CVA DX Award - from Brazil!

In August 2013 I had many QSOs with Brazilian hams in CVA DX Contest 2013 (Concurso Verde e Amarelo, see also my previous post here ). I send my log to CVA DX Contest Committee.

Yesterday arrives at home a parcel from Brazil, containing a beautuful wooden plaque: an award!

1st place in the category SINGLE-OP ONE 10m QRP.

OK, I'm the only ham who partecipate at contest in this category, but 5 QSO with Brazil in QRP in the same afternoon seems to me an amazing result.

I've used my FT817, 5W power out,  and my 10m Half Wave End-Fed antenna, described here.

Thank you very much to all Brazilian hams!

70 MHz mobile antenna, fast and cheap!

In last summer, I make some local QSO on 4 meters band with some hams using my Clansman PRC-351, and therefore I need a mobile antenna. The 4 meters band in Italy is used by very few users (almost only Fire Dept., I believe) and so the antennas for this band are very expensive, more than 60-70 euros for a mobile quarter wave!

Don't worry! I'm going to explain how to modify a 2 meter antenna for 4 meters operations.

You need a 5/8 lambda for 2 meters band. Almost any mobile 2 meters 5/8 antenna is built as shown in the following example:

Choose an antenna built in this way (to be sure, verify that hot wire and the braid of the coax are not in short-circuit).

This antenna is more than 1 meter long whip and a base coil with few turns. The 1/4 lambda in 70 MHz is 1.02 meters, so THIS ANTENNA MAY BE MODIFIED FOR 70 MHz. In order to do this, cut the whip until SWR dips at 70 MHz. Is very simple, and works for ANY 5/8 antenna for 2 meters band.


For the mod, I choose a well-built antenna; a Caletti Atlas, built by the Italian farm Caletti. I buy this antenna from a surplus reseller, is new in box and shipped with base, cable and connector for 7.50 Euro, a real bargain for a quality antenna!

This antenna is yet cutted for f >155 MHz and so is not useful for 2 meters, but is long 109cm (whip only), enough for my purpose. The firt thing is to measure the antenna with an analyzer; Nicola IZ8ITJ and his MFJ259B helps me very much for this job. The SWR, measured wuth the antenna mounted on a magnetic base over my car shows interesting results:


Resonance (3/4 lambda) between 159.9-161.5 MHz 
(SWR < 1.1/1)

Resonance: (1/4 lambda) 55.770 MHz 
(SWR 1.0/1)

in the ham bands:
Frequency       SWR
50 MHz               1.9/1
51 MHz               1.8/1
70 MHz               2.0/1
145 MHz             1.9/1

If you not are a fan of SWR 1/1, this antenna may be usable on 6, 4 and 2 meter with no mod!!!!

But my idea is to build a 4 meter whip, and then began to cut the whip measuring SWR with the MFJ259B. I stop at SWR 1.3. The antenna is:

Lenght: 85 cm
(from the end of the spring to the end of the whip)
Resonamnce (1/4 lambda): 70.200 MHz 
SWR 1.3/1 R=43, X=13

Using ICOM HM-118 Microphone on 706!

I've bought a (fake) ICOM microphone for using with my 706, an ICOM HM-118.The mike was bought on the 'Bay from a Cinese seller, and costs less than 10 euros included shipping! This microphone is not compatible with 706, but is very easy to adapt, only two wires to cut!

Look at the job of Greg AC2MC link The mod is very easy: cut the wires connecting to pin 3 and pin 8 of the RJ-45 plug. DONE. I've opened yhe HM-118, the internal view is below:

Using a multimeter I verify which wire connects to which pin of RJ-45. In my microphone, the pin 3 is yat disconnected (there is a cut blue wire from curly cable thet is non connected toPCB). If you cut the yellow wire you have finished the job. (WARNING: the color of the wires may vary on different mikes, check the wires before cut anything!).

