Remco.org

Seductive serendipity / Verleidende serendipiteit

August 8th, 2017

PraatPaalPatch (PPP) for 23cm FM-repeaters

Note: For the impatient click here and here.


Introduction

For some years The Netherlands owns nationwide covering 2m and 70cm
FM repeater systems (2m PI3UTR and 70cm PI2NOS).

Note: some links are in Dutch only, sorry.

In Dutch HAM slang a repeater is called ‘PraatPaal’ (Talk Pole <– direct translation ; -)

Availability of cheap Chinese handhelds like ‘Baofengs’ stimulate pollution on 2m/70cm.
The repeater systems attract lots of morons and/or trolls generating interference.

Combined with the fact that such a repeater system has a capacity of less than one (1)
Erlang makes ‘our’ nation wide repeater systems a sociological and/or social experiment.

An observed trend is that Full licensed HAMs tend to avoid ‘our’ nation wide repeater
systems because they don’t want to be associated with trolls and try to find their salvation
in other areas and/or aspects of the hobby.

One ‘escape route’ for repeater usage is to increase frequency, for which 23cm is a willing candidate
in my region. Novices are not allowed to use this band here and little (commercial) equipment is available.
This filters out unwanteds and trolls significantly.

A few years ago Bas PE1JPD designed his 23cm transceiver to stimulate activity on 23cm.
Bas’ project is quite a success and he was seduced to publish his project in FunkAmateur (iirc July 2017 issue).

Now (relatively) lots of Full Licensed HAMs here build 23cm NBFM transceivers and need a 23cm antenna.
In my region the 23cm repeater (PI6NOS) is located on a 160m tower and within LOS (line of sight) for many.

Simple 23cm antennas
Lots of designs of 23cm antennas are available and possible. A very popular/easy/simple antenna
is the Doppelquad (German, advocated by DJ9HO (sk) in the 80/90′s) or BiQuad (English).
And, yes/indeed, the Doppelquad is easy to construct (Google on it or see below).

the
Fig 1. Doppelquad (German) or Biquad (English)


However . . .

Although the Doppel/BiQuad is easy to construct, there is (now!) a competitive alternative:

The Patch Antenna -aah -aah! (or patch in short)

Patches are far beyond new. In fact, patches are old skool. They are/have been widely used
in all kinds of wireless systems like RC, WiFi, GSM, GPS, DECT etc, but queerly ‘underexposed’
in HAM scenes, despite perhaps (am)satellite usage like AO-40 (sk).

Although theoretically ‘free space’ patches have around 2 dB less gain compared to a
Doppelquad (Biquad), building a patch antenna is UTTERLY simple!

(perhaps too simple for the ‘common HAM scene’ ?)

In The Netherlands (most) 23cm repeaters have 28 MHz shifts: e.g. output 1298.xxx, input 1270.xxx MHz.
This means the patch has to be designed for 1270 MHz (50 + j0Ω), i.e. at the CPE transmit frequency.

I found one 23cm patch effort from G6GVI (1296 MHz) via Google.
However, this is a FR4 ‘dielectric design‘ (with according dielectric losses).

So, I calculated and built a ‘full size’ patch from scrap material for 1270 MHz, i.e. a patch with εr = 1 = air.

The result is screwed on a bookshelf in my shack, and indoors pointing at PI6NOS
(1270.375 in / 1298.375 MHz out). Below a picture of the contrapsion (click to enlarge in new tab).


Minimalistic PI6NOS 23cm repeater antenna setup, enough for regional work ; -)

In my previous post I built an Inmarsat patch according to 9A4QV’s dimensions.
I mailed Adam my interpretation. His response was:

“The patch should not be made of double or single layer FR-4 copper clad.
It should be made of a conductor plate only. You are introducing extra Er in the
air gap together with the extra copper layer. This will not work properly.”

Of course I considered this while building the antenna, but I do not agree
with the above statement because both sides of the PCB are electrically connected
on two places: the centre (Z = 0) and the feedpoint.

Anyway, this (thin, 0.6mm or so) FR4 PCB material has been crying for some usage
here for almost 30 years ; -) Of course brass or copper plate material suits perfectly.

