PDW Antenna issues

[madmarto]

Hi Guys,

I've been running PDW for about 2 years using an internal antenna but have finally gotten around to putting an antenna on the roof. My problem is that the system receives local voice comms using the external antenna but the local paging frequency receives nothing - I've tested it with a second handheld scanner using the h/h antenna beside the PC as well as up the ladder so I now the signal is good. I've been researching this for about 2 weeks and have not been able to find a solution, so here I am.

My setup is a UBC73XLT feeding via Disc Tap to a Windows 95 computer running PDW. Local pager frequency is 148.9125 and I'm approx 14km from the tower. The old antenna was a mini magnetic mount scanner antenna on the window sill and the current antenna is a 3ft stainless steel whip antenna mounted on the TV mast approx 3 metres East and up. The mini mag was good but in bad weather or on hot days the PDW signal strength would drop to 40-60% and result in no messages. Tests internal and external were done with the UBC73XLT, a UBCD396XT and UBCD436-PT all with the same results. I've discounted cable/plug issues, interference, etc (I even put the ext antennas on the outside of the window sill and got the same result) so this one has me completely stuffed!

Why would the external antennas (4 different antenna tested on the mast) all receive improved local voice comms in the 163/164 Mhz range but nothing on the paging frequency?

Thanks in advance for any help.

[madmarto]

UPDATE: It seems I had a short in the cable at the antenna base (the foil shield was to long on the dielectric insulator).
That is now fixed and the scanner is receiving the encoded messages, but PDW is not decoding them via the internal or external antenna.

The sage continues!

[madmarto]

OK, so after extensive testing, I'm after any ideas from the brains trust.

I got the best results with a 4.5db UHF Antenna. The location that gives the best signal for PDW to decode is with the antenna hanging from the curtain rail in my dining room (strength 430 our of 500).

Other locations tested were:
Base of the TV mast - 213/500
Top of TV mast - 413/500
on the back fence post - 386/500
on top of the clothes line - 425/500 (but still not strong enough for PDW to decode the signal)

So, a couple of questions.
- Why is having the antenna inside, horizontal, approx 20cm from the ceiling and on the opposite side of the house from the tower giving the best reception?

- What antenna do other people use, and where is it located? How far are you from the tower?

- Why is the UHF antenna giving better results than the other ones tested (2 steel whips - one untuned and one tuned to 164ish Mhz, piggy-backed to the TV antenna, and a spare 800MHz antenna I had in the shed)?

[comport1]

Hi Madmarto

I have been using a recycled VHF TV Antenna For Pocsag PDW for many years with 100% Decoding Rate all day every day. I am up to 60km from my Transmitter, and this works perfect!! I also have this split for AIS Decoding as well!

[madmarto]

Thanks for the info comport, it's just got me stuffed why I get better reception inside than outside. It goes against everything I know about radio comms and antenna selection and placement. I'll see if I can find a secondhand VHF TV antenna and see how I go

Sent from my SM-G900I using Tapatalk

[comport1]

Cheers madmarto

There is 1 problem i do have, and is that i can receive 2x Transmitter Stations (148.6375Mhz) and the 2nd one is closer to me, lower power, and only sends LOCAL messages to the Ambo's and Firies, which is a Microcell or Picocell Transmitter...

So what happens then, if BOTH Towers transmit the same message, at the same time, they literally wipe each other out, and you end up with a garbled message, or non-existent message. When i used to live closer to the 2nd Tower, its Power Output overrode the Main Transmitter, and i could decode 100%. But now i have moved further away, i have this problem! I have tried Attenuators, different Antennas Indoors & Out, and can not get it right, but i do have Dual Decoders 1 x 148.6375 & 148.5625 on 2 Seperate Monitors on the ONE PC. 100% Decode all day everyday, Except from my Local Tower, that i don't get the "Very Local" that i want to monitor...

Maybe that was the problem you were having when outdoors, you may be recieving multiple sites, but working indoors fine, cause you were only rx'ing 1 site?

Let me know what you think??

Cheers

[madmarto]

I had considered override from a second tower, but the AMCA database dispelled that. My next closest towers are Mt Granya (33.82Km) and Rutherglen (40Km). There is a second pager frequency at Mt Baranduda (148.6875MHz) which is used by DOJ/RAV but I don't see how this could interfere with my system at all.

[cjl_72]

Hi Guys,

I've been running PDW for about 2 years using an internal antenna but have finally gotten around to putting an antenna on the roof. My problem is that the system receives local voice comms using the external antenna but the local paging frequency receives nothing - I've tested it with a second handheld scanner using the h/h antenna beside the PC as well as up the ladder so I now the signal is good. I've been researching this for about 2 weeks and have not been able to find a solution, so here I am.

My setup is a UBC73XLT feeding via Disc Tap to a Windows 95 computer running PDW. Local pager frequency is 148.9125 and I'm approx 14km from the tower. The old antenna was a mini magnetic mount scanner antenna on the window sill and the current antenna is a 3ft stainless steel whip antenna mounted on the TV mast approx 3 metres East and up. The mini mag was good but in bad weather or on hot days the PDW signal strength would drop to 40-60% and result in no messages. Tests internal and external were done with the UBC73XLT, a UBCD396XT and UBCD436-PT all with the same results. I've discounted cable/plug issues, interference, etc (I even put the ext antennas on the outside of the window sill and got the same result) so this one has me completely stuffed!

Why would the external antennas (4 different antenna tested on the mast) all receive improved local voice comms in the 163/164 Mhz range but nothing on the paging frequency?

Thanks in advance for any help.

I am having antenna issues too but am.led to beleive that since i only monitor 148.6374 and 148.5625 i can get a fibreglass whip type antenna cut between the 2 at 148.6000 and that should work perfect fir both??? Or at least thats my understanding? Sound right?

Sent from my SM-G955F using Tapatalk

[comport1]

I use stand alone antennas for pager receiving. Recycled VHF TV Antenna Yagi pointing towards the Paging Transmitter works an absolute treat! Or a Home Brew Dipole made with RG-6 Coax, Aluminum Tube and a Plastic T Piece all from bunnings. Check out the below photos, shows both said antennas on my Tower....

PDW_YAGI.jpg

PDW_YAGI_2.jpg

Cheers

[cjl_72]

I use stand alone antennas for pager receiving. Recycled VHF TV Antenna Yagi pointing towards the Paging Transmitter works an absolute treat! Or a Home Brew Dipole made with RG-6 Coax, Aluminum Tube and a Plastic T Piece all from bunnings. Check out the below photos, shows both said antennas on my Tower....

PDW_YAGI.jpg

PDW_YAGI_2.jpg

Cheers

Does using a normal car type aerial cut between the 2 frequencies i monitor at 148.600 sound ok?

Sent from my SM-G955F using Tapatalk

[comport1]

When you say car type, do you mean a mobile whip? Google "RFI CD28 VHF" are an excellent antenna to use, cut and tuned centred for 148 Mhz will be fine. You do not have to be spot on with RX, so don't get to caught up in all that, I've accidentally used a UHF CB Base Antenna once without an issue. A wet piece of string will even work! (Just an old saying)

This is the VHF Antenna Whip i'm referring to...

cd28-41-50.jpg

Cheers