FT-857D + CB on 102" whip?

[KD0NNB]

I've decided to broaden my horizons and picked up a ham ticket (going to take General test soon). My plan of dropping a simple 2m rig in my truck has snowballed into getting a FT-857D with the FC-40 tuner. Currently I have a Uniden Grant LT CB in the truck with a 102" whip on a Breedlove EZN stake pocket mount. I managed to pull off a 1.1:1 SWR across the band.

What I'd like to be able to do is use FT-857D/FC-40 with the 102" for my HF, but still be able to use the CB with that same antenna. I know I could make it work easy enough with a simple coax switch, but I don't want to be limited to only one radio at a time. I have NO need to be able to TX at the same time. However, it would be nice to have RX at the same time when I'm not transmitting.

I know I could expand the FT-857D, but I noticed it only has 2.0uv receive sensitivity as opposed to the Grant's .5uv. That, and I don't want to void my warranty. My ol' Grant has been a great radio.

 

[office888]

LDG autotuner at the base of the 102" whip, and hook it up to your FT857.

Your 102" whip would be usable on 10-40m.

 

[W5LZ]

I think the only biggy would be connecting two radios to the antenna at the same time with no switching or isolation between them. That would mean a direct input of much more RF than either radio was ever designed to handle every time you punched the mic button. Using an antenna switch that grounds the unused terminals would be a sort of a 'minimum' protection to minimize that over-loading. Even if using different bands, there's gonna be a lot of RF getting into the 'other' radio.

I think you won't be too thrilled with the performance of that 102" whip on any band other than those very close to 10/11 meters. The further you get away from 10/11 meters the worse that antenna will perform, it's just too short for the lower bands. You can certainly get a decent SWR with a good tuner, but that doesn't equal decent performance at all. I have seen/heard it done with a tuner much more capable than that FC-40, and it just wasn't 'good'. It will produce a signal, just not much of one. What you find 'acceptable' can vary a lot, so trying it to see what happens is the best way of finding out.

I've no direct experience with an FC-40, but have heard some 'not so good' things about them. Take that for what it's worth (not much).
- 'Doc

 

[RatsoW8]

I know I could expand the FT-857D, but I noticed it only has 2.0uv receive sensitivity as opposed to the Grant's .5uv. That, and I don't want to void my warranty. My ol' Grant has been a great radio.

Dude...a 2uv sensitivity is much better that a 5uv. That means the 857D receiver will detect a weaker signal than the grant. Any Amataur transceiver will have tremendously better specs than any a CB radio.

 

[Road Squawker]

Dude...a 2uv sensitivity is much better that a 5uv. That means the 857D receiver will detect a weaker signal than the grant. Any Amataur transceiver will have tremendously better specs than any a CB radio.

i see you also picked up on that too


A typical specification might be that a receiver has a sensitivity of 0.25 uV [microvolts] for a 12 dB SINAD. Obviously the lower the input voltage needed to achieve the given level of SINAD, the better the receiver performance.

 

[Captain Kilowatt]

Dude...a 2uv sensitivity is much better that a 5uv. That means the 857D receiver will detect a weaker signal than the grant. Any Amataur transceiver will have tremendously better specs than any a CB radio.

i see you also picked up on that too


A typical specification might be that a receiver has a sensitivity of 0.25 uV [microvolts] for a 12 dB SINAD. Obviously the lower the input voltage needed to achieve the given level of SINAD, the better the receiver performance.

You both missed it. The 857 is 2.0 uV while the Grant is .5 uV that's 0.5 or 1/2 microvolts versus two microvolts for the Yaesu.

I wouldn't worry too much about the difference. It will be noticeable but not that great.

Doc.,what have you heard about the FC-40 that was not good? I ran my FT-857 with either a 102 fiberglass whip or a home made centre loaded 10 foot whip that was self resonant on 15m mounted on the rear hatch door of my Ford Escape and fed with an FC-40. It worked well on 20m and up and I did make some contacts on 40m. I haven;t tried it in some time now as I have removed all my gear from the vehicle and now just run a home station. I was just curious about what you heard about the FC-40.

