Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: RF Viewer & Touchstone Pro  (Read 1283 times)
KE2KB
Member

Posts: 135




Ignore
« on: October 15, 2014, 03:44:07 PM »

Hi;
I am in desperate need to find what frequencies are causing the intermod and desense issues I have on 2m and when scanning railroad frequencies (160-161.5Mhz) with my VX-150 and Ringo Ranger ARX-2B on the roof.
I thought perhaps a spectrum analyzer could help me - and be a lot of fun to use as well. I Googled, and found this one: http://nutsaboutnets.com/rfviewer/
I would be purchasing the one for $79.95. It seems to cover the frequencies I am interested in, but I cannot seem to find the one piece of info I am looking for: Can I disconnect the antenna from the USB dongle and connect my outdoor antenna to it?
I'm not sure I really need to do this, as the signals that are causing the intermod and desense should be strong enough to detect using the supplied antenna.

Once I can determine the strongest signals that are causing my problems, I can go to Par Electronics and specify a filter.

I find it hard to believe that I could purchase a spectrum analyzer system for less than $100, but I am willing to give it a try if I can be reasonably assured that it will help me.

Does anyone have this product, or know anyone who has used it for this purpose?
I am going to download the demo version of the Touchstone Pro software to play around and see  what it can do - and make sure it will run on my PC.

Thanks for your help

Frank - KE2KB
Logged
ND6P
Member

Posts: 96




Ignore
« Reply #1 on: October 15, 2014, 08:12:09 PM »

I had a similar problem on 2 meters and used one of these filters to take care of the problem.  It won't help with the RR frequencies though. 

http://www.eham.net/reviews/detail/4804

Jim/ND6P
Logged
WX7G
Member

Posts: 6136




Ignore
« Reply #2 on: October 16, 2014, 05:11:25 AM »

The intermodulation is probably being produced by your receiver and as such a bandpass filter is the solution. However, the DCI-146-4H filter will not work because it is centered on the 2 meter band and will not pass 160 MHz (it's down about 60 dB). DCI should be able to make you a custom filter.

« Last Edit: October 16, 2014, 05:16:38 AM by WX7G » Logged
KE2KB
Member

Posts: 135




Ignore
« Reply #3 on: October 16, 2014, 06:33:37 AM »

I was afraid of that. What I really need isn't another "toy" - the spectrum analyzer - but another radio, specifically designed for railroad use. Then I could dedicate my ham gear for hamming - and we all know that our gear performs best in the ham bands.
The issue is mainly that I am using an HT with an outdoor antenna, and thus overloading the front-end. Sometimes I take stabs in the dark in attempting to solve the problem, but mostly to no avail.
Perhaps I could find a railroad radio on Ebay - but technically it is illegal for me to own such a radio if its transmitter is still in-tact. While I know that I can trust myself to use the radio only as a monitor, I would need to disable the transmitter just in case someone were to get access to the radio, and use it for transmitting.

As for filters - I am afraid that having a custom filter made for me is going to be a very expensive proposition. Still, if I can spend good money on a filter, and not waste it on test equipment that will only tell me what I already know - I would be doing myself a favour.
In any case, railroads will eventually go digital, and I will need another radio to hear them. I don't expect that 2m amateur will "go digital" anytime soon, although we already have the capability of using digital modes on 2m - but I see that SSB and FM will continue to be used on 2m for a very long time to come. After all - experimentation and enjoyment is what ham radio is all about!

I am also noticing that interference is worse some days than others. There are a number of factors involved, including weather, day of week (not much pager activity on the weekends or late night), band openings - I am probably getting pager interference from distant cities when conditions are right (or wrong).

Regardless of what I have said here, I may go hunting for a real railroad radio, and modify it to remove transmit capability. Or perhaps a better 2m radio with extended receive might have a more selective front-end. A base unit probably.

Frank - KE2KB
Logged
KE2KB
Member

Posts: 135




Ignore
« Reply #4 on: October 17, 2014, 02:27:09 PM »

I wonder whether an inexpensive spectrum analyzer like the RF Viewer with its USB dongle might produce results of limited use due to the possibility that intermod could occur within its own receiver!
After all, the hardware used in professional environments cost thousands.

