Index

Personal

Photo

2m EME

2m ground gain

WSJT-screenshots

For sale

The QTH  

Low band HF frontend
ON900BN/P

VHF map

Linrad-toolbox

ON6BG-antenna coupler

 

 

 

 1. Qualifying the relative quietness of a QTH.

WSJT, a very popular small-signal communication program, has some  features of interest for the weak signal operator.

When configuring, WSJT's FSK441 or JT65, you're asked to set the input amplitude (noise) level to 0 (zero).
It is this indicator that will be used, to specify your QTH for its relative weak signal performance. It was found, here,that depending on the antenna azimuth the noise level differs significantly.

Fig. 1, hereunder, was produced by rotating the antenna in steps of 10. The values are arrived at, by waiting a full minute and by averaging the reading. It was found that these values vary quite a lot during the day and on week/weekend days. They also depend on the period of the year. The Christmas period is not particularly good with many electric shows outside the houses...
Usually, the "heaviest" sources quieten by the Quadrantids meteor shower. (3/4 January)

Fig. 1:  Relative noise level at this QTH. The origin sits at -5dB, the lowest measured value. Every following ring indicates a noise increase of 2dB. The outer ring corresponds to +5dB.

Conclusions:
-The external noise at this QTH varies a lot over a single 360 antenna rotation.
-There is about 8dB difference between the lowest and highest reading/heading!
-The best (lowest) readings/headings, here, are between azimuths of 30 and 100 and between 280 and 340, corresponding with farmers field's, highways, the airport.and relatively  unbuild area
-The worst directions for weak-signal copy are in the south-west where many, many houses line up.

Remark: This method can be used to track down local noise sources. It was found out that my laptop ac/dc-converter "costed" me 2 to 3dB in "sensitivity".
So for critical QSO's, we run on the laptop internal batteries.
 

2. Determing the ground gain antenna lobes:  

WSJT contains a nice feature, called EME Echo mode with which it is extremely easy to VERIFY, MEASURE your ground gain performance.
By sacrifying one single moon rise/moon set, you can easily draw the distinct ground gain lobes by keeping track of the:
- time
- signal level and
- elevation
For later reference and/or in order to duplicate measurements, you can also note down the
-date
-relative quality indicator Q 
-azimuth and used
-output power
The measurement dynamic range is directly dependant on your ERP. With just 13dB, already a lot of detail can be seen.

Unfortunately, I lost my original data and since I'm not QRV, it'll take more time to compare the predicted YO-values with this WSJT EME Echo Mode measurement.

Today, 18-01-2007, while cleaning up the lab, I found back the original paper copy of my measurements of 02-06-2004.
That day, the moon had a degradation of 4.18dB and the sky temperature a respectable value of 750K.

Beware: the data presented hereunder is not comparable with the 12el M data since they were made with the 4x4el vertical stack on a tripod on the balcony.
See below a picture from that period.

The 12el M was not even installed at that time. The antenna is phased by Aircom+ cable, carefully cut on a HP 8753C VNA (vector network analyzer) with
associated calibration test set.
With this measurement instrument, it was easy to cut out half waves so that the amount of Aircom+ phasing cable could be limited... (
@ abt. 2/m!)
I never liked seeing coiled up phasing cable on people stacking frames...

The top 4el antenna sits at about 9m above ground level, which corresponds to a modest 31m asl.
If I recall correctly the stacking distance is just over 1.2m.The array gain should be slightly higher than 13dB.

The antenna is a real "meteor reflection generator" and allowed me to make many, many nice VHF contacts.
This poor man's vertical stack was put to good use, until the building permit for the 12el M arrived. (and it did!)

The horizontal opening angle is so wide that it allowed me to make many EA7 and CT1 contacts "around the corner" of the house... (on E sporadic)
Indeed, I cannot rotate the antenna more than about 160 due to the house walls...
The array is too low in these southern headings since:
- the lowest two yagies shoot into the neighbours' trees which are close to 8m nowadays. (blocking)
- only the top antenna is clearing the roof.
The eastern headings are in the clear...

The 4 stack array can easily be turned by hand from the attic window, avoiding the need for a rotor. This reminds me of the following story:
 
One day during winter time (it must have been Quadrantids shower 2005) it was white outside and I couldn't turn the array the usual way, not even by
putting high force, so I went downstairs to inspect the tripod more closely.