Unfortunately I was not able to measure my Inmarsat patch because a good friend
almost immediately ‘confiscated’ my built. He currently uses my patch (or Adams ; -)
on a camping site somewhere in the neighbourhood to receive Outernet.

While typing this I received a phone call from him, mentioning he got his Outernet
setup working with his CHIP and has an SNR of around 6 dB with my patch.

Of course this is not an objective figure of merit. However, I was able to measure
my PraatPaalPatch this week and consider the results representative for my
interpretation of Adam’s Inmarsat patch because the two patches:

- operate in the same frequency region (1.27 vs 1.54 GHz), therefore . .
- have almost indentical dimensions
- are made from the same materials

The difference between the two patches is the polarization. Despite perhaps axial
ratio issues (Inmarsat patch), construction of the two patches is almost identical.


Measurements

The PraatPaalPatch was measured at two locations using two different setups:

- PI4RCG radioclub, R&S spectrum analyzer
with tracking generator and -20 dB directional coupler

- work, Agilent Network Analyzer

First location
When first measuring the PPP at our radioclub results were not promising.
I could hardly see a dip (around 1270 MHz). With some fiddling I discovered that the
dimensions of the patch plate were okay, so it had to be something with the match.

The nature of my fiddling led me to the conclusion that the patch-reflector distance
was too small. Initialy I calculated 12.5 mm (say 1/2″). By increasing this distance
with a M4-nut and pull out the feedpoint wire (so at this position the distance was
also increased with around 3mm) the patch came to life !

Below the result from the radioclub measuring session is depicted (click to enlarge).


Measuring the PraatPaalPatch at PI4RCG Radioclub (Photo by PE1PIP)

On the picture above it can be seen that the match @1270 MHz is almost perfect!
Return loss is around 42 dB (!) when pointing the antenna towards the ceiling.

Second location
At work the setup below was created (see picture below, click to enlarge)

Fiddling a little with the antenna revealed an even higher return loss of around 50 dB (!)
(see below, click to enlarge) but the ‘average’ RL was around 36 – 40 dB, which is very good.




PraatPaalPatch dimensions !

For Fres = 1270 MHz construction details are visualized below (click to enlarge)


Front view                                                          Side view                                                    Back view : -)

In text: reflector plate 180 x 180mm 2mm think Al-sheet (not critical), patch size 103 x 111mm
brass/copper plate (around 0.6mm thick, I used double sided FR4 PCB material). Patch centre
(determine with diagonals) is grounded with a 16mm M3 metallic spacer (I used a 1/2″ spacer + M4 nut ; -)
and feed point is in the middle of the short (103mm) side and 9mm from this patch edge.

Connector used here is N-female with flange. Wire from center pin of connector is around 2mm
diameter and fits neatly IN the center pin of the connector : -) In case double sided FR4 material is used,
solder feed point wire on both sides to ensure electrical connection. Feed point –  reflector distance is also 16mm.

Note: when the longer patch side (111 mm) is horizontal, antenna polarization is vertical.

PS. When you refer and/or build this patch and publish about it, please refer to this article and/or my callsign.
I do the same when I build stuff from others!

August 6th, 2017

L-band/InmarSat/Outernet patch antenna cf 9A4QV

Introduction
In my previous post I elaborated somewhat on Outernet being merely
a ‘nerdy’ technological project. Adam 9A4QV designed a L-band patch antenna
a while ago. Cutting two diagonal opposite corners yields circular polarization.

The two diagonals differ 90° in phase, the longer diagonal +45°
(so the antenna is inductive), the shorter -45° (so the antenna is capacitive).

+45 – (-45) = +90°, exactly what is needed for circular polarization (CP).
InmarSat L-band transmits with Right Handed Circular Polarization (RHCP).

This posting attempts to illustrate an utter simple patch antenna built
(in 20 minutes).

