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Equipment notes:

IC-781   IC-706   Vertical Over Salt Water   TS-850s   Selecting Coax    PL-259 Assembly

Easy and Effective Radials

Icom IC-781 Installation Notes, ALC mod, Fan mod

I bought one of the first in 1986 and have bought another one since. It is a fantastic radio, perhaps the best analog transceiver ever made. Operation of this rig is straightforward, except for the microphone. The 781 has much lower gain in its mike pre-amp circuit than does Kenwood or Yaesu rigs. This is because the 781 assumes the use of an electret condenser microphone while the other rigs assume a dynamic microphone. While there are some good engineering reasons why the rig is designed this way, many hams still insist on trying to mate incompatible dynamic elements to this rig. Now that there are inexpensive condenser headsets on the market for computer use, there an easy way out of this dilemma. While many of these are too bassy for communications use, two models I've used work well. They are the Plantronics 60 and the Heil IC models. These mikes will provide the proper ALC and compressor functioning to achieve good audio. 

If a dynamic microphone, like a Heil HC4 or HC5, is used with this rig, it is advisable to install a pre-amp between the rig and the mike. In my case, I simply modified an Icom SM-8 desk microphone to accept another microphone input. This was accomplished by removing the cable for the second rig and installing a normally closed mini phone jack in the hole normally occupied by the second rig cable. When a dynamic mike is plugged in, it disconnects the SM-8 mike element and inserts the dynamic mike element (put a small .01uf capacitor in series with the element to block DC). The SM-8 has a built in rig powered pre-amplifier, which is capable of providing adequate output to the 781 when driven by a dynamic mike element (the ARRL Handbook has a suitable circuit, if you choose homebrew). If you'd prefer a desk mike to a headset, the easiest thing to do is to remove the stock SM-8 element and replace it. I've done this with a Heil #5 dynamic element and it works great. When the 781 is modulated by a properly matched microphone, the ALC meter is easily kicked up with a relatively low microphone gain setting (around 10 o'clock), without the compression engaged. The bottom line is this: matching the microphone output to the optimum input level of the radio will greatly improve the audio performance.

The only other annoyance with the 781 has been the large spike generated on the leading edge of the output. Up to now, I have controlled this spike by keeping the drive level low, but my Alpha 87A often faults due to this high power spike. Moreover, amps with auto tune, like the 87A and the Acom 2000, never settle down because the spikes make the amp think it needs to retune.  Recently, I heard of people actually blowing their finals and decided that it was time to correct the problem. Thanks to the fine work of Vince, K1VF, the solution to the problem has been documented at http://www.mods.dk/mods.php3?radio=icom&model=ic-781&selectid=288#288

Vince discovered several capacitors whose values were switched, some incorrect resistor values, and a missing diode. It's a mystery why Icom produced 781's that don't match their documentation, and then denied knowing how to fix a problem that's correctable simply by putting a few components back where the schematic says they are supposed to be. Here's a summary of the fix:

On IF board: C47 = 2.2uf ; C48 = .47uf (swap C47 and C48); R108 = 100 ohms (was 4.7k); R112 = 4.7k ohms (was 1k); D15 = 1N5711 or 1N914 (was missing).

On PI board: R8 = 4.7k ohms 1/2 watt (was 5.6k) - This change raises the voltage to the ALC circuit from 7.5v to the specified 9v. 

I have performed this modification on my 781 and the spike is gone. The amplifier runs much better and no longer faults or strays into the red zone. My contest scores will go up and my tubes will certainly last much longer! If you don't trust your tech skills, get a qualified technician to perform the mod. Don't get in over your head.

