Posts by G8UGD

That's what I was trying to follow, not with a lot of success I must admit. I will continue to try.

Adrian

Sorry to ask, but I could do with a little bit of help to get me moving.

I use gnu radio to drive an SDR for DATV, I slightly reworked an existing flowgraph without any GUI, and use the generated .py file from a script in Linux.

I am wondering if I can pass variables from command line to the python file at run time.

For example here are the first few lines from the Python script.

#!/usr/bin/env python2
# -*- coding: utf-8 -*-
##################################################
# GNU Radio Python Flow Graph
# Title: Sr250
# Generated: Sat Aug 3 00:17:48 2019
##################################################
                                                                                                                                   
                                                                                                                                   
from gnuradio import blocks
from gnuradio import dtv
from gnuradio import eng_notation
from gnuradio import filter
from gnuradio import gr
from gnuradio.eng_option import eng_option
from gnuradio.filter import firdes
from optparse import OptionParser
import osmosdr
import time


class SR250(gr.top_block):

def __init__(self):
gr.top_block.__init__(self, "Sr250")

##################################################
# Variables
##################################################
self.symbol_rate = symbol_rate = 250e3
self.taps = taps = 80
self.samp_rate = samp_rate = symbol_rate * 2
self.rolloff = rolloff = 0.35
self.resample = resample = int(round(5e6/symbol_rate))
self.center_freq = center_freq = 2408.9e6

##################################################
# Blocks
##################################################
self.rational_resampler_xxx_0 = filter.rational_resampler_ccc(
interpolation=resample,

So it would be good to add the frequency as an external variable and possibly the symbol rate. I think the answer lies with Import sys, but to date my tries have failed me.

So if there is a Python Guru out there that could put me in the correct direction it would be appreciated.

Adrian

Hello Matthias, Thanks for the information. I am using my MHL21336 to drive the Bisonelectronics amp. It seems to work OK for now until I feel the need to get something better. Very similar results on output to yours. I do not have a VNA the gear to test mine fully, but it seems to be OK.

Adrian

Apart from the disadvantage of having more than one Co-ax going to it, holes through the wall etc. You could run one co-ax from vertical polarisation to a receiver for SSB and one co-ax for horizontal polarisation for DATV stuff, so in theory you can have two receive systems at the same time, there is no need for a 18 Volt PSU or buck up converter to get the voltage from a standard 12-13.8 Volt psu.

Typically if you have a 4 co-ax/connector lnb, it gives you the opportunity to modify it and feed with an external gps locked source for ssb RX and still have a V and H output.

All that being said I still run a standard un-moddified single port lnb.

Adrian

Thank you for your response, it is appreciated. One thing that still puzzles me is the length of the 'dipoles'

I get one leg of the dipole to be 35.3155mm for the too long and 28.013mm for the too short. these seem to be a lot longer and a lot shorter then 1/4 wave at 2.4GHz, I accept that there could be a change to the electrical length of the dipoles as they are close to 'ground' as it where. But even if I consider no shortening, I get the short length would be resonant at around 2.675GHz and 2.12Ghz for the long length. When I looked at the instructions for the POTY it showed theoretical resonances less than 35MHz above and below 2.4GHz.

Put me down as being a pain in the A**, I like to understand what is happening rather then just take it for granted, so I can ask a lot of questions.

Adrian

OK thanks for that, not sure if any clearer to me. I accept what you say, that is not an issue, I would guess that the different lengths from the feedpoint to each 'element' would also add a phase change as one would have a shorter path from the feed therefore the other lags behind, but that suggests to me they are not 90 degrees out. Not to worry I think if I get chance i will search for some simple theory on patch antennas. Guess I am only used to 1.4 and 1/2 wave style dipoles.

I wonder if anyone can just clarify where the resonant lengths are on this pic of a POTY, for the frequencies just below and just above 2.4GHz

Just helps my brain work a bit better!