Construction
Dimensions of 9A4QV’s L-band patch antenna are:

Reflector Size: 170 x 170 mm
Patch Size: 98 x 98 mm
Corner Trim: 21 mm from top right and bottom left corners
Coax Connection (Probe): 25 mm from bottom edge
Height of patch from reflector: 7 mm

Step 1. My reflector is made from 1mm thick aluminium sheet.
The patch is made from 0.5mm thick double sided FR4 PCB. I had some spacers and
cut one with a saw to 7 mm length. Anything else will do, as long as reflector and patch
are ~7 mm separated and electrically connected (the impedance Z = 0 Ω in the middle!).

I chose a N-type chassis connector instead of SMA, but your mileage may vary.
See picture below (click on it to enlarge in a new tab).

 

Step 2. Create correct dimensions with a caliper, drill holes accordingly . . .
and . . . ready ! See picture below (click on it to enlarge in a new tab)
Note: Fingerprints on the patch element are not mine ; -)


Side view depicted below (click on it to enlarge in a new tab).


Finally, one picture to summarize all (again, click on it to enlarge in a new tab : -)
Yes, I know I made a typo, it has to be corneRs instead of cornes ; -(

August 2nd, 2017

Possible Dutch APRS Outernet first !

Introduction
Outernet is active for some years now and attempts to realize specific goals :

Afbeeldingsresultaat voor outernet wiki

To provide information without censorship for educational, emergency purposes,
‘news, civil information, commodity prices, weather, construction plans for open source
farm machinery’, and other types of information.
Providing access to ‘courseware’, which includes textbooks, videos, and software.

Basically Outernet is a ‘broadcast datastream’ via the geostationary L-band Inmarsat infrastructure,
using very little bandwidth resulting in around 2.1 kbit/s downstream, and having global coverage.

Technology/equipment
From what I understood Outernet initially broadcasted from Ku-band satellites (like HotBird)
but changed to L-band. With this change a whole new community emerged, building L-band (1542 MHz)
antennas and receivers dominantly based on cheap RTL-SDR dongles.

Although the Outernet philosophy attempts to present itself as low level and
‘open’ as possible, the core files to decode the transmitted data are proprietary (to some extend)
and/or not public domain.

The latter urged Daniel Estévez EA4GPZ to reverse engineer the Outernet protocol.
Last year he gave a lecture at 33C3 in Germany on this topic (click here to watch his presentation).

Somewhat later/almost simultaneously Pascal Brisset F4DAV ‘hacked’ the Outernet protocol
(with assistance from the information provided by EA4GPZ ?) from a DVB-S perspective.

Having read a lot of information on the internet about Outernet today, Outernet advocates a
nice mission but I doubt it’ll have an added value, besides being a nice and nerdy technical project.

An illustrating posting can be read here.

Considering the latter, a nice technical project with ‘no use’, it is still fun to play with it, so I did.

APRS
The HAM-radio community seduced the Outernet CEO to forward APRS packets.

It took me some fiddling to understand how to route APRS-packets to Outernet but after
half an hour I read my first transmission relayed by Outernet!

Below a screenshot as proof (being the first Dutch HAM to have Outernet relayed APRS-packets ? ) !
(and yes, there is a wireless component involved, a 5.6 GHz HAMnet link !)

 

April 18th, 2017

IC-720A refurbishment (2)

Introduction
My intention is to interface my IC-720A to common QSO-logging / contest programs like
N1MM or WinTest. I am not familiar with Ham Radio Deluxe (HRD) and honestly I didn’t miss it over
the last years. Goal is to enrich the IC-720A with an USB interface to allow remote control.
Recently I received the IC-720A bus protocol description (tnx KA6BFB!) so there is hope : -)

Sequencing / timing
When contesting with amplifiers or using seperate RX-antennas, timing is of major
importance to prevent e.g. ‘hot keying’ or detrimental damage due to RF-spikes etc.

Besides the PTT switch on a hand mike, many rigs lack a ‘/PTT input’.
That is, a low current input to switch the rig into TX-mode by making the PTT line low (<– /PTT).

/PTT in
Below the rear side of the IC-720A is depicted. The ‘MEMORY’ cinch connector under the power
supply molex connector looked very tempting to serve as /PTT in.

In my previous posting an internal /PTT point was already addressed. Seemingly the most
easiest way to implement /PTT on the ex-MEMORY cinch connector is to wire an internal /PTT point
to this connector? No . . . !

