CHP antenna question

[picscan]

So I've been listening to CHP on low band no problem or so I thought, all channels are excellent. The other day I found my old Wilson mobile magnetic CB antenna in the garage so I hooked up my TRX-1, set it on the table in the backyard, I instantly picked up a call right next to the GG bridge, 42.4400. I had never gotten that channel before.
After that I came in the house and hooked it up to my discone that is 30' on a mast on the roof with the same size whip on top and it wouldn't pick it up so I went back outside with the CB antenna sitting on the patio and it picked it up no problem again. I was also hearing Truckee with the CB antenna which is rare for me, I'm in Sacramento. What gives and how do I make the one on the roof better? I also took the CB antenna on the roof and it wouldn't receive it up there, just sitting on the deck on the ground.

 

[prcguy]

So I've been listening to CHP on low band no problem or so I thought, all channels are excellent. The other day I found my old Wilson mobile magnetic CB antenna in the garage so I hooked up my TRX-1, set it on the table in the backyard, I instantly picked up a call right next to the GG bridge, 42.4400. I had never gotten that channel before.
After that I came in the house and hooked it up to my discone that is 30' on a mast on the roof with the same size whip on top and it wouldn't pick it up so I went back outside with the CB antenna sitting on the patio and it picked it up no problem again. I was also hearing Truckee with the CB antenna which is rare for me, I'm in Sacramento. What gives and how do I make the one on the roof better?

If the CB antenna picks up ok then a real tuned antenna for CHP at the same location would scare you. A friend on RR here is getting me a couple more surplus CHP antennas for future projects and they work great.

 

[picscan]

That would be nice. I just can't figure why I have the same size whip on the roof and why I use the CB antenna up there it won't work but sitting on the ground 30' lower it works better.

 

[DMS11B]

The CB antenna is closer in resonance/ wavelength than the disco.

 

[mmckenna]

That would be nice. I just can't figure why I have the same size whip on the roof and why I use the CB antenna up there it won't work but sitting on the ground 30' lower it works better.

What did you have the CB antenna sitting on? Was it a large metal table?

 

[picscan]

What did you have the CB antenna sitting on? Was it a large metal table?

It was a round glass table with metal legs and metal rim to hold the glass, I also set it on the concrete deck, maybe the rebar was helping? How would I get it to work on the roof without putting my wife's table up there? It doesn't work on my cars either, only that magic spot in the backyard. (just noticed that compass is 180° off)

 

[mmckenna]

It was a round glass table with metal legs and metal rim to hold the glass, I also set it on the concrete deck, maybe the rebar was helping? How would I get it to work on the roof without putting my wife's table up there? It doesn't work on my cars either, only that magic spot in the backyard.

It might be, probably the table frame more than anything. Might have also been the coax leading away from the CB antenna base. Ground planes are important, and the discone has a very poor one for VHF Low.

Getting a suitable ground plane for VHF low up on a mast would be a challenge. Not impossible, look at some of the old base CB antennas.

While hobby discone antennas often claim low band coverage, they aren't very good at it. Not surprising that your CB antenna setup worked better.

 

[picscan]

Thanks

 

[prcguy]

The CB antenna is closer in resonance/ wavelength than the disco.

Many Discones have a whip on top that resonates around 50MHz and it does perk up VHF lo some but nothing like a resonant whip. In fact I recently installed a Discone and wanted good CHP reception so I got a very long whip, about 65" and swapped it out with the original roughly 3ft whip on my Discone, then tuned it for a local CHP freq around 39MHz. The difference in reception was very noticeable.

 

[gmclam]

I have a discone on a 30' mast outside connected to my radios and have no issues with picking up CHP. While I don't monitor the GG bridge, I do monitor and receive Emerald from Sonoma county just fine.

Keep in mind that antenna is a SYSTEM, not just a thing out on a pole. While you'll have less issues with low band, there are lots of things to consider. First is coax from the antenna. Next is that a discone is going to pick up pretty much everything and that includes AM/FM broadcast, TV, cell towers and paging systems. You'll want to filter out the strong unwanted stuff for best reception.

 

[picscan]

Okay, for whatever reason SF, 42.4400 and San Jose 42.500 CHP are coming in fine now. I put a new metal mast on the roof instead of the fiberglass one I was using and it raised it about three more feet.