First Time tuning a MSF

krazybob · Post by **krazybob** » Sun May 25, 2014 7:46 pm

I have several MSF 5000's VHF 110 watts. They are complete and at least two are known to be working. O told my elmer that I wanted to learn how to tune them and well, he won't return my calls now.

I have the tuning manual but I don't know how to use the MSF RSS yet. I have the test set plugged in along with the CAT5 cable but I hear nothing when I key up a HT. I can hear the MSF when I manually key it. I am connected to a 200 watt Celewave dummy load and nothing on the RX port.

The tuning manual indicates to get to mode 0, channel 0 (I only have one channel programmed).

I need to know how to 1) get this into 0/0 2) sound coming out of the speaker so that I may tune.

Humbly, your student...

Bill_G · Post by **Bill_G** » Sun May 25, 2014 9:00 pm

You need the MSF test panel.

Read up about MSF's at Repeater Builder

krazybob · Post by **krazybob** » Mon May 26, 2014 1:06 am

Thank you but you must have missed it above where I wrote, "I have the test set plugged in along with the CAT5 cable but I hear nothing when I key up a HT." It happens

I appreciate you, Bill.

I solved the problem by wiggling connectors not likely used in some time. I know have audio. But I also have a 1 beep tone not over the air every 10- seconds. The unit has battery back-up capability but no batteries connected. At boot-up I get a E40, E41, and E49 but then - - - and the repeater functions normally. E40 is RX loop, E41 is TX Loop and E49 is RX Synthesizer Lock.

I AM using the docs the best that a rookie can. I am *assuming* that these are boot-up conditions that are clearing? As for the 1 beep every 10 seconds it doesn't come OTA. But I know that its there. I'd say that this is like pulling out my hair but I don't have any! When my daughter was diagnosed with cancer I shaved it to honor her life and left it that way. A fair trade!

Frustrating nontheless.

Bill_G · Post by **Bill_G** » Mon May 26, 2014 5:01 am

Oh no. I saw that. I needed to make sure we were on the same page. Read the Repeaterbuilder article.

krazybob · Post by **krazybob** » Wed May 28, 2014 12:44 am

I actually read the article before posting. It turns out that the contacts were dirty and after using an eraser head and some elbow grease I was able to get sound from the station.

I've searched Google and RB for the answer but I don't find anything on testing SINAD. I have cables made up for 1/8", 1/4" and alligator clips that plug directly into my HP Agilent 8924c. A very nice service monitor once the learning curve has been beaten down.

But here's a total green horn question. I have three MSF's and all three have hot receivers in the -126dBm range. But that is down at the grunge range. I mean who wants to listen to an HT that can hold the machine but is so noisy that people stop listening. As a green horn rookie I'll just ask -- do most of you tune for like -107dBm to -115dBm for 12db SINAD or some other range? I also have a Angle Linear dual band pass cavity that includes a 17dB preamp. But that seems like overkill and unnecessary if the MSF is already so hot on the receive. Comments?

kcbooboo · Post by **kcbooboo** » Wed May 28, 2014 3:33 am

There's a 500uF electrolytic axial-lead capacitor on the SSCB, right behind the CTRL jack. The negative end goes to the jack where it drives a headphone or small speaker (it's only got a 1/2 watt amplifier). You can connect your SINAD meter to that end. There's a nearby Analog Ground (A.G.) test point you can use for ground. The front panel VOL control will control the level; set it about half-way to give your SINAD meter a sufficient input level.

Most Motorola systems are set up for 20dB quieting to open the squelch. That's a very clean signal. Hams are usually more tolerant of noisy signals and set the squelch at threshold or just a couple of dB quieting. Your mileage may vary. PL/DPL usually overrides the squelch setting but this is not universally done in all radios.

Bob M.

Bill_G · Post by **Bill_G** » Wed May 28, 2014 4:36 am

krazybob wrote:I actually read the article before posting. It turns out that the contacts were dirty and after using an eraser head and some elbow grease I was able to get sound from the station.

I've searched Google and RB for the answer but I don't find anything on testing SINAD. I have cables made up for 1/8", 1/4" and alligator clips that plug directly into my HP Agilent 8924c. A very nice service monitor once the learning curve has been beaten down.

But here's a total green horn question. I have three MSF's and all three have hot receivers in the -126dBm range. But that is down at the grunge range. I mean who wants to listen to an HT that can hold the machine but is so noisy that people stop listening. As a green horn rookie I'll just ask -- do most of you tune for like -107dBm to -115dBm for 12db SINAD or some other range? I also have a Angle Linear dual band pass cavity that includes a 17dB preamp. But that seems like overkill and unnecessary if the MSF is already so hot on the receive. Comments?

