Troubleshooting, my setup, and RWC Simulcast G (multipath!)

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KB8TZX

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Hello, again, everyone!

I figured since my other posts on more specific issues evolved into troubleshooting, or discussion of, my receive setup that I would just open another thread to keep the other threads less confusing. (For reference, one of those posts was:
http://forums.radioreference.com/arizona-radio-discussion-forum/281036-maricopa-mcso-lcns-white-tanks-help.html

To reiterate some things and save all that bouncing, I am running a dual SDR (R820T USB TV tuner) setup utilizing SDR# (SDRSharp) as my radio software, the UniTrunker software to handle the trunk-tracking, and DSD+ (or DSDPlus, if you prefer) to handle the digital voice decoding.

I started exploring the local systems and have had a great deal of success hearing many of them with no issue. However, due to my specific location, I am unable to hear most of the really "local" activity due to multipath interference/distortion while receiving Simulcast G on the RWC. As my specific end-goal interest was to be able to listen to (and potentially stream) the talkgroups for El Mirage PD (4330) since it is essentially my back yard and no stream yet existed, this has been the bane of my existence since beginning this project. As I have learned here, their TG is only on this Simulcast and no others.

Initially, I thought I had found a nice (but temporary) solution in a home-brew dual Yagi-esque contraption I built (see: http://forums.radioreference.com/arizona-radio-discussion-forum/281988-improve-rwc-reception.html for more on that). The control data indicator in UniTrunker was "unhappy red," but UT was still tracking reliably, and the audio from my control receiver was easily and clearly decoded, after disabling the AGC and decreasing the receiver gain, unlike I had experienced previously. I re-did the whole thing with better wire, too, as an intermediate step to building a more permanent version given the results I thought I had achieved.

Sadly, there must have been confounding variables (weather affecting propagation, system issues, etc.) that allowed this arrangement to work so well. I have been able to get "improved" reception since then compared to the (included) vertical alone, but I am still having multipath issues that make the voice channels grossly unlistenable.

After some great information provided by others here on RR, I was able to dig up the site locations for the simulcast and did some crazy calculating with online tools to determine my air distance and heading to each one. I now see where some of my difficulties are coming from (assuming this contraption has a beam width of 30 degrees, anyway). One site is 5.2 miles away, another 6.5 miles with bearing of 285 and 254 degrees (perhaps reversed).

At this moment, I am considering the possibility that I will have to get a bit more involved in finding a "solution" to this issue in the way of not only building a real Yagi, but building a stack of 2 in order to get the beam narrow enough to deal with the interference.

So there is where the project sits for the moment, stalled by budget for antenna building supplies (minimal as these would be) to test my latest notion and lack of other creative ideas.

First of all, is there any merit in attempting the Yagi stack in all practicality - especially a homebrew array? Also, anything you can share to assist in making this thing functional would be fantastic, and my thanks to those who have already offered their input!

Dave
KB8TZX
 

KB7MIB

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Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2339; U; en) Presto/2.8.119 320X240 LG VN530)

Can you try pointing the antenna not directly at either site, but off to one side or the other? This may put one site outside the beamwidth of the Yagi enough to null it sufficently.
Aiming at the closest tower, or even directly at a tower, isn't always the best option. Try offsetting the heading, and see what happens.
 

KB8TZX

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Joined
Jun 3, 2011
Messages
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Location
Phoenix, AZ
Interesting that you mention this, KB7MIB.

I had thought of it, though not entirely understanding antenna patterns and how much signal would really be rejected/attenuated - whichever it really is - in the null (if one even exists on my extremely shoddy contraption). I pointed to the more northerly site at a bearing of 285 degrees and the moved several more degrees clockwise, away from the site at 254 degrees. However, it was to no avail. However, I believe you have validated my thinking that this would be a reasonable thing to have tried.

One reason this might be an issue is that there *is* a second site about twice as distant at 288 degrees. I had hope that dropping the gain on the receiver back a few dB would effectively make it deaf to that site if it could even hear it in the first place, but it might still be menacing the receiver. Still another site is at 353 degrees but it is quite a bit more distant but theoretically within the major lobe.

I am starting to think that I could be in possibly the best spot for their commercial portables with coverage coming from every angle... and the worst position for what I have and possibly even for some higher-end scanners.

I am feeding the two receivers off separate "Yagis" on each side of the paper roll, and the "driven" element of each is just the stock "candy kiss" antenna that you get with the SDR dongle, featuring a lovely MCX connector, all set atop a pie plate. Until I buy some of the adapters MCX/SO-239 adapters I see on eBay, I may be a bit limited on what I can do non-destructively. (Even then, chopping off the little antenna and soldering to the short run of spaghetti coax to a beam seems like it would also be about as daunting as soldering an MCX connector to RG-58... not to mention the prospect of being without antenna if I fail!)

I do not completely understand this Yagi stacking business, except to say that it appears it is an option to narrow the beam at the expense of something very obtrusive (needing two stacks or some form of combiner/splitter) that would likely be knocked over by children if it were to remain indoors and not buy me any points with my other half. I realize this might not be a solution, either since I still have two sites within even 15 degrees of one another. Attenuator?
 

KB8TZX

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Joined
Jun 3, 2011
Messages
18
Location
Phoenix, AZ
Just an update:

A friend and fellow ham (who is also a cellular system tech) offered me a suggestion today that I had not considered given my less-than-active status in the radio hobby as of late: a corner reflector antenna! Too bad I was hung up on the Yagi design or I might have found that by Googling the archives here at RR - because it's been asked. (Doh!)

I found some dimensions online (which may not be quite appropriate to the 770-ish MHz, but they're close enough) and threw some aluminum foil on the cut up corner of a kitchen mixer box, leaving just about of the bottom flaps to mark the approximate 90 degree stop. Slid the pie-plated mag mount in there about 4 to 5 inches from the vertex and aimed it.

I still get some hiccups right now, and that's after I dropped the angle of the reflector from 90 to around 60. And what hiccups I hear don't sound like the multipath trainwreck I was hearing before (probably some other decoding issues). It's looking encouraging, but I thought I had the magic bullet with that Yagi plan, too. Time will tell.

Other ideas, tips, tweaks, etc. still welcome and encouraged.
 
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