I should explain my setup here;
FT8800 dual band FM rig for recieve 8 element yagi with mast mounted 18 db hamtronics preamp 25 feet of 9913 coax
I use narrow fm mode for maximum sensitivity. Whoever claims that leaves on trees attenuates UHF is correct but taking this into account I base my observations on clear path passes.
I liked bruningas idea of reduced duty cycle or on time of the downlink. My experience with so-50 is that people would adapt to it quickly. A good way to save energy.
One shouldnt correllate transmitter current draw with solar panel output current as the transmitters are not on for the entire orbit. This brings me back to the battery issue:
How many cycles are the batteries expected to deliver versus depth of discharge? Is this information available on the web?
Thanks, pat
How many cycles are the batteries expected to deliver versus depth of discharge? Is this information available on the web?
For NiCads, 2500 cycles for about 50% discharge (167 days) 10000 cycles for about 33% 25000 cycles for about 20% (about 4.5 years) 55000 cycles for about 10% Etc Bob WB4APR
On Aug 25, 2006, at 10:08 AM, McGrane wrote:
I should explain my setup here;
FT8800 dual band FM rig for recieve 8 element yagi with mast mounted 18 db hamtronics preamp 25 feet of 9913 coax
Hasn't the FT-8800 been shown by some folks to have a "barn-door" wide receiver? I can't find the link for any real lab reports on it at the moment, and all the manufacturer's put on their brochures these days are the same numbers for just about every radio... .2 uV for 12 dB SINAD, etc... etc... etc... no real good specifications on how they perform with lots of off-frequency noise and or other crud.
Putting a high gain pre-amp in front of it without some bandpass filtering is likely just crushing it. Can you see how it performs without the pre-amp and do live comparisons? You may find the pre- amp is actually making things worse.
Amplifying noise and bringing in more out of band signals sometimes isn't very useful... (GRIN).
-- Nate Duehr - WY0X nate@natetech.com
Hello nate- this is a perfect example of what happens when people snip e-mails. Go back to the original: you will find that I noted that I have the radio set in the Narrow FM mode for greater sensitivity. pat
On Fri, 25 Aug 2006, Nate Duehr wrote:
On Aug 25, 2006, at 10:08 AM, McGrane wrote:
I should explain my setup here;
FT8800 dual band FM rig for recieve 8 element yagi with mast mounted 18 db hamtronics preamp 25 feet of 9913 coax
Hasn't the FT-8800 been shown by some folks to have a "barn-door" wide receiver? I can't find the link for any real lab reports on it at the moment, and all the manufacturer's put on their brochures these days are the same numbers for just about every radio... .2 uV for 12 dB SINAD, etc... etc... etc... no real good specifications on how they perform with lots of off-frequency noise and or other crud.
Putting a high gain pre-amp in front of it without some bandpass filtering is likely just crushing it. Can you see how it performs without the pre-amp and do live comparisons? You may find the pre- amp is actually making things worse.
Amplifying noise and bringing in more out of band signals sometimes isn't very useful... (GRIN).
-- Nate Duehr - WY0X nate@natetech.com
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
McGrane wrote:
the radio set in the Narrow FM mode for greater sensitivity.
Two things come to mind, and I want to make sure anyone reading this thread doesn't get confused:
The first is to make sure that the NBFM bandwidth is wide enough to pass 9600 baud transmission. Doesn't one need about 20 KHz? I'm sure someone out there knows. Don't forget that you have to account for being off frequency due to doppler, particularly if you are using 5-kHz steps.
Secondly, the mode setting on the radio is something that affects a filter in the IF chain, not the front-end of the radio. I think the issue with the FT-8800--and generally any other transceiver designed to double as a wider VHF receiver--is that the the front end amplifier is overloaded by a strong signal at *any frequency*. The classic receiver design has a (preferably low-noise) amplifier as the first thing in the receive chain, which boosts the incoming signal enough to overcome the following mixer losses. That ampflifier is being bombarded by everything from DC-GHZ, and will amplify whatever the transistor is capable of. (There is usually some sort of filter ahead of it in commercial equipment, but in the case of wide-band VHF receiver it's likely to be pretty wide).
Now as we all know, amplifiers have a limit as to how much output they can supply, and after an incoming signal gets too loud it will become distorted. This is familiar to many of us in urban areas when we suddenly hear a pager on the frequency of our favorite repeater. That is often an effect of that very strong signal being clipped and introducing new frequency components. Another effect is that a strong incoming signal to that front end--not matter what frequency it is on--effectivly swamps the amplifier so that the weaker signals one desires to listen to are not amplified faithfully. This often manifests itself as "deafness", but it is really because the front end is spending what juice it can supply on that big signal 50 MHz away from where you are trying to listen. No changes to IF filters are going to make that signal go away. When this happens one usually has to use some sort of a filter ahead of the amplifier, either to notch out the offender, or pass only the band of interest. This will allow the front-end amplifier to run in its linear region, and thus amplify all the incoming signals without (significant) distortion.
The lab specifications for front-end overload can generally be figured from the thrid-order intercept point (IP3), which essentially tell you how much distortion one gets for an input signal of a given amplitude. The "sensitivity figure" doesn't tell you anything about how the radio will perform in a high-RF environment.
I don't mean to lecture, but rather clear up some possible confusion.
