Technical Help sought


Apologies if this post seems a little off subject!

I have an FT817, (early model, not ND), and it hasn’t been used for about 3 years. The battery pack (NiCad FNB-72) has not been charged in this time. The voltage measured(with DMM) is currently 7.28V. Will this battery be ok to be used? Will it come back to life with a few charges or do I run the risk of damaging the FT817’s charging circuit? Also, I note that Yaesu now supply the FNB-85 NiMH battery pack with the ND model, is this newer battery pack compatible with the earlier FT817? Is the charging circuit different to accomodate NiMH’s instead of NiCads?

I have just been given a dummy load, which was being discarded at work. The sticker says it is a Radiall R404881000, 80w convection cooled/120w conduction cooled, 50 ohms, 0-4GHz. I cant seem to find much about it on the internet. To look at it just looks like a large finned heatsink with a N-type connector. What I would like to know is is this suitable for amateur use? I know it says 0 to 4 GHz, but does this really mean it will safely present a 50 ohm load from DC upwards? I would like to test a 1.5 watt tcvr at 3.5MHz, will this dummy load be ok?

A lot of questions I know! Looking forward to getting on the air again with the 817 (it’s currently at Yaesu for a fettle!).

Thanks in advance for any help.

Colin M0CGH

In reply to M0CGH:

Hi, Colin, there is a good chance that the battery pack will be OK, and you are unlikely to damage the charging circuit. The newer type battery pack is compatible with the older radio, but it would be cheaper to buy some 2500 mAH NiMHs at a rally and put them in the battery box (with the green wire cut) all you have to remember is that a high capacity NiMH battery takes longer to charge so you will need to run the charge cycle twice.

Dummy loads are just non-inductive resistors with a means of dissipating the heat generated in use. You’ll be able to use that one OK.


Brian G8ADD

PS I assumed above that you have the battery box provided for dry cells. That is wired to make it impossible to charge the dry cells, but if you cut and tape up the green wire between the box and the plug, you can put chargeable batteries in it and charge them normally.

In reply to M0CGH:

In an ft817nd I have:

Menu #11 BATT-CHG - Selects the battery charging time. 6/8/10h
8 hours for the FNB-85 NiMH
6 hours for the FNB-72

I guess that the menu is also in the earlier ft817s.

Nigel. G6SFP.

In reply to G6SFP:
Yes, the charge time menu is in the earlier FT817. For a set of 2500mAH cells in the modified battery box I found it took 2X8 hrs to get a full charge.


Brian G8ADD

In reply to M0CGH:

I would like to test a 1.5 watt tcvr at 3.5MHz, will this dummy load be ok?

At that power and frequency you could just lick your fingers and stick them in the output socket! :slight_smile: But yes, it will be more than adequate.

Radiall are a proper RF company. There’s an awfully large amount of junk sold into the amateur market, especially things like cheap and tatty RF connectors (PL259 especially), patch leads etc. But you wont find junk with the Radiall name on it. You should make it an aim of your hobby to find a big enough RF source on 3.9GHz to get that dummy load too hot to touch! If you can’t get it too hot on 3.9GHz you should give it to me and I’ll give it a good seeing to with the contest group’s solid state PA (about 90W) :slight_smile:

There’s little difference in charging NiCd from NiMH cells. Both require a constant current source for charging. The only real difference is that for smart chargers the charging complete conditions are slightly different, one goes into -ve delta V and the other is a flat delta V. The 817 is not a smart charger, it just bangs out a constant current for either 6 or 10 hours. If you put a bigger capacity pack in it will take longer to charge as the current is fixed. I agree with Brian, I’d use a battery box and individual NiMH cells rather than punt big money for a battery pack and I’d charge the cells separately in a parallel charger.


In reply to MM0FMF:

Thanks to all for replies.

To Andy, I have finally manage to navigate Radiall’s website and get a data sheet for the dummy load. It doesn’t say much but it does say that the load offers a VSWR of less 1.3 to 1 at 4GHz, reducing to less than 1.1 to 1 at DC. All I needed to do was have a closer look at the website! I was looking for ages last night on the Radiall website with no success, however I found the datasheet within 10mins this morning! BTW, peak power is given as 5kW! (not for long I would think!) I work for a microwave diplexer manufacturer, which is why they had the load, all their equipment seems quality stuff.

I do have the alkaline battery box for the 817, although I did a stupid thing with it! I tried to remove the battery box with the alkaline cells still in place, there was a small crackle, and the metal springs all went ‘soft’ with the plastic melting a little. Something must have shorted. I have managed to prise the springs back out a little, but they haven’t got much spring left!

I think the idea I like the most is using a separate charger and high capacity NiMH cells in the battery box (if it will still hold batteries). I’m also thinking of getting hold of a SLAB and making up a battery box with a non reversable power connector to avoid polarity error. I’m hoping that if a find a snug fitting plastic box, the SLAB terminations will be safely insulated, from things in my backpack.

My early FT817 has the same menu structure, with 6, 8 and 10 hour charge settings.

Looking at the date code, my FT817 was made in February 2001.

Cant wait to be multimode capable again!

Cheers, Colin M0CGH