XTL5000 base coverage problems

[Digital Man]

Greetings. I have an XTL5000 base station (L20KSS9PW1AN) that has pretty terrible coverage. I have it up on a 5 story building attached to a DB224B antenna mounted on a 20ft pole. Nice short cable run of 35 ft.
I'd like to cover as much mileage as I can, but right now I cannot even cover a parking lot that is about a mile away. I can see the lot from the top of my 5 story building. With a person in the lot using the XTS5000 handheld (H18KEH9PW7AN) trying to talk to my base station, he can hear me, but I cannot hear him unless he is in one perfect spot. With that same person in the lot using the handheld and then I stand on the roof with a handheld, we can talk fine. The 2 handhelds actually out-perform the base station on a DB antenna.

I've changed out antennas, cabling and location on the roof. None of it resulted in any gain. The handhelds still work better than the base station every time.
As a last resort I changed out the XTL5000 base station for the older Astro Spectra base station model (L04KKH9PW9AN) and it worked much better. Almost as well as using the 2 XTS5000 handhelds.

My system is conventional, digital, VHF, using DES encryption. Direct channel, no repeater.

So my multi-questions are: What am I doing wrong? Is there something wrong with the XTL5000 base station? Why do the 5 watt handhelds out-perform the almost 50 watt base station (you'd think the base station would have a way better receive)?

Any thoughts or help would be much appreciated.

[wavetar]

How are you confirming the antenna & feedline are good? It sounds to me like there's still something wrong there. Even though you say the "Astro Spectra works almost as good" as the two handhelds, fact is it should be performing a fair leap better.

[The Pager Geek]

Also, have you tried analog to compare?

Analog is easier to diagnose "by ear" than digital.
Static levels, audio, etc.

tpg

[Jim202]

You have to have something wrong in a big way here. I would start by putting your radio on a service
monitor and checking the operation of not the receiver on the base station, but while it is hooked up,
the transmitter as well. is the receiver set on the correct frequency? A slight fat fingered entry on
the keyboard while programming the radio will make a big difference.

If the radio checks out OK, then on to the antenna. Have you placed an SWR meter on the antenna
cable at the radio? You might find the radio installer has made up the connectors wrong and your not
getting a solid connection all the way to the antenna. The DB224 is a DC grounded antenna, so you
should be able to take an Ohm meter and measure the antenna system from the connector that mates
with the radio. Measure from the center pin of the connector to the shell of the connector. I would
expect to measure a low value of only an Ohm or so. If you don't see and resistance, like an open circuit,
you will have to open up the coax connector at the antenna and see what the problem is.

Then on the other hand you mentioned that you tried swapping out the base with a Spectra. That worked
good for you. Better go back and make sure the base is working correctly. Could be a good chance you
messed up getting the frequency into the radio.

By any chance are there any other radios on the roof of this building? If so, there is a slight chance that
one of them is radiating just enough signal to blank your receiver. Do you hear any type of funny noise
or a beating type tone when you do hear the portable? If so, this might point the finger to some sort
of interference to your receiver. You can try putting a T coax connector at the radio. Don't transmit,
but use a service monitor to generate a weak signal into the receiver. Then connect up the antenna
coax cable to the T. If the signal goes away when the antenna is connected, there is a good chance
the problem is external to your radio.

The Spectra has a better front end than the XTL receiver. You may be getting killed by a VHF paging
transmitter that is getting into your receiver. There are solutions, but your going to have to do some
Sherlock Holmes work to get down to the problem. If your channel is close enough to the source of
your interference, this might be your problem. My guess is that it may be a transmitter in the other
direction from the parking lot. Otherwise, the portables would have the same issue. Then again it
could be an intermod that is IF sensitive. I don't think the XTL and the Spectra use the same IF
frequency. I could be wrong, but don't have the manuals to look at right now.

Jim

[The Pager Geek]

To all the techies reading this and my answer for the suggestion of analog:

In my head I'm actually leaning more towards portable issue than base because of all the swap outs. If the XTS's are tuned incorrectly (a la 123ABC) the xtl won't decode the digital. XTL's are less forgiving. Thus, if it "works great no static" in analog, we then know it's a digital thing. Most commonly found to be an alignment issue.

He has already mentioned swapping antenna and bases, which leaves connectors / hardline .... or portables. The only remaining things not accounted for or swapped.

The only other thing as mentioned by Jim is interference. Desense/ noise floor issues that could possible be filtered, but it's easier to check A vs D. (Not sure of his test equip availability) Spectrum analyzer would quickly ID that...

There you have it...

tpg

[lm2032]

+1 tpg

I've seen the same issue with alignment. If the OP doesn't have test equipment and can try analog, that'll give him a good start.

Also, make sure everything is either wideband or narrowband, whichever is authorized by the emission designators on your license. Were the securenet modules added after the radios were purchased? Have the radios been aligned while secure? I know our local shops asks what the percentage of time is that you spend is secure vs clear and base their alignments on that percentage. Has anything else happened to this equipment? Don't forget to check your lightning supression equipment as well.

[Digital Man]

First, I'd like to thank everyone for their responses and help. Thank you.

