RE: [Repeater-Builder] Bandpass Cavity Insertion Loss
As it turns out, I have a questionable test cable. Either that or I have an attenuator turned on in my test set that I'm not aware of. I'm still learning how to use this HP8920. I removed the cables from the cavity and connected them together and my measured input was 1.75-2.0 db lower than the set output. In other words, the output is set at -15.0 dbm. The unit displays the received level at -17.0 dbm. Someone else mentioned adjusting the coupling loops. On this particular cavity, they don't appear to be adjustable. Both connectors are mounted on the same plate. There are no screws to loosen to allow the conector/loop assembly to rotate. Jamey Wright KD4SIY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] Behalf Of Eric Lemmon Sent: Friday, March 10, 2006 11:40 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Bandpass Cavity Insertion Loss Jamey, If your measurement is accurate, 3.2 dB insertion loss is excessive. A single bandpass cavity performs best when its insertion loss is between 0.5 and 1.0 dB. How are you measuring this? If you are using a spectrum analyzer with an accurate frequency reference, the preferred method is to put a barrel (double female) adapter between the two test cables and set the reference cursor to zero dB. Then remove the barrel and connect the test cables to the cavity. You can then read the insertion loss directly. If you're using the bandpass filter on the receive side, no more than 1.0 dB IL should be used. If you're using the filter on the transmit side to eliminate spurs or harmonics, 0.5 dB IL will usually be fine. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jamey Wright Sent: Friday, March 10, 2006 8:12 PM To: repeater-builder@yahoogroups.com Subject: [Repeater-Builder] Bandpass Cavity Insertion Loss I just got through tuning up a Phelps Dodge VHF bandpass cavity. The measured loss through this thing is 3.2 dB. I am generating at -10 dBm. The level measured on the output is -13.2 dBm. It is a Phelps Dodge VHF bandpass cavity but I can't find a model number on it. Is this amount of loss normal? Thanks in advance. Jamey Wright KD4SIY Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
RE: [Repeater-Builder] Bandpass Cavity Insertion Loss
All test cables and connectors on them exhibit loss, especially as frequency goes up .You need to account for these losses by knowing what they are at the freq you are working on, and even the service monitor is not perfectly constant across it's bandAlways do a loop check with the barrel first. (use a barrel that matches the connectors on the device to be tested. That way you minimize potential unexpected losses. after you know the expected loss, you can either bump up the generator to get you to a zero setting or subtract the difference from your device measured results... If you change the freq, check it again.until you learn your setup. Cables can exhibit differences especially at wavelength increments of your operating freq or near them... It is suggested to insert pads in the lines of the service monitor to help maintain a 50 ohm environment as the can changes impedance as it is tuned. If you put the correct pads in you can get your known loss to about 10 or 20 db increments and make the tests a little easier to calculateI generally do not need to use pads on high quality duplexers as they tend to be more impedance stable, and shift less while tuning At 900 mhz it gets real interesting as cables are MANY increments of the wavelength and can do really strange things... In this case a return loss bridge and tuning the proper way works a little better... BTW a return loss bridge is what is the approved way of doing this, although the method you are using seems to work for most of the world quite nicely :-) Doug KD8B At 11:42 AM 3/11/2006, you wrote: As it turns out, I have a questionable test cable. Either that or I have an attenuator turned on in my test set that I'm not aware of. I'm still learning how to use this HP8920. I removed the cables from the cavity and connected them together and my measured input was 1.75-2.0 db lower than the set output. In other words, the output is set at -15.0 dbm. The unit displays the received level at -17.0 dbm. Someone else mentioned adjusting the coupling loops. On this particular cavity, they don't appear to be adjustable. Both connectors are mounted on the same plate. There are no screws to loosen to allow the conector/loop assembly to rotate. Jamey Wright KD4SIY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] Behalf Of Eric Lemmon Sent: Friday, March 10, 2006 11:40 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Bandpass Cavity Insertion Loss Jamey, If your measurement is accurate, 3.2 dB insertion loss is excessive. A single bandpass cavity performs best when its insertion loss is between 0.5 and 1.0 dB. How are you measuring this? If you are using a spectrum analyzer with an accurate frequency reference, the preferred method is to put a barrel (double female) adapter between the two test cables and set the reference cursor to zero dB. Then remove the barrel and connect the test cables to the cavity. You can then read the insertion loss directly. If you're using the bandpass filter on the receive side, no more than 1.0 dB IL should be used. If you're using the filter on the transmit side to eliminate spurs or harmonics, 0.5 dB IL will usually be fine. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jamey Wright Sent: Friday, March 10, 2006 8:12 PM To: repeater-builder@yahoogroups.com Subject: [Repeater-Builder] Bandpass Cavity Insertion Loss I just got through tuning up a Phelps Dodge VHF bandpass cavity. The measured loss through this thing is 3.2 dB. I am generating at -10 dBm. The level measured on the output is -13.2 dBm. It is a Phelps Dodge VHF bandpass cavity but I can't find a model number on it. Is this amount of loss normal? Thanks in advance. Jamey Wright KD4SIY Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Bandpass Cavity Insertion Loss
--- Jamey Wright [EMAIL PROTECTED] wrote: I just got through tuning up a Phelps Dodge VHF bandpass cavity. The measured loss through this thing is 3.2 db. I am generating at -10 dbm. The level measured on the output is -13.2 dbm. It is a Phelps Dodge VHF bandpass cavity but I can't find a model number on it. Is this amount of loss normal? Thanks in advance. Jamey Wright KD4SIY It seems high by about 1 db or so. That is unless it has the high selectivity option, then it is about right for the 6 cavity filter (3 on each side). __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Bandpass Cavity Insertion Loss
If this is a single cavity, i.e. NOT a duplexer, then I would expect 0.5 to 1.0dB loss, especially if you can't adjust/rotate the coupling loops. This is also after taking into account any cable and connector losses. Bob M. == --- Ralph Mowery [EMAIL PROTECTED] wrote: --- Jamey Wright [EMAIL PROTECTED] wrote: I just got through tuning up a Phelps Dodge VHF bandpass cavity. The measured loss through this thing is 3.2 db. I am generating at -10 dbm. The level measured on the output is -13.2 dbm. It is a Phelps Dodge VHF bandpass cavity but I can't find a model number on it. Is this amount of loss normal? Thanks in advance. Jamey Wright KD4SIY It seems high by about 1 db or so. That is unless it has the high selectivity option, then it is about right for the 6 cavity filter (3 on each side). __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
RE: [Repeater-Builder] Bandpass Cavity Insertion Loss
Jamey, If your measurement is accurate, 3.2 dB insertion loss is excessive. A single bandpass cavity performs best when its insertion loss is between 0.5 and 1.0 dB. How are you measuring this? If you are using a spectrum analyzer with an accurate frequency reference, the preferred method is to put a barrel (double female) adapter between the two test cables and set the reference cursor to zero dB. Then remove the barrel and connect the test cables to the cavity. You can then read the insertion loss directly. If you're using the bandpass filter on the receive side, no more than 1.0 dB IL should be used. If you're using the filter on the transmit side to eliminate spurs or harmonics, 0.5 dB IL will usually be fine. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jamey Wright Sent: Friday, March 10, 2006 8:12 PM To: repeater-builder@yahoogroups.com Subject: [Repeater-Builder] Bandpass Cavity Insertion Loss I just got through tuning up a Phelps Dodge VHF bandpass cavity. The measured loss through this thing is 3.2 dB. I am generating at -10 dBm. The level measured on the output is -13.2 dBm. It is a Phelps Dodge VHF bandpass cavity but I can't find a model number on it. Is this amount of loss normal? Thanks in advance. Jamey Wright KD4SIY Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Bandpass Cavity Insertion Loss
Make sure the coupleing loops are rotated correclty. On 3/10/06, Eric Lemmon [EMAIL PROTECTED] wrote: Jamey, If your measurement is accurate, 3.2 dB insertion loss is excessive. A single bandpass cavity performs best when its insertion loss is between 0.5 and 1.0 dB. How are you measuring this? If you are using a spectrum analyzer with an accurate frequency reference, the preferred method is to put a barrel (double female) adapter between the two test cables and set the reference cursor to zero dB. Then remove the barrel and connect the test cables to the cavity. You can then read the insertion loss directly. If you're using the bandpass filter on the receive side, no more than 1.0 dB IL should be used. If you're using the filter on the transmit side to eliminate spurs or harmonics, 0.5 dB IL will usually be fine. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jamey Wright Sent: Friday, March 10, 2006 8:12 PM To: repeater-builder@yahoogroups.com Subject: [Repeater-Builder] Bandpass Cavity Insertion Loss I just got through tuning up a Phelps Dodge VHF bandpass cavity. The measured loss through this thing is 3.2 dB. I am generating at -10 dBm. The level measured on the output is -13.2 dBm. It is a Phelps Dodge VHF bandpass cavity but I can't find a model number on it. Is this amount of loss normal? Thanks in advance. Jamey Wright KD4SIY Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