Nuisance with /PTT’s  (i.e. active low) is that this ‘low’ state is relative towards a ‘high’ state.
Depending on equipment used these ‘high’ states may vary significantly. Therefore ‘paralleled’
/PTT lines may result in detrimental damage! Perhaps the Heathkit SB-200 may serve as an example.
In ‘high’ state I measured around 120V on the /PTT input connector (!) Imagine what would happen
if you simply join the PTT of your rig with the PTT input of the SB-200 . . .

Mostly this nuisance is overcome using relays as isolation instrument. However, I am allergic
towards relays (perhaps besides the RX/TX (coax) relay) and prefer solid state solutions.

Grounding the PTT line I measured around 80 mA current, which is too much to be called ‘low current’.
My initial idea was to use an optocoupler where the switching transistor side had to serve as
/PTT switch. Well, that didn’t work. Despite having enough current through the
LED side of the optocoupler I heard the RX/TX-relay switching, the ‘TRANSMIT’ light weakly
burned but no RF output power was present in RTTY mode or ‘key down’ in CW.

Perhaps my /PTT wasn’t ‘low’ (or ‘strong’) enough?

I took another approach which works flawlessly, see picture below.

‘/PTT in’ is wired inside to the ex-’MEMORY’ cinch connector and ‘/PTT out’ wired to the
grey wire on the MAIN UNIT connector used for the relay accelerator (cf. previous posting).

April 9th, 2017

IC-720A refurbishment (1)

Introduction
Around three weeks ago I won an IC-720A for almost nothing during a live sale
at our radioclub
(PI4RCG). It was presented defect, so I thought: “What the heck?”

Afbeeldingsresultaat voor ic-720a

The next day the rig was repaired within an hour. Main error was, guess what . . .
yes! . . . the rotary relay. After some fiddling, cleaning and lubrification of the
rotary switch everything worked as expected.

It appeared my IC-720A was enriched with a  FL-32 500Hz 9 MHz CW filter, so this good old
buddy may be a likely candidate for ‘permanent’ portable usage in our camper/motorhome.

(Note: I prefer 250 – 300 Hz bandwidth for CW with ~500 Hz pitch . . . )

Some googling revealed that this rig was a quantum jump in its time and (one of) the first rig(s)
able to be remote controlled by a predecessor of the current CI-V Icom (‘CAT’) bus/interface.

The IC-720A features a general coverage receiver in 1 MHz portions. Transmitting was limited to
HAM bands only. With nippers this limitation was ‘fixed’ within 20 msec ; -) (read on).

In order to ‘get the rig going’, N1MM+ and my Winkey compatible Arduino keyer forced the
IC-720A to give CQ in CW for around three hours with full power (100W).

After this endurance test everything worked well, but I noticed I had to enter around 50 msec
‘PTT preamble’ in N1MM+ . . . which is too slow for contest and/or pile up usage.

So, I decided to enrich the TX/RX relay in the FILTER unit with a relay accelerator.

After studying the IC-720A service manual (google on it) it appeared that the /PTT (‘SEND’)
signal towards the filter unit (containing the TX/RX relay) could be easily located and isolated.

The wire was cut and the relay accelerator was piggy bagged somewhere on the MAIN unit.

Below a picture ‘before’ is depicted, mods are marked with A, B and C.
(click on picture to enlarge in a new tab)

A. General coverage TX mod. Cut this wire. (period ; -)

B. /PTT (‘SEND’) wire to filter unit. Cut this wire.

C. μPC2002 (TDA2002) noise reduction mod: place 470n in series with 100 Ohm between legs 2 and 4

Ad. B
Cut the concerning grey wire around the arrow marked position (see picture above).
The piece connected to the connector on the MAIN board goes to the input of the relay accelerator.
The other side is connected to the relay accelerator output by lengthening the wire a little.

The results of B and C are marked B’ and C’ in the picture below (click on image to enlarge in a new tab)

To be continued . . .

April 3rd, 2017

FT-857 audio noise reduction mod

Introduction
Being into weak signal work, either in contests or DXing, I fight against noise.

