VHF/Brick amp preparation:
In this article we will discuss the merits of having a brick amp as they are called for two meters, or for that fact any band above six meters. Before I get in to any preparation let’s do some simple math to determine the advantage of those popular brick amps.
Most rigs of the FM mode only for two meters run on the average 50 watts, I have the ICV-8000 that produces an output of 75 watts. There are a few transceivers for two meters only, or 70 cms that give 100 watts output on the market.
Let’s take a look at what we get for our money I favor the T.E. Systems bricks because of the reliability and construction. For their 160 to 200 watt model the price is $440 it is ready to go depending on your installation. So, at this point a little math, we have 50 watts to start with as a reference and assuming that you will use 50 watts to drive the brick we come up with a 6 DB gain, or one s unit.
I base this on the gain achieved from 50 watts to 200 watts for easy figuring, in reality most of the 160 watt bricks produce somewhere close to 200 watts, so that is four times the drive power and this translates to 6 db, or one s unit.
Now since you can get these bricks that will drive fully with 25 watts as well the gain becomes 9 db or one and one half s units. The next step up in two meter amps is a 400 watt unit, so a little figuring it becomes with 25 watts drive about 12DB gain or two s units. If one uses 50 watts driving power the gain becomes 9 DB or about 1 1/2 s units gain. The price on this model is over $700 dollars.
For those of you that are serious minded about FM simplex those two s units, or even one unit will make the difference of being heard above the noise, or lost in it.
So, let’s revert back to my own station on two meters, with a 75 watt final, with the 200 watt unit I would gain about 4 db, enough to nudge the s meter about half a unit if it is detectable. With my 75 watts using a 400-watt amp, I would have about 7 DB gain or one s unit difference. We have to ask ourselves in both instances is the amp worth the cost versus the gain?
So what did I find out by using this 400-watt amp on two meters? The best way I could find is to check my own signal at various locations. At that time I was mobile with my ICV 8000 in the car and an SB6 antenna on the trunk lid. I had an errand to do in Owensboro, KY and that is about 30 miles from my location of Henderson. Since I never heard anyone on simplex from the area I assumed one thing, either no one was using the band, or signals were not making it. The terrain is irregular towards the East, but I was certain my signals were making it that far. Well, I had an FT 897D then and it had a beacon set up as an extra bell and whistle. So, I selected a non-used simplex channel and let the beacon sound off every ten minutes with a cw Id and grid square location.
I found out my signal was indeed good and strong in Owensboro in my mobile station, so anyone with a decent antenna system would have heard me very well. I of course wanted to check the very limits of my signal so the ultimate test was a trip I had planned to Marion, Illinois to the VA. Center, this was before the new VA center in Evansville. The same scenario using the beacon, about 400 watts feeding a two element 5/8 at 70 feet gave me a good signal. I kept tracking my signal it was good in Harrisburg and once I got to Marion and on the Parking lot of the VA my signal was s2 in the car. Still readable and anyone with a good antenna, rooftop, or better would have heard me fine. On a straight line from Henderson Marion, Illinois is about 75 miles it is 90 via highway travel.
Without the extra power my signal might not have been heard and not as well in the mobile, It may have been heard with 75 watts, but I have never copied any one from Marion in the last couple of years. However, I did work a station in Marion on two-meter simplex about five years ago with 75 watts and both of us had good signals.
One more test versus power and less power, I often copy the KD4ULE machine in Hopkinsville, Ky it is 75 miles to the south. With 75 watts in the morning hours I can hit the repeater fine, but once the sun comes up the repeater loses me. However, with 400 watts I can bring up the repeater and copy it s1, or S2 just about any time.
Based on my experiments having about 400 watts does make the difference on the long haul, it is pointless to have all that power if you only operate repeaters, you simply do not need it to access a local machine. However, if you are a simplex op you may find it necessary, or a big advantage.If you are a two meter ssb op you may find this amount of power helpful.
It is pointless to buy a brick 160 watt amp if you already have 100 watts output from your rig, the extra 60 to 100 watts will not make that much difference, about half an s unit. I also makes no sense to have 400 watts blazing away just to talk to your buddy less then a mile away from you. Same thing to access a local machine, pointless to have that much power, you will succeed in covering up most stations on the input causing a squealing sound on the output of the repeater when two fm stations are creating a hetrodyne. I am sure you have heard this sound when it happens.
If you just must have a brick 160 to 200 watts, or a 400 watt amp on your two meter rig then part 2 will give you some installation pointers.
Keep in mind a good antenna and height is also success in working simplex on two meters over a long distance. Now if you just must have an amplifier check Part 2 in a few days.
