Re: 8566 to measure 100W FM transmitter
TMC transmitters such as the GPT-750 use capacitor voltage dividers to make available a sample of the high power output (750 to 1000 watts in that case).
A few pF from output connector to .001 uF to ground. The small cap can be two inches of RG-8 or the like.? Roy sends.
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On May 23, 2019, at 6:30 PM, DW < wilson2115@...> wrote: Thanks, if the transmitter has a RF sample I will use that._
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Re: 8566 to measure 100W FM transmitter
Honesty I wasn't given much information about this station with the suspect spurs which might not actually be an issue, I also never been to before. I do work for a chief engineer who knows I have a spectrum analyzer and it seems I will find out what I'm dealing with when I actually go out there.
To add I actually have a 1kW dummy load so I could connect it that way if I have the appropriate adapters.
It could very well be a tower with many antennas and transmitters all running at once. Thanks again for the replies
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Re: 8566 to measure 100W FM transmitter
I would take care in how you are sampling the signal. If you are concerned with harmonics of the transmitter, the sampling method might incur different losses at the fundamental than at the harmonic, thus skewing the results.
If you are just concerned about the fundamental, this is not as critical. But if you are attempting to measure FCC out of band or harmonics, you might need to use a generator with known output to calibrate your sampler at various frequencies.
The other problem is with instrument overload from the fundamental, in which case you might need a notch filter to take the fundamental out and again, some calibration factors determined. I am sure that HP has some white papers that will walk you through these measurements.
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Re: 8566 to measure 100W FM transmitter
On 24/05/19 10:30 AM, DW wrote: Thanks, if the transmitter has a RF sample I will use that The spurious output may not be originating from the transmitter. Is it a stand-alone FM radio station, or does it share equipment rack, or mast, or antenna? Firstly see if you can borrow a bird wattmeter with a sampling plug-in, and a 250W dummy load. Check the spectrum coming out of the tx into the dummy load. If OK, unplug the dummy load and reconnect the antenna cable. Any change? If that all checks out, you now have an excuse to go out and get yourself a 85685a preselector for your 8566 :^) Also, do you know what frequencies the spurs are? Knowing that will offer further clues.
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Re: 8566 to measure 100W FM transmitter
Hmmmm, the spur complaint is it an ¡°all the time¡± or intermittent? ?We had a 2M repeater that was plagued with spurs, turned out to be a paging transmitter turned up to allowed +25% mixing with somebody else in our final. Crowded mountain tops can be very interesting.? Regards, ? Stephen Hanselman Datagate Systems, LLC 3107 North Deer Run Road #24 Carson City, Nevada, 89701 (775) 882-5117?office (775) 720-6020?mobile s.hanselman@...
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On May 23, 2019, at 14:38, DW < wilson2115@...> wrote: The reason for needing to measure this FM 99.1 transmitter is complaints of spurs so all I will be checking is if the expected signal is there and no spurs of that signal by turning the transmitter on or off. Amplitude is not critical just need a safe operating range into the 8566. Yes this analyzer is extremely heavy but I don't own a portable analyzer.
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Re: 8566 to measure 100W FM transmitter
Thanks, if the transmitter has a RF sample I will use that
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Re: 8566 to measure 100W FM transmitter
I might as well add my two cents.? I use a 30dB attenuator (300W) which feeds a 10dB directional coupler the tap goes to the SA and the direct goes to a HP 438. ? As many have mentioned be careful of the signal to the SA.? But if you are wanting to accurately observe the transmitter a direct connection is the only way to go, no pigtails. ?Any other method could impact measurements. ? Steve ?
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From: [email protected] < [email protected]> On Behalf Of Bob Albert via Groups.Io Sent: Thursday, May 23, 2019 2:41 PM To: [email protected]Subject: Re: [HP-Agilent-Keysight-equipment] 8566 to measure 100W FM transmitter ? There are several safe ways to do this.? What I do is put the transmitter on a dummy load and couple to the analyzer via a coaxial cable with clips on the other end, shorted together.? That makes a pickup loop which I couple to the dummy load, which usually has enough leakage to do the job. This method is frequency dependent but for a transmitter the bandwidth is so small so as not to matter.? Start with the loop a considerable distance from the dummy load and gradually bring it closer until you get a satisfactory signal. If you want a more stable, repeatable signal, use instead a direct connection via a simple attenuator, probably consisting of a 10k resistor in series with a 50 Ohm resistor.? That will reduce the 70V from the transmitter to less than one Volt.? You can do this with three connectors.? The resistors can be hanging in space.? The insertion loss of this network will be much less than 1 dB.? The 10k resistor will dissipate a maximum of one half watt so use at least a1 Watt rating.? Or raise it to 50k for a dissipation of 100 milliwatts and even less loss. On Thursday, May 23, 2019, 2:10:33 PM PDT, tmillermdems <tmiller11147@...> wrote: I would use a directional coupler such as a HP778D to get a 20 dB sample. Then pad the sample port with a 30 dB pad. That will get you to 1 mW into the SA. Note that the 778d is rated for 50 watts cw. There are couplers made for FM transmitters. You can also find a Bird sampler slug that will go in a Thruline wattmeter. Another option would be to build one out of coax. It is a pretty simple device. Maybe just a short stub antenna and grab it off the air? Just be careful not to overload the SA input. The mixer is not very forgiving. ? ? On 5/23/2019 3:50 PM, DW wrote: I should add the 100W will be driven to an antenna on a tower, I don't have a sampler so I'm limited to what I can sample, hopefully the transmitter has a sample port
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Re: 8566 to measure 100W FM transmitter
Thanks for all the helpful inputs, I think I should probably invest in a portable analyzer that is not so heavy and a sampler.
What I will use with what is available is the JFW 80db step attenuator, a coaxial cable connected to it with a short piece of wire on the end going through a resistor to the coaxial shield, one wire will have a 400 ohm resistor and another 200 ohm. I might also bring along an oscilloscope to be on the safe side as it has selectable 50 ohm inputs. Based on what I gather so far with my setup I should be ok if you agree although it could be better. If anyone suspects a hazard with my setup which could damage the 8566 let me know. Thanks
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Re: 8566 to measure 100W FM transmitter
There are several safe ways to do this.? What I do is put the transmitter on a dummy load and couple to the analyzer via a coaxial cable with clips on the other end, shorted together.? That makes a pickup loop which I couple to the dummy load, which usually has enough leakage to do the job.
This method is frequency dependent but for a transmitter the bandwidth is so small so as not to matter.? Start with the loop a considerable distance from the dummy load and gradually bring it closer until you get a satisfactory signal.
If you want a more stable, repeatable signal, use instead a direct connection via a simple attenuator, probably consisting of a 10k resistor in series with a 50 Ohm resistor.? That will reduce the 70V from the transmitter to less than one Volt.? You can do this with three connectors.? The resistors can be hanging in space.? The insertion loss of this network will be much less than 1 dB.? The 10k resistor will dissipate a maximum of one half watt so use at least a1 Watt rating.? Or raise it to 50k for a dissipation of 100 milliwatts and even less loss.
Bob
On Thursday, May 23, 2019, 2:10:33 PM PDT, tmillermdems <tmiller11147@...> wrote:
I would use a directional coupler such as a HP778D to get a 20 dB
sample. Then pad the sample port with a 30 dB pad. That will get
you to 1 mW into the SA.
Note that the 778d is rated for 50 watts cw.
There are couplers made for FM transmitters. You can also find a
Bird sampler slug that will go in a Thruline wattmeter.
Another option would be to build one out of coax. It is a pretty
simple device.
Maybe just a short stub antenna and grab it off the air?
Just be careful not to overload the SA input. The mixer is not
very forgiving.
On 5/23/2019 3:50 PM, DW wrote:
I should add the 100W will be driven to an antenna on a tower, I
don't have a sampler so I'm limited to what I can sample,
hopefully the transmitter has a sample port
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Re: 8566 to measure 100W FM transmitter
The reason for needing to measure this FM 99.1 transmitter is complaints of spurs so all I will be checking is if the expected signal is there and no spurs of that signal by turning the transmitter on or off. Amplitude is not critical just need a safe operating range into the 8566. Yes this analyzer is extremely heavy but I don't own a portable analyzer.
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Re: 8566 to measure 100W FM transmitter
I would use a directional coupler such as a HP778D to get a 20 dB
sample. Then pad the sample port with a 30 dB pad. That will get
you to 1 mW into the SA.
Note that the 778d is rated for 50 watts cw.
There are couplers made for FM transmitters. You can also find a
Bird sampler slug that will go in a Thruline wattmeter.
Another option would be to build one out of coax. It is a pretty
simple device.
Maybe just a short stub antenna and grab it off the air?
Just be careful not to overload the SA input. The mixer is not
very forgiving.
On 5/23/2019 3:50 PM, DW wrote:
I should add the 100W will be driven to an antenna on a tower, I
don't have a sampler so I'm limited to what I can sample,
hopefully the transmitter has a sample port
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External Clock board for 332xx series
Hi fellows,
?
Some years ago I made a external clock input board for my HP/Agilent 33220A.
?
I offer two remaining PCB¡¯s few weeks ago on this site and they immediately gone.
My question is, whether there is any more interest in this or to archive this project?
On my side, to make it cost effective, more than 7 orders are required. The price would be 99USD including the shipping cost to US or Europe and will take about 4-5 weeks to build-up (holiday season coming¡).
?
Design are based on original Agilent 33220-80001 (33220-66503) board and compatible with 332xx series of function / arbitrary waveform generators, but slightly modified.
Input impedance is 50ohm AC coupled, DC isolated from instrument housing and sensitivity of -13 +/-2 dBm. Input level for optimal jitter/phase noise is between 0 and 20dBm. Board is only 10MHz input, no loop back output!
?
Picture of board installed in my 33220a is attached. New revision will have MCL or Coilcraft 1:1 input isolation transformer.
?
Regards,
Milan
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Re: 8566 to measure 100W FM transmitter
What are you trying to measure, the fundamental, modulation, harmonics or what? #this will determine what bandwidth and accuracy you need
Is the measurement off-air or into a dummy load. If a load a power attenuator is best. if off-air some kind of coupler will be required. a resistive tap like
? or
would do and is reasonably broad band.
If looking at harmonics you will probably have to put a notch filter in the sampled ignal to reduce the carrier level and prevent spurious signals being generated in th analyser.
Robert G8RPI.
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Re: 8566 to measure 100W FM transmitter
First of all you must be very strong. The 8566 A or B is somewhat over 100 pounds and very bulky, if you have to take it to the transmitter. I have one of each and try to never move them.
I would keep the input power below one half watt on the 8566 input, to be safe. Never put in zero dB attenuator on the analyzer!
You will either need a large 50 ohm attenuator of at least 40 dB, with an additional low power 10 dB attenuator to sample the transmitter and protect the spectrum analyzer. That is what I have on the bench.
The other way to measure the transmitter is to use a high power directional coupler in addition to a small attenuator on the forward coupled arm, for insurance.
I routinely measure two 21 kW FM transmitter, but they have a built-in 55 dB directional coupler. However, I always use an additional attenuator at the spectrum analyzer, just in case.
If you are just looking at a SSB transmitter, at a very narrow dispersion, you probably can use just a test lead. If you are just interested in relative readings, such as close-in distortion, carrier or unwanted sideband suppression in a Single Sideband transmitter, that will work well.
Stuart K6YAZ
Los Angeles, California
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Re: 8566 to measure 100W FM transmitter
Why not just use a foot
long piece of coax, any kind will do, make a pig-tail out of
the far end and attach an alligator clip to the center
conductor and just lay it on the bench. It will make a dandy
RCV antenna.
If you are any where
near the transmitting antenna and the transmitter is
outputting 100W of RF at VHF you will have plenty of RF signal
to sample. If need be bring along either an adjustable step
attenuator and a couple 20dB or 40 dB fixed attenuators in
case the level is still too strong.