Rob Sherwood, NC0B, of Sherwood Engineering (famous for their Drake C-line enhancements), has a replacement cover for the internal power supply that adds a welcome cooling fan to what is one of the hottest parts of the rig - a circuit that is not cooled by the internal squirrel cage fan. I easily installed one on mine (don't crimp the power wire under the cover!) and it's sure to lengthen the life of this circuit. http://www.sherweng.com/IC781Fan.htm

Icom IC-706 Installation Notes

This rig requires an external relay when used with a linear amplifier. Switching an amplifier directly from the transmit/receiver contacts in the radio can damage the radio. W2ENY, http://members.fortunecity.com/w2eny/relay_706/ ,  makes a nice cable that does the job. This cable utilizes a relay to isolate the radio and will work with any amp. If you want to build one yourself, check out this circuit: http://www.k6xx.com/radio/ic706amp.pdf . This homebrew circuit uses a transistor interface and will fail if connected to a Heath SB220/201 or similar models having higher voltages than +40VDC and may cause damage to the radio T/R switching circuit and will also not switch an AC based amp relay. So, be sure to measure the amplifier relay voltage prior to using this circuit.

The Icom IC-706 is easily computer controlled. I use mine with N1MM for contest logging and DxLab for every day logging. However, to get the 706 to function I had to set the IC-706 CI-V address in menu 34 to 48H. Since I like to travel light, I don’t use a CIV with the 706. Instead, I use a 9 pin din to mini-phone plug cable with an integrated level converter. You can buy these on EBay but be careful that the seller has some good feedback. I once purchased one that didn't work.

The 706 has the same issues with dynamic mikes as does the 781. See the 781 notes above. I use an inexpensive boom headset made for computers with my 706. These computer headsets have condenser elements in them. That's what you need to modulate this rig properly.

A Temporary 160m vertical Over Salt Water

My first experience with verticals near salt water was the AH1A in 1993. We used a Battle Creek 
Special on 160/80m and HF2-V's for 80/40. The Battle Creek special is a custom antenna available for loan to major DXpeditions. It is a large trap vertical complete with a set of radials to run out on the sand. It is shipped in a wooden crate and requires many helpers to erect safely. It is a spectacular performer. However, my requirements were for something more lightweight and easy to set up.  

Over the course of several trips to Belize (V31DJ), I had the opportunity to experiment with various vertical configurations near and over salt water.  

My first attempt at a high performance vertical on this band was not too successful, but worked well on 80m. It consisted of an inverted L fed near the shore, with 7 ten foot elevated radials. The vertical portion of the antenna went up about 30 feet to the top of a palm and then out to a 32 foot fiberglass pole. Switching between 160 and 80 meters was accomplished by inserting and removing a jumper at the 160m point. We used an alligator clip to bypass the insulator. Since the fiberglass mast was so flexible, we simply hung a piece of nylon string off the insulator and pulled it down when we wanted to change the jumper. The antenna garnered exceptional reports on 80m, but wasn’t very effective on 160.  

In February of 2003, I returned again and this time I put up a dedicated 160 meter inverted L. this antenna consisted of a 20 foot Portaple ™ (a four pound aluminum mast), with a 32 foot fiberglass slipped over the top – total height about 50 feet and weight under ten pounds. I placed the antenna about 50 feet into a salt water lagoon and ran aluminum wire (low weight) up through the eyelet in the fiberglass mast and over the the crest of a two story home. The vertical portion of the antenna was brought out away from the mast at and angle and tied off to a post in the water. From there, one quarter-wave radial was run out toward the US at a height of about ten feet over the water using two PVC pipes as masts. This radial was not galvanically connected to the salt water. One radial was used on purpose, to skew the pattern toward the US for the CQWW160 meter contest. According to the second edition of ON4UN’s low band monitor, this is a near ideal 160 meter installation.  Typically, you see radials run into the salt water, but RF does not penetrate salt water except superficially.. In this configuration, the salt water is used as a ground screen, not as an electrical or RF ground. The return current path is provided by the elevated radial. A single EWE antenna was installed, aimed at the US.  Keep aluminum wire out of the salt water, it becomes brittle very quickly. Aluminum wire is available from Loews Hardware in the electric fence department.

