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!

First QSO in 4 meters!

On sunday, 16 feb, I've a first QSO in 4 meters band using my PRC-351. The QSO involved also 3 other hams in Benevento.

Working conditions:

• IZ8JJI/M: radio PRC-351, (wire) quarter wave antenna mounted on the roof of my car
• IZ8FQX Pompeo: radio PRC-351, 6 meters loop antenna tuned on 4 meters
• IZ8VKE/P Gaetano: radio Wouxun KG-699, 5W, rubber duck antenna
• IZ8UZV/P Cesare: radio Wouxun KG-699, 5W, rubber duck antenna

Clansman PRC-351 Military manpack

In order to experiment operations on low VHF FM (in particular 4 meters), I've bought another military radio: a Clansman PRC 351.

Frequency coverage: 30-76 MHz in 25 kHz steps, covering 6 and 4 meters ham band
RF Power output: 4 W
Power supply: 24 VDC

I've got the radio without accessories, and I'm going to use a Clansman Single Transducer Headset   (see info and photos on Armyradio web site) which I bought some times ago. Is simple to use, like a speaker-microphone.

I've no battery. To get the 24 VDC needed from a 12 V battery  I use a variable voltage notebook power supply similar to this:

The highest voltage is 24 VDC and Imax = 2 A, enough to supply the radio without any problem.

Using the radio is very simple: rotate the 4 frequency knobs (x10 MHz, x1 MHz, x100 kHz and 0-25-50-75 kHz). The ON-OFF knob have 4 positions:

• O: OFF
• W: Whisper (radio on, squelch on, low volume on headphone, high microphone sensitivity)
• L: Loud  (radio on, squelch on, high volume on headphone, low microphone sensitivity)
• *: squelch off, Loud mode

A real volume control is not present, but the audio in Loud mode is enough to understand voice also keeping the headphone in hand (in a quiet envoronment). No problem in any mode wearing headphone.

Building a 1/1 Current (Choke) Balun

Another simple useful device: 1:1 current balun, used as a choke for RF suppression. I've built this balun following this site: http://kambing.ui.ac.id/onnopurbo/orari-diklat/teknik/balun/current%20balun,%20current%20choke,%20choke%20balun,%2050%20ohm%2011.htm

The core is an FT140-43 toroid and the winding is made of RG-174 coax cable. On antenna side I added a 10kohm - 1W resistor in parallel between cold and hot connector of the PL for static suppresion. The final result is here:

SWR with 50 ohm dummy load is 1:1 160-10 meters, on 6 meters SWR is better than 1.5:1. At this time I've not tested the balun on the air.

Building a 4/1 Current (Guanella) Balun

I need a 4/1 balun for feeding balanced antennas, such as Up-and-Outer (my preferred antenna) or M3KXZ 'no counterpoise' antenna.

I've built one following the instruction found on this link: http://www.n0ss.net/qrp_4-1_guanella-type_balun.pdf

I use a single core, FT140-43 toroid, enclosed in a little black box, using two "banana" binding posts for wire and panel female BNC for feeding.

The result:

Another photo: Box closed and added 32mm diam. clip for fishing pole locking

Very simple to build! Results: VERY VERY VERY good! I.E. North Patagonia on 15m with 2.5 W using up-and-outer antenna! See http://iz8jji.blogspot.it/2012/07/a-great-qso-un-15m-with-lu.html

I've not used this device on 80 or 160 meters but the performance expected is not so good. I've tested the balun in 6m but the performance are very poor!