Instead to using the board circuitry, I decided to apply a mod similar to the HM-36 mod. The circuit of the SE5X mod is this:

For this mod I need to:

• cut the mic wire on PCB board (in my mike, is the black wire) - circled in RED in the image
• connect 2k Ohm Resistor and 0.01uF Capacitor in parallel (R//C)
• connect R//C with black wire coming from curly cable
• disconnect the red wire on electret capsule
• connect the other side of the R//C with hot side of the electret capsule
• connect a 4700 pF capacitor in parallel with the electret capsule

Is easy to see the mod in the following image:

The blue rings os microphone wire are two ferrite beads; between R//C and PCB I put a little strip of self-adesive foam to prevent short-circuits.

Job done! The mike seems to be ok, on-air test and reports in the following days.

PS: Greg AC2MC reports that UP and DOWN stiches are reversed if referred to 706, but in my HM-118 the switches are in the righrt order.

Icom 706

In the last weeks, I've bought an old ICOM 706 (Mark 1) for use in /P as an alternative to Yaesu FT-817. Ok, really I was in search of a 703 but....not found!

Thus radio is not very expensive (most hams prefer Mark II) but seems interesting.

The seller have no mic, and I soon arrange a cable for use the HM-36.

The cable is OK, and I've tryied the radio with LDG Z-100 and 9/1 longwire antenna at 10W of power, QSO with many EU and Azores.

Building a Short "Longwire" antenna

Ok, I'm not kidding: I'm really trying to shorten a longwire antenna.

The problem: a newcomer want his first antenna, want 40-10 meters at least, have no space, have a fishing rod only 7 meters long.

For first antenna I usually suggest at least 9 or 11 meters of wire and a 9:1 un-un. This not the most effiective antenna to build, but is a simple to build and low cost multiband. But 7 meters of fishing rod....

If you look at the table in my older post on 9.1 iun-un you find two suggested lenghts shorter than 9 meters: 6.5 and 7.5 m, but I was not able to maych it on 7 MHz using either LDG Z100 and Elecraft T-1, the minimal useful lenght for 7 MHz is 9 meters!

The only solution seems to shorten the antenna. But the "longwire + 9:1" is yet a compromise antenna, loading coils may lower further the effectiveness of the system, resulting a long dummy load!

As a last chance, I'll try to shoirt the antrenna wire using the reduced velocity factor of coaxial cables.

An RG58 cable has a velocity factor of circa 0,67: This means that for reach an ELECTRICAL lenght of  9 meters I need a PHISICAL lenght of 9x0.67 = 6.03 meters of RG58.

This is a known trick, for an example of using velocity factor for reducing wire lenght look at this project in Ham Universe.  You may read also a more accurate description of the effect of velocity size based antennas on G3TXQ web site.

The coaxial cable MUST be connected in this way: on one side of cable you connect only ONE conductor (central or braid); on the other side, connect braid and central togetther.

I'm able to obtain a match also in 40 meters with LDG Z-100 tuner.

Last news: the friend which is using this antenna reports suffcient performance, many european QSO also on 40m.

Buiklding a QRO 4:1 un-un with an unusual core

In Winter holidays, a friend ask me for a longwire balun and I've no toroid core available, then I look into my junkbox and I've found an old  TV EAT Transformer, like this:

I've read somewhere in the 'net that some hams use this core for building baluns and ununs, and I decidde to satisfy my friend's request using this core.

I'm inspired on the work of another italian ham radio operator, IK1ICD (you may look at his job HERE )

I arrange quickly a 4:1 un-un using the usual schematic:

I use 2x1 mm speaker wire, 2 and a half turn + 2 and a half turn + 2 and a half turn (...whew! simpler to look the picture below than describe it!)

The un-un closed in the box, ready to operate!

Another view:

Some Brazil QSO's in QRP!

Yesterday I was in air on 10 meters in /P, and in the early evening many Brazilian hams comes very loud and running for a Brazilian contest, CVA DX.

I arrange myself soon, and try to contact the PY friends.using FT-817 and my homebrew 10 meters half wave antenna described here; No tuner was needed, antenna matching is very good,

RESULT: 5 QSO in 1 hour....

• PR1T
• PU5DCB
• PU3TOT
• PT2CVA
• PT5T

FANTASTIC!