For general operation, nobody deliberately mistunes their receivers to set the receive threashold. You tune for best, and then set squelch for the appropriate quieting for your system. People would kill for a receiver system that worked down to -126db with 12db sinad. -118db to -114db is the typical sensitivity. Factor in site noise floor/ effective sensitivity, and you're feeling lucky that you get -114db sometimes.

Rcvr preamps are used to overcome known losses. ie: cavities, filters, multicouplers, etc. They don't necessarily solve problems, and they sometimes cause problems if they become saturated, or if they drive following stages into saturation.

MSS-Dave · Post by **MSS-Dave** » Wed May 28, 2014 5:04 am

Somewhere in my pile I may still have the pictorial that Motorola Engineering sent me years ago showing exactly what Bob is describing. I don't know if it's up on RB though. If I can find it I will share if helpful.

The Angle Linear cavity is great but you have to be careful with the final input level to the receiver. It's hot already if working right, too much gain will just overload it and make your noise floor across the band stupid high. I used ARR GaAs FET preamps on 440 and 900 MHZ MSF's with preselectors and found optimal gain versus noise floor tradeoff at between 5 and 10 dB. The amp makes 20 + so padding was in order. I could get 0.25uV (-119 dBm) @ 12 DB SINAD on most of the UHF boxes directly into the receiver. 900 machines were more like .35uV. Personally, I have never tested a VHF MSF receiver, mostly worked on PURC5000 and Nucleus.

With careful placement of filters, amps and pads along with doing SINAD testing, you could meet or beat these numbers on most sites. My best sites had 3-5 dB of "site noise" as I called it. A couple were in the 15-20 dB range and the repeater could not tolerate any gain in the RX system at all. In trunked systems where I used a RX multicoupler and a tower top amp, best net gain usually happened at 1-3 dB.

Sorry if I went way beyond the OP's question..... 3 cups of coffee = blah blah blah

krazybob · Post by **krazybob** » Fri May 30, 2014 8:05 am

I sure didn't mean to imply that I would detune the radio. Absolutely not! As you've indicated one can set the squelch opening at a specific uV. The only reason to use a preamp is the use of a Angle Linear dual band pass cavity and a DCI 4 cavity band pass filter. Combined they add about 1 dB insertion loss but the Angle Linear actually creates a 1MHz window in which the RX frequency is center tuned. Loss is minimal. I may be able to remove the DCI once I tune the MSF now that we know that contrary to my knowledge it wasn't tuned. Too many cooks in the kitchen; too many irons in the fire.

Thank you for your replies. I appreciate all of you and your wisdom. I may be slow on the uptake only because of my desire to understand what it is that I am doing rather than just doing it because I have been told to do it

As for the SINAD measurement, thank you! I searched Google over and over and found nothing. I was thinking of adding an 1/8" mono jack to the station tester and pulling audio of of there. In my mind it is no different that plugging into a mobiles speaker jack. Your thoughts are important to me.

Bill_G wrote:
krazybob wrote:I actually read the article before posting. It turns out that the contacts were dirty and after using an eraser head and some elbow grease I was able to get sound from the station.

I've searched Google and RB for the answer but I don't find anything on testing SINAD. I have cables made up for 1/8", 1/4" and alligator clips that plug directly into my HP Agilent 8924c. A very nice service monitor once the learning curve has been beaten down.

But here's a total green horn question. I have three MSF's and all three have hot receivers in the -126dBm range. But that is down at the grunge range. I mean who wants to listen to an HT that can hold the machine but is so noisy that people stop listening. As a green horn rookie I'll just ask -- do most of you tune for like -107dBm to -115dBm for 12db SINAD or some other range? I also have a Angle Linear dual band pass cavity that includes a 17dB preamp. But that seems like overkill and unnecessary if the MSF is already so hot on the receive. Comments?
For general operation, nobody deliberately mistunes their receivers to set the receive threashold. You tune for best, and then set squelch for the appropriate quieting for your system. People would kill for a receiver system that worked down to -126db with 12db sinad. -118db to -114db is the typical sensitivity. Factor in site noise floor/ effective sensitivity, and you're feeling lucky that you get -114db sometimes.

Rcvr preamps are used to overcome known losses. ie: cavities, filters, multicouplers, etc. They don't necessarily solve problems, and they sometimes cause problems if they become saturated, or if they drive following stages into saturation.

kcbooboo · Post by **kcbooboo** » Fri May 30, 2014 9:19 am

Regarding external preamps on MSF5000s: most of the preamps out there provide WAY TOO MUCH GAIN, something on the order of 15-18dB. If you connect one to an MSF5000, it'll look really great on the bench and your sensitivity will be out of this world, but once you connect it to the duplexer and antenna, it'll also amplify the noise and other stuff that you don't want.

