View Full Version : Power supply for TT amps
Does anyone know what kind of power these things want? I have a 500mw and a 1 watt model. The 500mw came with a 7.5v regulated supply, and the 1 watt came with a 9v regulated supply. They both seem to work the same on either supply. Does anyone have any idea what voltage range these will accept? Also I couldn't help but notice the radio side is labeled 'to injector' Is the only difference between the indoor and outdoor models the little hole drilled in the side to plug the power into?
georgew
01-21-2003, 10:05 AM
I tried to find this out myself, and had no luck. No one from TT has responded when I asked them.
In my very limited experience designing amplifier circuits, the required supply voltage had a very wide range of what would work. Typically things were better with higher voltages. 6 to 15 volts were typical ranges for small amps. However this was for low-frequency IC based amplifiers... the microwave world may be completely different than the low-frequency relm.
I would like to hear that the TT's will work finr on 6 to 15 volts, so I could power them from the same PS as the radio...
On the other hand, I am in the middle of field testing some TT amps, And it is starting to look like a 200mw demarc card may outperform a Orinoco card on a 1watt TT amp. The issue is not receive sensitivity, it is noise. The TT amp's produce so much noise that the gain provided does not help. I'm seeing noise bubble between -77 and -81db, compared to a /solid/ -98db without the amp. The 20db worth of noise overwelms any gain added by the amp.
I'm not done with the testing, as the tests I performed with the 200mw dmarc was long enough ago on a different antenna as to be invalid in my current environment, I only mention is as an ancidotal recollection. I will be retesting these cards in the current set-up and providing the results when I am done.
It is becoming clear to me that amp quality is more important than having an amp at all.
In this test I am using a 15 to 20db 180* waveguide antenna on the AP side, and the CPE side is an orinoco on a 2 foot LMR100 cable attached to a 13db $29 panel antenna supplied by superpass.
George
I took the cover off of my 1 watt amp, and it is as I suspected, the parts are there to power it from the ground, however, the trace has been cut by hand to prevent it from working that way, nothing a little solder wouldn't fix. I've got some pictures I'll post once I figure out why my CF reader isn't working. There is also a weak quarter-wave stub trace on the antenna side that I can see melting right in two if it ever takes a hit, and causing major problems if the amp actually survives it. The YDI had much better integral protection, looked like a 10 gauge quarter-wave stub on both the amp and the injector, but I wouldn't trust either one of them for a lightning arrestor.
lonnie
01-21-2003, 11:01 PM
Did you ever take one of the TT lightning arrestors apart? It simply uses the 1/4 wave stub and you pay good money for it.
We do not like the TT amps, and not just because they are from TT. We find they are noisy and are not reliable. In two years there is more than a 50% failure rate. Even the repaired, previously failed amps are failing. We had a stack of them left when we parted company and soon we will be through them. I would not dare to sell them.
If they are on a tower over 30 feet they get replaced with YDI or RF Linx. We find them to be about the same for quality and reliability. In two years of use, not one YDI or RF Linx has died.
georgew
01-22-2003, 01:54 AM
Quarter wave stubs make damned good lightning arrestors, wen you can use them. To a surge they look like a dead short. They also look like a dead short to the DC injector. I suspect that in an outdoor version of the amp, it will be the stub trace that is cut... that or they couldn't send power up the coax without it being 2.4ghz AC.
However regardless on how much current carrying capacity it has, it won't stop a direct hit from melting everything into a heap of slag. I know someone that had a direct hit strike his antenna. He had the tower grounded, twice, and all of his grounds were properly bonded. The hit didn't burn up anything but the radio, but it was the damage you could not see that was the most expensive... Everything electronic that was plugged into the wall was dead. Even the central air conditioning system. While you can properly bond your grounds to keep a ground wave from zapping you, in a direct strike the problem is not the ground only, it is the wires running from the house to the power and phone companies. Remember, lightning does not jump from the sky to the ground... it jumps from the ground to the sky... or from ground to a wire attached to a ground in a different location.
Today I set-up a marginal condition test, to see what I could see in a shootout between a Orinoco card going through a 1watt TT amp, compared against a 200mw zcomax card. Signal levels were higher with the amp, but the s/n was higher on the zcomax card.
The math was not exact, I figured I would loose 7 db of signal, and 27 db of noise for a total gain of 20 db by switching to a non-amped set-up. The actual gain was closer to 13db...
If you look at this, it makes you think the amp actually reduced the system gain rather than adding to it... However my test only tells one side of the story... In other tests, I was able to see better performance using the amp. In a simple netstumbler test, adding the amp caused the orinoco card to find over 20 AP's from my balcony, and without the amp I could find only 3 AP's. So the TT amp helps in some conditions, such as when you can hear the other end of the link, but the other end cannot hear you... but in general they are less than optimal.
Anyone want to buy a couple of 1watt TT amps? Only a few weeks old...
George
I think the amp would do more good on the CPE side, where you have a very directional antenna that doesn't pick up near the noise that a sector or omni would. On the TT amp, the quarter-stub was on the antenna side of the amp, not the injector side, so the power would already be off the line by the time it got there. I read a site about grounding and towers, it basically said everything connected has to have the same ground point, so that everything has the same ground potential at the same time. That way, even though it might be several thousand volts to someone outside, to the equipment, it looks like the normal voltage, especially since most of our stuff is run off transformers, which gives sort of an isolation from the power line. The site was very detailed about the actual flow of current from a lightning strike, how the center conductor will carry the voltage faster than the shield will, thus the need for something to keep the potential the same at the radio. I can't seem to find the page right now though, besides this is OT lonnie's gonna get us. I'll see if I can find the page and start a new thread.