Washington (858) high frequency mod?

[Hawkeye351]

Got a bone stock Uniden Washington (UPD858 - 2 button version) that the owner wants high frequencies installed.

He wants to keep the regular 40 channels, plus the high channels (frequencies). Him and his buddies hang on channel 40 on quiet days/nights and frequency 27.8450/ 27.8550 when heavy skip takes over the regular 40.

I know there are many mods/ways you can modify the 858 PLL, but which way would you all recommend?

Note:
Owner wants just the regular 40 channels and the high frequencies to get him to 27.845 and 27.855. Just one switch if possible.

This radio is stock, nothing ever done to this radio, tuning slugs still have what looks like the factory wax on the tops of all 3, the VCO still has the factory wax packed in it, D21/D22 still intact. No jumpers across the filtering for the xmit audio, hell, the modulation adjust VR has never been touched (it's set about the halfway mark), and the factory Tantalum cap is still in the C179 location (gonna replace it anyway).

Thanks in advance guys/gals...

 

[sp5it]

http://lesterscustoms.com/858_kit_inst maybe?

 

[BC Coyote]

You can get 27.455 to 27.805 with one switch. Make it two switches and you'll also get 27.855 up into 10 meters. Note that 27.815 to 27.845 are missing ? Just a weird quirk of the 858 chip that will require installing a third switch to access those four channels. You will ALSO need to broadband both rx and tx to go that high in frequency otherwise the radio will be deaf and power output will suffer big time.

There might be another way to do it but I modified lots of those 858 radios back in the day and I recall the frequency ranges accessed were pretty much the same.
You can also go way down below, all the way to 26.085, with that PLL.

 

[Shadetree Mechanic]

I think 27.8 is going to be a stretch, power will be low way up there. I hope he plans on using an amplifier?

@unit_399 has a page with good info:

HOME | 858ssb

unit399.wixsite.com

 

[Xracerx13]

858PLL channel mods and how to broad band with pics.
This is the easiest to read and comprehend.

N2KBK- 858 pll freq mod

 

[9C1Driver]

I see now, guy just wants a channel mod for extra's. When I first read this post I though you were referring to hi fi or wideband audio mods.

 

[BC Coyote]

I was referring to having to broadband the receive and transmit of the Washington in order to have it operate on 27.855
Doing the channel mod is easy in this case, but without broadbanding the radios receive and transmit circuits it will be pretty deaf up there, and will only emit a small amount of power, if any.

 

[nomadradio]

There are a couple of places where an RF transformer feeds a MOSFET gate from a step-down tap. Moving this to the "top" of the winding boosts gain enough you can stagger-tune the bandpass pairs L4 and L37 without losing performance.

Gotta have some pics of that trick here somewhere. Sounds like a hack 399 would have in his rundown for this radio's circuit board.

This does compensate for broadbanding the radio.

73

 

[loosecannon]

i was hoping someone like nomad would comment on the broadbanding.

Nomad, i have heard that doing the L4 broadbanding trick will cause an impedance mismatch but i don't remember where i heard this.

any chance you can assuage my concerns about this mod?
LC

 

[nomadradio]

Um, changing the tap point where a tuned circuit feeds into the gate of a MOSFET won't. The output of L4 to the gate of FET1 is feeding an impedance of megohms. If FET1 was a bipolar transistor, we'd be feeding into the base or emitter. Both of those are lower impedances, and the "tap down" impedance coming out of L4 would matter. This trick would create a mismatch to a bipolar transistor.

In this case it doesn't. The capacitance of FET1's gate will change the slug setting of L4. Changing from the tap to the top of the coil places more of the FET's gate capacitance in parallel with L4's internal resonating cap. Only moves the slug's resonant peak by a turn or so, but you were planning to spread L4 by peaking one slug below channel 20 and the other slug above, right?

And if you peak both of L4's slugs at the same frequency you might find the receiver's sensitivity exhibits too much of a good thing.

Moving the feed to C255 from the tap of L37 to the "hot" terminal will create a small impedance mismatch, but in this case, that's part of what broadbands the transmitter, by loading down the tuned circuit with the 3.3k resistance of R187.

Same rule applies as for L4. You'll have to retune, and should probably 'stagger' the peak of each of L37's slugs, one above 20, the other one below.

This does work. Never got around to looking at the signal on a spectrum display. Might be revealing?

73

 

[BC Coyote]

This does work

I can vouch for this as that is EXACTLY how my old Navaho 457 & 458 boards were
broadbanded. I figured out the staggered slugs thing by trial and error, nice to see it was based in sound science! I was on 26 MHz a lot back then, so I would peak one slug around 26.8 and the other around 27.5

Those radios covered 26.085 up into 10 meters and would rx and tx anywhere in that range. It did however lose some sensitivity on rx and power on tx towards the band edges. I always ran it with an amp (with a rx preamp option), so it didn't really matter.

 

[loosecannon]

are you guys moving to the full windings on both the primary and secondary of L4 and L37?

or just on the secondaries?
LC

 

[nomadradio]

Just the secondaries, each feeding into a fairly high impedance. Doing this to the primaries is overkill. I judged it too much of a good thing, but feel free to try it and see for yourself. Does serve to jazz things up a bit more. A bit too much for me.

73

 

[Hawkeye351]

I've returned this radio back to it's owner. After I told him I needed more than 1 switch, he told me to just forget it, lol...

Oh well, at least he's tickled pink with the receive and transmit performance it's doing now on the regular channels after the alignment.