiver ?

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G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

Simple 146.5MHz RBW receiver ?

Post by G4WIM » Sun Jul 23, 2017 9:27 am

HI,

I'm thinking of equipping GB3FT with a 146.5MHz RBW rx fed from a 4 ele yagi pointing South ish towards Manchester from Blackpool.

The rx needs to be as small and as reliable as possible, cost is a secondary factor.
I plan on making a very good filtered LNA assembly for it, so RF sensitivity will be handled by external hardware.

Any suggestions ?

73 Tim

g8vpg
Posts: 311
Joined: Fri Oct 11, 2013 9:35 am

Re: Simple 146.5MHz RBW receiver ?

Post by g8vpg » Sun Jul 23, 2017 2:05 pm

Tim,
What you are planning is the same as we have added to GB3ZZ. We have a 4 ele Wimo beam pointing Southeast. We are using a Roberto DG0VE Kon146-1100 combined LNA and upconverter, which has quite good filtering built in. It is important to use the 1130MHz LO frequency to place the output at the peak of the bandpass filtering. We are co-sited with a pager transmitter on 153MHz, and I had to use a VHF high band diplexer with all four cavities in series to notch it out.
For low symbol rates, your only receiver option is Minitioune. Enable the 22kHz tone on valid TS option and it will put out a 22kHz tone on pin 12 (I think - please check) of the NIM, which drives an NE567 tone detector to operate the repeater logic. Edit the .ini settings file so that the programme opens with all the necessary settings, mode etc enabled. Minitioune opens with the first frequency, symbol rate and PIDS in the preset list. Put a short cut to Minitioune in the start up folder so that when the pc restarts, so does Minitioune.
We initially ran it on 146.5MHz, sr333ks/s, H264, DVB-S, FEC7/8, no sound. However, recent tests with H265 give a far superior picture. When the input is put back into service soon, we are going to try 146.5MHz, sr250ks/s, H265, DVB-S, FEC7/8.
The VGA output of the pc is put through a VGA to composite converter and then applied to the DTX1 repeater transmitter.
The input works well and I can access it with a fairly low 4 ele Tonna at 9 miles with less than 1W during the winter with no leaves on the trees.
Please let me know if you need any further information. Good luck with your project!
73 Shaun G8VPG.
Last edited by g8vpg on Mon Jul 24, 2017 8:40 am, edited 1 time in total.

G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

Re: Simple 146.5MHz RBW receiver ?

Post by G4WIM » Sun Jul 23, 2017 8:28 pm

Hi Shaun,

thanks for the info - I will likely take the path you suggest including the upconverter.

Time to order another Minitioune rx although I thought they could tune down to 146MHz natively ?

Must admit I've not tested mine down at that freq and I guess you have good reason to use the DG0VE upconverter although looking in my junk box I have enough bits to assemble one including an old crystal based 1152MHz LO and a helical filters etc.

73 Tim

g8vpg
Posts: 311
Joined: Fri Oct 11, 2013 9:35 am

Re: Simple 146.5MHz RBW receiver ?

Post by g8vpg » Mon Jul 24, 2017 8:49 am

Tim,
The reason we used the upconverter was that at the time, the NIM tuner modules available did not tune down that low. The latest Serit modules tune 146.5MHz directly, so you really just need a good pre-amp and filter. I also built an upconverter exactly as you describe; Minikits pre-amp, bandpass filter, mixer module, 1152MHz source, MMIC to boost LO level, satellite line amplifier for extra gain at 1298.5MHz. It worked fine.
You need to ensure that the filtering gives a nice level passband from 146.25 to 146.75MHz, because any appreciable roll off over this range will degrade the video decoding quite badly.
73 Shaun.

G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

Re: Simple 146.5MHz RBW receiver ?

Post by G4WIM » Fri Jul 28, 2017 4:51 pm

Hi Shaun,

ok that makes sense - however I read somewhere that the rx phase noise down at 146MHz is degraded so maybe your solution is preferable.

Just finished building a minitouione rx for 146.5MHz and now have to select a suitable PC which has composite video output.

Would be interested to hear what you use.

73 Tim

g8gtz
Posts: 1156
Joined: Wed Apr 07, 2010 6:26 pm

Re: Simple 146.5MHz RBW receiver ?

Post by g8gtz » Fri Jul 28, 2017 5:28 pm

Hi Tim,

You are probably thinking of this - http://www.batc.org.uk/forum/viewtopic.php?f=105&t=5017

Despite indicate MER, the Serits do appear to work well "on air"

Noel

g8vpg
Posts: 311
Joined: Fri Oct 11, 2013 9:35 am

Re: Simple 146.5MHz RBW receiver ?

Post by g8vpg » Fri Jul 28, 2017 6:48 pm

Tim,
We used a VGA to composite video adapter to provide the input to the repeater transmitter. This transmitted the whole Minitioune page, but this was quite useful because people can see what sort of signal they are putting in. We are in the process of upgrading the software and doing a trial with H265 at 250ks/s. The video quality is really impressive, more like a 70 or 23cm signal.
73 Shaun.

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