Bruce,

Most vehicle electrical system designers have enough common sense to not share accesories like a lighter or power plug with systems noticable or required in normal safe operation.

A 50 watt radio is generally only around a 10 amp load.

I'd worry about a 100W HF SSB and CW radio, or 100W FM, but probably not much about a standard size FM mobile.

I stay off the negative post with the negative lead chassis-grounded accessories, and ground to the unibody. It is safer long term, if you ever should develop a negative battery lead resistance issue.

73 Tom

The idea of connecting the negative lead to the battery is idiotic, and always has been, in a standard negative ground system in a device that has a grounded negative rail. A direct battery connection of negative is just begging for damage.

This is very logical to see, if someone actually looks at the system.

My best guess is the silly idea started with floating ground two-way systems, like old Motorola radios with isolated negative busses inside the radio, and carried over without thought into devices with chassis connected negative rails.

That aside, the ICOM is live inside when connected to mains. Like many radios today, the PA section and many other components (PLL unit in the 706) have power connection to the battery with or without the radio power switch "on".

If you had a 100V spike, whether power was on or off would be a moot point for expensive PA section transistors. As a matter of fact, ALL of the high current components are across the battery wires without much protection, while the 13.8 switched buss is the only one likely to be unaffected by a transient.

If I was worried about starter induced over-voltage spikes, which pretty much are a non-issue, I'd have a high current disconnect relay between the radio and battery hot.

IMO, only a fool grounds a device with an internally grounded negative buss directly to a negative battery post or post connector. It does not belong there in common systems, because it obviously sets the installed system up for problems if a negative battery lead develops any significant resistance.

73 Tom

The hinged plate is a weak link, and negates the worry about significant concrete area. A hinged base is so weak that the guys or brackets are mandatory at any height. A proper bracket or guy system makes the base area a non-worry except for compression load.



That sounds about right for 25G if you have a lot of antenna area at the top. It looks like you need to consult with a PE.

 

It is not logical, because a guyed tower places the base almost entirely under compression load. The only requirement is the base does not shift or sink. A PE should be able to advise you on the safe Rohn ratings, and even a safe base size. The most critical part is the guying. You might be surprised at the 25G capability if the antenna is not too large.

That is what I don't like about SDR receivers. The front ends and RF sections have virtually no selectivity, often being mixers coupled without any real selectivity to antennas.

This means EVERY signal within coupling passband from the antenna port adds to the power the mixer has to process. While they test as good as a normal receiver for specs, a normal receiver will only subject the first mixer to signals inside the band range the front end filters are on.

Since the test does not reflect the hundreds or thousands of signals the SDR "mixer" sees, and only subjects it to one or two signals, it falsely appears competitive with filtered receivers.

This is separate from the overload worry you mention, except the overload worry extends to out-of-band signals. With a normal receiver, the system might tolerate 1/2 watt or more out-of-band. With the SDR, lacking band filtering, what it tolerates in-band is what it tolerates out-of-band.

The problem with the overload spec you posted is we do not know if it is just where the SDR system becomes temporarily useless, perhaps by overflowing an A-D conversion or saturating a mixer, or if that level is where non-recoverable electrical damage occurs.

Most receivers do NOT give a destructive power level guideline, but I have yet to find a receiver electrically damaged by my signal generators at +20 dBm or more in two tone tests. That's over 100mW from two generators combined at one time.

73 Tom

The real problem is when we install a better shack ground than the power line entrance ground, the wires through the house become a fault current path. Because of this, we want the shack ground bonded to the entrance ground with many, many, times less path impedance than the path through the house wiring or plumbing to the shack ground.

Otherwise...any surge current is mainly through house wiring.

Now if I was getting a pier near the mains meter, I might augment that ground. I can't imagine making a super low impedance shack ground, though, without have an especially good bond from it to the mains ground. I don't know what good it would do.

73 Tom

 
   

If this is a commercial application, how do they get around this rule:

§ 90.427   Precautions against unauthorized operation.
(a) Each transmitter shall be so installed and protected that it is not accessible to or capable of operation by persons other than those duly authorized by and under the control of the licensee. Provisions of this part authorizing certain unlicensed persons to operate stations, or authorizing unattended operation of stations in certain circumstances, shall not be construed to change or diminish in any respect the responsibility of station licensees to maintain control over the stations licensed to them (including all transmitter units thereof), or for the proper functioning and operation of those stations and transmitter units in accordance with the terms of the licenses of those stations.

***
(b) Except for frequencies used in accordance with § 90.417, no person shall program into a transmitter frequencies for which the licensee using the transmitter is not authorized.***


As far as I know, the FCC will not allow a user programmable frequency capability on a commercial radio. The radio can only be delivered to the end-user with the specific legally licensed frequencies of the end user, nothing more.

This means it could be programmed to cover a community's local licensed channels, but would not be legal if they could dial or program on any unauthorized channel. 

You can simplify the system into an ~8 foot wire base loaded with a 10  j1200-1300 ohm reactance over perfect ground. It doesn't have to be a trap to have the loss problem Dan found.

:-)

 

Interesting. This case has given me something to think about. 

The net reactance of the parallel L-C combination in the trap at 9 MHz (about +j1300) is driven by the top of the lower antenna section to a fairly high voltage and current. I'm trying to understand what the mechanism is.

If I place the top section over a GP and drive it through an inductor of 20 j1300, the inductor has 10 dB loss. 