The station can survive with 3-6dB of gain ahead of it; any more than that and you'll be in trouble. If you put all your filtering ahead of the preamp, and add a 10dB pad to the output on the way to the MSF5000, that'll be just enough gain to make up for all the coax, connector, and filter losses and give you a few db of gain.

Back in the 70s, Motorola made a preamp for the Micor radios. It provided a whopping 6dB of gain. That got the receiver from 0.5uV to 0.25uV. Most radios can't handle much more than that.

Bob M.

krazybob · Post by **krazybob** » Fri May 30, 2014 9:55 am

I calculated 3-6dB gain as beneficial. I have a 17dB from Angle Linear as well as attenuators. I can but a 10dB attenuator on it but where is the best place to put it? Before the preamp; after?

Bill_G · Post by **Bill_G** » Fri May 30, 2014 4:28 pm

krazybob wrote:I calculated 3-6dB gain as beneficial. I have a 17dB from Angle Linear as well as attenuators. I can but a 10dB attenuator on it but where is the best place to put it? Before the preamp; after?

Depends.

If you have 3db of constant site noise, it's okay to put a small pad before the preamp to keep that noise from saturating the preamp. If it's a clean site with very little noise, it's best to put it after the preamp to prevent it from overdriving the first stage in the radio. Sometimes you put in two pads - one before to knock down the site noise, one after to knock down the preamp into the radio.

Generally, preamps are only applied when you are driving a multicoupler to make up for the losses. You put a pad before the preamp to limit site noise, and you let the losses of the multicoupler pad the preamp into the attached receivers.

krazybob · Post by **krazybob** » Fri May 30, 2014 4:41 pm

Thank you for the reply, Bill!

I assume that the preamp goes after the band pass cavities that are needed and then a pad between the preamp and the radio. As you know the MSF's have excellent receive. Once I get everything tuned up tomorrow I'll have a better idea of how much the RX drops down.

But more importantly I am still wondering of there is a test point that I can connect the spectrum analyzer to so that I can see what the radio sees after the preselector. I don't know any other way of knowing if the FM broadcast junk is really there. I know that it is if I just plug the Station Master into the SA but not after the dual band pass cavities. I'd like to remove them but I see other repeaters in the vault that are running the DCI filters suggesting that they are having a problem. Then again they are using variants of GM300's to build a repeater. A MSF is a horse of a different color! It's a real repeater

Bill_G · Post by **Bill_G** » Fri May 30, 2014 6:49 pm

I've never had to tear into a MSF that far. All mine were 800M trunking stations at public safety sites.

kcbooboo · Post by **kcbooboo** » Sat May 31, 2014 3:15 am

krazybob wrote:

But more importantly I am still wondering of there is a test point that I can connect the spectrum analyzer to so that I can see what the radio sees after the preselector. I don't know any other way of knowing if the FM broadcast junk is really there.

See this reply to one of your previous posts where you asked the same question:
http://batboard.batlabs.com/viewtopic.p ... 88#p475786

Bob M.

krazybob · Post by **krazybob** » Sat May 31, 2014 3:22 am

Aw dang, KCBooBoo! Now I really look stupid is as stupid does...

Thank you. I had missed that reply somehow or my brain farted.

krazybob · Post by **krazybob** » Mon Jun 02, 2014 12:45 am

I don't appear to have made any progress. In fact I think I have a deaf receiver. This is odd because the repeater was at my home (150 feet lower than the mountain that the commercial site is on and covering only about 270°) on an 85 foot tower. I was doing exceptionally well with a .15uV sensitivity. All that we did was gently move the MSF and now I can't get the sensitivity better than .45uV.

I also seem to have run into a contradiction in the MSF tuning process.

L7,L8 andL9 are all set to maximum level obtained on the meters after several passes.

The next step was to terminate the pre selected by connecting a 50 ohm load to the preselector input I.E., the RX connector on the side. I forgot my little 60 watt dummy load so I connected my 200 Watt Cellwave dry dummy load.

The next and final step was to put a signal generator on frequency and put the probe into J1. I set the signal generator for 1mV, which is .47uV and I set the meter to position 2 and tuned for 25 to 35 uA's on the metering panel without difficulty. Tuning L10 and L11 until meter 2 indicated a maximum level was also no trouble.

Tuning the preselector was where I had problems. L1 and L2 tuned fine. But tuning L3, L4, and L5 for a MINIMUM signal as stated in the manual was wrong. I started with a MSF at -112dBm and by ear got it to -114dBm. Tuning for a minimum caused me to lose the signal. Previously we had -121 to -122dBm.

