I neglected to respond to WB6BYU's comment regarding my assertion regarding the combination of horizontal and vertical separation figures. He is absolutely right, the combination of the two is more complex than the simple addition I had suggested. Thanks for catching my error, Dale.

For all of the speculation about transients in this mobile forum, it is interesting to study the application note from Harris regarding surge suppression requirements in a vehicle (referenced earlier by AA4PB http://www.industrologic.com/autotransients.pdf).

The three most damaging transients are infrequent events in the life of a vehicle: load dump (disconnecting the battery while at high charging), losing the regulator, and getting a 24 volt jump start. The two next events with the greatest energy potentials are inductive load switching transients and alternator field decay. These later events have <1 J (1 watt second) of energy and happen often and at turn off, respectively.

My take on this is that while we might rely on internal transient protection on our radios, we would be well served to consider an additional level of protection with an appropriate varistor type device. It is a bit of belt and suspenders but may be worth consideration. It certainly would be an easy addition to most mobile radio installations. It could easily be added to the cut off circuit in the latest issue of QST that I mentioned earlier.

- Glenn DJ0IQ and W9IQ

Hi Tim,

I hope you are holding out OK in the weather.

I had another thought about your repeater project. When I was doing research for an article about duplexer designs, I came across several web posting from people who had made 2M duplexers out of metal barrels or metal buckets. Clearly far from ideal but when working on a rubber band and binding twine type of project, it might give you the edge you need. You might want to check them out.

- Glenn DJ0IQ and W9IQ

There is a nice article in the November 2012 issue of QST on page 43 for an automatic mobile power control that incorporates an adjustable turn off delay and a turn on delay to avoid starting transients. It looks like a simple one afternoon project.

My 50 watt dual band radio takes 12 amps on transmit. Leaving my DSO in-line for several days didn't show any spikes in excess of 15 volts coming off of my Yukon's front accessory socket - but everyone's mileage may vary...

When I would run my 706 radio mobile with 100 watts SSB, I would mount the body of the radio in the back of the Yukon and with a PowerPole block connecting the radio, a separate AGM battery, and the rear accessory socket together. The battery handled the higher current draw, the accessory socket would charge the battery, and the accessory socket turned off when the vehicle turned off. Not everyone has the luxury of a rear accessory socket, but it worked great for me for many years.

As was pointed out earlier in this thread, if you are going to wire directly to the battery, be cautious of tying directly to the negative terminal of the battery especially on newer vehicles that use current sensors in the negative battery lead.

- Glenn DJ0IQ and W9IQ

The PowerWerx timer sounds nice but before I spent $70 for it and then spent hours fishing power cables through the vehicle, I would get more quantitative by measuring the voltage at the accessory socket during full power transmit. A half hour of field testing could save a lot of unnecessary work and expense.  

Every situation is probably unique but I ran my 50 watt dual band radio off the accessory socket in my Yukon with no problems. The radio body even sat on top of the vehicle computer modules inside of the center console.

- Glenn DJ0IQ and W9IQ

Hi Mark,

I should also have commented on the minimum IP mask to be used with each of the private address ranges. They are:

10.0.0.0 - 10.XXX.XXX.XXX           (Mask of 255.0.0.0)
172.16.0.0 - 172.31.XXX.XXX        (Mask of 255.240.0.0)
192.168.0.0 - 192.168.XXX.XXX     (Mask of 255.255.0.0)

For most home users, the 192.168.XXX.XXX address range and mask is sufficient.

- Glenn DJ0IQ and W0IQ

Hi Mark,

I don't have direct experience with the LogMeIn hosted VPN application but let me offer some general comments related to VPN that may help you with the issue.

A VPN connection in this case creates a "tunnel" between your portable computer and the computer at your house. Once this tunnel is established through the log-in procedures, all traffic is routed through that tunnel. It is as if the two computers were on their own private network.

Some VPN tools allow certain traffic to be passed outside of the tunnel but a glance at the LogMeIn manual didn't show this option. There is an option in LogMeIn to see all port connections that are established or in progress. See Dashboard (Detailed mode) > Performance Info > Open TCP/IP Ports.