While checking and trying to get movement in the aluminium tube, it broke off  (it could not be turned due to ice forming ) and I was there holding the 4m long tube
with the 4 antennas in my hand in freezing temperatures and too lightly dressed!!
I needed help since the top section was guyed by 2 ropes fixed to the balcony.

So I quickly called the XYL upstairs and outside to help me lay down the antennas on the framework of balcony.
The tripod was later re-welded and this should not happen again...

This 4-yagi stack also allowed me to hear my first EME signals from this QTH  for the first time. It was nice to hear JH5FOQ loudly on CW .
These signals revealed the moonrise ground gain phenomena at this suburban QTH.

The Excel graph hereunder was derived from the WSJT echo mode produced values and the moon's elevation angle.
The graph shows a large and high gain ground gain lobe between 6.5 and 7 of moon elevation.
The other distinct lobe is between 3 and 4.5 of elevation.
Unfortunately,I did not persue my measurement effort beyond 8 of moon elevation.

It clearly indicates that "single yagi EME" with other stations having similar size of equipment, to be EASILY possible by using the digital modes.
In fact, the picture shows that I could have easily worked myself...

The "proof" of the sum are the several occasions, I've heard my echoes in CW-mode!!

 

3. Determining the RF-environment of the QTH:

The pictures were taken on 09/02/06 at 18h UT, by means of a portable Anritsu SpectrumMaster, type MS2721A.
( preamp OFF, so intermods generated by the measurement instrument should be very low if existent.)
The indicated values are peak (hold) values, obtained after a brief waiting period (1minute).
The antenna is the horizontally polarized 2M12 at 9m agl. (see here)
The measured spectrum is split up in three parts: 88-108MHz, 108-148MHz and 148MHz-960MHz.
The 4 main directions were considered: north, east, south and west.

This is the reference: a signal being  S9 corresponds to a level of -93dBm or 5V in a 50Ώ system. (on VHF, only) (1 S-point corresponds to 6dB)
So a signal peaking -43dBm in the plots below, corresponds to a level of S9+50 on the S-scale. This is a very strong signal.

88 - 108MHz
(click on the thumbnail to enlarge)

NORTH EAST SOUTH WEST

Conclusions:

1. Despite the supposed orthogonal polarisation mismatch, between the vertically polarized broadcast FM system (they could as well be transmitting slant 45) and the 2M12 horizontal "pickup" antenna, litlle or no discrimination is provided by the rotary 2m antenna. Most amplitude peaks stay within 5-10dB independant of the antenna heading. It is clear that the 2M12 antenna directivity properties (gain, F/B, F/S) to be limited to 144MHz.

2. From the above, there are no distinct "better" directions for strong out-of-band FM-signals.

3. The 88-108MHz snapshots can be summarized by 4 carriers upto -40dBm with a multitude of smaller carriers reaching -60dBm.    

         
108 -148 MHz
(click on the thumbnail to enlarge)

LOST

NORTH EAST SOUTH WEST

Conclusions:

1. The paging carrier (POCSAG) just above the 2m band (>147Mhz) is always visible and peaks at -45dBm. Its dual dipole array is at about 2km from my QTH with a NE-heading.
The good news is that the POCSAG-system will be dismantled in Belgium by mid-2006.

2. The high number of carriers is typical for a near-airport QTH. From previous measurements, the peaks can vary a lot during the day. So it really is a snapshot.

3. Besides the POCSAG-carrier, the amount of strong carriers within the low VHF-band is limited to one strong carrier at -40dBm. The remaining carriers are at least 20dB weaker.

 148 - 960MHz
(click on the thumbnail to enlarge)

NORTH EAST SOUTH WEST

Conclusions:

1. The very high GSM downlink broadcast carriers around 947MHz (at the right hand edge of the plots) reach impressive levels up to -30dBm.
From the antenna location, we can easily spot 6 cellular towers.
This is no surprise since the QTH is located at important crossings around the capital Brussels.

2. Other centers of UHF-activity are located around 196MHz and 527 Mhz with levels, always lower than -40dBm
 

4 A FM notch filter with 3 quarterwave coaxial cables

Read all about in in this pdf.