Europe is noisier than other parts of the world. In The Netherlands man-made noise
is becoming a significant issue, even a problem. However, with the right attention it is possible
to reduce noise/interference and become competitive on shortwave, even from The Netherlands.

Many people know me advocating the (vertically polarized) deltaloop on 40m. When properly fed
this antenna behaves like two stacked full size verticals but .  .  .  moreover, it reduces noise
during reception because it’s a closed loop/system. “If you can’t hear them, you can’t work them!”

In my quest reducing noise I was confronted with a kind of ‘nuisance after discovery’: audio noise.

My good old buddy, a FT-857 (yes . . . not a 857D), always assists me during holiday trips to
make contacts from exotic places. A few weeks ago I was in such an exotic place and was confronted
with a HUGE pile-up on 40m and tried to pull out weak JA’s and W’s out of the noise with my
simple setup: a (heavily modded) barefoot FT-857 (60 – 65W o/p) and 40m (vert. pol.) deltaloop in CW.

Blame my 70, 23, 13, 9, 6, 3cm, 2, 6, 40, 80 and 160m experience, but even on short wave you’ve weak signals!
Because I listened so much into the noise, my brains developed a kind of ‘weak signal filter’ in pile-ups.
During the last operation from this exotic place something became apparent to me which I (apparently)
didn’t notice before: unwanted audio noise in my (LoFi, NOT HiFi!) headphones.

Back in The Netherlands I decided to dig further into this issue.

Observation
Back home I inserted a weak signal (-140 dBm @7025.0 kHz) into my FT-857 and listened through my
headphones. While listening in CW-N (300 Hz BW) I was fighting against the perception ‘do I hear a tone or not?’.

In order to rule out some bias in myself I asked someone else to push the RF-on/off button of my
signal generator. My score was around 60% correctly detecting the tone or not.

With this applied weak signal I discovered I had problems in determining whether I could hear a tone
(or not) was related to the volume but increasing the volume also increased high(er) frequency noise
(more?) in the audio! Certainly a psycho acoustic issue is involved.

In other words, the high(er) frequency noise was interfering with my perception (whether there was
a tone . . . or not). In other other words, this high frequency noise was an extra load in filtering
the tone (in my brains?). The high frequency noise can be described as a ‘high pitched hiss’.

This led me to investigate the audio receive chain of the FT-857 and soon I focussed on the TDA2003
audio amplifier. Simply because this stage has an almost equivalent gain contribution in the whole
chain than it’s predecessing (RF and IF) stages. Assume that the -140 dBm signal has to be converted in
1W audio output (+30 dBm), the whole chain must have an amplication of 140 + 30 = 170 dB.

Knowing that generic audio amplifiers have (let’s say) 80 – 90 (if not 100) dB gain,
it’s relative contribution has might be significant (not for the overall noise figure (NF)
but more the timbre of the sound).

So . . . I decided to dig into the datasheet of the TDA2003 audio amplifier.

TDA2003
The TDA2003 is a standard audio amplifier. On the first page of the datasheet I found the standard application:

Immediately ‘Rx’ and ‘Cx’ drew my attention. Further in the datasheet it is explained that Rx and Cx
introduce a low pass behaviour in the above circuit.

In the FT-857 circuit diagram I noticed Cx and Rx were lacking (see below):

From the formulae given in the original datasheet, and assuming ‘B’ in the formula for Cx is
the cut off frequency, I calculated Rx = 100 Ohm, and Cx around 220 nF for B = 3000 Hz.
Because I hadn’t 220 nF and fiddling with  2x 100 nF parallel wasn’t my cup of tea, I chose 470 nF,
also to be on ‘the safe side’. Thus, 470 nF in series with 100 Ohm were connected between
legs 2 and 4 of the TDA2003.

Measurements
My first impression by ear was that the mod works, in a sense that I was more able to detect the tone.
Again someone else was asked to randomly press the RF-on/off button of my signal generator and
my score was 100% correct in determining whether there was a tone, or not.

We did a second test where I had to leave my shack. After I was called I had to take place at the table,
put on my headphones and the above procedure was repeated. At first glance I didn’t hear anything
but noise, but suddenly I thought I heard something. However, this seemed weaker than the previous tests.

