Moonbounce on 1296

[VK2JDS]

yes Dave you're right there!
Owens comments are taken on board too.
here is a test of adding a gif picture converted by gimp from a print-screen pasted into the wordpad file captured live on the toshiba laptop doing moonpings:

the bright white lines are about 3 seconds of cw key-down transmit with the small doppler shifting return ping visible above each one as the waterfall display rolls. i could hear the tone from most of them. vk2xso moved the dish around while we were pinging the other night and got a pretty good approximation of its beamwidth and shape

[VK2OMD]

... i was hoping to use a radio star as the sun seems wide.

Dave,

The ideal source is:

• a point source;
  sufficient intensity to be well above the noise (receiver noise, ambient noise, adjacent sky etc);
  known intensity.

Nothing is a point source, but sources that are small compared to the antenna beamwidth are almost as good as a point source. The angle subtended by the radio Sun is about 0.6°, and your 4.6m antenna (?) should be something like 3.5°... the error in treating the Sun as a point source will be small.

The quiet Sun is also of sufficient intensity to give you good S/N ratio if your antenna is working reasonably.

If the source you choose is too low in intensity, any improvement in accuracy due to possibly narrower subtended angle will be lost in poorer accuracy of noise rise measurement.

The Sun might be a good source for you initial setup work... even if only available to you on weekends.



Owen

BTW, an outstanding tool for capturing, editing, converting screen capture is Screenshot Captor, and PNG is an excellent format compared to GIF for most screen capture.

[VK2JDS]

Thanks Owen, 0.6 degrees sounds good, so today i attempted to pattern it using the sun as a source.
the 2 images here are only 27kb and 41kb so they wont overdo the downloads, but they show that on a difficult day with clouds and rain and a few good breaks of blue sky what can be done to get a graph of the antenna performance when using the sun as a source.

the image filenamed smoothed shows a graph of the feed as the sun moved away from its point of centre if you ignore the left bit when there was clouds and i was aligning it. it peaked at 403 millivolts, but averaged 398 millivolts at 12:50pm dropping steeply to 357 millivolts at noise floor at 13:00hrs.

the unsmoothed image shows a view of the peak with all the noise still in place. there is a slight noise reduction at the very peak but the average still holds up so i wouldnt like to say there was a dip there from that data. it went from 385millivolts on the left averaged, to 390 millivolts on the right with the appropriate timescale on the bottom of the screen. noise floor was a bit under 350millivolts. note that this is the agc voltage from the handheld, not rectified and filtered noise.

Now: how do you do this sort of graphing i hear you say. (and "i dont want to open up the radio!") but you will have to with what i did unfortunately. the radio i used is a ICQ7A, buy several, they are so cheap and so useful as signal sources , great at 3rd or 5th harmonic and receive really well up past the 23cm band, also great to get the AGC line out of them to put into a A-D converter which is what i logged using a program called skypipe.
google radiosky pipe. its freeware and extremely useful for logging things.

[VK2JDS]

now to the vswr on tx and rx ports after the septum is mounted on the dish. not good. it was 1.2:1 in free space but now on the dish its 2:1 on both ports and they are tuned to minimum, i retuned them and they were back where they were before when i finished. so , i will have to do a sweep and find out where its now resonant.
its pinging the moon ok , but not tuning up right so its got to be port measurements wrong or dipole lengths again with the dish now reflecting back into it.

the through power and port loss:
i applied power and got enough for full scale on the "calibrate" mode of the avair connected right at the septum while i stood on a ladder, the power coming out the rx port into a 50 ohm microwave rated load was lifting the meter, i took a guess by looking at the power scale, at
10 watts in = 200 milliwatts out of the receive port.(and i do mean a guess here)

cables are currently ldf5-50 from the 100 watt amp to the transmit port , ldf4-50 from the lna to the icom via t/r relays. These bits are all old and scrounged gear, the idea of what i am doing is getting a capable station going without going overboard and spending a lot. Actually the heliax came from the blue mountains field day very cheaply.

incidently we are heading to the blue mountains field day this sunday http://www.bmarc.org/winterfest.php
73's

[VK4GHZ]

still no luck with photobucket so the screen grabs will have to wait a while until they can be put somewhere.

You can directly load images to this forum.
Below the text entry box there is a tab "Upload attachement".
Click on that, and click browse to locate your image file.

This is applicable with both new posts, and when you edit an existing post... so you can add images to any of your previous posts quite easily.

