Discone Antenna & 700 MHz Yagi

[KD7JVRinAZ]

We just raised my discone antenna about 6 feet. We also put a 700-800 MHz Yagi inline with it, using a two way 'T' connector (not a splitter or a duplexer, just a plain 'T'). My scanner (BCD-992) is now working worse than what it was. I suspect that putting the Yagi inline has done more harm than good. I wonder, Could this be my problem?

 

[doctordialtone]

Must be your problem

I've never heard of a "BCD-992" either.

 

[KD7JVRinAZ]

Yeah, you're right, I had a stupid moment. Its actually a BCD996P2

 

[jonwienke]

With a T, you get loss from impedance mismatch, plus half of what's left goes to the other antenna rather than the radio.

 

[Ubbe]

Try to get hold of a diplexer that has a lowpass input below 500-700MHz and a highpass input above 500-700MHz that combines both antennas best frequency range into one coax. Or use one 500MHz lowpass filter and one 700MHz highpass filter and insert in the coax between each antenna and the T-connector. Mini-circuits got some filters like the BLP550 and the BHP700 for $35-$40 each.

/Ubbe

 

[KD7JVRinAZ]

Try to get hold of a diplexer that has a lowpass input below 500-700MHz and a highpass input above 500-700MHz that combines both antennas best frequency range into one coax. Or use one 500MHz lowpass filter and one 700MHz highpass filter and insert in the coax between each antenna and the T-connector. Mini-circuits got some filters like the BLP550 and the BHP700 fo

Try to get hold of a diplexer that has a lowpass input below 500-700MHz and a highpass input above 500-700MHz that combines both antennas best frequency range into one coax. Or use one 500MHz lowpass filter and one 700MHz highpass filter and insert in the coax between each antenna and the T-connector. Mini-circuits got some filters like the BLP550 and the BHP700 for $35-$40 each.
View attachment 76944
/Ubbe

Is there any way you can send me a link for this?

 

[BruceMN]

You could also me over loading the scanner (too much signal). When I added a discone antenna to my PSR-600 I could hear less than when the supplied whip was used. I added a 88-107 MHz band filter and the scanner came alive with activity.

 

[Ubbe]

RF Filters - Bandpass Filter | Low-pass Filter | High-pass Filter | Band-stop Filter | Diplexers and Triplexers - Mini-Circuits

Mini-Circuits is a global leader in the design and manufacturing of RF, IF, and microwave components from DC to 86GHz.

www.minicircuits.com

Click on Lowpass or Highpass and tick the box that you want connectors on the filter. The model number pretty much tells where the cutoff frequency are. Click on the model number and you will see the price for the filter and can also check the specification, like the insertion loss that are 0,5dB and attenuation of the unwanted frequency bands are more than 30dB for those filters I mentioned.

/Ubbe

 

[dlwtrunked]

You could also me over loading the scanner (too much signal). When I added a discone antenna to my PSR-600 I could hear less than when the supplied whip was used. I added a 88-107 MHz band filter and the scanner came alive with activity.

Yep, everyone needs to use such a filter. Many do not understand that even though you do not hear FM broadcast interference, it can dramatically cause de-sense causing weaker signal to simply not be heard. It does this by the strong FM broadcast station affecting the automatic gain of the receiver even though it is not on the desired frequency. It is the reason that ham radios near each other in cars will often not hear each other on a repeater---the input frequency (very strong since they are close) de-senses the reception of the repeater output frequency.

He may also have another problem, the signals from the antenna may be out of phase (this is a different than impedance) and cancelling each other (in fact there is not reason they would be in phase). The diplexer solution would help if that was the case.

 

[AzTac]

See those light towers and that big tan building in the background of your photo?? The towers are at Scottsdale Stadium and contain numerous cell phone antennas. The tan building is HonorHealth Osborn which is one of the largest Level I trauma centers in the Southwest. And while it's not quite visible in your photo, you're also literally in the shadow of the Scottsdale PD tower carrying the majority of the very active RWC Sim H traffic.

Your immediate proximity to these three facilities means you're being bombarded with radio signals in the 700/800 MHz range. As you may or may not know, simulcast reception (especially the RWC) is very susceptible to interference from nearby sources. To add to your woes is the fact that the Uniden BCD996 is simply not up to the task of handing difficult simulcast issues. You could erect a 1,000 foot directional antenna and use every filter known to man and it will not overcome the fact that you have three distinct overpowering radio sources raining down on your location.

I believe I've suggested to you previously that before you invest time and energy in antennas, filters, etc. you should consider trying to borrow (or buy with a return option) a Uniden SDS100 or 200 radio or a Unication receiver and see if either of these units work at your site. They may or may not work for you considering your challenging location. If they don't, sadly, you may be out of the simulcast monitoring hobby from your residence.

Believe me (I live not far from you and have already worked through these same reception issues...) when I tell you that you can chase these issues until you're a tired and decrepit old man and still not find a solution or you can try the solution that worked for me and many other people.

 

[KD7JVRinAZ]

I guess thats what I'm gonna have to do after all. I am very close to the Simulcast
H Tower. Its right on the other-side of the stadium and seen a lot of cell phone towers over there. I guess I will just have to break down and get an SDS-100 but in the meantime I can use my BCD-996 for Scottsdale and VHF/UHF.