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Reviews Categories | Receive Pre-amps | ICOM AG-25 external preamp Help


Reviews Summary for ICOM AG-25 external preamp
ICOM AG-25 external preamp Reviews: 7 Average rating: 3.7/5 MSRP: $$149.99
Description: External, mast mounted preamplifier for 144-148 Mhz
Product is in production.
More info: http://
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W9GB Rating: 4/5 Sep 13, 2014 10:35 Send this review to a friend
Affordable mast mounted pre-amp  Time owned: more than 12 months
This pre-amplifier is useful for satellite and weak-signal VHF operators. High noise levels can often be attributed to a failed FET.
Newer FETs have ESD / static protection, while older FET devices -- DID NOT !
Nearby lightning strikes can damaged a FET in these pre-amps.

The Icom mast-mounted pre-amplifiers (AG-25, AG-35) used the dual gate Toshiba 3SK121 Dual Gate FET.
Schematics/manuals for the Icom AG-25 and AG-35 pre-amps are available on the Internet.

Toshiba 3SK121 -- TOSHIBA TRANSISTOR Dual-Gate, UHF, 10V, Idss>20mA, Up<4V

In 2012 and 2013, Earl Andrews did a comparison of various Dual Gate FETs, used by Icom, Yaesu, Kenwood, and others.
http://www.earlandrews.com/dgshootout.html

Please note his comments about counterfeit products from China.
http://www.earlandrews.com/dgmosshootout2.html
 
KA2AYR Rating: 2/5 Aug 27, 2011 10:49 Send this review to a friend
I might be missing something...  Time owned: 6 to 12 months
I tried to use one of these as a "tower-top preamp" between an IC-910H and a mid-sized yagi. Turning it on got a big rise in noise, but no appreciable increase in sensitivity or readability (that's new out of the box, no prior use). I set it up on a bench with a service monitor generating about 0.10 uV on-frequency signal. Saw a dramatic rise in noise, but confirmed that receive sensitivity was not enhanced. Tried Glenn's null procedure, which did reduce noise, but that didn't help with signal level. Guess I got a bad one. I'll change the GaAs FET and try it once more before I move onto another manufacturer I have more experience with.
 
K3ICH Rating: 5/5 Jul 20, 2010 06:29 Send this review to a friend
Worth the Effort  Time owned: more than 12 months
I have one of these at the end of a 150' run of 1/2" hardline, connected to a pair of 11 el vertical beams for FM operation. There is no question that there is improvement in readibility with the pre-amp engaged. It is not "awesome" etc. but is noticeable. I could do with a little less gain, but it's not worth messing with.

That said, I have had a some of experience with antenna mounted GaAsFET pre-amps and have noticed a curious condition. Many times, the transistor would seem to be working because there would be the characteristic increase in background noise when it is activated. However, the signal to noise ratio would actually be degraded. End result, it's blown! Replace the transistor and everything is back to normal. You can't rely on the observation of increased noise to indicate proper function. If the S - N degrades, it's either mis-tuned or smoked! (This is usually the result of my sending many watts up it's tailpipe.)
 
XE1VE3OQC Rating: 4/5 Apr 24, 2010 12:33 Send this review to a friend
Adjustment can be done!  Time owned: more than 12 months
This may not be the best preamp for 2 meters but you can improve the noise figure by one small adjustment.
When you remove the case covering the preamp and holding the unit with the relays away from you, there is a small ceramic trimmer above one coil and to the left of an electrolytic capacitor.With the preamp placed on a non-static surface turn the preamp on, ( I use a FT-736r for sat downlink) then adjust the trimmer for a null.This will cut the noise figure down also by several db.Your ¨S¨meter will fall also by 2-3 S units however there is a perceptable notice on the noise floor. I tried this on several of the AG-25´s and the outcome was good. With this adjustment the gain is stable at 13db but the background noise is down and is much easier on the ears.

Glenn,XE1/VE3OQC
 
MW0EDX Rating: 5/5 Oct 1, 2008 14:35 Send this review to a friend
Does the job  Time owned: 0 to 3 months
I have 17 m long cable and mounted mine in the shack. Does the job, very nice. No extra DC required.

I also have AG-35 for 430 Mhz. Same - mounted in the shack, also good.

73 !
 
K4SAT Rating: 5/5 Nov 26, 2006 18:41 Send this review to a friend
Excellent Preamp  Time owned: more than 12 months
I have the series AG-25, AG-35 and AG-1200. I can say that all three have worked fine for me. I have had no indication of excessive overload. It should be noted that any preamplifier will cause the S meter to rise. If you are using the preamplifier with a very short transmission line this will be more pronounced, and yes, the background noise level will appear higher. However, the preamp noise figure is the important consideration and signal to noise level will improve in almost every case. In my situation the transmission line runs are long, so the preamplifier improves the system noise figure by overcoming the loss of the transmission line. The original reviewer may have had a defective preamp or was experiencing overload from a nearby commercial transmitter (which is a possibility).
 
W7RJR Rating: 1/5 Sep 9, 2006 01:55 Send this review to a friend
Buy a Landwehr  Time owned: 0 to 3 months
Installation of this external preamp is straight-forward and self explanatory. Required voltage is supplied by the coaxial cable and special circuitry in the ICOM 910/820H.

While the specs for this unit did not include the noise figure my impression was that it was awful. This preamp delivered about 15 dB of nothing but noise. The noise was so bad that my S/N ratio was actually degraded.

To make matters worse the unit actually failed after several hours of operation. My experience, your mileage may vary.

 


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