Posting pics was detailed in this help topic:
viewtopic.php?f=63&t=702

[VK2OMD]

...
the image filenamed smoothed shows a graph of the feed as the sun moved away from its point of centre if you ignore the left bit when there was clouds and i was aligning it. it peaked at 403 millivolts, but averaged 398 millivolts at 12:50pm dropping steeply to 357 millivolts at noise floor at 13:00hrs.
...

Using Quiet sun radio flux interpolations to look at Learmonth observatory for yesterday (22/8), the quiet solar flux at 1296 was around 56SFU.

Trying to make some sense of this, if you are telling us that looking directly at the Sun that the noise output was 398mV and the 'cold' measurement was 357mV, you observed a Y factor of 20*log(398/357) or 0.94dB.

I would have expected a much higher Y factor from a system like yours (although I don't know the full detail), probably in excess of 10dB. This measurement approach depends on the linear relationship of audio power output to total RF power input (including rx internal noise). The first thing to check is the linearity of your receive system, SSB mode, no AGC action, no clipping.

Measuring noise is problematic. I have not used SkyPipe and their online info is very limited. You may find the discussion at NFM and linked articles of interest.

Owen

[VK2JDS]

Hi Owen , yes i was logging the agc line from the handheld i use for meteor counting.
it would be great to have you out here having a look at this setup. i didnt want to go fiddling about with the icom 910 as most of us wouldnt, so the handheld at 1296.050 seems to work for at least shaping the feed response without actually being any sort of calibrated or calibratable device.
this morning I was being decoded by M0DTS and also got a good decode with quite visible trace from Howard G4CCH, this was while the moon was down into the treeline and heading over the ridge. Might get a chance early tomorrow morning if its visible into europe again.

[VK2OMD]

Hi Owen , yes i was logging the agc line from the handheld i use for meteor counting.
it would be great to have you out here having a look at this setup. i didnt want to go fiddling about with the icom 910 as most of us wouldnt, so the handheld at 1296.050 seems to work for at least shaping the feed response without actually being any sort of calibrated or calibratable device.
this morning I was being decoded by M0DTS and also got a good decode with quite visible trace from Howard G4CCH, this was while the moon was down into the treeline and heading over the ridge. Might get a chance early tomorrow morning if its visible into europe again.

Dave,

If you want to verify the performance of your station, one way of doing that is to make measurements that lead to calculation of a Gain / NoiseTemperature ratio (G/T ratio) which is a single figure that expresses the receive performance of your station. S/N ratio is directly related to G/T ratio, if you improved G/T by 1dB, S/N improves by exactly 1dB. You can do this with relatively simple equipment, most of which is already part of your station, and using a celestial noise source of known intensity.

G/T is the ratio of system gain to (total) equivalent noise temperature (ie receiver internal noise, noise due to system losses, and ambient noise).

The technique calls for measuring the ratio of total equivalent system input power (external and internal noise) from two noise sources of known power flux density (W/m^2), and calculating G/T.

The way that the ratio of total equivalent system input power is usually found is by measuring the (audio) output power of a linear receiver (SSB receiver with no AGC action and no clipping).

If you want to use some other indication of received power, you need to validate its linearity. AGC voltage, limiter current, RSSI, etc are all less likely to be sufficiently linear for the purpose.

Lest you should be forming the view that you have to tamper with the '910, you do not. You do not need to modify it in any way, or even take the covers off. You just need to make the measurements in SSB mode in the range of input below AGC onset which is typically about 20dB above the noise floor. If the AGC meter is always on the stop, then gain of the receiver is constant and it behaves as a linear down converter.

Without knowing the exact details of your station, my guess is that you should observe the Sun noise to be about 10dB higher than the quiet sky adjacent to it. We can work out the exact numbers if you want.

Owen

[VK4CDI]

Update.

Just got my 3.7Mx dish, now the fun begins......
Septum polariser/choke ring feed under construction, although N2UO suggests the septum pol./RA3AQ dual mode feed is better for 3.5-4 f/D ratios. Have to look at that. Bought a G4DDK 2 stage preamp, and was given a TH328, with the offer of a cavity and PS for free. The only thing missing is the time to put it all together!! What's everyone using for driving/tracking??

Cheers
Phil VK4CDI

[VK2JDS]

Here i have the radio hut right next to the dish and manualy move it by running in and out to watch the screens and move the dish to the moon. You have to move it every minute.
The counterweight is a milkcrate full of rocks chained to the end of a 4 inch steel tube about 2.5 metres long bolted to the back of the dishmount. I add or remove rocks as necessary to adjust for different gear weights etc on the feed arm. (stone age adjuster)
The stepladder is a vital tool in alignment and i use a sighting tool made from the wire from a bucket handle. Being a rifle shooter I sight through a small loop at the end of the wire which is mounted at the end of the counterweight arm and align the moon into a 1 inch by 4 inch gap in the mounting on the top of the spider box on the 4.6 metre dish here. its effective if the moon is visible.
When there is clouds I use a analogue angle meter from mitre10 and a compass.