So where did I go wrong and what might be causing the piss poor RX??? All we did was move it. Before leaving I had already packed the truck up and had the thought that I'd add the Angle Linear band pass cavities with the 17dB GasFET preamp that creates a 1MHz window.

Adding 17dB to -114dBm gives me what? -131dBm? As I recall 17dB is just a relative number but I don't know how this adds in now.

Humbly Yours,

Bill_G · Post by **Bill_G** » Mon Jun 02, 2014 4:01 am

Sounds like MSF hairs - molecular strands of plating from the housing to the coils, circuit board, etc. Blow out the VCO coils and presel with canned air. Open up the RF section, take the big metal cover off, wipe the inside of the cover with a rag, reassemble. The cover is particular about how much tension you put on the screws - think Goldilocks - not too tight, not too loose - just right. If you do it right, pressing on the cover does *not* cause noise in the rcvr / xmit.

Then you get to do an abbreviated version of the alignment again. Woohoo!

kcbooboo · Post by **kcbooboo** » Mon Jun 02, 2014 4:12 am

It sounds like you didn't follow the tuning instructions TO THE LETTER. Read the procedure. Now go back and read it again. You'll find there's stuff "between the lines". You skip some steps for some bands. Don't omit anything unless told to. There are probably several alignment procedure PDF files around on the web; some are more detailed than others. There is a 5MB PDF file on repeater-builder, Motorola area, MSF&PURC section, that has all the steps for all the bands.

You must start by backing out L1-L5, injecting a signal through the tuning probe into the hole between L1 and L2, peaking L1, then tuning L2 for a minimum. Once you get to that point, move the tuning probe to the next hole and tune ONLY L3 for a minimum. You may have to increase or decrease the input signal as you go, to keep the meter at 20-25 maximum, with the minimum in the 10-15 range. The tuning of the coil to the right of the probe should be a very sharp dip and easy to see. Keep moving the probe to the right and tuning the core after it for a minimum. DO NOT GO BACK and retune anything unless the instructions tell you to do that. If you retune anything to the left of the tuning probe, you'll end up chasing your tail as all of the coils interact. Follow the steps in order. Tuning the front end should take about 45 seconds; if you spend more time on it than that, your not doing it right.

I'm very sure that the alignment procedure is correct. There are an awful lot of MSF5000s out there and they all tune perfectly when the procedure is followed completely and exactly.

Bob M.

krazybob · Post by **krazybob** » Mon Jun 02, 2014 7:28 am

Thank you Bill and Bob. For the record I am tuning a VHF band 1 (158) and I am using the instructions from repeater builder.

Referring to page 4-12 it indicates that L3 and forward are ALL tuned for minimum but my experience was that I had to tune L4 and L5 for a peak or I lost the signal If I have done something wrong I'll do it again. Several times my SM warned me of signal overload and I had to hit RESET.

I would much rather be humble and tell each of you of my experience. You are each taking your time to help me and although I may be partially confused your help is invaluable.

I'll get some compressed air and go looking for "whiskers". LOL.

Thank you all. I appreciate each of you.

Bob

MSS-Dave · Post by **MSS-Dave** » Mon Jun 02, 2014 8:59 am

Make sure the VCO cans aren't locked down in transport. I don't remember if it made any difference on my UHF and 900 stations but something to check...

Dave

krazybob · Post by **krazybob** » Mon Jun 02, 2014 9:42 am

Thank you, Dave. According to the manual the VHF does not require the VCO's to be locked down for transport but there are coarse tuning instructions at this step.

I have a 60 watt Cell Wave load that accepts a Type N to RF Mini that I can plug directly to the preselector for tuning. Is this acceptable?

kcbooboo · Post by **kcbooboo** » Mon Jun 02, 2014 10:59 am

Any 50 ohm load will work, but it's usually easiest to leave all the cables connected and attach the load to the ANT connector on the side of the station. DISABLE the station so it can't transmit.

You insert the tuning probe into the first hole and peak the coil to its left. You adjust the coil to its right for a minimum meter indication. You then move the tuning probe to the next hole to the right and adjust the coil to its right for a minimum meter indication. You do this all the way across. Adjust the sig gen as you go if necessary so the un-tuned signal is around 20-30 and the signal at the minimum is still visible, around 15 or so. If you don't use enough signal, you won't find the true minimum tuning point.

Bob M.

krazybob · Post by **krazybob** » Tue Jun 03, 2014 7:35 am

The help from all of you is immeasurable and I know that "whiskers" wasn't just made up. LOL. But what about the manual telling me to set L3, L4, and L5 for MINIMUM when I found just the opposite 2- tuning for maximum - achieved a higher signal level?

I'll do it all over again.

Now then, when instructed to remove the VCO cover I was warned to unromantically reattach the cover as as screw tension. Should I be using a torque wrench, hand tight, hand tight plus 1/4...

I'm a greenhorn trying his best and dealing with an older radio.

krazybob · Post by **krazybob** » Tue Jun 03, 2014 7:08 pm

With respect given to all that are trying to help me I AM following the instructions. They are not difficult. When I get to the preselector I insert the tuning probe into J1 and tune L10 and L11 for MAXIMUM.

I adjust L1 to MAXIMUM and L2 to MINIMUM.

I then move the probe to J2/L3and tune for MINIMUM. J3/L4 for minimum. J4/l5 for minimum. Therein is the problem. When I tune for MINIMUM I lose the signal. I am reading page 4-12 verbatim. Whereas if I tune for MAXIMUM I was able to get more signal strength.

I hate being the FNG. I will keep trying.

kcbooboo · Post by **kcbooboo** » Wed Jun 04, 2014 1:26 am

The minimum should be a very sharp and noticeable dip. There may be another point where you're just so far away from the right spot that the signal level is reaching a minimum. That's not the right place. If you preset the tuning coils as specified, which is extracted almost all the way, you then turn them clockwise and watch M2 as you go. L1 should show an increase in the signal level. If the meter goes above 30, reduce the input signal. As you then tune L2, the signal will go through a sharp dip that should reduce the meter indication by about 10. When you get to that point, you only have about half a turn to go from maximum to the minimum for the dip, so rock L2's tuning back and forth for that minimum point. Move the probe to J2 and turn L3 clockwise and go for the same 10uA dip. etc. Try to keep the meter in the 20-30 range before you start tuning any of the front-end coils; that way you'll see the 10uA dip. With too much signal, you could miss it.

What frequency are you trying to receive? What's the band-split of the station: 136-162 or 146-174?

Bob M.

krazybob · Post by **krazybob** » Wed Jun 04, 2014 1:45 am

Excellent advice, excellent! My SM beeped numerous times indicating overdrive, I did preset the coils to 3/4" as specified on page 4-12 but I'll reset them and start over. If anything I'll get to know this machine quite well. I am a type 1 station in the amateur band.

If only they had placed the receiver on the top and the heavy power supply / PA on the bottom... like a paper weight. LOL.

Thanks, Bob.

Bob

krazybob · Post by **krazybob** » Wed Jun 04, 2014 9:18 am

One more question: I have to drive off the mountain that I live at -- I live on a repeater site LOL - and hit Home Depot at the bottom for compressed air. No Biggie.

But to clean the whiskers out it says to take care of how tight the screws are for the VCO cover for my VHF station (band 1). Do I need a torque wrench, hand tight, hand tight plus 1/2 turn?

Thank you, all of you. I sincerely appreciate you let me learn and grow with this experience.

kcbooboo · Post by **kcbooboo** » Wed Jun 04, 2014 9:52 am

Hand-tight is fine. Most of the hardware is Torx T10, T15, and T20. Just use two fingers to hold the driver and make the screws tight.

I would expect for a range-1 station that you'd have to turn the front-end tuning slugs in probably 3/8 inch before you'll see anything. Since it's easy to see the peak on L1, the rest should be at about the same depth or within 1/16 inch of each other.

Bob M.

krazybob · Post by **krazybob** » Sun Jun 08, 2014 2:50 am

Okay. Great!

I don't want to belabor this but tomorrow is return day to the site. I recall my first attempt tuning there were no sharp peaks -- I mean there wasn't a gradual rise and then a sudden drop-off. The same with the minimums. Is that what I should be looking for? I really appreciate all of you. My Elmer has been called away and I have a favored repeater that isn't doing as well as it could. It used to have a smoking hot receive and HT's were a breeze. Now they seldom get in.

The key symptom is that PL opens but more often than not there is no audio. Sometimes there's picket fencing. My home is only a couple of blocks below the repeater site (the repeater used to be here on my 85 foot tower and a side-mounted DB224e antenna) and I can hear them fine most of the time on the input using a FT-847. I went to Holmes Depot (yes, Holmes Depot -- Cheech Marin Salesman, "Eh Holmes. It looks like you could use a friend. You should call a friend to help you, eh?) and bought a small, metal ruler so that I can measure exactly 3/4" from the chassis to the end of the screw. I am serious about getting this right!!! I'll back everything out and set the generator for less tan 1mV. I noted that it indicated overdrive easily last time. I use a HP Agilent 8924c service monitor with PL encode set but as I recall the tuning instructions has me disable PL. But I want this sonamebeach opening squelch at .10uV when I am done! The only thing saving grace for me right now is an Angle Linear 17dB preamp.

As for blowing out the whiskers, I bought some compressed air. Will I need to retune the VCO? I don't want to get in over my head.

To complicate my life theres a "remote base" owner that was at the site before me. He has built a cross band repeater that uses 440 to talk in and out on 146.520 calling channel. He is *****ing that my Station Master was mounted too close to his antenna. He is using GM300/Radius/Maxtrac's. He is alleging that I am even taking out his 52.525 calling channel! I know that the MSF isn't dirty. If one uses crap with a plastic case one gets crap. He had it easy until I showed up with 1) a contract for top mounting on the tower, 2_ a coordinated repeater for the site, and 3) 47 CFR 97.205 on my side. He calls it a remote base but as far as I am concerned it is a cross band repeater. When .52 keys up it down links on 440 and vice versa. It may be semi-duplex but...

kcbooboo · Post by **kcbooboo** » Sun Jun 08, 2014 4:56 am

There is nothing to tune on the VHF VCOs.

Note the reading on M2 with no signal. It should be around 10 but each station is different. Set your sig gen output level for a reading of about 10-15 uA HIGHER than the idle value. The actual sig gen output level is not important. 1 mV is just a good starting point but you could need more or less. Go by the M2 indication.

As you tune L1 toward its peak, M2 will rise. Adjust/reduce the sig gen output level to try to keep the M2 metering around the same 10-15 uA higher than the idle value. The peak of L1 will be broad but there will be an increase followed by a decrease as you turn it CW. Rock it back and forth until you get the maximum indication. You want to keep M2 in its most sensitive range, which is 10-15 uA higher than the idle value. Only adjust the sig gen output value if M2 goes out of that range.

Once you get the peak with L1, set the sig gen for that same 10-15 uA higher than the idle value on M2 and start turning L2. You may not see anything for a while but there WILL be a sharp dip that you might miss, as it could be 1/4 turn to see it then not see it. Adjust L2 for that dip; it should be 5-10 uA less on M2. You can rock it back and forth until you get to the center of that dip.

Move the tuning probe to the next hole to the right of L2. Again, adjust the sig gen for that same 10-15 uA above the idle value on M2 and start tuning L3 for that same sort of dip. The tuning cores should all be around the same depth, probably within 1/16 inch of each other.

The "dip" here will have higher M2 values on each side of it. This may not be the "minimum" value which you could get if the tuning is way off. You can mis-tune the front end and find minimum values that are lower than the dip values. When you tune the core on the right side of the tuning probe, that tuning section absorbs the signal when it hits resonance, hence the M2 reading goes lower because less signal is reaching the rest of the receiver.

The 3/4 inch preset length is not critical unless your station is on a frequency very close to the low end of the receiver's range. They just want to make sure you tune for the correct spot.

Bob M.

krazybob · Post by **krazybob** » Sun Jun 22, 2014 3:41 am

Medical issues required me to take some time off to be with my sick daughter. I'm back at it and my Elmer will be meeting me Monday or Tuesday to try and get this baby up to spec.

I mentioned opening the VCO and blowing out pin whiskers and he yelled "WHAT???" He knows of pin whiskers in the preselectors but not the VCO. He eats and sleeps MSF's so I figured maybe I misunderstood.

Blow pin whiskers out of the VCO's and preselectors?

Thank you all. I appreciate you.

Bob

kcbooboo · Post by **kcbooboo** » Sun Jun 22, 2014 4:22 am

Any RF casting that's tin-plated can have tin whiskers growing inside it. This includes, but is not limited to:

the RX front end
the RX VCO
the TX VCO
the RX injection filter
the internal filter-duplexer (for UHF repeater stations)

Whiskers in the VCO are not likely part of your problem however.

Bob M.

krazybob · Post by **krazybob** » Tue Jun 24, 2014 2:02 pm

HAPPY DAYS! After all said and done we've got .12uV at 20dB quieting. WOW!

kcbooboo · Post by **kcbooboo** » Wed Jun 25, 2014 4:30 am

Could you tell us what changed (procedure, personnel, etc) that resulted in your success?

Bob M.

krazybob · Post by **krazybob** » Wed Jun 25, 2014 12:27 pm

Removing and opening the preselector and blowing out the pin whiskers.

Bill_G · Post by **Bill_G** » Wed Jun 25, 2014 7:18 pm

Yep. Been there, got the tee shirt, worn it out. Insidious little problem. Glad you got 'er going.

krazybob · Post by **krazybob** » Wed Jun 25, 2014 9:04 pm

Actually we got tone down to .07uV. But we got 20dB quieting at .12uV. Awesome! Now to connect Allstar... Our biggest fear is HT users will come to expect miracles all the time.

krazybob · Post by **krazybob** » Fri Jun 27, 2014 2:21 am

By the way, our success is in large part due to the advice given in this thread. I am extremely grateful. As a result I am going to preemptively pull the preselector on our two remaining MSF's before taking them to their sites.

