Afraid for my finals ft-817 with a 100w amp

[jolechiw]

Hey guys and gals,

I plan on using a Mirage B-310G (100w HT Amp) for 2m ssb work. I will be using a 146 4 ele arrow antenna, which has pretty low swr. I also have a ldg z100 but I realized it wont tune on 2m, as I thought it may protect the radio from any reflected power. The amp will put out 50w if I use .5w drive and I'm not as worried about that as the full output of 100w. I've been reading more and more and learning but figured I'd pick brains for reassurance. Feed line is 18ft RG8 (400UF) Low Loss. I figure ill just use 50w till i can get the MFJ-259C antenna analyzer.

 

[ka3jjz]

What the ????

Using a HF autotuner on 2 meters??? Something's wrong with this picture...

I'd ditch that setup in a heartbeat - why risk damaging the autotuner (not just the finals in the 817)?

If the antenna isn't working well in the 2m SSB range, then get one that does - like a loop or squalo....

Mike

 

[jolechiw]

Oh no I wont be using the z100, I just realized it wont work on 2m. I for some reason thought it did. But found out the opposite when I re-read the specs.

 

[FKimble]

oops

 

[ka3jjz]

Indeed it is, but I'm not entirely sure that Arrow antenna would work well down in the 2m SSB range.

If the SWR is OK then there's no harm in trying it.

I used to know a few folks in Howard County Md. that did 2m SSB work, and they used stacked loops or squalos. Sounds like a lot of fun when the band is open

Mike

 

[jolechiw]

So I should wait and get an analyzer. I've read swr is about 1.5:1 across the band but I guess that's just one persons report.

 

[KC8ESL]

So just buy an swr meter and test YOUR specific antenna. Just because an antenna has typical results on paper doesn't mean it always translates into practice.

Analyzers are really nice but swr meters can be cheap at a hamfest.

Also, let's get to the real issue at hand here. Your finals on your ft817 will be met by the amp with a 50 ohm load. The mirage amp is the device that would suffer with swr issues, if there are any.

 

[ka3jjz]

If it's the same antenna as the one I'm thinking of, this antenna is cut for around 145-146 Mhz. The SSB portion of the 2m band is around 144.200 to 144.275 Mhz - making the antenna a touch too short to resonate properly down that low.

You would do better with an antenna that is actually resonant in that range

Another thing to keep in mind is polarization. While most FM transmissions on 2m are vertical, SSB is often horizontal. There is a significant loss if you use the wrong polarization - something on the order of 10-20db. Whatever you use, make sure you set yourself up so that the antenna is in the horizontal plane.

Mike

 

[jolechiw]

I guess i'll be getting out the angle grinder then and hitting up the hardware store.

 

[ko6jw_2]

Before you modify the Arrow antenna consider a couple of things. The first is that you can adjust the gamma match on the antenna. Second, I have the Arrow 2m/440 satellite antenna and have used it with no problem on 2m SSB and no tuning was required with an FT-817. The only caveat with that antenna is that it can only handle 10 watts with the duplexer. Yours should not be a problem.

Get a good SWR meter or an analyzer if you want to experiment with antennas. It's well worth it.

 

[ka3jjz]

...Which means you wouldn't be able to use your Mirage amp on that antenna in any case...

There are, I'm sure, numerous plans on the net you can find for halo antennas and others you can use on 2m SSB

I would suggest talking to a few locals and find out what works for them. I have no doubt that you'll get a considerable earful of opinions - then jump onto the net and look for reviews and other technical articles on the subject. It's a good education

Mike

 

[jolechiw]

Yeah I just bought the analyzer, I have a yo yo tenna that I need to mark for bands and I have 3 antennas I'd like to build and experiment with. I started hamming to learn and I'm here till I die so I might as well invest in one now vs buying 3 swr meters as time goes on and yada yada. I did use the vswr meter on my 817 and 1 bar at 146.520 and 1 bar at 144.200. Looks good at an unofficial standpoint.

 

[ko6jw_2]

I would not trust the built-in SWR indicator on 2m or 440 on the 817. I think its really designed for HF and 6m. I've used it in a pinch, but prefer an external meter.

 

[jolechiw]

Yeah I have heard it's not very accurate. from what I can see all I can say is that its low...or at least the 817 thinks so. See I mean .

 

[prcguy]

I have a Mirage B-310G amp and the match between the radio and amp is not a problem. It takes about 1.5w drive for the amp to put out 100w, so your FT-817 would be running backed off around 66% and SSB service is low duty cycle. So even if the match at the input of the amp was not so good you should not be taxing the 817 at all. Why not run the amp to full output? They seem fairly rugged.
prcguy

 

[jolechiw]

I've just read countless reports of fragile finals, even in the newer version (ND). Just don't want to fry it with reflected power, although I guess the radio will tell me if it's unhappy with my choices : )

 

[wyShack]

I would not worry about reflected power -it would be reflected to the amp. I would be worried about the amp itself as most amplifiers for HT use are Class C (non linier) and usable only for FM. any SSB work would require either a linier by design amplifier or you may be able to change the bias yourself- if you do mod it yourself, remember that the power requirements and dissipation will go up possibly causing overheating.

Good luck and 73.

 

[prcguy]

The Mirage B310-G being discussed is a linear amp.
prcguy

I would not worry about reflected power -it would be reflected to the amp. I would be worried about the amp itself as most amplifiers for HT use are Class C (non linier) and usable only for FM. any SSB work would require either a linier by design amplifier or you may be able to change the bias yourself- if you do mod it yourself, remember that the power requirements and dissipation will go up possibly causing overheating.

Good luck and 73.