The 4.6 is really critical for aiming as its got a very narrow beamwidth thats why the open sights 2.5 metres long is required to sight up the dish. You will find the same thing so make a long open sight to aim with and set it up using the sun as a noise source. Otherwise a riflescope with a camera behind it mounted on the feed arm would be good , but would take a bit of aligning.
If a bit over half the moon drifts outside the slot on the sights then you wont see a return ping.

I chose to have the radio hut right near the dish, with its own batteries and solar panels. the heliaxes are then fairly short but put the hut on the south side of the dish.
this is an old pic but will give you an idea, there are no antennas or solar panels on the hut in this shot and the counterweight isnt there either.
In this thread I have posted up all of what i have done so others can see whats involved, got some great feedback from the guru's too, hope you will keep us posted here about your progress.
73's

[VK2JDS]

here is a trace on spectran from Leigh VK2KRR tonight using his 3 metre dish

[VK2JDS]

well, i put a oa91 diode (in series)and 0.047uF capacitor (across as a filter) off the line output of the IC910, background was 5 millivolts, sun peak was 21 millivolts through clouds.
then i moved the septum back a half inch on its mounts and will try again tomorrow morning with Howard G4CCH, he has a great signal if anyone wants to try and work him on 1296.080, i worked him at -10 db on spectran this morning.
my first EME cw contact.
Owen , if you can explain the mathematics behind these readings that would be a great help so other readers can do this and figure out their system.

system here is 4.6m dish, septum, serious microwave rated relay directly into 0.56db vk5eme preamp, ldf4-50 20 metres into hut > microwave relay > IC910h
on tx its a SSB electronics 100 watt amp (on loan) via coaxial relay into 20 metres of ldf5-50 straight into the septum.
the output of the borrowed amplifier is very dependant on what charge i have in the solar powered batteries
wheras the the vk3xpd 65 watter was pretty constant.
every time i ping the moon with carrier i see a nice white return ping from 60 watts upwards, and see a small ping with 10 watts barefoot from the IC910h
73's

[VK2OMD]

Dave,

First thing, lets grab the quiet solar flux for yesterday. Go to Quiet sun radio flux interpolations to find the interpolated solar flux intensity for 1296MHz yesterday. I got 56. I have reservations about your measurement through cloud, but lets use the data as an example, and build a framework for further measurement.

My preferred metric for understanding station performance is G/T ratio, so we will build a model to calculated the expected G/T for your station. An explanation from my web site:

This analysis focuses on a single figure of merit for the entire receive system, and that is the G/T ratio (the ratio of antenna gain to system equivalent noise temperature. G, Antenna gain is with reference to the antenna connector. T, system noise temperature, is the total system noise, including sky temperature (or ambient noise) referred to the antenna connector.

The G/T ratio is a meaningful indicator of system performance, unlike quoting receiver noise temperature in isolation of sky temperature and antenna gain. The ability to receive weak signals is directly related to G/T, the higher G/T, the better. Signal/Noise ratio is proportional to G/T (Signal/Noise=S*λ2/(4*π)*G/T/(kb*B) where S is power flux density, kb is Boltzmann's constant, and B is receiver effective noise bandwidth).

So, if changing the receiver Noise Figure from 5dB to 1db improves the G/T ratio by just 0.1dB, the real benefit of the change is just 0.1dB.

You need to estimate the gain / loss / Noise Figure of everything in the receive chain, antenna gain, and ambient noise. Lets start...

Your IC910 has specified sensitivity of 0.11µV for 10dB S/N. Lets convert it to NF assuming that the effective noise bandwidth is 2kHz. Using the Receiver sensitivity metric converter, we find that the IC910 NF should be around 4.8dB.

We need to know the loss in the 20m of LDF4-50A, yes another calculator: RF Transmission Line Loss Calculator tells us that at 1296MHz, 20m of LDF4-50A with a load and VSWR should have a loss around 1.8dB.

The specs on your LNA say 0.51dB NF and 33dB gain (for the two stage variety).

Lets estimate 0.2dB loss for relays in the absence of measured data.

Antenna gain for a 4.6m dish with 60% feed efficiency at 1296 is 33.7dB.

We also need some estimates of spillover noise and cold sky noise, lets start with 100K and 8K.

