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.

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

TS-50 to LDG Z-100 plus connecting cable

Using the infos gathered on the net and showed in my previous post, I'm ready to build a quick-and-dirty cable.

Purpose of the cable:
- DC supply the LDG tuner from TS-50 ACC connector
- enabling the "AT TUNE" button on TS-50

The sketch below shows the circuit (press to enlarge). The ACC conncetor is shown radio side.

The TT and TS lines are connected together via a 3.3 Kohm resistor. The + and - lines are connected to LDG power conenctor via a 1 A fuse on the NEGATIVE path of supply lines.The ACC connector used is a PC surplus connector as shown elsewhere in my blog.

The final result is in the photo below:

Ok, seems like a sort of wire patchwork (green, white, black, red, yallow....) but IT WORKS!

Using the tuner with this cable is simple:

- Press TUNE button on LDG
- Press AT TUNE button on TS-50
- Wait for a match
- REMEMBER to shutdown the carrier pressing again AT TUNE on TS-50

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.

SEM 52-S military handheld

Months ago, I've bought a german military handheld: a SEM 52-S. Specifications: see http://www.kpjung.de/e_sem52s.htm
Is an FM handheld with frequency coverage that includes 6 meters, 1 watt circa power out, very big and weighty, but so cool! 6 fixed channels programmable with internal contraves.




The radio is a SEM 52-S/FZ/46 and is not born as an handheld: is user on tanks with a mount, see http://www.greenradio.de/e_sem52sfz.htm, but is useable as handheld using a SEM 52-S battery pack (delivered with the transceiver).
I've also the antenna, a long (93 cm!!!) SEM 52A antenna, with fits perfectly in SEM 52S

• First Job: rebuid battery pack

The battery pack comes with a broken, unusable NiCd battery pack. The box is also very dirty and in bad conditions. I build a new battery pack using two docks for 4 AAA battery, and fit in 8x900 mAh NiMH AAA. The result is shown below:

• Second Job: arrange an alternative antenna

I have an original antenna, but is very long (93cm) and I want a smaller one for short-range contacts. I choose to modify a commercial item. I buoght an old 43 MHz whip antenna: 43 MHz is almost a dead band, and dealers are happy to sell one for a very discounted price. The antenna is a CTE model HP-FLEX/B.


The antenna is 54 cm long. Using the FT-817 as a tunig tool, I cut the antenna until a dip in SWR happens (I stop at 1.5:1). The antenna is now 36cm tall (from bottom of BNC connector to top of the whip. See the shorted antenna mounted on SEM 52-S


Next job: building a speaker-microphone (to do)

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.

PL support for camera tripod

I've built a simple support for using HF and VHF mobile antenas with a camera tripod.

The base is made of plywood. The support for BNC connector and ground connection is a small steel "L" piece, wich may be found predrilled (fits also BNC!) in any hardware store.


The two wing nuts are for radials. Detail view:

Two stands for FT-817

The first stand is an homebrew item, built with a CD case following the instructions of KR1ST:

The second stand is a commecrial item (buuh!): IKEA sell this item as an alarm clock, is cheap (7 Euros), light, give a touch of design to setup and tells GMT time for free ;).The idea is not mine, I've seen a post from IW4BIC in an italian FT-817 fan forum.

K2S: An Yaesu FT-817 Knee Support

It's very fun to going around in /P with an FT-817, few meters of wire and a fishing pole! I often sit on a rock or on a little foldable chair and have many nice QSO with the little radio standing on my knee.

But in this way the DC connector is stressed, and obviously my DC conector was broken soon (the connector on the radio, soldered in SMD to main printed board.....sigh!!). Very disappointing indeed.

OK, let's resolve the problem: I've built K2S (KISS Knee Support), which is used to avoid stress to DC cable while the FT-817 stand on knee.

Is very ugly and simple, but it works! Ia a piece of plywood cutted to fit the two "wings" on the back right side of the radio. Near the end of plywood i glue a slice of cork wine bottle cap to support on the left side of radio, geting me able to use the rear PL connector,

This is K2S, with the measures...very ugly!


A more clear draw:

K2S in action!



Looking closer...

Tiger Tail published in SPRAT!

I've sent the notes to build a Tiger Tail, as shown in my previous post http://iz8jji.blogspot.com/2011/04/boost-your-ht-for-almost-nothing.html to Colin G3VTT, and he agree to publish the notes in his column AAA (Antenna Anectodes and Awards) of SPRAT, bulletin of G-QRP club.

The notes were published in the Autumn 2011 issue.

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: