Please Help Identify a Mystery Device - Page 1
Forum section: electronics / rf-microwave

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 02, 2018, 11:44:25 pm
content: I bought a nice, old rack mount cabinet at an electronics swap meet last year. Inside it was a mystery box made by Sierra Electronics. (I made the purchase for the cabinet, not what was in it.)The only number stamped on the name plate was "691." It is has tubes and what look like some kind of tuned circuits with a separate circuit for 2, 4, 10, 20 and 30 MC (MHz).Does anyone have an idea of what this device is? I have attached a picture.Richard

author: Bud
author_rank: Super Contributor
timestamp: January 02, 2018, 11:55:28 pm
content: RF amp,ifier output stage with antenna tuner per band

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 03, 2018, 12:10:09 am
content: Good thought...Here is a picture of the back of the unit. There are a bunch of coax cables and there were five band pass filters in the empty space on the lower left, which I removed. There are no obvious RF input or output connectors. One of the pieces of coax from the rotary switch seems to be longer that all of the others. Maybe it was connected to another device?Maybe it is some kind of signal generator?Richard

author: Bud
author_rank: Super Contributor
timestamp: January 03, 2018, 12:25:51 am
content: Ah, indeed, each module has a quartz crystal and a OSC trimmer. More of a band oscillator thing.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 03, 2018, 03:52:25 am
content: Quote from: Bud on January 03, 2018, 12:25:51 amIt's a multiple band RF Exciter out of a transmitter.You can use crystals of various frequencies within each band, & adjust the controls to peak & load the device into the next stage.

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 03, 2018, 07:54:10 pm
content: It's probably as vk6 said, an exciter. So yes, those boxes are oscillators and thats a band switch. The wiring seems newer though, so it's probably been refurbished before.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 03, 2018, 08:02:22 pm
content: Thanks. So it would drive a transmitter that only uses CW? This would avoid changing crystals, etc. for each band?

author: vk6zgo
author_rank: Super Contributor
timestamp: January 03, 2018, 11:30:12 pm
content: Quote from: RCHRDM on January 03, 2018, 08:02:22 pmOr an AM transmitter with the modulation performed in a later stage.

author: Ghislain
author_rank: Regular Contributor
timestamp: January 04, 2018, 07:21:57 am
content: Quote from: vk6zgo on January 03, 2018, 11:30:12 pmAn AM transmitter is the most likely use case, the indicated frequencies coincide with the AM broadcast bands.Sierra electronics still is in business, I am sure they may be able to provide more detailshttps://www.sierraelectronics.com/

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 04, 2018, 08:21:04 am
content: Thanks! I did not find them when I looked. I have sent them a message.Richard

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 05, 2018, 03:32:31 am
content: Turns out that company is not the same Sierra Electronics.The best guess we have so far is that it is an exciter of some kind for a transmitter. As someone said, the five frequencies line up with the broadcast bands?Richard