Now, plugging all that into a G/T model:

VK2JDSpreliminaryGT.png

(Click on the picture to see a full size / readable version.)

From G/T, given solar flux intensity we can calculate expected sun noise rise.

But before getting carried away, we need to review all of the assumptions above.

Are you still with me?

Owen

[VK2JDS]

yes we all are Owen , this is exactly the sort of help we need.

its a single stage preamp, claimed gain 21 db (no need for all that extra gain with the 2 stage version, its just setting the front end NF)
0.51 is its optimised setting , i suggest we start at 0.56 if we can as most of us building this preamp wont have access to a lab.

todays measurements : quiet sky average with preamp 1: 5.1 millivolts, sun noise 16millivolts, now preamp 2 was cold sky 2.9 millivolts, peak sun 16.3 millivolts peak, average 16.1

interesting to note as the sun rose and temperature increased on the preamp casing the noise level increased as we would expect... maybe i should hunt up a peltier device.. however please note the earlier preamp 1 cold sky 5.1 millivolt reading was taken at dawn, while the 2.9 millivolts on preamp2 was not long afterwards. so there was no heating involved.
73's

[VK2OMD]

yes we all are Owen , this is exactly the sort of help we need.

Ok, we is you and me! The stats show there are few lurkers, this is not an interesting topic to most hams.

its a single stage preamp, claimed gain 21 db (no need for all that extra gain with the 2 stage version, its just setting the front end NF)
0.51 is its optimised setting , i suggest we start at 0.56 if we can as most of us building this preamp wont have access to a lab.

Ok, lets run with 21dB gain and 0.56dB NF, I have updated the model.

I will also plug in 0.1B of loss in the feed system. My model is based around the feed connector or flange as the reference point, and loss on the space side of the connector needs to be entered at cell C26. (Other tools seem to implicitly make the reference plane somewhere just in front of the antenna.)

Can you open Excel spreadsheets? If so, I will attach the spreadsheet, it much more useful to be able to interact with the spreadsheet, try some scenarios and check the outcome.

todays measurements : quiet sky average with preamp 1: 5.1 millivolts, sun noise 16millivolts, now preamp 2 was cold sky 2.9 millivolts, peak sun 16.3 millivolts peak, average 16.1

I am interpreting this to mean that this is an audio measurement in SSB bandwidth, and that the radio is in USB mode. Is that right?

An issue with this method of measurement is the confidence limits on each measurement value. If you wrote down 10 successive measurements, how variable is the data?

What are you measuring the output of your diode/filter with? Is it a digital multimeter? See Accuracy of narrowband audio noise measurements with a digital multimeter.

Now, the audio output power is proportional to the total equivalent noise input power ONLY if the gain of the receiver is constant. The S meter indicates AGC voltage. If the S meter changes between measurements, the gain is not constant. Safest position is NO AGC, NO S meter deflection with either reading.

It happens that AGC commences about 20dB above the noise floor of most receivers of this type, and I believe from tests with Rex (7MO), his 910 behaved in that way. Your RX NF of 4.8dB and 4kHz ENB means its noise floor is about -136dBm (from the sensitivity calculator you tried earlier). Your AGC threshold is probably about -116dBm. That means that if you put a sig gen on the receiver and increased the level from -130dBm, the audio output power would climb fairly linearly until about -116dBm where it would flatten.

My calcs say your noise from the Sun (56SFU) in your system should be around -111dBm equivalent at the receiver input terminals... that is probably just enough to lift the S meter a smidgen and spoil the measurement.

Of course, your receiver could (should) be a little better than spec, exacerbating the problem.

Did you get S meter deflection during any of the measurements? If so, we have to deal with that.

The assumed receiver NF is with no AGC action, ie no S meter deflection, and I assume the internal preamp ON (though I cannot see such in the specs or service manual).

What do you mean by "preamp 2".

Owen

[VK2JDS]

no S meter display at all which is good.todays milivolt readings were averaged over 30 seconds.

i was testing 2 preamps in diecast boxes , and preamp 2 is the second one i tried, they are both vk5eme minikits preamps.

using ssb mode on the IC910h yes.

still waiting for the narrow CW filter from Lee Andrews, its bound to arrive any day now.

there is no internal preamp

[VK2OMD]

no S meter display at all which is good.todays milivolt readings were averaged over 30 seconds.

Ok, I have suspicions about your audio measurement. There are a number of issues, but the biggest one at the moment is the 1mV measurement.

You want a linear DC out for AC in, and you want good resolution from the instrument.

