SWR and Power Meter Accuracy
Is a high degree of accuracy necessary when measuring SWR and power? It depends on what you intend to do with the measurement.
Most of us just need to adjust our antennas for minimum SWR. As long as that minimum can be determined to be less than 1.5:1 we have met our goal. It does not matter if that value is 1:1 or 1.2:1.
Likewise, most of us just tune our amps for maximum output. Knowing the exact value of that output does not make the amp work any better. A relative indication of power out is more than adequate for most uses.
How to save $1000 on Ham Radio Equipment
You can save at least that much by following consumer purchase rule number one. Don’t spend money or time on stuff you don’t need. I guess we could debate the need for any radio equipment. We could live without radios but we have already decided to live with them so there is no need to consider such debate.
There are three fairly expensive devices that most hams covet that are really not necessary. These include, a watt/SWR meter, an antenna analyzer, and an antenna tuner.
Most modern radios offer built-in automatic antenna tuners. Manufacturers started doing thus to keep their solid state SWR protected transmitters delivering power. Without these tuners the solid state rigs will start folding back on power output with SWR levels as low as 2:1.
With the built-in tuners high SWR levels are no longer an issue until we upgrade our stations with a power amplifier. Suddenly we find ourselves in the market for a high power/high dollar tuner to keep the new amp from melting down. We can end up spending big bucks treating the symptom of a problem that can easily be avoided by choosing a resonant antenna system at little or no cost.
As a bonus we can completely avoid concerns regarding tuner efficiency and feedline losses by choosing an antenna system that offers us less than a 1.5:1 SWR. Try it. You might be able to hear better too.
The second unnecessary item is the antenna analyzer. Most modern transceivers can do all the antenna analyzing necessary. The transceivers have built-in SWR meters and are far more accurate and stable than most antenna analyzers. Okay, a good analyzer will also tell you what impedance the antenna is reflecting back to the transmitter. Do you really need to know that to trim your antenna to a lower SWR?
The third Item is a good SWR/Power meter. A really good device can cost as much as $1000 all by itself. It will give you an accurate indication of power output but you can also get that by reading the plate voltage and plate current off the meters in your amp without having to spend additional money.
Keep in mind that knowing how much power the rig is delivering to the transmission line is not going to allow you to make more contacts.
Also, that high dollar antenna tuner might make your powerful amp happy but it is not going to keep all that happy power from frying your 300 ohm twin lead if the SWR is high on the feedline.
If your antenna tuner is in a box sitting on your operating desk it is more of an impedance matching network that a tuner. Impedance matching is a good thing because it allows your transmitter to develop maximum power.
However, if your transmission line is long, lossy and has a high SWR, that power might be dissipated in heat before it gets to the antenna. Also, under those conditions, power ratings of the tuner become inconsequential because the impedance mismatch on the antenna side of the ‘tuner’ may very possibly have increased the voltage across the output capacitor to a value sure to arc and destroy the plates.
So what is the solution?
Don’t use antenna tuners. If all your antennas are resonant you don’t need tuners.
SWR and Power Meters
Is it worthwhile to pay extra for a power meter that can measure up to 2000 watts and beyond?
If we want to measure and monitor the output of a powerful amplifier we would need such a device.
Perhaps a better question would be, ‘Why do we want to measure the output of our amplifier’?
Have we received reports from long time ham friends that our signal has become weaker? Maybe we just want to check and make sure our tubes are not soft. Whatever the reason, an accurate measurement of the amplifiers output is not going to improve the signal. In addition, a truley accurate, high power, watt meter is going to be expensive. You would be better off spending that money on new tubes if you suspect the old ones to be soft. Besides, you can get a pretty good idea of the power level by noting the plate current and voltage under load. The product of plate current and plate voltage times .6 is a good indication of power out.
Tubes are not the only thing that can go soft. Plate voltage can droop due to aging electrolytics in the plate supply. A lower plate voltage will result in lower plate current as well.
You may also want to make sure you are not expecting more output than your amp can deliver. Don’t confuse output with input. Most amp manufacturers prefer to quote power input and list it in PEP. PEP is normally about twice what you can expect from a key down CW condition and to be linear an amp can only deliver about 60% of the input power at its output. That means a 600 watt PEP input amp is only capable of delivering about 200 watts constant carrier key down output.
Input only sets the cost of running the amp. Output is what is useful to the amateur radio operator. The benefits of knowing precisely what that output is do not justify the cost. So, no, you should not pay extra for a high powered watt meter.