For 2004, I departed from the resonant radial scheme and went to a system with 25 forty foot radials about a foot over the salt water. This was pretty easy because, as you can see below, the mangrove swamp is prolific and provides handy tie off points for the radials. I achieved the best results to date with this system. For those who have studied the subject, as I have, the question of how to optimize  RF ground system for a vertical over salt water is not so easy to answer. A careful study of "Low Band DXing" for example can be quite confusing because the information, while useful, is often contradictory. John quotes some sources who say that just a couple (or even one) elevated resonant radial is ideal, while others say that at least six elevated radials should be used and they should be very high off the ground (.1 or .15 wavelengths). Others say that a bunch of non-resonant radials will work better unless these ideals are met. While I continue to gather data, I don't yet know what is correct. However, everyone seems to agree that throwing a wire into the salt water is not the answer. The 2004 experience suggests that a counterpoise of a bunch (ten to twenty) fairly short radials (30 feet), do a great job when the antenna is over salt water.  

Antenna description and photo for V31DJ - February 2003 at the QTH of V31MD. The feed point is tied to the post in the the left foreground. The vertical element is run up through the eyelet on the 50' pole and over to the white PVC mast on the house. Also visible are the R7 vertical on the left in front of the house and the HF2-V on the right. The A-3 Yagi is barely visible behind the PVC mast. The radials for the 160 vertical are not visible, but run away from the post to PVC masts set in the salt water lagoon.

Kenwood TS-850 Notes, Mods

The TS-850 has been my travel rig of choice for serious contesting since I used it on Howland Island in 1993. This rig has many advantages. For those who want to learn more, refer to the ARRL product review at www.arrl.org, and to the personal owner reviews at www.eham.com. 

The only serious disadvantage to the 850 for an all-band operator like me is the lack of a provision for a separate receiving antenna for the low bands. There are three fairly easy ways to overcome this drawback. The first, which I used at V31DJ, is to install an external pre-amplifier, such as an Ameco PT-3 or a Palomar P-310X. These pre-amps have t/r relays built in to protect the pre-amp from a transmitted signal from a transceiver. I used the Palomar and installed a small toggle switch on the back of the unit to switch the EWE into the pre-amp instead of the transmit antenna. All I had to do was lift the wire running from the xmit/rcv relay to the band switch and connect it to the common of the dpdt switch and connect the ewe and a wire from the relay to the other poles. I also had to install an rca jack on the back of the unit for the ewe input. With this simple mod, I was able to use the relay in the pre-amp to automatically switch to the receive antenna on receive and to the transmit antenna on transmit. When the pre-amp is turned off, the transmit antenna is in-line all the time. Another alternative is to use an external coax relay from www.rfparts.com. A good one is the CX-230 for under $100. This would be switched by the rig. Finally, a simple mod to the radio is possible as discovered by WA3WJD. See http://www.mods.dk. Another mod (shown on that site) that is highly recommended is the Noise Blanker mod, which entails the removal of two capacitors. Wow, what a difference!

My previous Kenwood was a TS-830s, which I really loved. In the 1982 ARRL DX CW contest as V3MS, I was running a nice big pileup, and I felt the need to crank down the bandwidth. I vividly recall using the VBT control to the point where I could just hear a few calls in that massive pileup. I was looking forward to the same effect with the slope tuning on the TS-850, but initially I was disappointed. Initially, I just thought is was a dumb feature. Then I figured out that I was the dummy. Because I was using a 270 and a 500 Hz filter. The VBT barely worked at all. Switching out the 270 for another 500 "turned on" the slope tuning feature and it works great - just like the old VBT. I have mismatched SSB filters, but the slope still works. It's not optimal, but it works ok. Still, I'm thinking of matching those, too. 

Recently, my friend V31MD experienced a receiver failure on his 850 (serial number 3xxxxxxx range). The symptom was that the receiver was deaf - absolutely no signals and a white noise background. The problem turned out to be the 6631 DDS chips on the CAR Unit board. Kenwood, recognizing a problem, has upgraded the design of these failure prone chips. I don't know the serial number of the change, but the new chips are numbered 66312 and they are stock in my 850 serial #50900145. My original 850 worked fine for many years, but failed in Belize during the storm season. It's possible the earlier chips were static prone, I really don't know.  Certainly, there are many 850's with the earlier (6631) chips that have never failed. For those who can't afford a sudden failure (DXpeditioners like me!), it might be a good idea to do a bit of preventive maintenance and replace any 6631's, even though it's expensive. While it is "possible" to replace them individually, it is not advisable to do it because these chip are surface mount and have many many leads. Fortunately, a plug replaceable CAR Unit board is available from Pacific Coast Parts, www.pacparts.com,  for $208.61.

