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prcguy's mast mount filter/preamp/diplexer thingee

Ubbe

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Stockholm, Sweden
There is no preamp on this input and even with 40ft of LMR400 from the antenna to the tower top box, then another 150ft of 1/2" Superflex Heliax to my radio, the signal levels are great.
There's 0,3dB loss in the LMR400 at 40MHz and 0,9dB in the 1/2" so only 1,2dB loss in your coax feed at 40MHz. In comparison, if someone uses 200ft of RG6 it would be a loss of 2,5dB.

/Ubbe
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
Right now signal levels are fine in the VHF lo range but I will have a 2-way splitter in the line sometimes that will degrade VHF lo. VHF hi and above will be fine with the preamps at the antennas.

There's 0,3dB loss in the LMR400 at 40MHz and 0,9dB in the 1/2" so only 1,2dB loss in your coax feed at 40MHz. In comparison, if someone uses 200ft of RG6 it would be a loss of 2,5dB.

/Ubbe
 

mancow

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Feb 19, 2003
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I think you should return that antenna and get your money back.
Got the FedEx notification today then a pic from the wife. At first I didn't know whether to be concerned or excited until I saw the name.

Oh you rotten **** ****** it's s on now.

; )
 
Last edited:

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
Update.....
Been a little busy to finish the latest version of the tower top filter/preamp but I did connect the new amp in line with the new FM broadcast band trap filter to my large Discone. The amp is 75ft down the coax from the antenna and 75ft from the radio so I'm not experiencing the full benefit of having the amp at the antenna, but so far it looks real good. There is no more FM broadcast stations scattered through the VHF and UHF air bands like the other amp was causing (IMD) and my noise floor is about the same as with no amp in line.

Tuning around the VHF and UHF air bands is nice and I tuned in a couple of weak but readable UHF ATIS stations with the preamp in line and with the preamp bypassed they were too weak to copy. This new MiniCircuits ZHL-1010+ amp and the MiniCircuits ZBSF-95+ FM broadcast band trap filter are working great together and there is no need for any attenuation after the amp to reduce the noise floor.

I'm making some major changes to the tower top filter/preamp like installing coaxial transfer relays which will bypass the filters and preamps when the power is removed then switch the filters and amps in line for each Discone when power is applied. This will allow me to A/B the system with and without preamps and to take the amps out of line if I'm transmitting with high power in close proximity to the Discones which might damage the preamps. I also had to buy new Bias T injectors to handled the nearly 2A of current the new amps and relays will need. The new amp gets noticeably warm, but that will help keep condensation out of the box on cold damp nights. Lots of new holes to drill and tap plus cables to make or buy before this project is complete.



Upgraded amp arrived today for the 118 to 512MHz section of my tower top filter/amp. Ever see an LNA like this that will put out a watt of power and has a heatsink? I'll try it this weekend but can't mount it permanently in the box until the new 88-108MHz notch filter arrives next week.

View attachment 72435
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
Another update.....
I was a little concerned about a UHF repeater on site feeding 40W to a Yagi antenna only 6ft from the receive Discone with the new amp in line. I measured -2dBm into the preamp when the repeater is keyed up, which won't damage anything but its a whopping big signal for any preamp to deal with. I find I can listen to weak VHF air, 2m amateur, UHF air and even UHF amateur stations just 500KHz away from the repeater transmit frequency when the repeater is keyed up with no detectable degradation in reception. That's impressive and it also says a lot about the Icom R8600 I have connected to the Discone and preamp.
 

kayn1n32008

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Sep 20, 2008
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In the 'patch
Another update.....
I was a little concerned about a UHF repeater on site feeding 40W to a Yagi antenna only 6ft from the receive Discone with the new amp in line. I measured -2dBm into the preamp when the repeater is keyed up, which won't damage anything but its a whopping big signal for any preamp to deal with. I find I can listen to weak VHF air, 2m amateur, UHF air and even UHF amateur stations just 500KHz away from the repeater transmit frequency when the repeater is keyed up with no detectable degradation in reception. That's impressive and it also says a lot about the Icom R8600 I have connected to the Discone and preamp.
That’s impressive.


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