I have done this dozens
of times to monitor my own RF signal at various frequencies
when I do not want to go to the trouble of connecting up a
directional coupler and a step attenuator. You do not need to
go to the trouble to capacitive couple to the actual
transmission line of the transmitter.
Gedas, W8BYA
Gallery at
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 5/23/2019 2:56 PM, DW wrote:
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I have a 8566 and I need to sample the signal of a 100W FM
transmitter. I haven't seen the transmitter but I was told the
following below.
Take a piece of wire and attach it to the end of the cable that
will go to the 8566. One end will go to the center conductor and
the other will go through a resistor to the shield of the cable.
This wire will loop once around the transmission line. So far I
made two various wires, one with a 400 ohm resistor and another
with a 200 ohm resistor. I will take a 2W attenuator with me for
good measure. Any thoughts on this, thanks. I ask this as I'm
being cautious about the input level to the 8566 as I know it
doesn't take much to destroy the front end of a spectrum analyzer.
Thanks
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Re: 8566 to measure 100W FM transmitter
I built one of these:
You might want to use a larger resistor and make it a 50 dB tap. I use that for my amp output. Of
course you have to calibrate it using a SA and TG or a VNA because the
attenuation is not exact, but I have had good results through HF feeding
the output to a SA or 50 ohm scope input.
Regards,
Mark W7MLG
I should add the 100W will be driven to an antenna on a tower, I don't have a sampler so I'm limited to what I can sample, hopefully the transmitter has a sample port
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Re: 8566 to measure 100W FM transmitter
I should add the 100W will be driven to an antenna on a tower, I don't have a sampler so I'm limited to what I can sample, hopefully the transmitter has a sample port
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Re: 8566 to measure 100W FM transmitter
I believe it is 99.1mhz I have a 90dB manual step attenuator so that should help some along with a resistor to help pad down the levels, how hot do sample ports usually run on small FM transmitters I wonder. Thanks for the replies
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Re: 8566 to measure 100W FM transmitter
Do you need to measure it on the air? What frequency is the Tx?
Is there a sample port on the transmitter?
Regards
On 5/23/2019 2:56 PM, DW wrote:
I have a 8566 and I need to sample the signal of a 100W FM
transmitter. I haven't seen the transmitter but I was told the
following below.
Take a piece of wire and attach it to the end of the cable that
will go to the 8566. One end will go to the center conductor and
the other will go through a resistor to the shield of the cable.
This wire will loop once around the transmission line. So far I
made two various wires, one with a 400 ohm resistor and another
with a 200 ohm resistor. I will take a 2W attenuator with me for
good measure. Any thoughts on this, thanks. I ask this as I'm
being cautious about the input level to the 8566 as I know it
doesn't take much to destroy the front end of a spectrum analyzer.
Thanks
|
Re: 8566 to measure 100W FM transmitter
the best Thing woud be to use a power attenuator e.g. 40 dB /500 W plus another 10 dB attenautor between the? Output of the poer att and Input of the SA. Remember 100 W = +50 dBm, so an overlal attenuation of 50 dB (40 dB + 10 dB) will give You 0 dBm = 1 mW at the Input of Your SA, save enough for Yoru Instrument.
Henning Weddig
-----Urspr¨¹ngliche Mitteilung-----
Von: DW <wilson2115@...>
An: HP-Agilent-Keysight-equipment < [email protected]>
Verschickt: Do, 23. Mai 2019 20:56
Betreff: [HP-Agilent-Keysight-equipment] 8566 to measure 100W FM transmitter
I have a 8566 and I need to sample the signal of a 100W FM transmitter. I haven't seen the transmitter but I was told the following below.
Take a piece of wire and attach it to the end of the cable that will go to the 8566. One end will go to the center conductor and the other will go through a resistor to the shield of the cable. This wire will loop once around the transmission line. So far I made two various wires, one with a 400 ohm resistor and another with a 200 ohm resistor. I will take a 2W attenuator with me for good measure. Any thoughts on this, thanks. I ask this as I'm being cautious about the input level to the 8566 as I know it doesn't take much to destroy the front end of a spectrum analyzer. Thanks
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RFI-EMI-GUY