5 The combination of the FM-notch filter with a state-of-the-art 2m LNA

Peter, PA3BIY made available one of his 144 MHz LNA's for this measurement campaign.
The LNA properties were verified by means of a recent :
-Agilent spectrum analyzer E4404B (9kHz- 6.7GHz) with noise figure (NF) software application and an Agilent 346B noise head.
-R&S ZVB4 Vector Network Analyzer (VNA300kHz- 4 GHz) but without N-connector calibration test set.


1. The measured NF and gain as read from the analyzer:
@ 144.0 MHz:  0.21dB and 23.3dB
@ 144.2 MHz: 0.21dB and 23.2dB
No plots were taken but the NF curve looked rather flat between 140 and 150MHz.
The measured values are in line with the measurement protocol accompanying the original PA3BIY-LNA.

2. The gain and return loss plots

With the unavailability of the N-connector calibration set (sent out for calibration...), I was left with just the normalization of the setup.
So please consider the return loss measurements with care,the gain curves (insertion loss) should not be much different from reality.  
Care was taken to reduce the LNA-input signal to just -50dBm so that it was still in its linear region even with a gain of 23dB.
I have also taken the touchtone tables to derive the correct amplitudes from both real and imaginary values for every MHz.
 
- the standalone LNA:

To be added but are OK indicating a broadband match
Insertion loss (dB) Input return loss (dB) Output return loss (dB)

*the GAIN curve indicates :
     an in-band gain of 23dB,
     a pronounced roll-off on the low frequency end but FM-signals (
@100 MHz) are still boosted by 8dB,
     a much less steep  roll-off at the high frequency end with positive gain values extending far beyond the measurement region. ( > 400MHz)
*the RETURN LOSS curves:
    for the LNA-input: the dip appears nicely at the frequency of maximum gain and it is an impressive 20dB +/- several dB's (remember: only normalized setup!)
    for the LNA-output: to be added based upon the touchstone tables (see first appreciation, hereabove)

-the combined FM notch filter + LNA:

The FM notch filter was the final design, described under chapter 4, based upon all 1/2" corrugated cables, with < 0.08dB in-band insertion loss and a rejection
of nearly 30dB between 85 and 100 MHz.  

Insertion loss (dB) Input return loss (dB) Output return loss (dB)


*the combined GAIN curve indicates :
     -an in-band gain that dropped just slightly due to the added notch filter losses.
     -the low frequency roll-off is appreciable with attenuation values in excess of 20dB between 85 and 100MHz.
     -a roll-off several dB better at the high frequency end but at higher frequencies, the filtering performance is similar to the LNA itself... (except for the resonance)
*the combined RETURN LOSS curves:
     -at the input: the dip still appears at the frequency of maximum gain and it is 20dB +/- several dB's (remember: only normalized setup!)
     -at the output: idem but the match is even better at the in-band frequency and much more broadband outside this frequency range.
     -the impact of the uncalibrated measurement cable at the LNA output port can easily be seen...

Conclusion:

Despite the fact that a true and calibrated vector network analysis was not possible, the combo performance of this LNA with the FM notch filter
is promising for future integration in the 2m setup at this QTH... 
I hope to add a plot of the 12el yagi (@ 9m agl and 33m asl + FM notch filter + LNA1 + narrow BPF to this column, soon.

Midwhile, I hope to complete a homebrew LNA2, based on a U310-FET.
Suggestions are always welcome!
 

6 The combination of FM-notch filter, state-of-the-art 2m LNA and high Q bandpass filter on the 12el yagi @9m agl.

A number of screen shots were taken around 20h local time, on 27/12/2006, with the handheld FSH3 spectrum analyzer from R&S.
(capable of measuring spectra from 100kHz to 3GHz, settings LNA off, auto resolution and video bandwidths, continuous sweep, max hold trace mode, rms detection )

This time, a number of combinations of the above filtering solutions were tried and are shown below on a real antenna system.

For sake of comparison with the plots under chapter 3 above:
-the selected antenna heading was due east
-the same frequency spans were selected

The different configurations were grouped by frequency span, which should help to understand the behaviour of the different building blocks in the system.
The bandpass filter in use is a solid piece of mechanics about 42cm long and 12cm diameter dual cavity pipes.
The insertion, return loss and coupling between both cavities can freely be altered to shape the bandpass characteristic according your own wishes.
This is how the bandpass looks like:


Smaller varieties are in use near the Arctic circle and Greece.

