[MRCA] RF Generator wanted

Thu Mar 19 17:09:05 EDT 2020

As far as I know, with the exception of some other more exotic HP synthesized generators, the 8640B has the widest output amplitude range out there. (-140dBm to +20dBm)  It has a very well shielded attenuator that is supremely accurate, and is free from spurs and intermod products, because it is a cavity oscillator that is divided down to the operating frequency.  It can then be phase locked for stability.  Nothing comes close for receiver measurements.  It does require TLC now that it is at least middle aged, but it is modular, and comes apart like a set of Legos.  Parts are available, as there are many donor unit out there.  Don’t discount it.  The HP 606B with the 8708A PLL unit is a nice second place, although even older and bigger.  (I have a late model beige cabinet one, built in the early seventies!, as are the older fluke synthesizers such as the 6060,6080,8080, etc.  The URM-25 attenuator is not particularly accurate, and will not stay accurate even if calibrated (I have had a half dozen, the URM-25F is somewhat better in this respect).   Presently , my general use Signal Generator is an HP/Agilent/Keysite (made through all three eras) 8648B, which fulfills 90% of my testing needs.  It is available used for around $400. And it is nice, compact, and lightweight.  Covers 9 kHz-2000MHz, and has -136 dBm to +13 dBm attenuator range.  Models A-D are frequency ranges ( A is 1000MHz, B is 2000, C is 3200, D is 4000).

Scott V. Johnson W7SVJ

5111 E. Sharon Dr.

Scottsdale, AZ 85254-3636

H (602) 953-5779

C (480) 550-2358

 <mailto:scottjohnson1 at cox.net> scottjohnson1 at cox.net

 <mailto:scott.johnson at ieee.org> scott.johnson at ieee.org

From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> On Behalf Of Ray Fantini
Sent: Thursday, March 19, 2020 11:29 AM
To: comcast <kg2bz at comcast.net>
Cc: Mrca Mailing List <MRCA at mailman.qth.net>; milsurplus at mailman.qth.net; MMRCG at groups.io
Subject: Re: [MRCA] RF Generator wanted

Signal generation is easy, the problem now days is that I have reached the point where I want to confirm receiver sensitivity at different frequencies so you have to have the ability to calibrate the output of the generator and a calibrated attenuator to be 100% that the radio is working correctly. These early synthesized radios suffer from insensitivity and in the case of USB only radios when trying to copy AM if the time base in the radio is not dead on it can be an issue. The GRC-106 receivers exciters RT-662/834 produce an annoying heterodyne if not dead on carrier when used in AM mode. They use the same product detector in USB or AM with only inserting a carrier in the AM transmit mode to produce a quasi AM signal.

The big Motorola 2000 series monitor produces signals at calibrated levels but get the idea that the AM on it was only an afterthought, when doing VHF or UHF FM its great but working on this old HF/SSB stuff is requiring a different tool set. Had to come up with a power meter that works down in the 2 to 30 MHz range along with things like the two tone generator for testing the transmitters and amplifiers, now I want to be able to provide a clean low distortion AM signal for checking distortion on the receive side.

Something like the things years ago when working with VHF FM stuff and using the SINAD meter to tune for best audio.

Have not pulled out one of the older Motorola Service monitors or a Cushman  to see if it has better AM, have been saving them for you to get you working with one.

Ray F/KA3EKH

From: comcast <kg2bz at comcast.net <mailto:kg2bz at comcast.net> > 
Sent: Thursday, March 19, 2020 2:08 PM
To: Scott Johnson <scottjohnson1 at cox.net <mailto:scottjohnson1 at cox.net> >
Cc: Ray Fantini <RAFANTINI at salisbury.edu <mailto:RAFANTINI at salisbury.edu> >; milsurplus at mailman.qth.net <mailto:milsurplus at mailman.qth.net> ; MMRCG at groups.io <mailto:MMRCG at groups.io> ; Mrca Mailing List <MRCA at mailman.qth.net <mailto:MRCA at mailman.qth.net> >
Subject: Re: [MRCA] RF Generator wanted

what about using an lm or bc221?

Sent from my iPhone

On Mar 19, 2020, at 12:09 PM, Scott Johnson <scottjohnson1 at cox.net <mailto:scottjohnson1 at cox.net> > wrote:

My choice, for the last thirty years, is the HP 8640B.  I believe it to be among the best generators for receiver measurement and alignment.  The only problem is the nylon gears, which tend to shrink and crack from the brass hubs.  There are people making and selling gears, and even at $300 for a set that, it is still worth owning one.

Options include a doubler to 1024 MHz, reverse power protection (recommended),and variable frequency modulation.  The Military version in the yellow case is to be avoided in my opinion, as it lacks phase locking and is generally a pain in the keister, unless you (like me) collect such things.

Scott V. Johnson W7SVJ

5111 E. Sharon Dr.

Scottsdale, AZ 85254-3636

H (602) 953-5779

C (480) 550-2358

 <mailto:scottjohnson1 at cox.net> scottjohnson1 at cox.net

 <mailto:scott.johnson at ieee.org> scott.johnson at ieee.org

From: mrca-bounces at mailman.qth.net <mailto:mrca-bounces at mailman.qth.net>  <mrca-bounces at mailman.qth.net <mailto:mrca-bounces at mailman.qth.net> > On Behalf Of Ray Fantini
Sent: Thursday, March 19, 2020 8:04 AM
To: milsurplus at mailman.qth.net <mailto:milsurplus at mailman.qth.net> ; MMRCG at groups.io <mailto:MMRCG at groups.io> ; Mrca Mailing List <MRCA at mailman.qth.net <mailto:MRCA at mailman.qth.net> >
Subject: [MRCA] RF Generator wanted

Everything old is new again! Been working a lot with repairing a lot of GRC-106 receiver exciters and noticed that my Motorola Communications Service Monitor produces a lot of phase noise and poor-quality AM on the HF bands. Decided that what I need is something like an old school URM-25 or maybe if I can find one a URM-144/SG-823 being I already have a SG-376 that I got last year that I have been using a lot for SSB work. 

As always not looking to spend a bunch of money on this but can always do a trade. Lot of crazy prices for URM-25 generators on eBay but use to seeing them at Hamfest for $20 to $50 price range. Did not realize until recently that you more often than not need vintage test equipment for working on vintage radios.

It’s amazing what happens when you take modern items like the new generation of digital scopes today and look at things like modulation levels for AM carriers! Or operate DVM in high RF environments.

Ray F/KA3EKH

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