-Andy K0SM/2
----- Original Message ----- From: "Andrew T. Flowers, K0SM" aflowers@frontiernet.net To: amsat-bb@amsat.org Sent: Saturday, August 26, 2006 6:59 PM Subject: [amsat-bb] Re: front-end overload was: echo
The lab specifications for front-end overload can generally be figured from the thrid-order intercept point (IP3), which essentially tell you how much distortion one gets for an input signal of a given amplitude. The "sensitivity figure" doesn't tell you anything about how the radio will perform in a high-RF environment.
I don't mean to lecture, but rather clear up some possible confusion.
-Andy K0SM/2
Hi Andy, K0SM/2
I have just read your thread it is a good good article, congratulations !
I would like to add few comments.
I agree with you that the third-order intercept point (IP3) describes the amplitude of third-order distorsion products when more than one signal is present at a receiver input.
But when a receiver is tuned to a weak signal than a strong adiacent signal may cause an apparent decrease in receiver gain and this is better described by the 3 dB compression point wich is essential to tell you how much the gain of your receiver will be reduced in presence of an in-band or out of band strong and undesired signal.
I aegree with you that the only cure is to increase the selectivity at the front end of the receiver to attenuate the strong and undesired signals wich are adiacent to the receiver passband because gain compression or desensitization occurs when the input voltage from the undesired signal is large enough to exeed the bias on an RF amplifier or mixer and drives the base or the grid to conduct.
I aegree with you that high receiver sensitivity is the antithesis of good cross-modulation and compression performance expecially in a high-RF environment.
For those who are interested to go in more details in to the above matter I recommend to read the article:
"Receiver noise figure sensitivity and dinamic range,what the numbars means" by James R. Fisk, W1DTY Ham Radio Magazine October 1975
Upon request I can send a compressed file of the above article to everybody.
Best 73" de
i8CVS Domenico
Hi andy- thanks for the education but I'm using narrow fm for the phone downlink , not packet. I did try a diplexer with a .25 db loss between the antenna and the mast mounted preamp but noticed significantly lower recieve at or near fringe. I'm in a rural area. Big power stations are not a problem. Thanks for info, pat
On Sat, 26 Aug 2006, Andrew T. Flowers, K0SM wrote:
McGrane wrote:
the radio set in the Narrow FM mode for greater sensitivity.
Two things come to mind, and I want to make sure anyone reading this thread doesn't get confused:
The first is to make sure that the NBFM bandwidth is wide enough to pass 9600 baud transmission. Doesn't one need about 20 KHz? I'm sure someone out there knows. Don't forget that you have to account for being off frequency due to doppler, particularly if you are using 5-kHz steps.
Secondly, the mode setting on the radio is something that affects a filter in the IF chain, not the front-end of the radio. I think the issue with the FT-8800--and generally any other transceiver designed to double as a wider VHF receiver--is that the the front end amplifier is overloaded by a strong signal at *any frequency*. The classic receiver design has a (preferably low-noise) amplifier as the first thing in the receive chain, which boosts the incoming signal enough to overcome the following mixer losses. That ampflifier is being bombarded by everything from DC-GHZ, and will amplify whatever the transistor is capable of. (There is usually some sort of filter ahead of it in commercial equipment, but in the case of wide-band VHF receiver it's likely to be pretty wide).
Now as we all know, amplifiers have a limit as to how much output they can supply, and after an incoming signal gets too loud it will become distorted. This is familiar to many of us in urban areas when we suddenly hear a pager on the frequency of our favorite repeater. That is often an effect of that very strong signal being clipped and introducing new frequency components. Another effect is that a strong incoming signal to that front end--not matter what frequency it is on--effectivly swamps the amplifier so that the weaker signals one desires to listen to are not amplified faithfully. This often manifests itself as "deafness", but it is really because the front end is spending what juice it can supply on that big signal 50 MHz away from where you are trying to listen. No changes to IF filters are going to make that signal go away. When this happens one usually has to use some sort of a filter ahead of the amplifier, either to notch out the offender, or pass only the band of interest. This will allow the front-end amplifier to run in its linear region, and thus amplify all the incoming signals without (significant) distortion.
The lab specifications for front-end overload can generally be figured from the thrid-order intercept point (IP3), which essentially tell you how much distortion one gets for an input signal of a given amplitude. The "sensitivity figure" doesn't tell you anything about how the radio will perform in a high-RF environment.
I don't mean to lecture, but rather clear up some possible confusion.
-Andy K0SM/2
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
--- McGrane tmcgrane@suffolk.lib.ny.us wrote:
Go back to the original: you will find that I noted that I have the radio set in the Narrow FM mode for greater sensitivity.
Pat...does not that particular menu item on the 8800 refer to the MIC GAIN only??? <Menu #44>
73, Gary -K8KFJ-
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hello garie- the narrow setting affects the recieve quite audibly. take care, pat
On Sat, 26 Aug 2006, Garie Halstead K8KFJ wrote:
--- McGrane tmcgrane@suffolk.lib.ny.us wrote:
Go back to the original: you will find that I noted that I have the radio set in the Narrow FM mode for greater sensitivity.
Pat...does not that particular menu item on the 8800 refer to the MIC GAIN only??? <Menu #44>
73, Gary -K8KFJ-
Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
McGrane wrote:
Hello nate- this is a perfect example of what happens when people snip e-mails. Go back to the original: you will find that I noted that I have the radio set in the Narrow FM mode for greater sensitivity. pat
Ah, if I'd have seen that I would have not bothered to reply at all. You're not using the radio correctly for what you're attempting to accomplish.
Good luck.
73, Nate
participants (6)
-
Andrew T. Flowers, K0SM -
Garie Halstead K8KFJ -
i8cvs -
McGrane -
Nate Duehr -
Robert Bruninga