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Reviews For: Drake SP-75 external true RF clipping speech proc.

Category: Audio Accessories for Transmitter & Receiver

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Review Summary For : Drake SP-75 external true RF clipping speech proc.
Reviews: 3MSRP: $200-ebay
A TRUE RF speech proc for any rig.
Product is in production
More Info: http://
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
NU0C Rating: 2022-04-16
Hidden feature Time Owned: more than 12 months.
I won't repeat what other reviewers have already written. The SP75 is an excellent processor that can really be used with any rig and with careful adjustment will have excellent audio. I never turn mine off.

The only downside is that the level adjustments are screwdriver holes in the back. If you like to mix up your microphones, for example a headset for contesting and a desk mic for casual operation, you may find yourself fiddling with the levels for best results. You can either use external padding or a little pre-amplification (emphasis on "little") to equalize the levels between mics or you can move the adjustments to panel mounted pots on the rear panel. The access holes are an almost perfect fit in size and location for standard panel mount pots and with the proper knobs it can actually look like it is Drake original!

Although the manual explicitly states not to add extra grounding between the rig and the processor, YMMV as they say. I found it beneficial under certain circumstances to add a ground strap between the chassis of the processor and my TR7. It is also good practice to avoid the "pin 1 problem" by ensuring that the shield of the mic cabling is connected to the shell of the 4-pin Foster connector as described in a Heil tech note online.

Now for the hidden feature. Not really hidden but I think that a lot of ops miss the obvious. The SP75 has two switchable inputs on the rear panel labeled Tape and Patch. Either one of these is an excellent point for injecting TX audio for digital modes, RTTY/SSTV, etc. I've been doing this for several years with great success. No fancy external interface needed, just follow good ground bonding practices between the equipment. Don't forget to turn processing off when using these modes!

I also have MFJ, Daiwa/Kenpro, and Comdel RF processors but honestly the SP75 works so well I have not tried the others out.

73 DE NU0C
AL7KC Rating: 2019-03-21
My Secret Weapon Time Owned: more than 12 months.
Took me a while to find one for my TR-7, but it was well worth it! Wouldn't want to live without it, as it has helped me to work many new countries! If you actually use your TR-7 as a main operating rig, you want this for the extra "punch!" It is my secret weapon for DX!
WA2JJH Rating: 2004-03-14
A great external RF speech proc. Time Owned: 3 to 6 months.
The years when I could not run an AMP, I always thought a good speech proc. would give me a chance with the kilowatt crowd.

The answer can be no, marginal or yes!
Never like audio compression. You get every sound in the shack!

The idea is to bring increase the RF envelope and the rigs average power to be closer to the peak envelope power.

Every rig that I owned had the RF PROC built into the rig. It can be done externaly!

I am not going to go into all the technical details. See the Drake pages.

You mic input is mixed with a local oscillator RF signal, then filtered with 2 ceramic filters to get a CLEAN SSB signal. The SSB signal is amplified then RF clipped. The RF processed signal goes through another ceramic filter to shape and clean the highly processed SSB.

Only a simple ceramic filter has to be used to make the signal squeakly clean. This is because the SSB signal is then converted back to audio.

The added bonus is a noise gate. when your not talking the audio is attenuated by 20 db.

This means you can use your VOX with this PROC.

If you want to see how true RF clipping speech processing will make you stand out CLEANLY, check out ebay! Forget the AUDIO DSP PROC in you rig.

You will see up up a 4 fold increase(20db) in average power(do not use more than 10db, your finals may only handle 2-3 fold increase), without ANY extra background noise.

There are pots for rig and mic matching as well.
This was designed for the Drake TR-7/T-4 rigs. You will have to do a simple mod. to power this most excellent speech processor.