Improve your chances of contacts, by Alex VK2HAS.

[gil]

This article was originally posted on the PRC-320 Yahoo group: https://groups.yahoo.com/neo/groups/prc320/info by Alex VK2HAS, reposted here with permission.


I have come up with a theory.  Here it is "most Clasnman 320 owners are obsessed with their whip antennas".  I can already hear the yells of denial but the fact is, all the photos exchanged show the radios in use with the whip!  Think about it.  The whip antenna was developed for mobile battle use and for short range contacts, also the ease of tuning to almost any frequency.  The literature suggests 25 miles maybe?  Yes, Yes we all know they can work for longer distances, I myself have spoken from NSW to Whales in the UK at 5 by 7 on the whip but dam I picked the best take off locating in the world and waited uptill the propagation gods had declared a propagation free day, think about it the whip is the most unlikely antenna to achieve anything!  We can all do better than that!

So what did I do?  I sat down and put an article together to improve every ones range both local and DX when using their 320 with little expense and effort. My challenge to 320 owners, Read this and do it!  Be the first 320 from outside of Australia to talk to me. I plan to put this up on the group files when I have time.  Alex ever waiting for a 320 contact VK2HAS.

Hello members, many of you have exchanged photos of their radios on the whatsapp, great to see them.  I can't help but notice how popular the use of the whip antenna is.

It appears in almost every photo members put up.  I know it's so easy to set up and tune but out of all the antenna systems a 320 could use the whip is the most unlikely to succeed when trying for long distance contacts. Now don't get me wrong it is possible and many have done it including myself but these contact are not the normal. If you guys are looking at becoming proficient in DX or long haul coms. You need to get on the air with something a little more efficient than the whip.  I know we have some very talented people in this group that have mastered many different antennas with great success but we also have many (especially) new members who find antenna theory a little difficult and I'd like to suggest a very simple and cheap antenna that will definitely get the 320 talking to the most distant stations when the propagation gods are smiling.

I suggest building a simple ¼ wave elevated resonant 20M antenna.  This same antenna can be scaled down for the 15 &10 meter bands.

First a little theory (simple).  A ¼ wave vertical has a resonate vertical length of ¼  the wave length you plan to transmit on:  use this calculator to give antenna measurements:  http://www.csgnetwork.com/antennagpcalc.html

When making our antenna for the 20M band both vertical element and radial length are pretty close to 5.023M long.

Now because our 320's only put out about 25 watts of power it's very important to get all of that power into the resonant vertical element.   Our 320's have a 50 ohm output socket called the TR socket and can be used by removing the tuner link (dog bone) and plugging your transmission line directly into the TR socket.  This will remove the internal tuner but the reflector meter will still operate!!!

We will be using 50 ohm coax cable only, say RG58 with a BNC connector to connect directly to the TR socket.  Now to get maximum power transfer between our 320 and the antenna the antenna must also present a 50 ohm load.  If you use a ¼ vertical antenna with the radials laying on the ground or stretched out  parallel to the ground like most people do the antenna will present a load of close to 33 ohms, maximum power will not be transferred into the vertical element (it will still work but not as good as it could).  By elevating the feed point to about 3M you can get your 4 radials sloping down at approx. 45 degrees.  At exactly 45 degrees the load presented by the antenna will rise to close to 50 ohms. Maximum power transfer will occur! By making the 50 ohm transmission line (coax) restively short we can reduce losses in the cable.  Transmission lines lengths should be odd multiples of the ¼ wave length transmitted.  For our 20M antenna a ¼ wave 3/4 wave or 1+1/4 waves length should be used.  These are electrical lengths and take the velocity factor of the cable into consideration.  By using these lengths any radiated feedback generated on the coax outer shield will present it's lowest value to the transmitter, hence reduced any feedback.  Suggested coax lengths for 20 meters are 4.17M, 12.51M or 20.5M

2 or 3 clip on ferrites RF noise filters from ebay:

http://www.ebay.com.au/itm/5pcs-Clip-On-Noise-Suppressor-EMI-RFI-Filter-5-7-9mm-Cable-Ferrite-Core-Filter-/401120312767?var=&hash=item5d64a23dbf:m:m9xq7Ji29J5tRUlMMjRdkIQ

are a good idea just before the coax connects to the radio, this will also help kill any RF feedback.  I also have a couple clipped onto my PTT cable just before it pugs into the set.  You can get them on ebay for a few dollars

OK now lets look at the antenna's reputation and benefits.