 

88 - 108MHz

12el yagi antenna  
connected directly (consisting of 8m Aircom+ cable) case1
+ LNA case2
+ FM notch filter + LNA (FM notch filter in front) case3
+ FM notch filter + LNA+ high Q bandpass filter with reduced span (1kHz) no signals can be seen bigger than -110dBm! case 4
+ LNA + high Q bandpass filter <-86dBm in 20MHz span. case 5

Observations:
Compared to the signal levels of chapter 3, the case 1 plot shows larger power levels for more carriers. (which is a bad trend...!)
There are 4 FM-carriers at or about -44dBm!
Adding the LNA with still 10dB of active gain in the FM band, does no good! (case2) I count 4 carriers between -30 and -40dBm with one massiev one at -25dBm!
Case 3: adding the FM-notch filter reduces all these strong carriers to peanut levels smaller than -65dBm.
Adding the bandpass filter makes (cases 4 and 5) make these FM-carriers disappear in the noise... (so to speak)

 

108 - 148MHz

12 el yagi antenna  
connected directly (consisting of 8m Aircom+ cable) case 1
+ LNA case 2
+ FM notch filter + LNA (FM notch filter in front) case 3
+ FM notch filter + LNA+ high Q bandpass filter <-80dBm in full 40MHz span, in reduced span: 126.6MHz @-90dBm and 136.8 @-83dBm. case 4
+ LNA + high Q bandpass filter 136.8MHz @-70dBm. Case 5

Observations:
Comparing case 1 with the plot in chapter 3 learns us that the strong POCSAG-carrier above the 2m band to be gone. They ceased operation in mid-2006, as planned.
The levels have dropped compared to chapter 3 but this is possibly due to my short waiting period and low airport activity around the time the measurements were taken.
Case2: the LNA boosts a good number of carriers to very high levels between -30 and -40dBm. Being so close to the 2m band is troublesome and need attention.
Adding the FM-filter (case 3) does some good to most carriers (drops the levels by 10dB or so) but this plot shows that some air-traffic communication can get to high
and unexpected levels. Watch the carrier at 126.6 @-25dBm!!
Luckily the LNA output is followed by a high quality dual cavity bandpass filter that effectively kills the carrier nearby the 2m VHF-band. It provides some 65dB
attenuation on the 126.6 MHz carrier.
This plot is the proof that the a bandpass filter following the high gain and not really selective LNA to be a necessity at this QTH!!
Of course, combined with the LNA preceeding FM notch filter...!

A curiosity: While taking some in-band 2m plots, a motorbike drove by, producing this spiky plot on the FSH3-screen: 
Spikes with levels reaching -80dBm on the back side of the beam! (F/B of the 12el M should be higher than 20dB)

 

148 - 960MHz

12 el yagi antenna  
connected directly (consisting of 8m Aircom+ cable) case 1
+ LNA case 2
+ FM notch filter + LNA case 3
+ FM notch filter + LNA+ high Q bandpass filter <-80dBm in full 812MHz span. case 4
+ LNA + high Q bandpass filter idem. case 5

Observations:
Comparing case 1 with the East plot of chapter 3 for the same frequency span, we note that that the GSM900-levels have increased a bit. No doubt due to the
recent location of a MOP (multi-operator pylon) close-by... The other levels seem to have decreased in strength.
As usual case 2 (with the LNA) brings the smaller signals alive with most levels reaching -40dBm, with the GSM900-carrier well above the -30dBm-level!
This indicates that there is no selectivity contained within the LNA and that meaures are necessary to avoid mixing products inside the LNA and further down the
Rx-chain.
What does the FM-notch filter bring? (case3) The levels get some 5dB weaker but still very strong.
Luckily the bulky bandpass filter is there to bring rescue...It knocks down the signals by some 40dB to levels weaker than -80dBm.
The span was not decreased to check how low the carriers in this frequency band really are.
 

