Chris: In addition to what type of diode detector you might build or
purchase, keep an eye out on ebay or other equipment exchanges for "wave
meters" or "frequency meters". These are available in both coaxial and
waveguide form. They are mechanically tunable cavities with a graduated
frequency scale and typically provide a 1db dip at resonance. A basic test
setup would be uW Source > wave meter > diode detector. With the source in
operation, monitor the detector current (or voltage) and tune the wave meter
until a slight to moderate current (or voltage) dip occurs. Then read the
indicated frequency from the wavemeter scale. At low diode current levels it
may be easier to observe a voltage dip if the microwave source output is
low---like in the .1 to 1mw range.
For higher level uW sources you can use a circulator and place the
wavemeter and dector on the isolated port to monitor the source signal
through the circulator.
I have purchased wave/frequency meters for as little as $15~$30 each
and they are invaluable (along with a detector) as basic microwave test
equipment.
I use one frequently with my HP141T spectrum analyzer as a means of
verifying a frequency measurement, especially when mixing hetrodynes are
present on the analyzer display.
Mike wa3tts
----- Original Message -----
From: <vhfcontesting-request@contesting.com>
To: <vhfcontesting@contesting.com>
Sent: Saturday, August 16, 2008 11:00 AM
Subject: VHFcontesting Digest, Vol 68, Issue 23
> Send VHFcontesting mailing list submissions to
> vhfcontesting@contesting.com
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://lists.contesting.com/mailman/listinfo/vhfcontesting
> or, via email, send a message with subject or body 'help' to
> vhfcontesting-request@contesting.com
>
> You can reach the person managing the list at
> vhfcontesting-owner@contesting.com
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of VHFcontesting digest..."
>
>
> Today's Topics:
>
> 1. Re: Quick To the Mystery Machine! [The Case of the Phantom
> Pre-Amp] (Chet, N8RA)
> 2. Re: VHFcontesting Digest, Vol 68, Issue 22 (MICHAEL SAPP)
> 3. Re: [VHF] Re: Quick To the Mystery Machine! [The Case of the
> Phantom Pre-Amp] (Zack Widup)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 15 Aug 2008 17:05:59 -0400
> From: "Chet, N8RA" <chetsubaccount@snet.net>
> Subject: Re: [VHFcontesting] Quick To the Mystery Machine! [The Case
> of the Phantom Pre-Amp]
> To: "'VHF Contesting Reflector'" <vhfcontesting@contesting.com>
> Cc: 'Zack Widup' <w9sz@prairienet.org>, 'Les Rayburn'
> <les@highnoonfilm.com>
> Message-ID: <2E0E497EA5BB4C9C8E3A7B63BDE239FE@pd2800>
> Content-Type: text/plain; charset="us-ascii"
>
> FWIW- I am no expert:
>
> How much gain did the preamps have?
>
> There is some discussion in listening for weak signals to try and keep the
> front end gain such that the ambient noise is not higher than the AGC
> threshold of the receiver, and thereby activating it (as shown by the
> S-meter going up). The concern is that if the AGC is reacting on noise,
> then
> some AGC circuits will "intermodulate" the noise with the desired weak
> signal and make it fuzzier and more difficult to copy. If the preamp that
> worked the best had the least gain, maybe that is in play here.
>
> If the radio has an attenuator, try the other preamps again and then add
> in
> an amount of attenuation that is about 3 dB or so less than their gain,
> and
> see if that makes them sound better.
>
> 73
> Chet, N8RA
>
> -----Original Message-----
> From: vhfcontesting-bounces@contesting.com
> [mailto:vhfcontesting-bounces@contesting.com] On Behalf Of Zack Widup
> Sent: Friday, August 15, 2008 4:14 PM
> To: Les Rayburn
> Cc: VHF Contesting Reflector; vhf@w6yx.stanford.edu
> Subject: Re: [VHFcontesting] Quick To the Mystery Machine! [The Case of
> the
> Phantom Pre-Amp]
>
> I'm guessing that the devices which performed well were actually
> noise-matched and the others weren't; perhaps they were just tuned for
> maximum gain? Many component manufacturers supply the gamma (optimum) for
> best noise match for the device, which is not the same as the maximum
> gain/power out match.