Once the VPN tunnel is established, then the IP address of the computer in your house becomes directly available at the remote computer. If the public IP address of your router is 92.125.125.4 and the IP address of your home computer is 192.168.10.2, then pinging 192.168.10.2 would result in a ping response. The public IP address, (92.125.125.4 in this example), no longer matters since the VPN software has created the tunnel effectively "directly" connecting your two computers.

Similarly, if the VPN tunnel is successfully established, then the potential of port blocking by a hotel or network provider no longer matters since all your communication goes through the encrypted tunnel. The hotel can no longer tell what ports or protocols you are using since they are all in the tunnel. I have run into some hotels that block VPN but based on your description, this is not your problem.

You never mentioned if you have ever had this system working or if this is an initial configuration problem. It would help to know. I suspect that you have incorrectly configured your IP-Sound remote IP address. It should be set to the IP address of your home computer (192.168.10.2 in my example above). You should also make certain that the UDP port address of the IP-Sound software is the same on both computers. The default is 4444. With your VPN software, I don't see any reason to change that.

One other problem that plagues some first time VPN users is the selection of the addresses for their home computer network. Home IP address ranges should not be picked at random but should be selected from the list of so called non-routable (private) IP addresses specified in RFC 1918. These are:

10.0.0.0 - 10.XXX.XXX.XXX
172.16.0.0 - 172.31.XXX.XXX
192.168.0.0 - 192.168.XXX.XXX

If you are using anything other than these three ranges, I strongly recommend you reconfigure your home network (everything behind your router) to use one of these address ranges. If you pick an IP address outside of these ranges, the client VPN software may assume you are trying to talk with a computer outside of the tunnel when it sees an attempt to communicate with a routable (public) IP address. In your example, you said your home computer was on 5.x.x.x. If that is really the address range, then you should make this change.

Be careful not to end any of your static (fixed) home network addresses with a .0 or a .255. These are reserved for special uses.

I hope this helps but I am happy to stay engaged in this discussion if this background information doesn't help resolve the problem.

- Glenn DJ0IQ and W9IQ

Hi Tim,

Here is some more information for you related to the antenna portion of your project. For vertical dipoles on 2 meters, here are some working numbers that may help you relative to antenna separation:

Horizontal Separation

 30 ft - 30 dB
 50 ft - 35 dB
100 ft - 40 db

Vertical Separation

 5 ft - 20 dB
10 ft - 35 dB
30 ft - 55 dB

Combining horizontal and vertical separation allows you to practically add the dB's of each together.

The working rule of thumb for a 100 watt repeater on two meters is to achieve > 85 dB of isolation when operating at a 600 kHz spacing or >75 dB when operating at a 2 MHz spacing. Your requirements will be less than this since presumably the HT you will use as the transmitter will be putting out <5 watts. This is tempered, however, by the poorer qualities of the receive HT compared to a commercial grade receiver.

There are some other practical considerations:

1.) Coax cables that are not double shielded will substantially reduce the antenna isolation numbers if the transmit and receive cables are in near proximity to one another. Keep them as isolated from one another as possible.

2.) Keeping the two HT's physically separated will help to improve the system performance. Consider mounting each HT very near the respective antennas and run power and audio with well filtered cables. You may also wish to put each HT into some type of grounded, metal container for additional filtering protection.

3.) Make certain to include several baluns along the length of each antenna cable. A couple of 6-8 inch turns of the coax every so often will help eliminate common mode currents. These can cause potential antenna pattern alteration and source of additional receiver desense.


Good luck with the project!

- Glenn DJ0IQ and W9IQ

Hi Tom,

I am glad it worked for you. I agree with your assessment of the Excel help  - it often provides cloudy clarification!

- Glenn Dj0IQ and W9IQ

Hi Tom,

Using your example of cell B67 containing the input variable to the equation, I believe you will find a simple version of the IF statement to be as follows:

=IF(B67<1,50*((1+B67)/(1-B67)),9999999)

The formula says that if B67 is <1 then use your formula otherwise return 9999999. There is no need to continually recompute the resultant if B67>=1.

You can of course change the number to the right of the comma to be any result you wish in the event B67>=1.