 

[W5LZ]

Captain Kilowatt,
Probably the 'usual' you hear about most tuners. Just didn't have much 'reach', meaning probably not quite enough inductance for whatever they were trying to make work where it wasn't ever meant to work. Typically just not enough antenna there to be very practical. I wouldn't put much importance on it. Most tuners have enough capacitance to 'shorten' just about anything, but few have an over abundance of inductance, especially the 'smaller' tuners. Like, where would you put the required coil(s), you know? I think I've heard the same sort of thing about most tuners, some that I've used and still use. All of them will have one or two antennas it just won't do.
- 'Doc

 

[Captain Kilowatt]

Agreed with that Doc. I thought maybe you had heard something specific about he FC-40 like failure rates or something.

 

[KD0NNB]

I forgot to subscribe to my post. Thanks for all the replies! I was about to say that someone missed a decimal. I actually decided to scrap the tuner idea and just use hamsticks or the like when I want to change bands. I'll either just use a coax switch or expand the radio to do 11M when the time comes. I'm not worried about being able to perform the expansion mod, rather voiding my warranty.

 

[Captain Kilowatt]

FWIW the 857 is not that great a performer on AM but there are some settings in the hidden menue that you can change to make modulation a lot better. Also if you mod the radio for expanded TX you will loose the automatic repeater offset on VHF/UHF.

 

[VA3ES]

I've thought about this issue at length (and depth). I run an FT-857D in the mobile, and a 10M radio too. For the 10M antenna, I use a Larson NMO34 coil with their 64" whip (W640) and their spring (SPRINGB). It works very well on 10 and 11. It uses the NMO mount which is popular with most hams for VHF/UHF antennas. You can simply swap the 10M antenna for the VHF. To use that antenna on 11, I use a either a CB-type antenna tuner with the MFJ-1705H bypass switch, or a PCD-5 CB tuner/SWR bridge unit. The PDC-5 has it's own bypass switch. For general ham band use, I too use hamsticks.

The whole problem with trying to load a 102" whip on the ham bands is that there will be severe losses unless the tuner is right up against the whip feed point. You would need to mount the tuner right at the point where the whip feed point is, and feed the whip with copper ribbon. The current at the feed point is extremely high and losses mount up rapidly at that point. Then there is the aspect of weird reactances which are exibited by a 102" whip on the ham bands. On 40, you might even need a capacity hat.

 

[Captain Kilowatt]

That's true Ed. I had my antenna mounted on the rear door of my Escape and the tuner was mounted just inside on the rear door itself. The feed going to the antenna was a heavy copper braid that was only about six or eight inches long and well insulated. Losses due to high RF current were not so bad above 15m, tolerable on 20m but on 40m things could have been better and on 80m I used a hamstick.

 

[VA3ES]

That's true Ed. I had my antenna mounted on the rear door of my Escape and the tuner was mounted just inside on the rear door itself. The feed going to the antenna was a heavy copper braid that was only about six or eight inches long and well insulated. Losses due to high RF current were not so bad above 15m, tolerable on 20m but on 40m things could have been better and on 80m I used a hamstick.

There are a lot of issues involved with trying to feed a "short whip" on bands below 14Mhz, and in particular below 8Mhz. The short whip has a very low Z, and a very large capacitive reactance which must be conjugated. You need a big L but you won't find it in the tuner. That L must be in the antenna circuit, and is usually found as a big coil in the center of the antenna. To be effective on 75M a whip would have to be 12' tall, even with a big coil, hence a capacity hat.

One could construct a custom tuner for a 102" whip, but it would have humongous edge wound coils. To be frequency agile, the thing would have to take up the entire trunk.

The final problem is ground losses which mount as you go down in frequency. The best place for a loaded 75M antenna is in the middle of the roof. Mounting it on a trailer hitch or even a trunk mount is not efficient enough.