>
> 73, Zack W9SZ
>
>
> On Fri, 15 Aug 2008, Les Rayburn wrote:
>
>> 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
>> _______________________________________________
>> VHFcontesting mailing list
>> VHFcontesting@contesting.com
>> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>>
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting@contesting.com
> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>
>
>
> ------------------------------
>
> Message: 2
> Date: Fri, 15 Aug 2008 17:25:26 -0400
> From: "MICHAEL SAPP" <wa3tts@verizon.net>
> Subject: Re: [VHFcontesting] VHFcontesting Digest, Vol 68, Issue 22
> To: <vhfcontesting@contesting.com>
> Message-ID: <FEEF7102FED24908ACB8E6594A7E6841@your27e1513d96>
> Content-Type: text/plain; format=flowed; charset=iso-8859-1;
> reply-type=original
>
> PHANTOM PREAMPS
>
> Ray: A preamp is only useful if the G/T ratio of your antenna is large
> enough (i.e. 3db beamwidth narrow enough and sidelobes small enough) to
> reduce noise sources other than from the direction where it is pointed. If
> you live in a high noise environment, it would make little difference shy
> of
> overcoming coaxial line losses or existing receiver inadequacies,
> especially
> given that your antenna is limited to being on the horizon for weak signal
> tropo. Just make sure what you have installed as a home station is
> functional and working reasonably well. Sooner or later mother nature will
> drop a tropo, aurora, m/s, or e's opening in your lap. The trick is being
> around and having your modest equipment functional when that happens.
> Most
> of the 30 plus states I have worked on 1296 MHz occurred in the "Great
> Thanksgiving Tropo Opening of 1986" (21st Central States VHF Proceedings,
> 1987, pp34-41). Be patient, stuff happens. 73 Mike WA3TTS
>
>
>
> ------------------------------
>
> Message: 3
> Date: Sat, 16 Aug 2008 09:18:54 -0500 (CDT)
> From: Zack Widup <w9sz@prairienet.org>
> Subject: Re: [VHFcontesting] [VHF] Re: Quick To the Mystery Machine!
> [The Case of the Phantom Pre-Amp]
> To: Les Rayburn <les@highnoonfilm.com>
> Cc: VHF Contesting Reflector <vhfcontesting@contesting.com>,
> vhf@w6yx.stanford.edu
> Message-ID:
> <Pine.LNX.4.64.0808160911440.18696@bluestem.prairienet.org>
> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
>
> Hi Les,
>
> Well, to simplify it, what you want from your preamp is the optimized
> noise figure. This represents the lowest value for noise figure you can
> achieve at a given frequency or small range of frequencies.
>
> A noisy amplifier can be modeled as a noiseless amplifier plus a noisy
> source. If you design an amplifier so it's matched to the noisy source,
> you've achieved the optimum noise figure.
>
> Optimized noise figure does not go hand-in-hand with maximum gain (it
> isn't too far off in most cases, however).
>
> Manufacturers often include in their data sheets a parameter called "gamma
> (optimum)" which can be used to design an amplifier using the given device
> for lowest noise figure. But with the right equipment it can be done by
> tuning the amp even if you don't have that data.
>
> I hope this helps!
>
> 73, Zack W9SZ
>
>
> On Fri, 15 Aug 2008, Les Rayburn wrote:
>
>> Zack,
>>
>> Sorry, I forgot to mention. I'm a newcomer to VHF/UHF...and a filmmaker
>> by
>> profession. Can you put that into English and run it by me again? "Noise
>> matched"? Matched to what exactly?
>>
>> Signed,
>>
>> Slow in Alabama (but not compared to the locals!)
>>
>>
>>
>>
>> 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
>>
>> --------------------------------------------------
>> From: "Zack Widup" <w9sz@prairienet.org>
>> Sent: Friday, August 15, 2008 3:14 PM
>> To: "Les Rayburn" <les@highnoonfilm.com>
>> Cc: "VHF Contesting Reflector" <vhfcontesting@contesting.com>;
>> <vhf@w6yx.stanford.edu>
>> Subject: [VHF] Re: [VHFcontesting] Quick To the Mystery Machine! [The
>> Case of
>> the Phantom Pre-Amp]
>>
>>> I'm guessing that the devices which performed well were actually
>>> noise-matched and the others weren't; perhaps they were just tuned for
>>> maximum gain? Many component manufacturers supply the gamma (optimum)
>>> for
>>> best noise match for the device, which is not the same as the maximum
>>> gain/power out match.
>>>
>>> 73, Zack W9SZ
>>>
>>>
>>> On Fri, 15 Aug 2008, Les Rayburn wrote:
>>>
>>>> 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
>>>> _______________________________________________
>>>> VHFcontesting mailing list
>>>> VHFcontesting@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>>> ------
>>> Submissions: vhf@w6yx.stanford.edu
>>> Subscription/removal requests: vhf-request@w6yx.stanford.edu
>>> Human list administrator: vhf-approval@w6yx.stanford.edu
>>> List rules and information: http://www-w6yx.stanford.edu/vhf/
>> ------
>> Submissions: vhf@w6yx.stanford.edu
>> Subscription/removal requests: vhf-request@w6yx.stanford.edu
>> Human list administrator: vhf-approval@w6yx.stanford.edu
>> List rules and information: http://www-w6yx.stanford.edu/vhf/
>>
>
>
> ------------------------------
>
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting@contesting.com
> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>
>
> End of VHFcontesting Digest, Vol 68, Issue 23
> *********************************************
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|