Be real careful with this problem. A perfect dipole is ONLY horizontally polarized exactly broadside to the dipole. As we move off broadside toward the ends, polarization tilts progressively more vertical. This means the perfect horizontal dipole antenna is only perfectly horizontal in two directions along the earth, and becomes more and more vertically coupling prone as we move to the ends.

If I have a perfect dipole and perfect vertical spaced a reasonable distance apart to get out of near field or induction fields, the maximum null between the two is exactly broadside to the dipole. There is increased coupling as we near the end of the dipole to the vertical, and then, depending on geometry and distance coupling can null again (although generally reduced from the broadside null) as we move exactly off the ends.

So we see.... the rough answer is generally the best null is usually when the dipole is centered on and **broadside** to the vertical. In the real world, a problem like this would require an auctal measurement of coupling power or coupled loss.

There is some measured data here:

http://www.w8ji.com/antenna_coupling.htm

13 dBm seems extremely low. That is only 20 milliwatts, and I routenly make IMD, desense, and IP3 measurements at +20 dBm or more (100 milliwatts). I've never found a receiver that could be damaged by 100 mW.

What receiver do you have??

73 Tom

Interesting comments.

I think that is a myth for most traps, which commonly are parallel tuned.

The series-tuned traps in a Butternut vertical are an exception. A series-tuned trap is subject to damage because a capacitor is in series with the element and an inductor. Forcing current would result in I*X voltage drop across the capacitor. Make no mistake about it, the series circuit in a Butternut is a form of trap, and despite marketing claims has loss.  The trap is just series resonant instead of parallel resonant.


With parallel tuned trap, like most standard traps, the idea forcing current out of band can cause trap failure strongly appears to be false. Peak voltage and peak circulating current occurs when the trap is "trapping". If the trap can handle 1500 watts near resonance, it can certainly handle well over that power out-of-resonance.

Let me give an example that I think might turn the light on. When running a standard trap triband Yagi on 20 meters, like a TA33 SR, the antenna will handle 3-4 kW easily. This is because the traps are not "trapping". There is very low voltage and almost no circulating currents in the traps. They only carry normal common mode antenna currents.  Take that same Yagi on 15 meters, especially exactly at trap resonance, and trap loss peaks. The trap has highest voltage and highest current at the SAME time, because it is a tank circuit! As a matter of fact if we increase resonant Q, we also increase voltage and current! That same Yagi will arc and fail at 1000-1200 watts at exact trap resonance (fortunately the traps are slightly out-of-band).

I disagree with a claim using a tuner is a recipe for trap failure, unless there are special cases. A Butternut trap would be a special case, because it is an abnormal series-tuned trap. It could have a great deal of capacitor voltage if common mode current is high.

73 Tom  
 

This is specifically about copyright goods that are made and purchased overseas, and imported into the USA without permission to be resold.

It will never have impact on anything except copyright protected things purchased overseas and then imported to the USA for sale.

I think Wiley and Sons are correct. Someone bringing millions of dollars worth of foreign made copies of copyright books into the domestic market specifically for sale without permission is wrong.  Wiley should sue him, and Wiley and Son should win.


11-697 KIRTSAENG V. JOHN WILEY & SONS, INC.
DECISION BELOW: 654 F.3d 210
CERT. GRANTED 4/16/2012
QUESTION PRESENTED:
This case presents the issue that recently divided this Court, 4-4, in Costco
Wholesale Corp. v. Omega, S.A., 131 S. Ct. 565 (2010). Under § 602(a)(1) of the
Copyright Act, it is impermissible to import a work "without the authority of the
owner" of the copyright. But the first-sale doctrine, codified at § 109(a), allows the
owner of a copy "lawfully made under this title" to sell or otherwise dispose of the
copy without the copyright owner's permission.
The question presented is how these provisions apply to a copy that was
made and legally acquired abroad and then imported into the United States. Can
such a foreign-made product never be resold within the United States without the
copyright owner's permission, as the Second Circuit held in this case? Can such a
foreign-made product sometimes be resold within the United States without
permission, but only after the owner approves an earlier sale in this country, as
the Ninth Circuit held in Costco? Or can such a product always be resold without
permission within the United States, so long as the copyright owner authorized
the first sale abroad, as the Third Circuit has indicated?

I don't know what they have you do, either as a team partner or working for them, but you should consider a different job.

I like 200W radios with AL1200 amplifiers, or 3-500Z amplifiers. 100W radios are plenty for 8877 amplifiers.

In a linear amplifier when quiescent current is small compared to operating current, efficiency decreases by the square root of power change. Half the power is sqrt .5 = .707 of original efficiency. 1/4 the power is sqrt .25 = .5 of original eff.

Let's say the input power is 400 watts for 200 watts out, 50% eff, linear stage, and negligible quiescent current.

400 input 200 output  = 200W heat =50% eff
346.4 input 150 output  =196.4 w heat = 43.3%
282.9 input 100 output =182.9W heat  = 35.35% eff
200 input 50 output = 150W heat =25% eff

Heat does not drop much in the PA with power reduction, but it does in the power supply!  1/4 the power is half the supply heat.

The same way I pick up ET's without a UFO.

Hi Dave,

The small  loop is only magnetic field dominant within 1/8th wave, then, still in the near field, it is electrical field dominant from about 1/8th wave to a full wave out. So the majorty of near field area in a small loop is electric field dominant.

A small dipole is electric field dominant out to 1/8th wave. Then, still in the near field, it becomes magnetic field dominant.

At about 1 wave out any small antenna is the same.

You can see the field impedance change in the graph I posted.

73 Tom