My radio is an Yaesu FT-7800. I bought an amplifier for it off ebay for 100 dollars even. It's model PA3-1FE. It is currently tuned for 150mhz, but I will probably open it up and change that to the ham band exclusively. It's 15-40w in, 80-120w out. I bought it on a whim because 100 dollars is literally fraction of the retail price. I still think it's nice to have. Will this amplifier really make a big difference as far as range goes? Will it be unsafe? What do you guys think of amplifiers in general?
120 watt VHF amplifier
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how much power do you currently put out? doubling power out will produce some range increase, but to really see a difference you need 6db gain in radiated signal power. the thing is that YOU may talk out farther but you won't be able to HEAR any farther than you could. so your range really won't be much better. if you can hear a distant repeater now but can't legibly hit it, then the amp may fix that issue for you. but if you don't already hear the other repeater/simplex folks then you still can't carry on a conversaiton with them.
as far as price, that is a great price for that amp. we used to use them on small paging systems and they held good so long as you did not need continuous duty.
as far as price, that is a great price for that amp. we used to use them on small paging systems and they held good so long as you did not need continuous duty.
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kb0nly
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Good amp, will definitely make a difference. Be prepared to do some in depth work on it though. Your going to have to retune the input and output of the amp to get full power output. I have worked on a few of those, 150-174 is their rated split, you have to add some trimmer caps to the input to bring down the SWR for the radio, basically like building in an antenna tuner. I know some guys that bought commercial amps like these and a cheap 2m tuner from MFJ to fix that. But you also need to tweak the output filtering of the amp or else you loose a lot of your power there because its effectively filtering out the 2m band below 150Mhz. Most of the ones i worked on just needed a cap or two on the output side to tweak it. Do some google searching lots of good info available online from others that have already done it.
Should have ask those question before you bought the amp. $100 you could of saved..
Be careful
Your radio, at full power, will over drive that amp but I don't know if 50 watts would be enough to hurt it. The problem you are going to have is dropping the operating range down to 2 meters without messing up the low-pass filters on both the input and output. If you have the ability, and can get the need information to make the modification, then that amp at that price is a good buy (if it works).
Don't expect to increase your transmit range by more than maybe a mile or two. You are only going to increase your transmit power by about 3 dBw and you will have a hard time noticing any difference. This amp also will do nothing to increase your receiver's sensitivity so any increase you get will be in one direction only.
Your radio, at full power, will over drive that amp but I don't know if 50 watts would be enough to hurt it. The problem you are going to have is dropping the operating range down to 2 meters without messing up the low-pass filters on both the input and output. If you have the ability, and can get the need information to make the modification, then that amp at that price is a good buy (if it works).
Don't expect to increase your transmit range by more than maybe a mile or two. You are only going to increase your transmit power by about 3 dBw and you will have a hard time noticing any difference. This amp also will do nothing to increase your receiver's sensitivity so any increase you get will be in one direction only.
jim202
Member
You didn't say if this was for base or mobile use. If it is in mobile service, you can go from a 1/4 wave whip to a gain antenna and get 3 db gain right there. It is easier to use antenna gain to improve your coverage that it is to boost the TX power out.
Then you still have the issue of the receiver not getting any better with the higher transmit power out. Now your going to be heard, but you can't hear the station trying to get back to you.
N4KVE
Member
Before you put the screwdriver to the amp, try it first to see how well it works. I have a TPL amp that's 5 in & 100 out. It's tuned for 457 mhz. So when I tx at 447 mhz it puts out 90 watts instead of 100. I'm not going to touch it to possibly gain 10 watts. If the sticker says it's tuned for 150 mhz, it should work fine at 146-147 mhz, however if it's tuned for 166 mhz, then it will have to be retuned. GARY N4KVE
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kb0nly
Guest
The amp that the OP bought is rated for 20-40 watts input according to the spec sheets i have on it, however it will works down to about 10-15w, anything lower and it won't make much if any power.
prcguy
Member
The amp will make slightly more than a 3dB improvement over the stock radio at full power, which is not much.
The amp is tunable and you need to tune it for max power while monitoring for the lowest DC current at max power.
prcguy
The amp is tunable and you need to tune it for max power while monitoring for the lowest DC current at max power.
prcguy
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kb0nly
Guest
Not much, but can make the difference. I run a 170w amp on 2m here at home, sometimes its the difference between holding that repeater or not, even with the yagi.
If it's only going to lower the amp output, I may not re-tune it right away. I might just run 50 watts into it as long as that won't damage it. I have a 5/8 wave 3dbi gain NMO VHF antenna on the roof of my truck already, so I might even use it with my base setup. Will this possibly change the receiver sensitivity of my radio? I do already have a diplexer in my truck for the separate VHF and UHF antennas, so will combining a diplexer and an amplifier guarantee lowering RX?
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kb0nly
Guest
It will increase the amp output by retuning it, not lower it. DO NOT RUN 50W into it though!! These are a two stage amp, a driver stage and the final stage. You will blow up the driver stage running 50w into it, even running the max input of 40w makes them run hotter than you know what, i wouldn't recommend more than 20w.
You have two choices.... You can program your VHF memories in the 7800 with the 20w power level selected each time you write the memory so your always running 20w with the amp inline, this is how i setup my amp at home with my FT-8800, or you can modify the amp and bypass the driver stage which i have done as well. Of course that takes a lot of work and technical know-how as well.
It should not do much to the receive sensitivity of the radio, other than of course the usual loss you get from adding additional connectors and such inline. The T/R relay in these do add a bit of loss but its small. You won't lower the receive anymore than you already have using the diplexer, the biggest loss you have in the system is the diplexer, adding the amp will be only a small fraction of the loss.
