EMRFD Message Archive 9205
Message Date From Subject 9205 2013-10-03 20:24:29 prysm678 w7zoi Spectrum Analyzer specific questions Hi all
I built a spectrum analyzer based on Wes's and Terry's 1998 QST article. I had to make a few changes due budget reason some of which turned out to be headaches.
Anyway it is now working much better now than before it is not however as good as the original so I wanted to find out if it can be improved.
So my questions
1. Is it normal for my noise floor changes when I adjust the IF gain?
2. Using ladpac cascade.exe at 300kHz RBW I am suppose to have an MDS of -104dbm, but so far I only get -94dbm of usable display.
3. I also see a few small spikes -88 to -85dbm that randomly pops out every so often is this due to a noisy 2nd LO or IF filter rejection?
4. I am also seeing only a small thin noise floor instead of the thick line that w7zoi.net is showing.
9211 2013-10-04 13:39:25 w7zoi Re: w7zoi Spectrum Analyzer specific questions
2. Your -94 implies a noise figure of about 25 dB. That's normal for a SA. You didn't state any assumptions you made in CASCADE.
3. Probably spurious responses from local VHF signals.
4. You have too much video filtering. What is the cap
9213 2013-10-04 18:43:08 prysm678 Re: w7zoi Spectrum Analyzer specific questions
I am not sure if you realized this, but I am the guy that has been bugging you about this for a few weeks ago. I just received my copy of the EMRFD and realized there was a mailing list dedicated to it.
I am using the latest ladpac 2008. here is my input for cascade.exe
1. mix1 - ADE1-ASK Gain = -6.5 NF = 6.5 IP3 = 15
2. mmic1 MMG3007 Gain 18 NF = 3.8 IP3 = 30
3. 1st filter Gain -10 NF 10 IP3 = 100
4. mix2 AD1-ASK Gain = -6.5 NF = 6.5 IP3 = 15
5. amp1 Gain 20 NF = 6 IP3 =30
6. 2nd filter Gain -12 NF 12 IP3 = 100
7. IF amp AD603AQ Gain = 30 NF = 8.8 IP3 = 15
Bandwidth = 300000
As you can see I am not using a highlevel mixer and most of the minicircuits parts I replaced. I also configured ad603 with bandwidth of 30Mhz because I am using an IF of 25Mhz.