I'll try and answer some of your questions here.
I tested the cable and antennas with a watt meter. I always got better than 45 watts and less than 1 watt reflected. Even so, I've run new cable, tried different antennas, and built the connectors myself.
Today I tried an analog channel (it uses a slightly different frequency) and got exactly the same results. Meaning the two handhelds worked better talking to each other than the Spectra base station and the handheld talking to each other. There was something different though. The analog channel actually sounded worse on all the radios. Lots of background noise and static. And occasionally a faint "beating" type noise that Jim202 predicted. When we switched back to the digital channel it sounded much better, but that was only when we could talk, which wasn't that often.
I've triple checked my programming of the frequencies and astro and dpl codes. They are correct. And since the problem followed me to the different analog channel, I feel good about that.
Counting the different XTL and Spectra base stations I've tried so far, I'm on radio number 4. All of them have had a good receive sensitivity on the bench of -121db. I understand the T connector test you've mentioned and can do that. If that's the case, if I'm picking up some type of external interference, is there a fix?
The secure modules were purchased with the radios when new, not installed later. Can we tune the receive side? The CPS tuner I have only gives me tx tuning.
And I've done all the testing with and without lighting protection. No change.

Thanks again for all your suggestions. I'll be here trying to get this resolved.

[lm2032]

They're not cheap, but you could put a cavity on there to filter the other junk out. Google Sinclair. They're got good stuff.

[The Pager Geek]

I'd say Jim got it. Sounds like you're getting desens'd by something close.

If you are in a high RF environment (anywhere close to a city) you NEED filtering. Consolettes don't have any, and are essentially a "mobile on power supply." Mobile front ends are supposed to be wide for greater freq range, but this degrades the filtering needed.

Sinclair, RFS or my personal favorite Tx/Rx.

You really should look at it with a spectrum analyzer to see exactly what is pissing your radio off...

good luck
tpg

[chartofmaryland]

If you were hearing garbled audio in analog, then you may just have an interference problem.

I would make sure the interference is not TOO close to your frequency or NO can / filter will help your problem. It may just be a problem of location. Period.

You need a spectrum analyzer to determine your problem with a couple of attenuators if the analyzer is older then some to see how bad of a problem you have.

Also make sure your Unmute standard in the Rx options screen is set to Standard instead of Unmute And /Unmute Or. If you cannot use the radios at all after changing the unmute rule then your definitely have a desense problem.

CoM

[Digital Man]

All,
I've spent a lot of time on the roof lately trying to figure out my communications problems and have even tried something that helps a little bit. I had a Sinclair duplexer, model Q202G, sitting around, so I used 2 of the canisters inside as a filter. I tuned the two canisters to my freq and then tuned 1 canisters reject to 300k above the freq and the other canisters reject to 300k below. This seems to have helped a little, but is no means the magical fix.
About my roof: it is crowded. The more I look the more antennas I find. I have moved my antenna to the absolute edge of the roof, over 50 feet away from the nearest other antenna.
I've also looked at a spectrum analyzer for a while and monitored it and found all kinds of activity close to me. Lots of spikes within a 5mhz span, 2 or 3 within 500K.

I understand that a filter may not correct all, but is my Q202G as good as what I can get from Tessco (Sinclair, EMR, etc)?

Thanks again for teaching me.

[Jim202]

You have all but confirmed my original thoughts that you were having problems from another transmission
causing you interference. Your headed in the right direction in thinking that placing some cans in series
with your antenna cable will solve the problem.

My guess is that if the problem is there all the time, your being hit by a paging transmitter. Your in for
the fight of your life if this is the case. These monsters are on the air just about 100% of the time.
If not, then they only go off for a few seconds. Anyway, your going to have to find the exact
frequency that this transmitter is on. They run about 300 watt transmitters, so it won't be hard
to figure out which signal it is. Your next goal is to create a notch filter to try and reduce the
signal into your receiver.

Pass cavities will not do the job. They are too broad to reduce interference that is close by. The
notch filter should be able to provide something in the order of 30 to 50 db of attenuation. This
may still not be enough if your issue is a paging transmitter.

You might try locating a CDM mobile and see if it does any better. Not that their front end is
better, but the case is much better shielded than many of the other radios out there. You
might have an issue with the radio case itself leaking enough RF to cause your problem.

It now boils down to doing your homework to identify the signal or signals causing your problem.
You might just have to spend some time up on the roof around midnight to work during a time
that most of the radio traffic is at a minimum. If you have access to the room where all the
other radios are, all the better. It is a well known fact that AC plugs have been know to fall
out of the wall on paging transmitters on occasions. You just happen to be walking by and
found the power plug laying on the floor and put it back into the wall socket.

Jim

All,
I've spent a lot of time on the roof lately trying to figure out my communications problems and have even tried something that helps a little bit. I had a Sinclair duplexer, model Q202G, sitting around, so I used 2 of the canisters inside as a filter. I tuned the two canisters to my freq and then tuned 1 canisters reject to 300k above the freq and the other canisters reject to 300k below. This seems to have helped a little, but is no means the magical fix.
About my roof: it is crowded. The more I look the more antennas I find. I have moved my antenna to the absolute edge of the roof, over 50 feet away from the nearest other antenna.
I've also looked at a spectrum analyzer for a while and monitored it and found all kinds of activity close to me. Lots of spikes within a 5mhz span, 2 or 3 within 500K.

I understand that a filter may not correct all, but is my Q202G as good as what I can get from Tessco (Sinclair, EMR, etc)?

Thanks again for teaching me.