Baofeng BF-F8HP Transmit Problem

[jk77]

Does anybody know if the Baofeng BF-F8HP has a protection circuit that reduces power in the presence of a high SWR?

I connect my F8HP to an N9TAX Slim Jim. The Slim Jim is supposed to have a good SWR on 2 meters, but I can't think of any other cause of my problem. When the battery is more than half charged, the radio will not transmit with high power through the N9TAX. Sometimes I cannot even open the repeater and other times I can open the repeater but I'm told that my transmission is unintelligible. When I am using a whip, I can open the repeater but I suspect that I'm not readable because no one responds to my request for a radio check. I am far from this repeater. However, when the battery drops to around 50% or less I have no problem reaching any repeater or talking with anyone on high power. I also don't have any problem no matter the condition of the battery if I set the transmit power to MID (intermediate) power. This is the second radio exhibiting this phenomenon.

CTCSS is set correctly (and as I mentioned the radio works if I reduce the power). I do not have this problem on my other radios.

I have tried switching batteries without luck. Any ideas?

 

[jk77]

I've done some testing, and I'm beginning to think the problem is with the slim jim antenna which is located in the same room as my HT. The HT works on the HIGH setting with a whip antenna.

I was studying the radiation pattern of the slim jim and found that the best place to be out of the radiation field of the antenna is on the axis of the antenna and below it. I placed my HT there and voila, things improved. Not 100% but they did improve.

Does anyone think that being in the same room with a high gain antenna using the high power setting can overload the radio and cause a transmitter malfunction?

 

[bharvey2]

Am I understanding correctly that you are trying to listing using another radio in the same room? If so, you are likely "desensing" the second radio. In layman's terms, the close proximity and power of the first radio are overwhelming the receive circuitry of the second radio thereby inhibiting its ability to pick up any signal. (I'm not trying to be condescending with the description)

Moving the radio to another room and turning up the volume or better yet, finding a cooperative listener (doesn't need to be a HAM) and getting the radios further apart would help with the problem mentioned above.

Good luck!

 

[jk77]

No. I'm not listening on another radio in the same room. I am gauging this on whether I can open the repeater and whether I am intelligible to other hams. Most times I can't even open the repeater and when I am successful with that, I am not intelligible. However, if I reduce power to 4 or even 1 watt this problem vanishes.

 

[WA0CBW]

Most forms of "J" pole antennas can be very finicky about RF coming back down the outside of the coax. This can cause many problems and I suspect that may be your problem.
BB

 

[jonwienke]

+1^^^

If you're using a slim jim or J-pole antenna, it needs to have an RF choke on the coax where it attaches to the antenna (either a ferrite bead or a coil in the coax) or you will get RF radiating down the coax. This will raise SWR, decrease actual radiated RF power, and can cause damage to the TX final transistors and/or garbled/distorted audio on the other end.

 

[jk77]

Thanks guys. I'm going to a hamfest tomorrow, and hopefully I'll be able to pick up some ferrite beads on the cheap. I'd also like to pick up some decent coax to be able to put some distance between me and the antenna.

 

[jk77]

Well, the beads didn't work. I bought 3 of those snap on beads and still I can't transmit on high power and get out. I even tried making a coil out of the coax to act as an RF choke, and it also didn't work either. I am stymied.

 

[WA0CBW]

Now would be the time to put some test equipment on the radio to see what it is doing. Do you have the same problems when using a dummy load?
BB

 

[jk77]

I'd love nothing better than to use some test equipment, but the test equipment costs more than the radio. I am now firmly convinced that the problem is not the radio but the antenna or, better yet, the radio+antenna system. I have confirmed yet again that I don't have this problem at all when using the whip (any whip) antenna.

 

[WA0CBW]

Your problem could be as simple as a shorted or open connector or something wrong with the antenna. See if there are any local hams that have an SWR meter or an antenna analyzer that would help you check out your antenna/coax/connector setup. Ham radio, like many other hobbies, require some "accessory" equipment to make sure your station is operating correctly.
BB