I turned up the volume somewhat and after my brains ‘locked’ into the situation I was able to score
around 70%. It seemed my assistant reduced the signal generator level to -146 dBm by inserting a calibrated
20 dB attenuator and adjusting the output of the signal generator to -126 dBm !

Of course I was curious if I could determine the yield of the mod in a more objective manner.
A few years ago I used the ‘Analyzer2000′ program to determine and optimise signal to noise ratios (SNR).
However, it seems that this program doesn’t run anymore on 64 bit Windows systems. As alternative I installed
Spectrum Lab from DL4YHF. Despite Spectrum Lab is advertised being able to determine SNR’s, I couldn’t
find a separate SNR option or button at first glance. This program is significantly more versatile and
complicated than Analyzer2000, so I reckon I have to dig further in the manual ; -).

Anyway, as alternative screenshots of the waterfalls were saved in order to see the difference in noise
performance. ‘Before and after mod’ screenshots are saved into the animated gif depicted below.
In this animated gif three filter responses are displayed from top to bottom:
CW (CFIL, i.e. original filter), CW (2300 Hz BW, ‘SSB-filter’), and CW-N (300 Hz BW).

The crispy yellow points are the FT-857 audio beeps when selecting another filter.

Conditions: signal of -140 dBm @7025.0 kHz inserted into the antenna connector of the FT-857.
Audio extracted from the front headphone connector with headphones as parallel/speaker load.

It can be seen that the screenshot taken at around 19.48 hrs (‘after mod’) is more dark/black in the
higher frequency region than the 19.36 one. Of course this method is very ‘wicky whacky’ but it gives
some visual information about the audio (power) distribution. There may be some slight volume differences
between the two screenshots, due to implementation of the mod . . .

Anyway, the mod works for my brains, may increase (perceived) SNR with around +6dB as determined with a
‘wicky whacky’ method, and . . . is easy to realize!  See picture below (click to enlarge in new tab).

 

January 16th, 2017

ADF4351 evaluation board microwave beacon

Introduction
Building transverters for 23, 13 and e.g. 9 cm in the nineties was a tedious job.
First hurdle was building a local oscillator (LO). Typically a crystal oscillator
between 90 – 100 MHz was multiplied towards the desired LO-frequency.
After some fiddling and tuning lots of sky trimmers several milliwatts (mW)
of LO signal was obtained to inject into mixers.

Nowadays building LO’s is a piece of cake due to enormous developments in PLL technology.

ADF4351
Analog Devices released a PLL chip with an internal oscillator some years ago: the ADF4351.
Despite very interesting specifications, these kind of PLLs reside in very small (SMD) packages.

Fortunately some ‘evaluation boards’ exist, making experimenting much more easier.
A few weeks ago I found such an evaluation board on Ebay for around U$ 25.

Despite the fact that these boards may contain a ‘fake’ ADF4351 (an ADF4350 with ’4351′ on it)
I gave it a try (Google on ‘ADF4351 evaluation board’).

Alain F1CJN made a signal generator with a similar evaluation board and an Arduino.
However, for my purpose his approach was too complicated for me. I don’t need displays, buttons etc.
Therefore I consulted the ADF4351 datasheet and started programming myself.

As gadget I wrote a simple beacon keyer in conjunction with the PLL initialization code.
This code may be optimized/simplified when inserted into an ATTiny13a or similar microcontroller.

ADF4351 control pins LE, CLK and DATA are ‘onboard grounded’ with 10k resistors. Interfacing
a 5V Arduino is simply done with 5k6 series resistors because the ADF4351 operates at 3.3V.

When the code is entered into an ATTiny13a (or similar small 8 pin DIL microcontrollers) and
powered with 3.3V, interfacing the PLL board is simply a matter of connecting wires and we’re done!

Below a picture of my test setup with an Arduino NANO is presented (click on image to enlarge in a new tab).

Here is a short movie how it sounds on 2320.829 MHz (when programmed for 2320.850 MHz).
What you see is a FT-480R (old skool 2m allmode rig) with an old skool DC8UG 13cm transverter
in receive mode. Keying of the ADF4351 is done with bit5 in R4.