Frank - KE2KB
Logged
SHORTWIRE
Member

Posts: 31




Ignore
« Reply #5 on: October 18, 2014, 02:50:18 PM »

I find it hard to believe that I could purchase a spectrum analyzer system for less than $100

That's because you CAN'T!

It looks like it might be only a glorified  DVB-T stick with 8bit 48dB dynamic range.
Hint: RTL-SDR

Such a thing works with the ZADIG driver and the free, limited version of Touchstone.

It can do something like what it says, but don't for a moment believe that it can compete with even an Rigol DSA-815, to say nothing of the nightmare of getting the RTL-SDR driver running well, without needing frequent restarts and fiddling and Windoze vomiting on you..

It might perhaps give the RF Explorer a run for it's money, though, but that ain't saying much( I got both..).  Grin

« Last Edit: October 18, 2014, 02:52:59 PM by SHORTWIRE » Logged
KE2KB
Member

Posts: 135




Ignore
« Reply #6 on: October 18, 2014, 03:05:54 PM »

I read somewhere that hams are using this sort of inexpensive analyzer to locate SAT signals. Maybe with a directional antenna that would work pretty well.
I think that if I am going to spend any money on upgrading my radio system on 2m, I will buy a better radio - one that can handle the strong signals presented to my poor little VX-150 from pagers, the local cops, and everything else that is fighting for bandwidth on 2m.

For what it is though, the VX-150 is doing a nice job. I can have hours of operation free of intermod late at night and on weekends. My FT-530 is much worse with intermod.

Frank - KE2KB
Logged
KE2KB
Member

Posts: 135




Ignore
« Reply #7 on: October 20, 2014, 09:16:03 AM »

Actually, if I just buy a notch filter for 155.700Mhz, it would probably solve most of my problems. That freq is my local cops. Monitoring them on another radio, I hear them at the same time I hear the intermod on 2m. Perhaps a double-notch for 155.700 and for the strongest pager station would do even better. I believe PAR can do multiple in one unit.

Frank - KE2KB
Logged
WA2ISE
Member

Posts: 158




Ignore
« Reply #8 on: October 20, 2014, 12:05:33 PM »

You might be able to build a filter, see
http://www.changpuak.ch/electronics/Coaxial_Stub_Filter_Designer.php

However, you can see that the simplest filter, a coax stub, is rather broad and will impact the desired freqs.  But when it comes to intermod, you likely need only knock the interferer down maybe 10dB to get rid of the intermod.  And also have less impact on the desired freqs.  Maybe the stub with a resistance between it and the main coax?  I haven't tried it, but maybe to cut the attenuation of the notch from say 50dB down to say 10dB down, and as the coax is 50 ohms, insert a resistance of a value that makes the notch look like 10dB.  dB's are 20 log ratio, or is it 10 here?  Lets say it's 20, so with 20 log (ratio)=10, I want to know what ratio I need to make it happen.  getting rid of the 20, log (ratio)=0.5  Okay, so I need something that when log-ed gives me 0.5.  Do that by doing 10^0.5, which gives me 3.16.  To be sure I haven't messed it up, 20 log (3.16) gives me pretty close to 10.  So I want a voltage  divider that, when loading a 50 ohm source, will drag it down the 10dB, or 3.16 ratio.  The stub, at the resonant frequency, will look like a dead short, But we want a dead short with a resistor in series connecting to the 50 ohm coax.  Looks like a 22 ohm resistor should do it, at resonance we'd get the desired ratio reduction, off resonance the drop will be less.  Oh, I'm ignoring various issues like the interaction of the antenna's impedance at its various resonances, but not being a professional RF engineer, hopefully what I'm assuming and ignoring won't much matter.  YMMV   Cheesy   
Logged
KE2KB
Member

Posts: 135




Ignore
« Reply #9 on: Today at 02:32:24 PM »

Honestly, I don't have the patience to work with home-made filters right now. I'm not too good with stuff like that - everything seems to take a lot longer than it was supposed to, and then it only works marginally.
I think that my best option is to get a different radio. Maybe a mobile rig, or a fixed rig (I don't want to use the CB term "base station", but it is probably still the correct term), since the fixed rig would be designed to work with an outdoor antenna, it would probably have better specs in regards to front-end overloading. The problem is that I don't have the cash for it right now.
So I guess I'll just have to deal with it. The VX-150 actually works quite well on weekends, and nights - when the pagers aren't nearly as busy.

Frank - KE2KB
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!