I run a FT-8800 at home with a pair of amps, a RF Concepts 170w VHF and 100w UHF, i use a diplexer before the amps to split the radio output, and a second diplexer after the amps to combine their output to a single feedline because i run tower mounted antenna switching for selecting various verticals and yagi's. The system works great, i lose a small amount of output power to the diplexer, and a small amount of receive signal, but both amps have a builtin preamp which i adjusted the gain of to compensate for system loss without adding much to the noise floor.
I have other brick amps, both commercial and homebrew for SSB on 2m/70cm as well. I have been tinkering on amps for many years.
Using the diplexer and dual antennas is actually best in your situation. You wouldn't be able to transmit UHF through that amp, you would lose most of the transmitted signal to the filtering and the relay in it, which is very lossy at UHF. And receive would be greatly affected as well. If you ever wanted to use a dual band antenna you could put a diplexer before and after the amp and jumper the UHF ports of the diplexers.
CalebATC
Member
Come on, you should know this!
It will not change the sensitivity of the radio at all, but a preamp will. Two way different things! You may want to get a good two meter preamp, and then you will have a pretty kickin setup, especially for some weak signal operation!
A better antenna will help too- a nice Hustler or Diamond or any other type of a high gain antenna will increase NOT only your receive, but your ERP! My ERP is 150 watts here, where that's what your amp and your antenna will do for you!
Good luck with it, and sounds like a pretty cool project! This will definitely help you out! Seems like you got a GREAT deal too!!
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kb0nly
Guest
I have not taken a specific measurement, however, i can tell you that without the diplexers inline one distant repeater, distance of 60 air miles, is an S7 on the yagi and a S5 on the vertical, with the diplexers and amp inline its an S6 on the yagi and a S4 on the vertical. So not a huge loss. Flip on the preamp and its S9+ on both so no worries.
I can hear mobiles on simplex for 40 miles easy on average days, with the preamp its a bit more. This is using only a 6 element yagi thats supposed to be 10dB of gain. I keep saying i should borrow some gear to really calculate the actual loss going through those diplexers.... Its been three years and i still havent done it, no reason to. LOL
With the hills i got around here UHF mobile is a different story, those same repeaters i can hit from home i cant even hear mobile most days.
It happens every time, you guys never fail to amuse me. (;->) I on the other hand being a firm believer in KISS (not Gene Simmonds KISS) will keep it stupidly simple as usual. Once upon a time a friend was having connection problems with his local packet BBS and as luck would have it one day at a hamfest we ran across a 5W in, 100W out commercial VHF amp. The price was right (unlike e-Pay) for old junk box "what the heck is this thing, give ya ten bux fer it" parts so he took a chance and back at the shack I had at it.
After connecting a suitable DC supply, watt meter and microwave line termination (glorified dummy load) the three trimmers (input, IPA, output) got the golden screwdriver tune for maximum smoke treatment. I could have metered the RF output or DC input, smoke is smoke and when full capacity of this magical substance was achieved the amp worked flawlessly. Problem solved, no more endless retries as the ack/frack flails about in error correction; a solid, reliable connection every time. Bottom line... unless you live in the shadow of the tower a 5W HT makes a lousy data rig. (;->)
The really big clue is ferrite core inductors, (like the 80-10M 100W no tune CB amps in disguise) making outboard amps exceedingly broad across the band and often tune out of band without modification. Now Chris, pay attention to yourself and stick to the plan.
"It is currently tuned for 150mhz, but I will probably open it up and change that to the ham band exclusively."
No probably about it, unless you retune it you bought yourself a $100 funny looking paperweight.
"It's 15-40w in, 80-120w out."
Stay within its ratings, too little drive, too little power out to make a significant difference. Push it too hard and you let the magic smoke out. Class C FM amps work best when driven near maximum but don't press your luck. Leave some headroom and NEVER forget these things were designed for ICAS so a CCS old buzzard transmission just may send the silicon reactor core into meltdown before the heat sink gets hot enough to give your fingers a warning.
"I bought it on a whim because 100 dollars is literally fraction of the retail price."
Treat it with respect and it'll be the best $100 you ever spent.
After connecting a suitable DC supply, watt meter and microwave line termination (glorified dummy load) the three trimmers (input, IPA, output) got the golden screwdriver tune for maximum smoke treatment. I could have metered the RF output or DC input, smoke is smoke and when full capacity of this magical substance was achieved the amp worked flawlessly. Problem solved, no more endless retries as the ack/frack flails about in error correction; a solid, reliable connection every time. Bottom line... unless you live in the shadow of the tower a 5W HT makes a lousy data rig. (;->)
The really big clue is ferrite core inductors, (like the 80-10M 100W no tune CB amps in disguise) making outboard amps exceedingly broad across the band and often tune out of band without modification. Now Chris, pay attention to yourself and stick to the plan.
"It is currently tuned for 150mhz, but I will probably open it up and change that to the ham band exclusively."
No probably about it, unless you retune it you bought yourself a $100 funny looking paperweight.
"It's 15-40w in, 80-120w out."
Stay within its ratings, too little drive, too little power out to make a significant difference. Push it too hard and you let the magic smoke out. Class C FM amps work best when driven near maximum but don't press your luck. Leave some headroom and NEVER forget these things were designed for ICAS so a CCS old buzzard transmission just may send the silicon reactor core into meltdown before the heat sink gets hot enough to give your fingers a warning.
"I bought it on a whim because 100 dollars is literally fraction of the retail price."
Treat it with respect and it'll be the best $100 you ever spent.
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