The onboard 25 MHz (TCXO?) evaluation board reference results in a ‘reasonable’ frequency
stability (doesn’t sound bad eh ?) but is a bit off (i.e. -21 kHz) frequency.
Goal is to use a GPSDO reference for ultimate precision and stability.

Here is my Arduino ‘sketch’. No libraries, just plain code. Have fun! : -)

December 17th, 2016

Es’hail2 dual band dish feed (2)

In this post I elaborated somewhat on the construction of an Es’hail2
amateur transponder feed.

Yesterday I (re)measured the 2.4 GHz feed a on a vector network analyser @work.
After some fiddling with the matching stub a truly fine 50Ω match was obtained!

I reckon the pictures below are self explanatory (click on them to enlarge in new tabs).


Fig.1 Test array in the laboratory                           Fig.2 Smith Chart between 2300 – 2500 MHz


Fig.3 Close up of matching stub                           Fig.4 Return loss response between 2300 – 2500 MHz

 

October 29th, 2016

FokzBox 2m fox hunt receiver

As active fox hunter Mischa PA1OKZ designed his own interpretation of
the ultimate 2m fox hunt receiver aka the FokzBox (Dutch only) in 2013.

The demand was big and around 250 receivers were succesfully built by
a large diversity of people, including me. Although Mischa ran out of
material and stated being fed up with the project, pressure on him led
to the mysterious discovery that his PCB manufacturer had 25 PCB’s left.

With some effort Mischa managed to collect all components to build
25 receivers and announced an order time frame to the community.
Within a few minutes all 25 receivers were sold.

In practice this means around 25 people are building their FokzBox now.
Sometimes they encounter problems and recently I heard somebody talking
about ‘the picture of PA3FYM’.

To facilitate builders, here it is (click on image to enlarge in a new tab):

FokzBox of PA3FYM (with some mods, but ignore them, PCB is v1.0).

 

September 23rd, 2016

Condor16 met gele stip!

A priori: because Condors are ‘hauptsächlich eine Holländische sache’
this posting will be in Dutch.

Inleiding
Naar aanleiding van mijn vorige post omtrent Condor-software en -ombouw doneerde
Jan PE1FWD mij op basis van deze oproep destijds afgelopen week een Condor16.

De geheime overdracht des Condors vond in de avond van 21 september jl. plaats op het
Gedempte Zuiderdiep te Groningen. Een biertje bij Cafe De Oude Wacht voldeed als betaling.

Het bleek een Condor16 met gele stip te zijn. Interessant is de gecultiveerde gedachte dat
Condor16′s met gele stippen ‘in principe niet geschikt zijn’ voor 144 – 146 MHz. <– ??

De mogelijke oorsprong van vorenstaand statement valt te duiden m.b.v. onderstaand
screenshot van een bekende Condor-informatiesite (klik om te openen in een nieuwe tab):

Ook andere Condor-experts deden mij jarenlang geloven dat ombouw van een ‘gele stip’
teveel werk was en om die reden dus oninteressant zou zijn.

Ondanks dat honderden Condor16′s met mijn software succesvol zijn omgebouwd (al dan niet met
FYM-ctcss), bezat ik zelf geen Condor16 (<– ‘PTT’ versie) maar wel een TMC82 (<– ‘PVD’ versie).

Dus de gift van de gele stip was voor mij kwa twee aspecten zinvol:

1) een ‘echte’ Condor16 te hebben voor de softwareontwikkeling
2) ondanks ‘horrorverhalen’ een gele stip ‘aan de praat’ krijgen

Handelwijze
Zonder ‘aanziens des stips’ brandde ik een EPROM met mijn software en liet mij niet hinderen
door de gedachte dat ik een ‘niet geschikte’ Condor16 onder het mes had.

Met gevaar voor eigen leven verwijderde ik de behuizing en bereidde me op het ergste voor.
Immers, een bevriende Condor-expert had me afgelopen week nogmaals bevestigd dat er aan
gele stippen’ teveel moest gebeuren om ze geschikt te maken voor 144 – 146 MHz.