Thank you all that shared!

MSS-Dave · Post by **MSS-Dave** » Sun Jun 29, 2014 7:32 pm

krazybob wrote:Actually we got tone down to .07uV. But we got 20dB quieting at .12uV. Awesome! Now to connect Allstar... Our biggest fear is HT users will come to expect miracles all the time.

Are you getting these numbers directly into the receiver from the SG or through your cavity preamp setup you described in the earlier posts? Glad you were able to find the whiskers were the problem.....

Dave

krazybob · Post by **krazybob** » Tue Sep 09, 2014 11:23 pm

The figures were with the the duplexer and Angle Linear preselector out of line.

I am very disappointed after hours of work. It seems that their remains a "haze" across the input. I don't know if it is Heap's Peak and the FM transmitters with antenna down tilt right into our antenna, or if it is the Verizon equipment right below us.

The FM transmitter of 99.1MHz has an antenna located at 142 feet on their tower. They are obviously using down tilt to get their into the Inland Empire and the high desert on the other side. Our antenna is at 85 feet and has an 18 degree vertical beam width. That suggests that kilowatts are being directed right into our receive. We are 1.2 miles away from Heap's Peak. Heap's is notorious.

I don't get it! If I use an Angle Linear dual cavity preselector tuned for our input it seems to me that the noise floor should drop by 90dB. That's been measured and is what Angle Linear quotes. It creates a 1MHz window around the RX input. The receive is tuned right on the money. Before we moved the repeater to a commercial site the antenna was a side-mounted DB224e that provided awesome HT coverage of So. Calif. An HT was picked up in Palm Springs as it traveled west to Redondo Beach just below Santa Monica where our signal then was 40 over. The HT was full quieting from a 2nd floor apartment at the waters edge. The results in between varied along the parking lot freeway known as the 91 but came right back up. We never lost the signal. We are 1.7 miles away from Heap's but still LOS. Now we cannot hear an HT to save our souls. Even a 50 watt mobile using a unity gain antenna 50 miles away is just above the squelch.

Am I dealing with Heap's or Verizon?

Here is the symptom. A user will key the repeater but no audio or broken audio is present. I am .56 miles from the repeater and at an altitude of 6150 feet. Using my FT-847 with excellent 2 meter RX and a Hustler G7-144 fed with LMR-400 and I often hear the mobile or HT at varying signal levels. I can work San Diego with arm chair copy. I can switch to flip-flop reverse and work the station directly as if I were the repeater. Even if they are S1 I can usually work them. But the repeater just keys on and off. You know that someone is there but they just cannot open the door. Am I dealing with the squelch being too high? My elmer is a die hard commercial guy that insists on operating on commercial terms. His position would be that a commercial repeater is not expected to cover 110 miles as we did before moving the repeater from my home. We had awesome coverage over 270 degrees. I wanted 360 degrees. I got it at a high cost.

So where do I go from here? My SM only goes to 1GHz so I can't see if Verizon is contributing or the sole cause. But even if the squelch were lowered the "haze" would still be there. I have a DCI 4-cavity filter that creates a 1MHz window across the 2m band at 90dB. Suppose I put that in front of the Angle Linear and create a funnel. 4MHz -> 1MHz -> great signal? I wonder what Verizon's local oscillator frequency is.

MSS-Dave · Post by **MSS-Dave** » Wed Sep 10, 2014 4:29 am

If you are reasonably sure that the 99.1 FM is causing the problem, make a 1/4 wave stub notch filter for 99.1 and put it in the RX line. May or may not work. Sure sounds like straight up RX overload to me.

Bill_G · Post by **Bill_G** » Wed Sep 10, 2014 5:20 am

Do a rx desense measurement so you quantify the amount of impairment you are experiencing. Then, any changes you make to address the problem can also be measured.

Receiver Desense Testing Procedure

krazybob · Post by **krazybob** » Wed Sep 10, 2014 7:18 am

MSS-Dave wrote:If you are reasonably sure that the 99.1 FM is causing the problem, make a 1/4 wave stub notch filter for 99.1 and put it in the RX line. May or may not work. Sure sounds like straight up RX overload to me.