Getting ahead of myself, I will also state that you don’t need a high power SWR meter either. A low powered simple resistive bridge can be built with very short lead lengths allowing its use up through the UHF region.
Also you don’t need a dual meter dual pot sensitivity adjustment. A single meter with sensitivity pot in the return lead of the meter will work just fine if it is switched from the forward circuit to the reflected. First, reading forward, you adjust for full deflection. The you switch to read reflected. If the reflected reading is at half scale the SWR is 3:1.
I already have a decent SWR meter, but, if I were looking for one today, I would buy the least expensive CB meter I could find, gut it, and install a resistive bridge for a pickup. I have seen prices as low as $15 on Amazon. That is less than you would have to pay for a meter, switch and case.
When you make a cable just long enough to reach the computer it will probably not reach when the computer is relocated to the other side of the room. Cables should be long enough to reach all corners of the room plus three feet. Those extra three feet are called a service loop. The service loop keeps you from having to streach the cable.
Back in the days of thin-net, extending a network cable required another 15 foot section of RG58 coax with BNC connectors on each end and a double female coupler. Todays network cables boast four conductor pairs requiring eight connections in two places into a fairly expensive double female coupler. The contacts are gold plated to retard corrosion but they are expensive because most people don’t use them. A direct splice of the wires, soldered and insulated is a far better solution than pushing two contacts together even if they are gold plated.
Protected: A Good Quarter
Unless I know the people involved, I tend to avoid estate sales. I am particularly leary of estate sale items that show up on classified listings.
For instance, I recently found a Drake TR4C being offered as an estate sale item without power supply, as is, for $325.
There are several problems with this offer. First, is it worth $325? If it is in good working condition it certainly is worth $325. It may even be worth the additional $40 it will take to have it shipped. All this worth is based on it being a working transceiver in good condition.
It is being sold ‘as is’ without a power supply. To check it out the seller has no way of knowing what it is as. We have to assume that it is probably not working. Chances are very good that this orphaned radio got that way for good reason.
Hams are not given to retiring equipment that is working well. Should it be working well when retired as it is being replaced with a newer rig, the retired rig will end up being sold. If it is not worth selling, it may end up on a shelf, orphaned, with its power supply sold separately. The transceiver remains on the shelf until it is rediscovered when the ham passes on to the happy hunting ground.
After the surviving friends and relatives pick over the goodies he left behind, the remaining flotsum is readied for the ‘estate’ sale. Those items left after the first sale get listed on the classifieds.
After spending 30 years in a closet, idle and orphaned, the TR4C is most likely in even worse condition than when it was first abandonded there.
So is it really worth $325 plus shipping. Not until it is refurbished, provided with a power supply and microphone, and checked out for proper operation.
Its ‘as is’ value would not justify a $40 shipping charge.
50 Percent Off !!
Why is this offer only extended on stuff I don’t need?
I can’t save money by buying stuff I don’t need.
I can save money by ignoring the offer.
So when I see that offer I take 100 percent off.
I guess I am just a greedy old fart.
Netflix is still one of the better deals on the internet. We became subscribers early on when they were a mail order only CD rental outfit. It cost about seven bucks a month, no late fees, you could keep the CD as long as you wanted but had to send it back before they sent you another CD. That policy was instrumental in proving what a joke Blockbuster had become.
It was a little strange doing mail order CD rental but with a large number of distribution centers it became possible to do a one or two day turnaround.
Once they offered on line real time streaming, things took off. We became less inclined to do the mail order rental in favor of the immediately gratifying on line streaming feature. Both on line streaming and mail order rental were being offered for about eight bucks a month.
There were few if any new releases, some titles were only available on CD, out of tens of thousands of titles there were only about one hundred that were interesting, but they were only charging eight dollars a month for the service.
Before long subscribers were informed that they could choose between on line streaming or mail rental CD and still only pay eight dollars a month subscription fee. If they wanted both mail rental and on line streaming they would need two subscriptions, one for the mail order rental and one for the on line streaming. A nice way to announce a doubling in subscription fees without any improvement in programming.
We had long since given up on mail order rentals in favor of on line streaming so we did not experience any undue negative effect.
Recently I hear Netflix is considering an additional increase in subscriber fees but only for new subscribers. That tells me it will not be long before old subscribers will be saddled with higher bills as well.
Unless the programming improves comensurate with the price increase we may be faced with having to bid Netflix goodbye and good luck. You see those hundred movies of interest will all have been viewed at least once by us and none are interesting enough to view twice.