The angle of radiation is about 20 degrees, this will give a good close in ground wave and a good skip angle for DX work.

Many user of the antenna claim that at extreme distances it will out perform a good dipole.  The ease of installation is a great asset.  You can use a tree with one point of support or a relatively short mast, look here for a mast:

http://www.ebay.com.au/itm/HAM-Radio-Telescopic-Squid-Pole-HEAVY-DUTY-7-METRES-/122044560803?hash=item1c6a6c35a3:g:Lz4AAOSwQItT89F7

These masts are very good quality!

A meter of PVC on the bottom of a 7 M mast and you have the correct length. For the adventurer it is easily transported, (you could tie these onto your bergan or carry frame), light and can be erected in minutes. The radials can be used as guy supports for the vertical element.

Tuning is done by using the 320's built in reflector meter (what a marvellous thing this is!), unlike SWR meters the reflector meter reads the opposite, the higher the reading the better the match. One o'clock is good! 3.00 o'clock is excellent!

Ok to tune start off with a vertical element length a little long, say 5.080 or even 5.1M which is going to be too long, set your frequency to top of band and your set to ANT on your selector switch and transmit by pushing the PTT and hear the tuning tone, note the meter reading, now set frequency to the centre of the band, say 14.2000 and lastly to the bottom of band and repeat.  If the meter reads higher as your go down in frequency the antenna is too long.  Trim off 1cm and repeat until you get max reading at say 14.2000 Mhz.  Close to centre of band.  Done!

I have attached a hand drawing of a ¼ wave vertical elevated antenna and some photos of how I constructed my feed point using a simple SO 239 panel mounted socket.

An extremely efficient and cheap antenna that will get you not only across your country but across the world.

Note:  Many constructors recommend 6 instead of 4 radials.

To construct my wire antennas I use medium speaker cable that I split or tear apart.  Cheap and very effective, even solder a couple of lengths together to get the required lengths.

Station location.  This is a very important factor in how successful your antenna operates, although the above antenna will operate if erected in your suburban backyard it's probable not the best place for it.  These are the station locations I prefer.

If possible away from Suburbia and the RF noise generated in such places.

On top of a hill with a long slopping drop off in the direction I'm interested in.

Close to the ocean or a salt water lake, I don't mean in the car park or a park adjacent to, I mean within ½ a wave length (10 meters) of the water.

Following these tips will greatly increase your antennas performance.

Well that's it!  Even I could follow these instructions.  Good luck and let me know how you get on.

Alex  VK2HAS.

[gil]

I think the MFJ 17ft. telescopic whip would be great for this application, mounted on a 3m painter's pole. Using the radials as guy wires is a great idea!

Gil.

[cockpitbob]

Great read.  I keep hearing about the benefits of a vertical with elevated radials.  It also never occurred to me to make the feed line length a multiple of 1/4wave.  With 1/4wave, whatever impedance is at one end(low) will be the opposite at the other end(high).  My Dad (ex Navy radar and radio tech) said lots of waveguides were mounted on conductive mounts that were 1/4wave long.  They insulated better than non-conductive mounts.

But as usual, I disagree with his obsession for getting the SWR as low as possible.  You really don't loose much power with an imperfect SWR.  With a 2:1 SWR you are still radiating 89% of your power (assuming a short feed line so its losses are small).  My only concern with SWR is keeping it low enough to not blow the transmitter's finals.  Here's my favorite chart on SWR vs. power lost.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiPgdGE_Z3OAhWLXh4KHXIQBiIQFggeMAA&url=http%3A%2F%2Fwww.skyworksinc.com%2Fuploads%2Fdocuments%2FVSWRreturn.pdf&usg=AFQjCNHgx3K7PHxSI00_NpVVCc7riisb2g&sig2=8pqaL7c7GlhEjXi8FAkoBw