A stub only gives us, what, 20dB? I have a full size cavity that can do that without leaving an exposed piece of coax in a room full of other transmitters. But I get your point. I seriously doubt 20dB is going to make any difference over a 90dB tuned filter. Would the stub come before the filter or after? I'm open to all ideas even if I sound skeptical.

krazybob · Post by **krazybob** » Wed Sep 10, 2014 7:40 am

I forgot to answer your question about 99.1MHz. We placed the service monitor on 99.1MHz and using a simple 1/4 test whip we measured -1dBm!!!! Let me type that again. -1dBm!!!! But I've also got a Verizon triangle right below me. I need to rule it out but I don't know it IF LO frequency.

MSS-Dave · Post by **MSS-Dave** » Wed Sep 10, 2014 4:00 pm

krazybob wrote:
MSS-Dave wrote:If you are reasonably sure that the 99.1 FM is causing the problem, make a 1/4 wave stub notch filter for 99.1 and put it in the RX line. May or may not work. Sure sounds like straight up RX overload to me.
A stub only gives us, what, 20dB? I have a full size cavity that can do that without leaving an exposed piece of coax in a room full of other transmitters. But I get your point. I seriously doubt 20dB is going to make any difference over a 90dB tuned filter. Would the stub come before the filter or after? I'm open to all ideas even if I sound skeptical.

I have built 1 and 2 stub filters around this design using RG213 and "N" TEE connectors.

http://www.hb9amo.net/fmcoaxialfilter.php

I second Bill's recommendation about the desense testing. The only real way to see what having the complete RX system hooked up to the receiver is doing. If you are getting -1 on a test antenna on the monitor of the 99.1 station, I would venture you are into +10 or more down the coax. I've seen +40 dBm at 469.8 on a receive line before. Came from a new DTV station 3 miles away under test. They had a bad mask filter on the transmitter that caused them a 6 month delay in turn up after the FCC shut them down.

Even with all the brute force filtering going on, there could still be enough energy to swamp the front end on the MSF since it is so hot. It's going to take time for sure to weed out all you could have going on there. I don't think an LO from cellular would appear but if enough energy is there, you could have images whacking you RX directly at the mixer in the RX.

IMHO, find the strongest signal(s) left on your RX line (at the input to the receiver after the filters) using the service monitor or a spec-an and try to knock that down as much as you can. Probably will be the FM station. The more out of band energy you can attenuate will be helpful in narrowing where your issue may be.

You indicated that you got .12uV@20 dB of quieting directly into the receiver. What do you get with all the filters and the cavity preamps in line? if you still get .12uV or even better for even 12 dB of quieting, there may be too much total gain going on with the combo of external amp and internal "hotness" for that high of RF site.

Dave

krazybob · Post by **krazybob** » Wed Sep 10, 2014 5:08 pm

Excellent suggestions from all.

Dave, we have .12uV before the filters and .18uV after the filters. That comes to about -125dBm I think. But that's the MSF that did fine at my home .5 miles away and 1.7 miles LOS from Heap's Peak. I am honestly not sure how much longer I want to fight this thing. I can just as easily move back to my home. There must be a reason there are few tenants in the repeater vault. I've lost so many users...

krazybob · Post by **krazybob** » Wed Sep 10, 2014 7:56 pm

I have no discernible spike after the Chip Angle preselector that creates the 90dB 1MHz window. I just talked to a user 50 miles away at S7 and the repeater should have her easily at 10 over S9. Yet she can barely hold the machine.

krazybob · Post by **krazybob** » Sat Sep 13, 2014 6:17 pm

It is looking more and more like a piezo crystal filter is the only remaining solution. It will have a loss of 3-7dB loss. A preamp afterwards is supposed to attempt to recover "some" of the loss.

krazybob · Post by **krazybob** » Sat Sep 27, 2014 7:35 pm

Well, we pulled the repeater possibly to soon today. We first checked the spec analyzer before everything. We then inserted the duplexer and saw a reduction in grunge. Lastly we inserted the Angle Linear band pass cavities and the grunge was further lessened. Even the output of 147.090 15KHz away from our input of 147.105 was acceptable -- until we located an uncoordinated repeater on 147.075 outpu8t -- 30KHz from our input.

The end result was that we returned the repeater to its original home. We repeated all of the tests and even with a Angle Linear dual band pass cavity in place followed by a 17dB preamp the grass has obviously been mowed. NOTHING grungy on the repeater.

Except that the squelch seems too high and stations are still trying to get through. I can hear them on my FT-847 loud and clear while they struggle to pop the squelch on the MSF. One can hear the repeater coming up but the signal is not passing. The pin whiskers have been blown out and the RX tray retuned. It seems that all that is left is to try decreasing the squelch. It seems to have changed simply by moving the repeater. Is this possible? The TX side is clean with zero reflected at the output of the duplexer to the antenna. It seems to me that if there were an issue with SWR before the duplexer it would have been on the output. Perhaps not.

We're almost there!!!

Any thoughts at this stage?