7 The impact of the FM-notch filter, high Q 2m bandpass filter on the Linrad-setup noise floor
Leif, SM5BSZ suggested that the high Q 2m bandpass filter would be impacting the Linrad-Rx noise floor.

The Linrad S-meter in (long averaging period ) RMS-mode was used to quantify the level change when including the above filtering elements  in the
existing antenna line.  (composed of the 12el M at 10m agl @ a heading of 50) and always fed through less than 10m of Aircom+ feeder.

This heading is one of the quiet directions at this QTH . (see higher-chapter 1-relative noise level at this QTH)

For the run between the shack on the attic and the lab room (1floor lower and at the other side of the house) another Aircom+ cable was taken.
This long run is abbreviated "cable" in the table, hereunder.
The FM-notch filter is abbreviated as λ/4f.
The high Q 2M bandpass filter is abbreviated as BPF.

The measurements  were taken on 22/01/2007, between 20h30 and 21h00 local time. Sometimes cars were passing in the street resulting in higher readings.
All measurements were performed on an uncalibrated Linrad system resulting in irrelevant absolute values.

A high number of plots were taken for future reference. They will be presented, hereafter in the order they were taken:
The Linrad S-meter can be found in the top right corner of the screen. The most right part of the S-meter plot is relevant for the measurement setup.

Remark:
starting with the LNA measurements, the Rx-frequency was shifted up by about 6 kHz to fall inside an Rx-area free of birdies.

Unterminated cable
Not connected to anything
Terminated cable Antenna to cable   Ant+LNA
to cable*
Ant+LNA+BPF
to cable** 
Ant+λ/4f+LNA+BPF
to cable**

-109.6 dBm

-109.1dBm

-108.6dBm

-92.4dBm

-94.9dBm

 idem

 

Dummy load+ λ/4f+
LNA+BPF to cable**
Dummy load +
LNA+BPF to cable**
Dummy load +
LNA to cable*
Terminated cable

-96.6dBm

idem

-94.9dBm

-108.9dBm

* : one asterisk indicates one extra RG213/U jumper cable
**: two asterisks indicate two interconnecting RG213/U jumper cables
The above jumper cables will (slightly) worsen the measurements. Exact losses of these jumpers on 144MHz are yet to be determined.
 


Observations: (from left to right)
-connecting the antenna from a 50Ω termination adds about 1/2 dB of noise. (without LNA attached)
-inserting the LNA in the antenna line increases the noise by level by more than 16dB
-inserting the BPF has an attenuation of about 2.5dB.
This is a high price to pay and re-tuning the bandpass filter for lowest insertion loss will probably be sufficient for use with elevated antenna systems.
Using the adapted 2m bandpass filter in a switched relay configuration may/may not be sufficient for working on the horizon.
-as expected the losses of the quarter wave based FM-notch filter are not detectable.
-connecting the dummy load (@280K) instead of the antenna lowers the noise by about 2.5dB.
This practically means that the environmental noise at the time of measurement and for the given QTF to be about 500K.
This noise floor can be taken as the reference for the plot of chapter 1. This lowest value is also valid for QTF's from 50 to nearly 90.
-the virtually zero insertion losses of the quarterwave notch filter are again confirmed at this stage
-with the dummy load termination, the bandpass filter insertion losses indicate through losses less than 2dB.
-comparing both terminated cable measurements indicates that the measured noise level increased slightly at the end of the session.
(or from measurement inaccuracies)
 

8. After-LNA bandpass filter measurements

During last August 2007, I had the opportunity to measure and tune a pile of Kathrein VHF bandpass filters on a vector network analyzer with calibration test set.

These filters are dual and triple cavity filters that offer the possibility to tune:

-their input and output return loss (VSWR),
-center frequency and
-insertion loss and corresponding filter bandwidth.

Here, you see the untuned filters, ready to be put in the car...

The filter-measurements were summarized in this pdf.

I was, lucky, recently to be able to buy such a 2 cavity bandpass filter on Ebay, from a french OM, nl. Franois, F1CHF.
He was so kind to drive 60km (from the place, he was staying at his holiday) to deliver the masterpiece at our camping place in French department Ardche.
This is also ham spirit!

In this datasheet, you can find the type numbers and corresponding data. BTW: there are long and shorter variants.
It should be easy now to recognize these beauties during your next hamfest visit.