My TS-850 has been modified as follows:

Noise Blanker mod; CW sidetone volume mod; DVK volume control mod; computer and internal keyer mod. All the mods are pretty straightforward and  answer most of the complaints I've ever heard about features lacking on this radio. All mods are shown at www.mods.dk with more good info at http://n6tr.jzap.com/850repair.html. If you're not a contester, just do the noise blanker mod. It's easy.

Selecting the Right Coax

When I was planning the AH1A station setup, I selected RG-213 for the coax. If I were doing it again today, I'd make a different choice. RG-213 is great coax, but for DXpeditions it has one major drawback - weight. Its advantage is that it is rugged and can handle the legal limit on ten meters and digital modes. Since AH1A, all my DXpeditions have used RG-8x.  The power handling capability of RG-8x is lowest on 10 meters (assuming no higher bands are utilized) where it's rated at about 700 watts for a 50% duty cycle. On the lower bands/cooler air temps/lower duty cyles, the rating goes up. While I've never had a problem using this coax running, variously, 600, 800, and 1KW output in tropical locales, I was clearly skating on the edge of this cable's power rating. However, I've learned to forget about running full power in most instances, anyway. For example, on Howland we used 5kw Yanmar diesel generators, one for every two stations. Still, we weren't able to run more than 800 watts output. On Christmas Island (T32) we used the compound's generator that supplied 110v and again could only run about 800 watts. My current travel amp is an Acom 1000 running 900w, max.  If the plan is to run more than that, I think it's worth stepping up to the LMR-195, which is smaller in diameter than RG-8x and has three times the power handling. It takes the same connector used with RG-58/U.  This coax has a power rating of 2kw with a 50% duty cycle. Thus, it covers just about every contingency, including operation on 6 meters with an amp running 1.5KW or more than 500 W output on digital modes. LMR-195 is the best compromise between weight, size, and power handling capability for a DXpedition running high power, but it's expensive. For lower power, less critical applications (under 750 W out on ten meters CW), RG-8x is fine. 

LMR cables are available from RF Parts.

http://www.rfparts.com

Easy and Effective Radial System

When I went to Howland Island, we hauled along some rolls of chicken wire to use for radials in order to get on the low bands fast. We just rolled them out in the sand and connected them to the vertical ground connection. Although they seemed to work, this was not an entirely successful experiment in my view. The chicken wire was very stiff, heavy, had poor conductivity and rusted quickly, compromising the electrical connections. For this reason, I don't recommend galvanized steel chicken wire radials.

Recently, I installed a Hustler 5-BTV as a reference antenna and for use on 30 meters. I needed some radials to make it work properly but I was too lazy to lay them out individually, much less bury them. So, I went to Lowe's and bought several rolls of aluminum garden fencing wire. The stuff I bought was about two feet wide and thirty feet long. I also bought some ground staples. To install, I simply rolled them out extending from the base of the vertical. They over lapped a bit close to the vertical base. I secured these to the ground with the ground staples and cut them as needed with sheet metal scissors.  At the base, I soldered aluminum wire to a corner of each of the rolls and connected them all together electrically. It's important to make a solid, long term electrical connection. Then I ran one lead up to the ground connection on the vertical. This is the equivalent of a lot of radials! The grass grew up through the fencing wire and now they are completely invisible. Note that aluminum doesn't readily accept solder due to the oxide coating on its surface. To get around this, I sanded the aluminum, put some light oil on it, wiped off the oil and used a hot gun. I was able to get the solder to bond effectively using this technique.

I know a lot of hams are running verticals in limited space areas and struggling with poor performance due to an inadequate radial system. If the space is truly limited, there's no reason not to fill the entire available area with this fencing to provide a good ground plane. And, it will disappear into the grass in a very short time. I have not made any measurements (other than SWR), but my results with this antenna are satisfactory.

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