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:

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!

Building a 9:1 Un-Un for longwire antenna

I'm always fascinated by the "magic" 9/1 un-un for longwire antennas, also called "Magnetic Longwire Balun". You build this device, connect the transceiver and a longwire antenna of almost random wire, and GO!!! No SWR on 160/10 meters, no Tuners, perfect.....OR NOT?

The background study:
If you google "Magnetic Longwire Balun" you may find a lot of experiences of many ham operators all around the world about this antenna. The cores used for Un-Un are various: ferrite sticks, FT and T Amidon toroids and even cores from old TV EAT transformers.

There is also a SWR table versus wire lenght, found somewhere in the 'net attached to manuals of commercial longwire antennas (click image to enlarge):

I suggest to look at M0UKD web site for a quick guide to build a 9/1, If you want to deep in with different cores and expected performance, read:

• G3TXQ web site contains a very good article (http://www.karinya.net/g3txq/unun/) on cores and ratio comparison for 9/1 and 4/1 un-un.

•  G8JNJ web site has a very good article (http://g8jnj.webs.com/cometcha250b.htm) on building a clone of the Diamond BB6W wideband antenna (scroll down...). The balun used is a 6/1 but there are some interesting facts and tests on various cores.

Building the 9/1 Un-Un 
My requirements was:

• 80m to 6m use
• QRP or max 100W power
• light and little for portable use

I use an Amidon toroid, a T130-6 with 9 turns trifilar using insulated stranded wire. For the box, I choose a grey PVC coupler (40 cm diam.)  and two caps. Connectors are PL female for TX and M5 screw for antenna wire.

The Un-Un have no hooks for hanging, but I arrange also two insulators made of hard white plastic (teflon?) from a chinese chopping board. The right one is for connection to Un-Un (using the third hole for hanging) and the left one is for wire end.

The SWR of Un-Un with a 470 ohm dummy load was measured and better than 1.3:1 from 3.5 to 50 MHz..
I've made several 9/1 for me and for some friends using different materials. On-air performance is sufficient, not bad for a so simple antenna.

Cores used in the Un-Un :

• Amidon toroid (T200-2, T130-6, FT140-43, FT240-43)
• Unknown Yellow-and-White toroids (I suppose are for switching power supply)
• Ferrite sticks from old AM radios

In order to chioose the core material, mind this simple facts:

• Using Amidon cores (in particular TXXX-2 and -6) the losses are relatively low and the performance of the antenna is better, but in the lower bands you may need a antenna tuner to obtain good SWR. Otherwise, if you don't like to bring ATU, try to use a "long" coax feeder (more than 10 meters)
• Using low frequency toroids or ferrite sticks the losses incrase a lot, but this lower your SWR and you don't need an ATU at all.

Another 9/1 Un-Un I made for a friend with ferrite stick

UPDATE!
Look my new "Shorted" longwire antenna

Coaxial stub half-wave end-fed antenna for 10m band

I'm a true fan of end-fed antennas, and I've built one for 10 meters band.
The antenna itself is 5 meters long, and matching is obtained using lambda/4 coaxial stub. The matching method is the same used in J-Pole antennas: a lambda/4 * VF (velocity factor) transmission line shorted at the end.

I've used RG58 cable for matching line and 1mm PVC-covered copper wire.
The sketch below shows the building detalis:


The left side of coax is shorted; the right side is connected (only central conductor) to half wave wire (braid is not connected). At feeding point I've used a BNC T adapter to connect all together.

I use the antenna mounted vertical on a fishing pole and attached directly on the rear connector of my FT-817 (no cpunterpoise, no choke, no balun, no antenna tuner on 10m). SWR is acceptable (1.5 - 1.8 between 28.400 and 28.600).

Today in the morning I've got some nice QSOs. The most remarkable is Japan (Yeah!!!!)JA1NVF with 5W SSB! Not bad anyway, eh?

This antenna, tuned with my Elecraft T-1, is useful also on 12 and 15m. Build one for your preferred band, is an "instant" antenna, very cheap and simple to build. Of course, if you've a few meters of twinlead for build matching line, the performance may be better (modify lenghts....).

07-08-2014 UPDATE: Using this antenna I've many QSO with DX locations (Brazil, Argentina, Japan), and I won the 2013 CVA DX Award, see here.

Simple window loop antenna

I've no way to set any antenna on the top of my building. This is the reason because I'm often in /P. But also at home I've some QSO using strange antennas. This is one of them: a window loop!

I've a window 158x140 cm pointing to east, with no other buildings in the way. A wire installed in the window perimeter is circa 1 wave lenght in 6 meters.


Anyway, the loop is not resonant on 6 meters: is not a perfect 1 lambda, the wire is too near to radiator etc., so I use this loop as an untuned loop, connecting a tuner in the low right corner of the window, as shown above:



Results: amazing! Hungary and Ukraine in 6m! I use this antenna also on 10, 12 with good results. On 15 meters the results are acceptable, but I've got very few QSO in 20 and 17 meters.

Next step: trasforming the untuned loop in a short magnetic loop for the 20 and 17 meters.

Racal ANT-129 tripod support

I've built a more stable support for my military antenna. The support is made with a almost square slice of steel tube, a gift from Mimmo IZ8SQL, which had also the main idea of the support (TNX Mimmo!). Other items may be easily found in any hardware shop.

Parts needed:

• nr. 1 slice of square steel tube, approx 5cmx5cmx5cm
• nr. 1 inox bolt M10x20 (10mm dia x 20 mm lenght)
• nr. 1 "big" 10mm nut (lenght approx 3 cm
• nr. 1 20mm electrician grey PVC coupler
• nr. 2 10mm washers
• nr. 1 banana female connector

Drill three holes in the square tube:

Mount the banana connector, the bolt and the big nut on the support:


Cut the PVC coupler to the same lenght of the big nut. Cover the nut with a few layers of electrician tape: in this way the nut fits snugly in the coupler. Mount the coupler with the help of a rubber hammer. The final result, before painting, is this:


The support varnished, ready to operation:

My new Military whip antenna Racal ANT-129

A few weeks ago, I've bought via ebay a military whip antenna for a few euros. The whip is a Racal ANT-129, collapsible in 8 sections, total lenght 260cm circa, and seems rated for 21-30MHz.

The base of the whip is terminated with a M10 screw (10mm metric), is very easy to find a nut for radio connection. I arrange a quick base with a camera tripod and a piece of wood. I've connected the whip with a wire to my Elecraft T-1 tuner using a 5m wire counterpoise. The antenna needs NO tuner for 21 and 28 MHz, (ok, SWR is not 1:1, but may be acceptable) and with tuner loads in 20, 17 and 12 meters. No way to use this antenna in 7MHz and less. The foto below shows me (left) and Nico "The President" IZ8KTL (right) near antenna, tuner and FT-817 in /P. Many nice QSO with european hams. (TNX to Carmine IK8GYQ for photo)


I've built a more stable support for my whip, I'll show it soon! Stay tuned.