Thanks

Adrian

So I have been straining over a magnifying glass and doing searches on the internet for SMD markings. If anyone with the same amp would like to verify my findings, I would appreciate it.

I have drawn out a bias circuit, sorry it is not in Ki-cad or similar as I do not yet know how to use circuit programs.

V104, V107 and V201 are marked 1PN which I believe to be a NPN transistor similar to FMMT2222.

V108 is marked as W2F 2d. Which I believe is similar to PMBT2907A and a PNP transistor.

V105 is marked R1E and appears to be a 1.2 Volt fixed shunt regulator as in a LM4041.

Lastly V106 marked RAC again a LM4041 type device this time adjustable shunt regulator.

The Green circles are my idea of ground points, resistor values in purple and what voltages I measured in Blue.

The Analog Device AD5259 I have reduced to a variable resistor in the diagram between 1.2 Volts and GND.

Not sure what is going on with V107 as it seems to be just using a diode junction.

Anyway the point for me is understanding the biasing of the power devices, with the left hand one being at a measure 1.9 Volts and the right hand side one at 0.57 Volts.

Adrian

It's a repeater, is it DX any more then speaking to some one down your own street via the satellite?

Now ducking for cover

Just throwing a question out there, I guess the answer will be no, but does anyone have a circuit diagram for these amps I would love to follow the bias circuit. My eyes are definitely not good enough to follow the components and tracks on the board to figure it out. There seems to be some checking that the peak amp (classC) is powered before it allows bias to the class AB? device and have noticed a track that runs around the bottom of the board for this, wondering about using this track for bias of the normally class C device but would need to work out the switching part first.

Or does anyone know where/what the boards came out of, i.e. equipment model number etc, and I would try and give some company a message request.

Adrian

I would be very doubtful of getting a good VSWR at 2.4GHz by using resistors in parallel, at these frequencies dummy load resistors tend to be co-axial in nature. Have a look at this page http://millimeterwave.free.fr/ATT_DISPONIBLES.htm and see if anything takes your fancy, it really depends on if you can deal with 7/16 connectors. Also you will need more that 40 dB in total to not damage your power sensor. A quick look on Ebay (UK) and I see some 50 Ohm loads 25 watts for about £11, they will only be rated for intermittent use I would suggest, but they say they are good to 3GHz or even some resistors that can be bolted directly to a heatsink that will take a lot more power if cooled correctly, so please do have a look around various outlets before you decide.

I am probably guessing wrongly, but wonder if you will be trying to test a Pyrojoe 20 watt amp or similar, if you can give your self some margin in case it is 25 or 30 or even more Watts output.

What ever you do be careful at these frequencies and powers as you are taking microwave frequencies now and soft tissue damage is always a possibility.

Very carefully! with the aid of something like a Ebay 30 dB directional coupler, a 30 dB attenuator and a 50 Watt dummy load good for 2.4GHz. The directional couplers seem to be very good are are covered by a few posts on the forum, they cover 800 to 2500MHz and are cheap to buy, I picked up a 50 Watt dummy load for around £30 UKP and you can get a N connector'ed attenuator for similar money, so probably not a cheap option but one which could save your power meter.

Amp through directional coupler to the load, -30dB port to another 30 dB attenuator to your power meter, so if you assume 43dBm with your 20 Watts you will get a signal at the power sensor of +43 - 60 = -17dBm

Adrian

More prep work going into things

I made another ID filter for 2.4GHz and tried to neaten things up by putting some of the gear into a box. This is the present stage.

The box layout

The Bison amp has now got a cowl over the heat-sink fins to help cooling for a fan to be directed in at one end. Only using one of the two amps, the other is there in case of mishaps!

Next is to get an outside enclosure to house it all in and fit the PSU's and control.

Adrian

I do not need to use wide scan or for that matter do I need to use the low SR button although I generally have it ticked.

If the offset for the LNB worked in Version 0.8 then it should be working in Version 0.9.