Onderstaande foto geeft weer hoe ik (na openmaken) het RF-deel van de gedoneerde Condor aantrof
(klik voor grotere foto in een nieuwe tab):

Niets bijzonders! Na aanzetten had ik wel een knipperend display, dus de PLL(s) lockte(n) niet.

Nadat de -in bijenwas gesealde- VCO-messingkernen waren ‘bevrijd’ en de kapjes ‘boven’ de VCO’s
waren verwijderd, lockten beide VCO’s ( i.e. geen knipperend display) nadat ik de messingkerntjes
‘door de onderkant’ draaide (zie foto onder, klik voor vergroting in nieuwe tab).

Hierboven: ‘doorgedraaide’ messingkernen voor VCO-locks @145 MHz (displayfrequentie).
De VCO-spanningen (MP RXvco en MP TXvco) bedroegen ca. 1V, hetgeen erg (te) laag is.

Op de print bij de VCO’s zitten ‘foezelpads’ waarmee een condensatortje parallel met de VCO-kring
geschakeld wordt. Gevolg is verlaging van de resonantiefrequentie en ‘mooier’ inregelen van het
betreffende VCO-kerntje. Besloten werd om voor beide VCO’s de foezelpads (rode pijltjes) te activeren.

Inderdaad, de VCO-spanningen konden mooi ingeregeld worden. De messing kerntjes zitten ongeveer
in het midden en resulteren in VCO-spanningen van ca. 2.5V bij 145 MHz (displayfreq).
Zo ingesteld locken de VCO’s tot ca. 160 MHz (displayfreq).

Hieronder een foto omtrent ‘voor’ en ‘na’ bij het RXvco, voor het TXvco geldt dito.

Afregelen ontvanger
Met een meetzender werd 145.000 MHz in de ontvanger geinjecteerd en na afregeling bedroeg
de gevoeligheid ca. -125 dBm bij ca. 10 dB SINAD. Dit is werkelijk prachtig! Niets padjes
solderen of allerhande griezelverhalen dat er ‘teveel’ aan moet gebeuren om de
RF-ingangstrappen geschikt te maken voor 144 – 146 MHz.

Afregelen zender
Het vermogen @145 MHz bedroeg in stand ‘HI’ ca. 7 Watt, gemeten met een HP-432A bolometer.
Dit is wat aan de lage kant. Ik vermoed dat er nog een paar extra Watten te halen zijn
wanneer de driver en eindtrap onder de loupe worden genomen.
Ik kon vanuit mijn QTH met een simpele rondstraler binnenshuis probleemloos over PI3UTR werken.

Hieronder een foto van het onderhavige exemplaar (klik voor vergroting in een nieuw tab).

Conclusie
De voorlopige conclusie lijkt gerechtvaardigd dat m.b.t. dit Condor16 gele stip-exemplaar geen
verrassingen zijn geconstateerd met mijn software (v3.05). Of dit toeval is, weet ik niet.

Maar . . . ! Ik heb inmiddels een tweede Condor16 met gele stip gekregen.

Toevoeging 26 september jl.:

Na openmaken van de tweede gele Condor16 bleek dat deze al gemodificeerd was.
Er zat een sticker in waarop stond: “145.650   111 – 112 dBm” (zie onder).

Met de meetzender @145.000 MHz kon ik bij ca. 10 dB SINAD de gevoeligheid wat
beter krijgen, nl. -118 dBm en heb het maar gelaten zoals het is.

Ook in dit exemplaar waren de ‘padjes’ waarmee extra condensatoren parallel aan
ingangskringen worden geschakeld ‘geactiveerd’, alsmede de padjes bij de VCO’s.
M.a.w., wanneer dit wordt gedaan, performt de zaak goed rond 145 MHz.
Dit exemplaar leverde trouwens max. 12 Watt RF output.

Omdat in deze Condor16 geen FX315 CTCSS chip zat, heb ik gelijk maar FYMctcss ingebouwd.
Hieronder een gedetailleerde foto van de inbouw (klik voor vergroting in een nieuwe tab).


Eindconclusie
Op basis van vorenstaande ervaringen hoop ik het fabeltje weggenomen te hebben dat
Condor16′s met gele stip ‘ongeschikt’ zijn voor ombouw naar 144 – 146 MHz !