Diode voltage drop compromises linearity. Can you measure speaker audio, say at 200mV or higher (but without clipping)?

i was testing 2 preamps in diecast boxes , and preamp 2 is the second one i tried, they are both vk5eme minikits preamps.

Ok, for simplicity, lets just deal with Preamp #1 to avoid confusion.

using ssb mode on the IC910h yes.

Good. Doug (3UM) in his presentation to Gippstech 2008 suggested AM mode was ok or possibly preferred. My experiments indicate that linearity of audio noise power output to total equivalent noise power input is good in SSB mode, and poor in AM mode.

still waiting for the narrow CW filter from Lee Andrews, its bound to arrive any day now.

there is no internal preamp

Ok, the narrower filter will change the sensitivity in µV, but the NF will be almost unchanged. You will get less audio power output with the narrower filter, but the ratios remain good.

Good re the preamp.

You didn't tell me if you can open Excel 2000 docs?

As the model develops, here is a pie chart of the expected contributions to your receive system noise Teq (ie up to the antenna connector).

It is pretty good, the LNA is the main contribution, overall RX Teq is 65K... (NF=0.87dB) that is pretty good... so far!

Owen

[VK2JDS]

Thanks Owen, looks good so far. I chose to use the line output of the radio as its also compatible with oodles of other radios for people who will likely read this series of posts many years into the future doing their own EME setups.

I can use the headphone output if you like and make some measurements from there.

preamp 1 seems to have a higher basenoise level than preamp 2, so will look into that but interesting to note the maximum voltage from line out on sun noise peak on both preamps was virtually identical.

i have found the temperature of the casing affects cold sky noise significantly.

i am running preamp 2 now. waiting for moonrise tonight to test pings then try again early tomorrow morning.

i can open excel spreadsheets under linux so thats ok.
i have had several emails from people watching this thread who are keen to get going , so keep the info coming. 73's see you off the moon. Dave

[VK2OMD]

Hi Dave,

Thanks Owen, looks good so far. I chose to use the line output of the radio as its also compatible with oodles of other radios for people who will likely read this series of posts many years into the future doing their own EME setups.

I can use the headphone output if you like and make some measurements from there.

I just restate that the measurement technique depends on the audio output power being proportional to total receiver equivalent input power.

The above shows measurements that I made of a particular measurement scenario to understand the linearity of the receiver in this respect. These measurements were done with a CW oscillator right down to the noise floor, so they include noisy measurements.

Part of getting meaningful results is understanding and controlling measurement uncertainty.

I wrote NFM specifically for making high resolution measurements of noise in SSB receiver bandwidth. It is a Windows application which will be unattractive to those who do not use Windows.

BTW, you mentioned that you have a 500Hz filter coming. Whilst that may be good for communications, measurement of noise in narrower bandwidth has higher uncertainty.

preamp 1 seems to have a higher basenoise level than preamp 2, so will look into that but interesting to note the maximum voltage from line out on sun noise peak on both preamps was virtually identical.

i have found the temperature of the casing affects cold sky noise significantly.

Ok, the absolute noise power out of the preamp isn't the vital parameter, noise figure and gain are more important. A preamp with higher gain may produce higher noise and yet have a lower noise figure.

You will hear lots of Rules of Thumb (ROT) about whether gain is more important or NF more important. They are indeed ROT, there are some notes at Noise and receivers. The definitive answer comes from the G/T model spreadsheet I showed in an earlier post.

Re the temperature issue... get the freeze spray and hair dryer out.

I was concerned that my gain measurements of a 2m preamp varied every time I measured it, and over a range of almost 10dB. I went looking for temperature sensitivity, and top of the suspect list was a ferrite toroid in the tuned input circuit. The component was highly temperature sensitive, much more so than the tuning Cs and other air cored inductor in the input circuit. No surprises there I hear you say, everyone knows that ferrites are quite temperature sensitive and their use in narrow filters is problematic. Clearly this design was not suited to a masthead preamp where temperatures here would vary from -10° to ove 50°.

i can open excel spreadsheets under linux so thats ok.
i have had several emails from people watching this thread who are keen to get going , so keep the info coming.

Ok, I will attach it to another post.

Owen

[VK2OMD]

i can open excel spreadsheets under linux so thats ok.
i have had several emails from people watching this thread who are keen to get going , so keep the info coming.

Here is the spreadsheet.

http://www.vk1od.net/lost/VK2JDS-GT.xls

It uses VBA macros, let me know if it works for you (ie recalculates properly when you change things in the yellow cells. (VBA macros do not work in some Excel pretenders.)

I may update the spreadsheet from time to time if I get feedback that anyone is looking at it!

Owen