25 watts UHF & 5.5 dbd 5/8 over 5/8 antenna..

[YWHIC]

As the top asks..

I have a 5/8 over 5/8 UHF antenna on GMRS 462/467 and a 25 watt UHF radio with the antenna about 25 feet up on my roof with ground plane radials on it (not sure if you need that) with just 12 feet of RFC double insulated 240 cable..

How many watts make it out??

Guessing like 70 watts??

[Will]

You loose a portion of the signal in the coax cable. And YES you need the ground radials on your "mobile antenna".

ERP would be about 20 watts.

[MSS-Dave]

Well...

RFC240 shows loss equivalant to LMR240. At 465 MHZ at 12 feet, loss is 0.6 db. A full size colinear UHF antenna like that is typically rated at 5 db gain. Convert 25 watts to dbW to make it easier to work with. That equals 13.98 dbW. Add 5 db for antenna gain = 18.98, subtract 0.6 loss for the cable = 18.38 dbW. Reconvert that to watts = 65.865 watts ERP. OP not too far off....

Dave

[Will]

Dave, the problem is those antennas do not have 5 db gain. , maybe over a dummy load.

[tvsjr]

Dave, the problem is those antennas do not have 5 db gain. , maybe over a dummy load.

You better tell the manufacturers that... if I was doing ERP calculations for a license, I think I'd use whatever numbers they list.

[MSS-Dave]

Dave, the problem is those antennas do not have 5 db gain. , maybe over a dummy load.

You better tell the manufacturers that... if I was doing ERP calculations for a license, I think I'd use whatever numbers they list.

Yup. All I have to go on is the listed gain rating. I just guessed on gain based on OP's description of the antenna. I won't even go into the dBd versus dBi issue. Whether that antenna actually makes that or not is going to depend on way too many variables in the real world and if the manufacturers quality control is decent.

I will support the ground plane radial suggestion. That design antenna requires a ground "image" to work against so the signal doesn't shoot mostly straight up. A 1/2 wave antenna does not require that.

I'd like to know however how a 5/8 over 5/8 colinear antenna properly installed doesn't have any gain over a dummy load?

Dave

[YWHIC]

Its a Browning BR-450 5.5 dbd rated antenna.. so far with just a handheld 4w I got 6 miles of coverage thru some rough terrain..

I did get the Tram mount with 4 GP radials coming off for it..

Doing the 25w radio test drive today... to another 25w mobile radio in my car.. have to see if I gain anything.. hoping..