Glenn DJ0IQ and W9IQ

Hello John,

I agree with the other replies that if you are ready to take the test, go ahead and take it now. Your only exposure is the cost for the test and even if you don't pass the first time, your learning experience and nerve relaxation will make it worth the effort.

Barry's comment about answering questions in the context of the old exam is a very good point. I remember taking my Novice exam just when the FCC removed the restriction that Novice operators could only use crystals on HF - no VFOs prior to that. The test was still based on the old crystal only rules even though VFOs were then technically permitted. That memory was certainly in the dusty corners until reading Barry's advice.

Good luck with the exam!

- Glenn DJ0IQ and W9IQ

I neglected to mention in my earlier post that a proper copper joint compound should be used on the clamps to minimize corrosive effects.

- Glenn DJ0IQ and W9IQ

Hi Jon,

I have used these type of clamps in the past and have not had any problems. I did however, put a 4 inch PVC pipe around the top of the ground rods cut flush with the ground. I capped this with a flat 4 inch PVC pipe cap. This gave me about 12 inches of exposed ground rod below the ground level that I could inspect simply by prying off the PVC cap.

Over time, some soil and grass accumulates over the cap so it is almost invisible to the casual eye. It really works nicely because the clamp assembly is easily inspected and as long there isn't standing water in the area, it also keeps the clamp assembly dry minimizing corrosive effects.

For the earlier question about what wire to use to bond the ground rods together, remember that the issue during a lightning strike is the surface area of the conductor, not the gauge per se. This is why you often see flatter bar stock used because for the same amount of copper, there is more surface area to handle the skin effect of the lightning pulse. Copper pipe is also a reasonable alternative. The challenge of course, is properly bonding the bar stock to the ground rods which is why most opt for heavy gauge wire. If you can weld the grounding system, then consider a solution that maximizes the surface area of the conductors.

- Glenn DJ0IQ and W0IQ

What I find is often lacking in the discussion of grounding systems for lightning is a realization that a lightning strike presents a pulse with a very rapid rise in current (high di/dt). So attempts to analyze the system from a DC or resistance perspective will lead to incorrect conclusions.

The pulse nature and fast rise time of the lightning strike means that the current flowing in the grounding conductor will exhibit skin effects similar to that of continuous RF current with which we as Amateur Radio operators are more familiar. This means that heavy, round conductors are improving lightning grounding only due to the increased surface area of the copper - the inner part of the conductor is largely "wasted" copper since it hardly participates in the current flowing to/from the ground.

A lightning strike will often be less than 1/10 the skin depth of standard 50/60 Hz household current. Considering the potential current of a lightning strike can be in the 30,000 Amp range, having adequate surface area to carry the current is absolutely critical.

In order to maximize the surface area and minimize the amount of "wasted" copper, most professional tower grounding systems use wide copper straps or bars. For the same cross sectional area of copper, as the frequency rises, a "flatter" shape will carry AC current more efficiently. From a code inspection standpoint, these are selected and rated to exceed the minimum code requirement.

Professionals that deal with designing lighting protection systems often reference GPR - Ground Potential Rise. Simply put, this is a calculation of the inductance of the Earth compared with the inductance of the grounding system. By then applying estimated pulse rise times and assuming a particular strike current (in kA), the voltage rise of the grounding system during a strike can then be calculated. Notice that the calculations are based on inductance, which can be correlated with the surface areas of the conductors involved and other factors.

There is much more to implementing a proper lightning protection system. There are nice resources on the Internet and easy reading, practical application booklets available from some of the equipment manufacturers. If you would like a more technical treatment, look for the wealth of information on the topic from IEEE and classic reference texts.

- Glenn DJ0IQ and W9IQ

Hi Bob,

I understand what you mean about the SMD components. My bifocals make the situation nearly unmanageable at times. I recently bought a microscope that connects to my computer - what a great tool for only 25 Euros! I can easily work on the board just by watching my PC screen. It yields the added benefit that I can quickly spot any solder balls or other gremlins before powering up the board. I use it now regularly for repairs as well as new project construction.

I wish you well with the project. Hopefully you can net another nice 817 for the effort. With the warm weather now in Germany, I am getting ready in an upcoming weekend to head out to a mountain peak with my 817, solar panel, and assorted gear to see who can work.

- Glenn DJ0IQ and W9IQ