It is a bit of a pain setting up the new minitiouneConfig.ini for version 0.9 but I had two editor windows open to make it easier to copy frequencies from minitioune.ini to the new config file.

I can not remember having to do any special changes to the ini file to make it work, so a bit baffling why it does not work for you if 0.8 was OK. Hope you get it sorted soon.

Click on the Oscar 100 button to get a selection of frequencies for different SR rate. Also 3 memory buttons you can use for frequencies and SR rates which can make it easier when jumping between a couple of specials for yourself say during a QSO!

You also have 8 presets rather than 5 and I believe some fine tuning internally particularly for QO-100 although what I am not sure. I do find the dials at the bottom easier to read.

Adrian

OK I have to ask a question here regarding OXCO's if you are more knowledgable, I use a 10Mhz Oscilloquartz type 8661 which is a double oven style unit, it seems to be reasonable for my up converter. The board it is mounted on would have been internally installed in test gear and I have wrapped it in 5 or 6mm styrofoam not a lot of foam and I can feel heat though the foam. It dropped the power requirement by 0.5 watt. So is this a bad idea?

Adrian

Well sat some point during the testing the RF2126 1 Watt amp fried it self, so possibly why so little output. Back to playing and waiting with some replacement chips on order.

Do not worry! I am only in to a dummy load and sniffing into my Spectrum analyzer at present, still some time from going to air.

I have been playing with my Hackrf generating a 1000K SR DATV test signal.

This is my line up at present

Hackrf, to RF2126 amp to MHL21336 Amp through 2.4GHz filter to 30 dB coupler and dummy load with the sample port to the spectrum analyzer.

The line up:-

Everything for testing is from a 12 Volt PSU so the the RF2126 amp has a DC converter down to 5 Volts and the MHL21336 has an DC buck to 26 Volts.

This is a spectrum display at present with 10 MHz per division Horizontal and 10 dB per div vertical, so I am looking at present with around 50 dB down on any spurious signals.

This is the same view but now at 2MHz per division.

I think I may be able to reduce the spikes there as they are the sample rate used on the Hackrf so I believe increasing it from 10 to 12Mhz may reduce the spikes to an even lower level.

I was trying to use this small amp stage after the Hackrf,

but, the frequency response is so wide that it amplifies any and all spurious outputs from the Hackrf and helps pass them to later stages so unless I build another ID filter, (Which I may well do!) then I will not use it in the line up.

But I still do not have anywhere near enough signal going this way to actually drive the main PA into any sort of power level.

I put the bisonelectronics amp on the output as it was for a test and was disappointed. The shoulders increased to at best -40 dB at worst -35 dB below peak signal.

A 1000SR test signal

A simple test shows that the amp has around 20dB increase

But we are still taking less than 1 Watt!

That is a far as I got tonight playing with it all across the bench I need advice on how to proceed and what are realistic figures I should be expecting on shoulders, yes i have seen some saying -35 dB down are OK and some saying that is not good enough?

Is anyone using a bisonelectronics amp as the final stage and how does it perform and what drive level do you need to get to?

Adrian

I have been playing again and made a 2.4GHz ID filter.

The top line is with a back to back connection and the bottom trace 10dB per div vertical and 50MHz per division Horizontal.

Not brilliant as I guess loss is around 1.5 dB. It still could be useful between a driver stage and main PA for DATV to clean up things before the output stage.

I am pondering placing a few more screws in there to allow a small change in the coupling between stages, but not sure if it would give any benefit.

Adrian

OK thanks guys for the feedback, there has been posts about letting operators know if they are putting out bad signals, but it is good to have confirmation of what I see and think is the cause.

What I would like to see if possible from the Amsat team is a General post/sticky of problems with signals and what could be the likely cause of the effect. Put it with the Operating guidelines so that operators can easily find it and look for themselves, it may or may not be of use, but may help.

Adrian

@G0MRF It's an 8 hour drive round trip for me so I doubt it.