Pardon me if I mix my metaphors but, "Riddle me this, boy wonder"....
Months ago, when I started on this mis-adventure, I purchased an Icom IC-910H,
along with the Icom mast mount pre-amps. Now, I can hear some of you moaning in
despair already in the background, but we all have to make mistakes in order to
learn from them. The decision to purchase the Icom pre-amps was based mainly on
ease of use.
After a few dozen QSO's, it became obvious that engaging the pre-amp button on
the rig served mostly to raise the S-Meter reading on the rig by bringing up
the local noise floor, but did little to improve the all important
signal-to-noise ratio. I sought all manner of advice on an upgrade, and
received a variety of opinions. Most of them reminded me over and over that
simply moving to another neighborhood that would allow for a nice tower would
eliminate the need for pre-amps all together.
Sometimes, I do wonder if any of you gentleman are:
A.) Married (and young enough to worry about your future bedroom activities)
B.) Have checked the housing market in the past few months
But I digress. Ignoring the advice to commit both marital and financial
suicide, I opted instead to accept an offer to borrow a trinity of pre-amps in
the form of the Advanced Receiver Research MSPXXXVDG-160 series. These are mast
mounted GaAsFET preamps rated at 160 watts. They had belonged to a rather
serious DX'er who had long since upgraded to some exotic tuned cavity, radio
astronomy model not suitable for mere mortals. They had been sitting in his
collection of VHF parts for about two years.
Alas, I discovered that they also appeared to have been damaged at some
point...since only one of the three was working. I returned them to AAR, where
they quickly repaired them, and at my request, bench tested all three to insure
performance. With great joy, I installed all three---and quickly went about
trying to conquer the known world with my indoor antenna farm.
I quickly discovered that these amps, while an improvement over the Icom amps,
still mainly brought up the noise floor and increased S-Meter readings, without
a noticeable improvement in signal to noise.
Disappointed, I turned my attention to trying to get a Beko 300watt 432 amp
that I had also been loaned working properly on 220 volts. I was advised to
contact Jerry at SSB Electronics for help. I did and proceeded to take up about
two hours of his time for an amp that he hadn't sold, and had no obligation to
support. ( Now that's what I call customer service)
Out of guilt, mixed with desperation, I also ordered an SSB Electronics SP-7000
mast mounted pre-amp for the 432 band. Truthfully, I expected nothing except to
sleep better at night haven not taken advantage of a small-businessman. When I
replaced the ARR pre-amp with the SSB Electronics amp, I made an amazing
discovery. When activated (I'm powering it via the feedline from the IC-910H)
the S-Meter barely moved at all. At first, I thought it must be defective.
A few hours later brought a weak CQ on the calling frequency of 432.100---I
switched on the pre-amp, and the signal noticeably improved. I was easily able
to make out the call sign and grid square...but the noise hardly changed. A
couple of weeks later, I verified this over and over again during the ARRL UHF
Contest. The most hopeful event was that I could also copy a lot of stations
who couldn't hear me, even in CW. (Once I get the Beko Amp going, hopefully
that will change)
For those of you would be Nancy-Drews out there still reading along, this
brings us to the mystery.
1. All three devices use similar (if not identical) active devices (GaAsFET).
Upon internal inspection, construction also seems similar. Why the marked
differences in performance?
2. I've read some articles that say the impedance match to the antenna can
dramatically affect the S/N ratio, but none of the amps came with instructions
for how to adjust for this. Is this commonly done?
3. Before I rush out to buy two more SSB Electronics amps (2M and 222), is
there anything I can do to the ARR units to improve their performance?
For those who wonder why this is such a concern for me, I've also discovered
that a db or two difference in performance can make or break 2 Meter meteor
scatter contacts...and my system, due to it's indoor location suffers a bit of
deafness. Most MS operators say that good, low noise pre-amps can make a lot of
difference on these bands. In hindsight, I should have ordered the SP-2000 to
start with....
As always, gang, it's free Scooby Snacks to those who help get to the bottom of
this one. Darn those meddling kids!
73,
Les Rayburn, N1LF
EM63nf
Les Rayburn, director
High Noon Film
100 Centerview Drive Suite 111
Birmingham, AL 35216-3748
205.824.8930
205.824.8960 fax
205.253.4867 cell
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